Help with how to sew a tricky seam

My solution to this has always been to use a ‘bucket’ groundsheet: one where the groundsheet fabric curls up at the sides for 100 – 150 mm. There is no seam at ground level.

I have only had to rely on this a few times. The most memorable was one night at Medlow Gap in a cloudburst. MG is a hardened dead-flat helipad in the mountains, and we had over 25 mm (1″) rain in about 1 hour. There was, literally, 25 mm of water on the surface: no slope, no flow. The groundsheet was, again literally, floating while we sat on our air mats inside. It was kinda funny, even at the time. But the groundsheet fabric was waterproof and we stayed dry.

Cheers

Geoff, I’m building a complicated tunnel tent, which I’ll report on when I’m done. I’m using RSBTR 1.1 oz (30D) MTN silnylon 6.6 (1.5 oz finished). RSBTR makes fabulous claims for its strength and HH. It is sil/sil coated. I has a very crisp texture, translucent. Might be a good candidate. I’ve been doing a lot of bonding with it; I love bonding. I use Loctite flowable windshield silicone, a fantastic product for that and for seam sealing. I use a plastic putty knife to squeeze out the excess material.

If you do wind up using a seam, I see no need to use a lap felled seam. The seam has no stress on it. I think a simple two-layer stitch would suffice, with careful seam sealing. This is what my Warmlites have. Easy to sew, easy to inspect, easy to repair, though I doubt you’d ever need to reseal with silicone. In the old days, yes, like my old urethane Warmlite, in which the sealants would eventually peel, but I’ve never seen a problem with peeling silicone sealing in my newer Warmlite or my own tarptents.

The other alternative is what I plan to do: use a light 20D fabric, e.g., RSBTR regular 1.1 oz at 1.24 oz or even something lighter, and don’t expect it to stay waterproof; its function is to keep out critters and wind and dust. I always use a thin plastic ground sheet under my tents (a plastic “disposable” party tablecloth) as poke protection and as a better vapor barrier than cloth (little holes don’t affect the VB function). Then I carry a fresh polycryo sheet to use in case of heavy, pooling/running rain. The idea is to use the Cliff Jacobsen method: put the waterproof sheet inside the tent, where it is protected. Easily replaced or patched, easier than a tent floor. I haven’t had to use it yet, since I don’t frequent a lot of wet places. For the tent I’m making, the larger polycryo sheets will roll up the walls for a bathtub effect.

Nice shot of the Warmlite internal wind stabilizers. I will be building in my own version, front and rear, permanently mounted and adjustable, but with the addition of a horizontal brace, which will make it bomber for heavy snow load, I hope, even though I don’t plan to camp it the snow. Don’t know why Warmlite doesn’t have that as well.

One more tip– if you do use a seam, with this fabric and probably other silnylons, there is no need for it to be hemmed or to conceal the edges. Just leave the cut edges raw. They never ravel. That’s what Warmlite does and it works, conventional appearances be damned.

Moab – priceless advice – this is what BPL is all about!

You raise a couple of questions.

First, I’m starting from scratch with bonding, though I’ve found a couple of people in Europe who have been kind enough to pass on some tips.

1) Do you think the windshield silicone would bond sil to sil/PU blend? Or a sil/PU on both sides? This would open up my choice of fabrics. These would be sheering or low tension seams, not peeling seams.

2) Have you experienced creep at all? My shelter will be heavily used. I’ve seen people claim that for regular use the bond needs to be reinforced with sewing, for, say, a ridgeline. But sewing seems to negate most of the advantages of the bond. I’m not a gram-weenie so am happy to use a large overlap for the bond if that would be longer lasting – the weight penalty is trivial to me. Is there any case for a wide lap, or is it just a waste?

Second, the issue of one heavy-duty floor @ around 60d, or a lighter Mountain Sil floor with a footprint.

Stephenson’s are a bit coy about the weight of their fabrics – I’d be interested in your estimate of the denier of their current floors.

The heavy duty floor has the advantage of simplicity. But once it goes, the whole shelter is pretty much done.

The modular floor is more flexible and should last longer, and I can match the footprint to the conditions – eg something light for grass, Tyvek for gravel etc. But it’s marginally more hassle. I was playing with the idea of some kind of attachment mechanism so I can clip the two layers together – especially for pitching in high winds.

I was tempted by the Mountain Sil floor, because I can definitely use the Wacker E41. It’s a technical sealant and my two contacts in Europe have had good results with it. You’ve got me thinking that maybe that’s the way I should go.

I haven’t come across the idea of the “inside footprint” before, but as a Scot I camp in some very boggy places so I’m not sure it would work for me. I think I’d go for a conventional footprint.

And thanks for the tip on unfinished seams. I cut with heat anyway, so the edges wouldn’t fray. I have a Cordura Lowe Alpine climbing sack I bought in the 1970s. It’s had literally 1000s of days of use on the crags and as a day-sack, and the unfinished flat seams are still fine. It’s reinforced with a second row, but the first row is undamaged. I use it as a seat and abuse it horribly and it soldiers on. I think we sometimes over-engineer things!

