How to Improve this Silnylon Hydrostatic Head? Longevity? Effect on Weight?

I’ve taken mineral spirits:silicone caulk (10:1?) and brushed it on.  Maybe adds a few tenths of an ounce per square yard.

A problem with manufacturers is the EPA doesn’t like it when the mineral spirits evaporates into the atmosphere, which you don’t have to worry about

I’ve coated bottom and it worked for many trips.  The surface that I sleep on held up.  The surface against the ground started coming off, but that shouldn’t be a problem for tarp.

Set up tarp, put on solution, wait 2 days.

But, I use low HH silnylon mid and it doesn’t leak enough to worry about.  Yeah, there’s some “misting” in heavy rain.  A very small amount of water in a fine mist can be detected on your skin, but it doesn’t get your gear wet enough to matter.

Besides, there’s sometimes condensation on the underside which gets knocked off by rain, and rain splash, and humidity.  The small amount of water from misting isn’t important.

If you sleep on it you need high HH.  If you have a horizontal surface maybe.  Sloped surfaces – not important.  Just one opinion : )

Jerry,

You said, ” I use low HH silnylon mid and it doesn’t leak enough to worry about” What shelter are you referring to and do you know the actual HH or just that it mists?

HH is not all about the silicone coating. Tightness and type of weave of the base fabric also factor in a lot.  A very tightly woven fabric with all the threads the same size (especially when smaller/thinner fibers), is going to tend to be more waterproof after a silicone coating than say a more loosely woven fabric that is also ripstop (larger/thicker threads woven in with the smaller/thinner fibers).

But adding more silicone coating can definitely improve the HH of a fabric that lacks sufficient HH to begin with.  As far as weight, it’s hard to say how much.  Most common silnylons start off with a 1.1 oz/yd2 30D ripstop nylon fabric, and end up weighing between 1.3 and 1.5 oz/yd2 with the silicone coating.  If you do a thin enough coating and only one side, you probably will add about .1 to .2 to the above.   I can’t say how much it would tend to increase the HH, but my guess is probably in the range of 100mm to 300mm, depending on how well you apply it, etc.   It’s probably better to use silicone adhesive rather than caulk btw.

I’ve also experimented with adding silicone (adhesive type) to very breathable fabrics to add a long lasting DWR, as well as decrease the air permeability and increase the HH some.  It can be done, but it’s important to start off with a fabric that doesn’t have any DWR to begin with.  Otherwise, the silicone adhesive won’t be able to bond to the fibers/fabric itself, and it doesn’t bond to the DWR because the DWR has very low surface energy (typically lower than even silicone itself, and that’s what makes it a DWR coating to begin with).  When doing this, it’s best to do this while stretching the fabric out as much as you can, and on a hot summer’s day.

Hi Ethan,
Both “arid” and “multicam” are patterns used on fabric. They have no relation to the quality of the fabric or coating. Possibly ‘arid’ is just a marketing attempt to imply the fabric has aramid (as in kevlar material) strength. I could find no evidence to support that when searching on Google.

The RBTR product page also mentions that its product may be waterproof breathable. There are so many fabrics that make this claim, I think one has to stick with fabrics that have a demonstrated ability to transmit water vapor. There are a number of these available from the DIY materials vendors. If you are looking for a ~one oz WPB material for shelters, join the club. BPL did market a 1.5 oz eVent years ago, and there have been some posts by purchasers. But none have demonstrated its use in a shelter. As I’ve often posted, I purchased some 1.8 oz Epic Malibu formerly used by Black Diamond for its single wall tents. Many of my posts received comments by Roger Caffin, BPL editor, that can be summarized by, “You will get wet!” Because I can make a well ventilated light weight netting inner tent that I know will keep me dry and weigh less than a single wall Epic tent, there is not much reason to invest a lot of time with the Epic.

“1) Is higher HH sil always heavier than lower HH sil? In other words, is HH all about more silicon coating?”

No, and no. HH is all about the quality of the coating and its application. Richard Nisley has reported on BPL very high HH on the RBTR 1.04 oz membrane coated with ‘PU2000.’ I’ve sent a number of more heavily coated silnylons to Roger for testing that had poor HH. Of course with a high quality coating, more of it will be more WP.

“2) For LG to reach 3000 HH, anyone know what the weight per square yard of their sil is?” Suggest you ask them. No one is going to cut up an expensive LG mid to find out.