Thanks again for your input!

Geoff, many conversations here. But first, I misspoke earlier: the silicone I use is not Loctite, it’s Permatex 81730 Flowable Silicone Windshield and Glass Sealer.

1) Sorry, I don’t know anything first-hand about sil/PU blends etc. You’ll just have to test a sample. And then there are sil/PEU fabrics, which are supposed to be better, I forget how (or was it degradation over time?).

I don’t like the idea of PU in my fabrics because I’ve seen what PU does over the years—it seems to absorb water and turns to gum and peels. It has a shelf life, unlike silicone. I think the main reason it’s being used is that it allows the factory seam seal tapes to adhere. See this from http://www.thetentlab.com/MoonLightTents/Waterproofness.html: “The term “sil/peu” means that one side has an extremely water repellant silicone impregnation and the other side has a PolyEther based polyUrethane coating -PEU- (so it can be taped).” Does PU or PEU help with with HH? I don’t know. Is such help necessary?

The most important question is why would you be using a sil/PU fabric instead of a high-quality sil/sil if you are going to seal the tent the traditional sealant way instead of with tape? And I wouldn’t be afraid of the traditional because it’s not hard to do and I’ve never seen an instance of it leaking, where I have seen cases of seam tape peeling in jackets and pants.

For an advocacy for sil/sil, dig into Slingfin and their great tents and tarps. Ryan wrote about their light tarp and its uberlight sil/sil recently.

2) I do like bonding in the right applications (reinforcements and precise positioning being my primary uses) but I don’t recall the claimed advantages bonding might have for a ridgeline, and I think I read some of those articles in German about bonding. Personally, I’d just do a DLFS and seal it nicely. Bonding can be very finicky and would be difficult to do a narrow bond (though you would need a wider seam than you’d have with sewing) and there are ample opportunities to f___ up bigtime and little with bonding, or at least to make things messy, whereas seams can be fixed generally. Also, I don’t look at ridgelines as being high-stress seams, so depending on your design you might get by with even an ordinary flat seam. The “ridgeline” in the Wamlite is just a flat seam (as is the entire tent! including the floor-to-walls). And bonding anything is likely to be heavier than sewing and sealing.

I haven’t finished my tent and haven’t used bonding in earlier shelters, so I can’t speak to creep, but I doubt you would ever see “creep” in a properly designed and executed bond unless it was perhaps a guyline anchor and subject to the wrong forces. And I doubt there would be “creeping”, more like catastrophic separation or ripping, but that would take a lot of force. Yes, sewing over a bond would seem to partially defeat the purpose of the bond.

As a caution, when you bond, you want to aim for a finished “adhesive” probably just a couple or few molecules thick. Something on either side of that will be weaker. I first spread several thin lines around on one piece to be bonded, then spread it out slightly evenly with a stiff card, apply the second piece of fabric, then start in the center and work outward with a plastic putty knife until you start to get not very much excess material coming off the edges. You don’t want the finished piece to seem thick, but it is possible to go too far—if the fabric pieces start slipping around or separating, you’ve gone too far. Practice.

Maybe the Wacker is good but I know the Permatex is fabulous (and doesn’t stink and doesn’t hardly dry in the tube so it’s easy tor reuse over and over if you keep a long wire deep in the small dispensing hole—to reuse, unscrew the nozzle and push the wire farther in, scaping the inside of the nozzle as you go, then clean it off). Just be sure you don’t get into the old McNett stuff (or GearAid or whatever they call it now).

3) My latest Warmlite is from 2005 and it is definitely 30D, and not super waterproof either (I’ve used that fabric for other projects and tested it), but nonetheless I’ve never had a fabric leak—except the worn floor. I don’t know what they use now.

4) As for a heavy vs. light floor, if your floor, whether heavy or light, starts to get too worn, you can simply recoat it with a method similar to bonding. But it will add a lot of weight and stiffness. Is there an advantage to having a heavier fabric in the floor with respect to waterproofness? I doubt that, or can a heavier denier carry a thicker coating? I don’t know.

To me the purpose of heavier fabric is to better resist puncture, and you can already guess that my position on that is that no fabric can resist a lot of puncture stress and it’s better to prepare your bedsite carefully and to have something disposable or easily field repairable to take the hit. I’m speaking from experience with cactus spines, burrsage, ponderosa pine needles and cones, stiff dead bunchgrasses, sharp limestone fragments etc.

5) The “inside footprint” idea comes from Cliff Jacobsen. He’s an oldtime who has written a lot of books about canoeing and camping secrets. He is highly experienced canoeing the US and Canadian northwoods and I’m sure he’s spent many many nights with water pooling under his tents, and this is his solution.

6) I used to cut my silnylon with heat (soldering iron with a tile blade) but now I’ve learned there is really no point to it. Heat is dangerous to me, very easy to f___ up with and get an over-melted edge or stray hole in the fabric, very very toxic fumes etc. Now I know that a cut edge of a good silnylon simply will not fray, so I exclusively use an Olfa rotary cutter with a fresh blade. Yes, heat is great for Cordura and other very coarse-threaded fabrics, and probably the only hope for keeping them from fraying, but it’s not useful for silnylon, IMO.

Write here or PM if I might help with anything else. And let’s see the final result!

Hi Moab – once again, thanks for a terrific reply. Much appreciated!

FABRIC

On the fabric issue I’m planning to use a 40d silpoly/PU for the fly. And that pretty much means the RSBTR 1.6 oz Silpoly, as there’s nothing else with a proven track-record on the consumer market that I can find.

On the PU issue they tell me there’s only 2% of PU in the blend, for technical reasons. Their copy is a bit misleading. As you may know there are two forms of PU. The old hydrophilic form is the reason for the bad reputation. It’s still used on cheap products and if you leave it damp it peels and smells. The newer aliphatic form is much more robust – this is what RSBTR uses in its PU fabrics so at 2% I don’t feel it’s a deal-breaker. Their 1.6 has been on the market some years now and reviews are positive.

So why this choice?

On the silpoly vs silnylon issue I’ve been chatting with Mike at The Tent Lab – a very experienced trade designer of hiking tents as you know. In his view the lower stretch of silpoly in the wet is a game-changing advantage vs silnylon 6.6. He’s done a lot of practical testing, and his unambiguous advice is to go for the silpoly. His only caveat is not to go too light – 20d is the absolute limit of safety. As this is a guy with access to the labs and repair shops of the big brands I’m taking him seriously.

I see a lot of Hillies here in the Lakes, and on a cold wet morning they can look pretty saggy and sad, even with their outstanding Kerlon 6.6 nylon.

As for the 40d, I’m specifically building the shelter to take big winds in Scotland, Sweden etc. There’s a tent-maker here who tests silpoly extensively in Scottish conditions and his strong advice is to go for 40d in a 3.5 season shelter. He does offer 20d but only for more sheltered use. The lower bias stretch helps it cope with wind and light snow, there’s a bigger safety margin strength-wise, and it’s reportedly much easier to sew as you can iron in a crease.

The fly is only 6.7 sq meters, so I’m only taking a 70g penalty for the more robust fabric. A small price to pay for greater safety and a quieter night’s sleep, I think.

BONDING

You’ve talked me out of bonding the ridge – given the conditions I’m designing for I guess I should go with the tried and tested full flat fell seam. I’ll restrict bonding to the tie-outs, where I have a proven design to work with.

FLOOR

RSBTR are keen on their 1.6 oz HyperD for this application. My floor is only 2.8 sq m so the savings on anything lighter will be trivial. Unless you want to talk me out of it I think I’ll take their advice, and protect it from underneath with polycro or Tyvek depending on conditions. If it starts leaking with age, I can extend its life with your inner-bathtub idea.

The alternative would be the Mountain Sil, but it’s notoriously slippery which is a consideration when I’m often camping on slopes. And 1.1 oz does feel scary-light for a floor, even with such a good fabric.

As you say, in the end it’s mainly about good preparation of the site – but on tundra gravel is often difficult to avoid.

CUTTING

I take your point about the fume danger of heat cutting. In fact just before we had this chat I’d ordered my first cutting mat and wheel – they arrived today. I think I’ll switch over as you advise.

A very productive thread! Have you written up anything about your tunnel project? Given your knowledge and experience, it would be very interesting to see what you’ve come up with.

Geoff, it sounds like you’ve thought out your project very well.

I guess I’m spoiled as the places I haunt are not nearly as severe in wet as what you anticipate. Curious to see what shape of shelter you’ve settled on.

I don’t know anything about HyperD.

Yes silnylon can be slippery. Some people paint lines of thinned silicone sealant across the tent as sort of non-slip treads.

I’ve started to write up my project but I haven’t even finished the tent yet. Still plenty of opportunities for it to turn into a disaster. I did write a post during the planning stage, to give you an idea of what’s brewing: https://backpackinglight.com/forums/topic/tunnel-tent-design-help-purpose-of-slanting-poles/

Here’s a couple of pictures of my patterning mockup. As you might imagine, in this design, silnylon stretch becomes a useful feature in creating a sleek form, not a deficit, especially since the tent will be adjustable from a single point without leaving your bed, or you can have a bungee take up all the overnight slack.