“3) Is there a way to raise the HH of the RSBTR Multicam sil to 3000 (at least for the top of the shelter) without making the fabric significantly heavier? I’ve heard of people painting or spraying the tops of shelters with diluted silicon. Which mixture to use? How much weight would it add? How long would the coating.”

This appears to be the nub of your inquiry. DIY coatings have been posted about on BPL for years, with varying degrees of claims of success. And there have been endless threads about the sprays. But no one has demonstrated a significant increase in HH with a minimal weight penalty, let alone durability. Call me cynical, but if many of the industries, with all of their high tech manufacturing equipment, cannot produce high quality light sil/pu coatings, then what chance does a DIYer have in his garage? Very few of us are Thomas Edisons. Forunately, we can find a few higher HH materials in the 1-1.1 oz range on the DIY market.

“4) Anyone know a source for Multicam Arid or a similar quality camo sil (similar to color range of Arid) that has a higher HH?” Try Judy Gross at LHG. The Korean made silnylon she sent me was tested by Richard at ~2400 HH, and around 1000 HH after simulated aging. That much reduction in HH is common with his aging protocol, and he tells me the materials are still better than most of those used by shelter manufacturers. For a long time, Judy had the Korean camo on her website, and probably still has some.

It really depends on how high of an HH you are trying for. I usually take a good qualty SilNylon at about a 2000mm HH, then treat it slightly (with about 20-30:1) Mineral Spirits/Caulk after the first year. I do both sides so it is roughly doubled. I don’t really keep track, anymore. I thin it untill it won’t leave a “shiny” coating on a piece of scrap. Then I add a little more caulk to the mix. A lot will depend on the thickness of the caulk you are working with. Even the “GE” brands differ a bit from tube to tube. I have a new 9×9 flat tarp I made last year as an over the fire tarp where it will likely catch some sparks. I think the material ran about $50 and was a second. I re-coated it because new, it weighed about 11oz, or about 1.2oz per yard before seaming. It misted a bit, but it worked. I would NOT sleep under it, though. Any misting, even from condensation, will dampen everything. Here in the NE, water is a real problem, and with 100% humidity, it always penetrates everything after three nights of rain. After the coating it was about 13.3oz, or I added about 2oz in coating, or, right around 1.5oz/yd. Last fall in some torrential type rains for two nights it didn’t leak/mist a bit. An old tarp that has been re-coated about 3 times, seams 4-5 times, it now weighs about 17oz. It started at about 12oz. After three re-coatings, it added about 5oz to the tarp. This one I have used as a solo tarp after rebuilding it from an old “fire” tarp. (The pinhole marks were all removed.) I forget the dimensions, I think I added two triangular pieces to the front beak and narrowed it down to 6′. Anyway, it fits in a grease pot. Another 12×9 tarp had a heavy coating to begin with at 1.5oz/yd. I coated everything once and it added about .1oz/yd. Another was done (8×10) that was also successfull out of reflective material. Another was done in “orange” for a friend 8 years ago that is still in use today. He has done nothing with it other than use it.

So, coatings are generally, around .1oz/yd per application. Usually doing both sides is recommended. I did one many years ago that was at a 10:1 and it was like rubber, after that. Not real great, it added .4oz per yd after a single coat and wanted to stick to itself. I cut it up into ground cloths and used them for several years.

In every case, it was adequate for a tarp or tent fly. I would guess around 2500-3000mm HH. On one trip, I actually made a gallon “bottle” out of one till I got to an otherwise dry camp. Then I refilled everything, including my pot and cup. It carried the water for about 8mi and was still full of water and serviceable as a tarp at camp. (Getting the water out was fun, though.)

@Sam, still digesting this thread. Agreed Muticam Arid is a particular Multicam pattern that works well across a wide range of global zones, no relation to any material composition. The Multicam patterns are Arid (works well in N California among lots of other zones), Tropic (works better in wetter greener zones), Alpine (snowy winter environments) and Black (night). The RSBTR Multicam Arid Intruder is a silnylon material they ordered printed with Multicam Arid.

http://multicampattern.com/multicam_patterns/

Justin at RSTBTR got back to me with this info from Kyle about this material: “The Minimum HH on the Intruder is 1000mm. It uses a different coating method and is not as consistently coated as our treatments on our other coated materials. Because of that, the minimum number is 1000. You can use an DIY dip to increase the HH.”