As far as choosing a fabric, I’ll offer this repost of what Ron Bell of Mountain Laurel Designs had to say on BPL, and say, we can all choose whichever set of facts we like and we’ll probably not go wrong (it’s enough to make you crazy):

“My observations about UL tent fabrics I’ve learned over the last 20yrs.
1: Some equal weight Silnylons and SilPolys are way better than others.
2: Some 20d silnylons are way better than some 30d Silnylons.
3: Some 20d silpolys are stronger than some 20d and even 30d silnylons.
4: Some 20d silnylon stretches way less than some 20d silpoly, even when wet.
5: Some/Most of the 20d silpoly and 20d silnylon availble to DYI’ers though resellers are not as good as the ones used by some tent manufacturers.
6: No one on any forum hardly ever talks about dry stretch on the bias.  That is very important to making curved or large panels function well. Some equal specs fabrics ( 20/30/poly/sil/pu/nylon/etc) stretch on the bias very much different. Some as much as 400% more than others. I think that the dry stretch is far more important than wet stretch, at least for MLD shelter. It’s not part of marketing lit so no one talks about it.  I’ve seen some dry stretch (nylon and poly/ ripstop and non ripstop) that is bad and only get worse when wet. Could this be part of the over generalized myth of wet stretch Silnylon vs SilPoly?  Is there even a lab test standard for this? I don’t know. I only know how I measure.
7: Some Silnylons wet stretch less than other Silpolys.  Some silpolys stretch a LOT less than other silpolys. Same goes for Silnylons.
8: Some runs of the exact same fabric from the same factory perform different. What vintage year was your 20dSilwhatever? Ohhhh- 2017 was a great year!
9: All discussion of tech fabrics exist in a tiny time compressed bubble, but get repeated as current fact for many years.
10:  Labs tests on any tent fabric is only a starting point to understand the end shelter. Design, construction and sealing often is more important to any end function vs the raw material.
11: A DYIer tent fabric choice is almost always great, no matter what happens. Same fabric in a mfgrs tent is not always that great.
12: A higher HH coating can make a fabric weaker due to the higher+longer heat drying process of curing the coating. Do you really want a super high HH…maybe not?
13: Some 10/15d silnylons are stronger with less coating. How little can your marketing shaped perception accept?
14: I finally saw a 20d SilPoly that, on balance for 10+ factors, I think is sort of pretty good. Nope,  I can’t say what it is except that it’s nothing on any list or post from any place anyone here has ever noted.
15. Be careful making generalizations. They can often be generally wrong. I’ve been wrong so many times I now understand the massive amount of what I do not know,  maybe. Probably Ok to disregard all I’ve said above, except #14 and #15.”

Moab – checking the link to your initial post about the canted poles, it turns out that we’ve discussed your project before!

It’s a very interesting concept. I see that you’ve found a way to execute the two peg erection, which should offer all kinds of advantages. As you said, there are a number of ways to reinforce the pegging points.

Given that your two pegs would be so critical, do you know the Delta Peg design? The holding properties are remarkable. https://deltagroundanchors.co.uk/

The plastic ones are popular in Scotland for camping on soft ground, despite the weight. Just a couple on the critical structural guys can be a life-saver. The steel ones would be better for hard ground such as the Moab, but much too heavy for UL. But it shouldn’t be too hard to find someone to weld up a couple of lighter ones to the same design if you can’t do it yourself.

They were local to me and I had a chat with them about a lighter version for the hiking crowd, but couldn’t convince them of the market potential. They are well known in the much larger frame tent and marquee markets and are happy to leave it at that.

I admire your ability to live with a 30″ headroom – though I guess if you’re mainly cowboy camping it would be bearable. In the wet and cold for months on end I think I’ll need more space, though I’m keeping it to a minimum. It seems that we both prioritise footprint – in the end there’s not much point to a fancy shelter if you can’t find a place to pitch it.

On fabrics, Ron is pretty much on the same page as Mike at The Tent Lab – ie there is huge variation between different manufacturers and even different batches for the same fibre, and they can be greater than the differences between nylon and poly. Mike says that it’s mainly down to the skill of the finishers, which seems to be more of an art than a science.

So us MYOGers are at the mercy of chance. That’s why I’m trying to stick to fabrics with a bit of a track record. Mike openly laments that some of his own designs are compromised when manufacturers don’t bother to ensure that the fabric batch is up to spec before ordering a run.

But they both say that this isn’t such a big deal for tiny UL shelters, so long as we design around the limitations.

I’d consider the Mountain Sil as an alternative, but right now they only have it in black which isn’t workable for me. It’s only rarely in stock so if you like it you’ll want to snap up supplies when it’s around!

Seems that we’ve both been gestating our projects for a couple of years. In my case life and health got in the way, but I think I’ve solved most of the design issues and am ready to go. I simply need to run up a few side projects first to polish up my very rusty sewing skills.

Do please post when you get your beastie finished – it’s an innovative and interesting design. Most of the bivvy tents on the market are pretty underwhelming and overweight, so it’s an excellent field for MYOG.

Delta peg is an interesting idea. Maybe Vargo Outdoors could get interested in getting with them to make a titanium version.

For my tent the forces on the pegs are predominantly horizontal, not lifting as shown in the Delta drawing. And can be made even more horizontal by pegging from an extended cord.

For what it’s worth, it would be easy to make my design with more headroom: simply start with a taller pole, maybe one with a simple hub at the top to keep the tent from getting too wide (it’s currently 44″).

Do send us a picture of your concept some day. Good luck, and stay warm even if you can’t stay dry.

Geoff, please note the post that included:  “The most important question is why would you be using a sil/PU fabric instead of a high-quality sil/sil if you are going to seal the tent the traditional sealant way instead of with tape?”

First, you can get high quality silpoly from a Yama tarp that is polyester, so won’t slip and slide so much on the top or on the bottom.  Would not use it for a canopy, because would want to let light in.  But for a floor, the darker color is OK.

Second, there has been a lot on BPL about ‘sil/sil’, almost like a religion.  Some of the PU is not PU anyway, but PEU.  And does anyone have any reliable test results?  Haven’t seen any.

Third, if you practice site selection, the bottom of  the floor will remain much dryer; visibly so, and when the tent is struck.  It’s the canopy that takes the hammering.  So it’s looking for a problem instead of a solution.

Also, I have had problems with some the tent fabrics coming from RBTR and Dutchware.  That’s one of the reasons for harvesting tent fabric from tarps.  It doesn’t take much when building just one tent to use the best fabric available.  And it’s still way cheaper than a  laminate tent.  Granted, it weighs less.

Finally, I respect your challenging to build a tent with adhesive only, sans thread.  But that is something that I would not trust for a trek of any duration.  So for me, sewing is a blessing, not a curse.  And I’ve spent way too much on unsewn laminated fabrics, that use flimsy plastic outers for waterproofing, and are not even woven underneath the wrap, so are next to worthless in a blow, as was shown on BPL of a trek led by Skurka.

Bottom line, I think that BPL is becoming more like the disinfo groupies who infect media at every turn.  But if you do use adhesive, it is very expensive to get the best, and I’ve seen no proof on BPL that it lasts in extended outdoor use.

If it’s going to be all about dropping a few ounces of weight, the penalty could be a very expensive one, in every way.

Couple thoughts

Can you build it is such a way as a replacement floor or method of attachment can be done if original constructions methods need improvement.

I have some 70d ripstop nylon with the silnylon PU blend on one side only,  made into a shower cap that my wife still uses from the 90’s so I wouldn’t worry about a small percentage of PU in the blend losing water proofness (though I have had some blends that I purchased as 2nds that had an odor, which may have been the PU off gassing)

I made a view barrier for my backyard from the odiferous fabric and it lasted for 3 years of full sun and weather exposure before a high wind tore it at the single sewn seam. The coating appeared intact.

So the sewn seam might have contributed to make the older fabric weaker.  Blimey, had not seen this before, even on an older tent that made many long trips in Colorado etc. for decades.  It  was a PU/nylon Eureka!, which are not known for their durability compared to higher quality tents.   The PU coating finally lost its waterproofing in a few spots near the peaks, and would not take a recoat despite many attempts; so the tent was cashiered.  But the fabric did not tear, at the seams or anywhere else.

So suspect it was the fabric PU coating on my tent that wore out.  And note that in the BPL post about the Skurka trip that I mentioned earlier, it was the bonded DCF tents that tore on the laminate; whereas the woven sewn fabrics did not fail. The photos of the torn DCF tents are frightful, though.  Would TNT have made a difference? Still I guess that’s one small strike against sewn seams.  I always use lap felled  sewn seams, and not the faux kind, and that may be an answer to prevent tears on material like Dave’s worn out odiferous fabric, not to mention the fabric on 1.08 ounce (measured) silpoly that Yama uses.

Sam – your idea of harvesting tarps from makers who can access good fabrics is a counsel of perfection, but way beyond my budget I’m afraid. On top of the fabric, I’d be paying for the maker’s labour and profit, plus shipping, import tax, handling fees and UK sales tax… It would get ruinous pretty fast. And in any case, Gen has rationalised his range and doesn’t seem to be offering flat tarps these days. I’ll have to take my chances with RSBTR, I think, where I can cut expenses with one consolidated order.

Taking advice from experienced builders, the most suitable fly fabric for my 3.5 season project is a 40d Silpoly. This leaves me with a choice of one – the RSBTR 1.6. I know two well-regarded cottage makers who use it with success, so how bad can it be? They advertise the coating as a blend, but as I posted above it turns out that the PU content is trivial, and it’s the modern aliphatic form which performs far better than the stinky old hydrophilic form which is the root of PU’s bad reputation.

As for bonding vs sewing, I’ve already been persuaded to abandon the idea by Moab Randy. I have been in touch with a couple of people in Europe who claim success, but they aren’t using their gear so intensively – and windy, exposed treks are probably not the right place to experiment. Plus sewing is technically easier, so there’s that.

And yes, I’m suspicious of the faux Flat Felled seam for serious weather. One advantage of the RSBTR 1.6 is that you can reportedly iron in a crease. This makes sewing a true Flat Felled through 4 layers much more practical on a single needle machine. I’m also told that it will take basting tape more easily than a slick silnylon, which is another prop for a newbie sewer like me and helps seal the seam.

Dave – thanks for pitching in. As a newbie it’s always good to hear from someone with your experience!

Yes, I’ve been thinking about a replaceable floor. Unless you can suggest something smarter than I’ve come up with, I don’t see why I couldn’t simply rip and replace the seam. Or failing that, cut it off and re-sew with a slight loss of width and height, but not that you’d notice. After all, tent repair services replace floors as a matter of routine, so I don’t see why it shouldn’t be practical.

Or Moab Randy suggested a way of getting by with leaky bathtub floors by using a light waterproof lining on the inside instead of a footprint – a new idea to me.

As I said to Sam, the top-end modern PUs don’t stink up, especially when they only make up a couple of % of the blend. Your view barrier would likely have been the old hydrophilic type, which is another story entirely. Sadly, it’s still used on some cheap products, so PU’s bad reputation is still with us…

Hi again Geoff,

I note that you talk about sewing a true flat felled seam, which I refer to more descriptively as a double lap felled seam (DLFS), by ironing in a crease and then trying to fit the pieces together and then trying to hold them together with pins. I’ve seen Youtube videos advocating this and I can’t imagine a better way to discourage MYOG projects than to make people think they have use such an awkward and time consuming method (one that would be almost impossible on really light fabrics or those with soft hand). You don’t.

I will write about this again when I write up my tent, but I’ve studied this a lot and seen a lot of confusing terms. One seamster from a prominent UL tent manufacturer even wrote in to say you cannot make a true DLFS on a home machine, claiming you must have a special folder or double-needle machine or some such. So people on BPL are resorting to all sorts of ineffctive variations on the faux felled seam.

Eventually I found an easy way to do it (not on BPL), so simple that I should have thought of myself a long time before, but I think it only works well for straight seams. It requires three passes through the machine. I just used it to join the long “ridgeline” seam in my tunnel tent. This is the method:
• Mark a line for your seam width on one of the two pieces of fabric with a Sharpie (metallic silver or gold or bronze work best on silnylon). I used 7/16” because I’m klutzy and inexperienced; you might get by with less.
• Lay the second piece of fabric over the first, like a shingle, one piece to the left, one to the right, until the cut edge on top aligns with the marked line. Pin the fabric every three inches or so with tiny silk pins perpendicular to the seam length.
• Stitch down the middle of the seam width. No need to lock your stitches at beginning or end, no need to be precise in getting it in the middle; this is only to position the fabric. Remove the pins.
• Tightly fold both pieces of fabric over as a unit ONE TIME in the direction such that both cut edges are hidden inside the seam and you haven’t added anything to the seam width. Pin it again.
• Stitch down through all four layers of fabric close to the fold (about 3 mm in from the fold) on one side, then remove the pins.
• Turn the tent over and stitch down close to the other fold. You are done.

If you try to do this with two curved pieces of fabric or one piece curved one straight, you will quickly see that it’s not manageable (try it with pieces of paper and you’ll see). Eventually I came up with my own way to make a true DLFS except that it includes five layers of fabric (and also three passes through the machine), and it works equally well for straight and curved seams. I prefer it to the first method mentioned, even for straight seams. It’s easier to feel the place to make the first fold. I have just used this method to join the “cone ends” of my tent to the center (the edges are actually curved, especially in the rear). It works really well. And the thicker the fabric the easier it will be. This is my method:
• Mark a line for your seam width on one of the two pieces of fabric with a Sharpie.
• Lay this first (marked) piece of fabric right on top of second piece such that the edges align and pin it securely, maybe every two or three iinches or so, depending on the curve or lack thereof.
• Stitch carefully down the marked line. Remove the pins.
• Tightly fold the fabric over once right on the seam you just stitched and then fold once again. Pin it securely.
• Stitch your first line maybe 3mm in from the edge of the fold. Remove the pins. You will see that the original stitch line is right at the fold and visible. Not a problem, since the stitching doesn’t go through to the inside of the tent, and you’ll be sealing all this anyway. But if the appearance bothers you, fiddle with the direction in which you fold and then the stitch line will only be visible inside the tent.
• Turn the tent over and stitch your second line. You are done.

Practice one or both of these many times and you’ll be on your way.

Geoff; Once I have the right fabric, the rest is just a fun hobby with tools that have been in the workshop for a long time.   So for a tarp running $150-250, that’s the cost of the project unless some doodads run out, which seldom happens.  But see now what you mean if a tent maker is going to be paid for all the work.

Also, am sorry to hear about Gen’s issues with flat tarps, and that is why I already bought some for the next project.  But even with a cat-cut tarp ceiling, there is plenty of usable fabric, and sometimes it is possible to harvest the tarp for a new project.  Believe me, am not wealthy by any standard.

Geoff, Dave, and Moab Randy; Thank you for all the info about tent design, construction and materials.  With a large ping-pong table to work with,  most of a tent canopy can be built and shaped along seams held only with fine pins.  Often, some of the seams will be cat-cut; such as the ceiling(s), and the vestibule(s), depending on the design and orientation of the fabric. But for me, they are not cut until after the  fabric panels, with plenty of seam allowances, are pinned together to make the upper canopy shape.  And adjusted to make the shape as taut as possible.  Sometimes a light carbon rod is bent at the right length to mark where the seam should go to maintain a cat-cut.

Once the taut shape is accomplished, then the panels are marked with lines to show where the seams will go.  Placing the marks to come out with a flat felled seam is a little tricky, because such seams are not sewn in the middle.  But for me, there is no cutting and sewing until the seams are adjusted for the tautness.  I’ll study your posts further for ways to approach this.

So with the right design, there is measuring, but not much other math involved, and is more like what happens in a tailor shop, but simpler because tent panel shapes are much simpler than clothing.  And as I found, there are ways to simplify the construction even more:

The span between the above 2 peaks is sewn with a straight seam, but adjusts by itself to a curve when the ceiling is tightened.  So no cat-cut curves for that.  The side panels (which make the tent more comfortable than an A-Frame) are bowed out by the four flexible carbon poles (visible in the photo inside the fabric).  The equally sized front and rear vestibule panels (not shown in the above picture of the model) require 4 seams joining them to the ceiling. Since the leading edges  of the ceiling are held straight and tight when the poles are installed, no cat-cuts are needed at the seams joining the ceiling and the vestibule panels.

So the structure is tight and fairly easy to build.  The biggest challenge, noted by Roger Caffin when he saw the design on a BPL post years ago, is how to install the poles under the canopy as shown in the above photo. This led to a major redesign. The final (hopefully) conclusion was to use some small light and strong pole clips from Dutchware, making it easier to install the poles outside the canopy, thus making the canopy an inner wall, sewing the vestibule panels to the inner wall, and as is usual, using single walls for the vestibule panels for the front and rear of the tent.  Then the inner wall can be covered by a narrow fly with some overhang on top.  The overhang on the fly, would also add ventilation, but like any vent, must be covered against blowing rain..  The narrow size of the fly makes it lighter than most, and easier to install.

The problem then became finding an inner wall that would breathe and maintain the shape of the wall in the picture.  Pole sleeves would take more time to install, and in any case would just destroy the stretched taut shape of the woven silpoly inner.

Also, the inner wall if coated only with durable water repellent (DWR) would soak out immediately during pitching; so needed  something more water resistant.  The answer was to use some membrane 1.1 from RBTR, and drawing from Stephen Seeber’s findings on BPL, give it just enough time in the washer to remove some of the water repellent, yet maintain some breathability.  This  approach may sound bizarre; but has been used by tentmakers, including Go-Lite on its ponchos; but Go-Lite’s fabric was too dark to use as an inner tent; whereas the Membrane comes in a light green.  So with a bit of washing, the membrane may provide a material that will repel water long enough to pitch without leakage, and breathable enough to add to ventilation as an inner ceiling.  Yes, I know, hope springs  eternal.

But the point is that the shaping, cutting and sewing are not the biggest challenges.  Rather, it is the endless niggles.  Like how to lighten the weight of the vestibule zippers, or limit them to the front vestibule (I use Warmlite # 3 zippers that are stronger than market #3’s, but  almost as light; specifically, around 0.11 oz per running foot plus the weight of each pull).  So for a solo tent, with a large side entry front door, is it really necessary to have a full zip at the rear side, a shortened zip, or no zip at all, just in the rear.  And is it better to eliminate the weight of a full rear entry door, and extend the main floor into the rear vestibule for a dog or small child, or just to lay down the pack and other gear where it can dry out away from sleepware in the main tent.

The late Jack Stephenson said that tent making is “a form of insanity.”  But as Jack and his family and others have found, there is nothing like being able to stay warm and dry in a tent of your own design and making, while a wind and rain storm is raging just outside.  And please excuse me for not sticking to the OP’s issue.  As Jack suggested, and I’ve tried to show, tent making involves numerous issues that must be considered with each other.

I have done a bivy that has the same problem

I sew the floor piece and hem the edges – fold over twice and put a row of stitches through it.

That could be flat, or a “bathtub” floor where it extends up all sides and inch or two (like Roger said in “Australian” : )

Then I hem the top piece, the tent

Then I just sew the tent to the floor with 1 row of stitches (or 2)

Since you’re sewing through 3 layers of fabric, it’s stronger.  If you did 2 rows of stitches it would be about the same strength as a flat felled seam.  There isn’t a lot of force on it anyway because the floor doesn’t pull on the seam like the tent does.

If you had to replace the floor, just cut it off and sew on a new floor

Jerry – great suggestion! I think that’s the way to go.

Did you find that seam-sealing was enough to prevent significant leaks?

I was hoping to use one of the RSBTR XL extra-wide fabrics for the floor. This would give me enough width for a small bathtub, which would help keep out the damp. But I’ve just checked and they are short of stock. If I have to use normal width I’ll have to sew the seam with a flat floor, because I really don’t fancy a seam down the middle of the floor as well. So leaking would be more of a danger.

I didn’t seam seal.  In my case, if it’s rainy I’ll put up my tarp, so there’s little rain flowing over the seam.

Make sure it’s like shingles on a house – the upper fabric goes over the lower fabric so any water will naturally flow to the ground, not onto the floor of the tent.

I don’t seal any tent seams anymore – they don’t leak.  You could not seal it, use it, and if you found that water was leaking in in some cases then go back and seal it.

Sealing it is pretty easy so maybe do it and be done with it.

I don’t worry about bathtub floors on tents.  I never camp in a puddle.

Once I camped, it rained, a puddle formed, I noticed there was water around me but my mattress was 1 inch thick, more than the puddle depth.  I just went back to sleep.  In the morning the puddle was gone.  I try not to repeat that and avoid camping in spots that will become puddles.

If your fabric wasn’t wide enough, forget the bathtub floor.

Hi Randy (I’m guessing that’s your name?)

I think I have a way to sew the double lap felled seam. The key is a very sticky basting tape by 3M, which just about holds on a sil coating. I got turned onto basting tape by the guys at SailRite who are evangelists and use it for pretty much everything they do from sails to cushions…

It’s a simple procedure, but it’s easier to do than describe:

1) Lay out panel 1 right side up.

2) Stick basting tape that’s the width of the seam along the edge of panel 1.

3) Stick the edge of panel 2 to the basting tape, right side up.

(For practicality, I do 2 & 3 in 1 meter stages)

4) Fold the overlapped strip to one side and pin or clip. This gives you your 4 thicknesses.

5) Sew the two rows of stitching, using the edge of the folds as a guide.

Makes a substantial leak-resistant seam.

I’ve been trying this with some silnylon offcuts and so far so good. A bit more practice and I’ll be confident.

Plus I’ve had a chat with a guy in the UK who builds his own gear to a remarkable standard. He tells me that you can iron a crease in the RSBTR 1.6 silpoly, which would make for an even nicer job. He showed me closeups of his DLFS efforts, and they’re neater than my tarp from a well known US cottage maker. He also has a trick for using a felling foot to keep the seam straight.

Speed doesn’t worry me – this is a hobby and I’ll invest whatever time it takes!

But if my plan doesn’t work out, I’ll certainly give your 2nd method a try. I’ll have a cat cut so the 1st method probably doesn’t apply.

Hi Sam

Yes – the devil is in the detail for sure. I’ve been worrying away at this project for a couple of years, but never felt I had nailed my design goals till now. I already have a decent tarp, so there’s been no rush.

Your shelter has an innovative approach to the panel poles, which makes it both interesting and challenging. Have you had it out in the field yet? I’d love to hear how it went.

Your dilemma with the pole attachment is typical of the details that will make or break usability.

I have a similar issue. For storm-worthiness and ease of use I’m going to use my walking poles to create an inverted V at the entrance to my A frame, attaching the poles to the seams to support the side panels. Surprisingly, there’s no walking pole A frame on the market that offers this, but I know from experience that it makes for a much stronger shelter with much easier entry and exit and more convenient cooking.

But how to attach the poles? Sleeves are optimal mechanically, but a pain to erect, especially as my poles may have snow baskets at the end at times. So then you think, what’s the simplest option? The answer I came up with is to slip the poles through loops of tape sewn into the seam and tighten the loops with military spec cord grips. Quick, simple, failsafe, flexible enough to accommodate any diameter of pole, cheap and doable. But being a bear of little brain, it took me some time to think of it.

But on the whole I prefer to avoid innovation – my general approach has been to steal the best bits from proven designs. For example with a single wall shelter thru-draft is vital, and far from ideal in commercial designs. And because it’s a tiny shelter I want a view in the rain or it will be a coffin. So I need a front door and large rear vent I can leave open in anything short of a full-on storm. There’s a classic 4 panel vestibule from the wonderful old Saunders A frames that solves one issue. And a design from a tiny UK cottage maker that solves my rear vent. And I nicked the flexible door design from another obscure shelter I had back in the ’80s so I can dial in the level of venting and insect protection I want. And so it goes.

The other design challenge, as with all lightweight equipment, is making the right tradeoffs. For example I’m trading off a little speed of pitching for a lot more storm-worthiness and usability. For me that’s the right choice. On the other hand the Tarptent ProTrail, another single wall A frame, makes a number of compromises in storm worthiness and vestibule functionality to achieve a lightning fast 4-stake pitch. For sheltered camping in the heat I’d choose the ProTrail. Horses for courses…

As you say, something of a mad hobby, but very fun.

Hi Jerry

I’m typically camping in places like this:

Peat-bog from horizon to horizon.

Bathtub floors are very popular in these parts!

very nice.  I love pictures of where people go.

I normally camp on dirt/gravel.  Water soaks into the ground but when it rains a lot there will be puddles.  It is possible to see where the puddle will form.

Geoff, the seam method you describe sounds like the first one I described but with the addition of tape instead of stitching to hold the pieces together. Good for a straight seam. But I don’t see why tape is necessary to make the seam waterproof. Simple sealing should do it. And a ridgeline is at low risk for leaking anyway (if that’s what you’re building), since no water is pooling there. But maybe the tape, by adding stiffness, helps you to fold a neater fold, so that might be worth it alone.

But I would be very interested to know of a basting tape that would stick to silnylon for other purposes. I’ve tried two types (one from Sailrite) and neither did a thing. What is the specific tape you use? Thanks.