I’ve used 2nds silnylon from owfinc.com that I got maybe 6 years ago.  Several batches.  So I figure it has low HH.

I’ve made a number of tents that had one ridge with a pole on both ends.  I’ve cut those up to make two mids which have more headroom for sitting up during long rainy periods.  Also, the perimeter of the tent almost touches the ground to minimize stuff blowing in during windy/rainy periods.

When it rains hard I feel some misting.  I can feel it on exposed skin.  But when I feel my sleeping bag underneath it doesn’t feel wet.

Some condensation in some conditions is unavoidable.  It forms on the bottom side of the tent.  It doesn’t matter how waterproof the tent material is.  Sometimes it will drip onto me, although with steep walls it tends to just run down the sides.  If there’s a heavy rain, it will knock some of the condensation off.  This is much more than any misting.  Except it seems like the condensation occurs when the sky is clear and the tent cools from radiative heat loss.  When it’s rainy, I don’t get so much condensation.  I suppose you could have a clear start of the night where condensation occurs, then there could be a heavy rain.

Now that I know more about this, I would try to get silnylon that had a higher HH for a tent.  For a floor, high HH is necessary.

Before adding silicone to a tent, I’d use it for a while and only add silicone if there was excessive misting – that is, there was a rain storm when my sleeping bag got noticeably wet.  If you add the silicone after you make it, it will also seal the seams.  I have never waterproofed my seams and never noticed any leakage.  Any water tends to just flow down the seam.

Once I had a velcro strip sewed to the tent (to hold the door open) that started dripping water in a rain storm, so I sealed that.  Horizontal seams would be more likely to leak.

It might be worth while repeating a few known facts about ‘waterproof fabrics’. All my comments here can be backed up by photos I have taken myself during testing I have done myself.

• Most any fabric can be made more waterproof by removing the ripstop feature. With modern fabrics, ‘ripstop’ is solely a marketing buzzword, and it brings nothing to else to the value of the fabric. High pressure testing shows that almost all leakages occur along the ripstop threads, due to the distortion these larger threads introduce into the weave. Photographic evidence of the lines of leakage abounds.
• The biggest advantage of silicone coating may not be the waterproofing effect but the strengthening effect. The result of having all the threads encased in a pliable ‘rubber’ is that any tearing force is distributed across many threads rather than just the 1st thread in the line. We are talking here about doubling the tear strength of a fabric, or more. Also, the bonding massively stabilises the fabric and prevents the weave from falling apart.
• When a fabric is silicone-coated and is being torn, the ripstop threads do not add significantly to the tear strength, if at all. Photographic evidence exists.
• Silicone coating is not 100% waterproof. It is for a start slightly porous, and very thin areas can give away. Also, strangely, silicone polymer is slightly water-soluble, so the coating will dissolve away over time in water (but it does not go ‘gooey’).
• PU coatings come in two forms: the older (water-based?) layer coated onto the surface of the fabric, and a newer version sometimes referred to as TPU or thermoplastic PU. We do know that the older surface coating absorbs water and degrades over time – it goes irreparably gooey or sticky. I do not know enough about TPU to be sure, but I suspect that it does not suffer hydrolysis in the same way.
• A fabric coated with the older form of PU loses up to half its tear strength compared to the base fabric, due to the way the surface coating focuses the tear stress onto a single thread. Yes, that does mean that the same fabric coated with PU might have a tear strength only one quarter of what it would have when silicone-coated.
• On the other hand, PU and TPU give a far higher hydrostatic head than a silicone coating, weight for weight.
• You can easily tape-seal a seam with a PU coating, using various technologies. It is harder to tape-seal a silicone-coated fabric as you have to use a special siloxane adhesive to bond to the silicone coating, and these siloxane adhesives are expensive. Many vendors will try to tell you that you cannot tape-seal silnylon, but that is just (wilful) ignorance on their part. Yes, I DO tape-seal my silnylon articles with such tape, and yes, it works. Technically, the siloxane adhesive actually bonds INTO the silicone polymer, so the bond as very strong, but it takes >72 hours to form.
• The latest developments in coated fabric is a dual silicone/TPU coating: silicone on one side and TPU on the other side. This works well, and correctly used always has a higher hydrostatic head rating. The TPU side can of course be tape-sealed as well.
• What is more interesting however is to closely examine an Si/TPU fabric during hydrostatic pressure testing. If the water is against the TPU side, all is well and there is nothing to see. But if the water is against the silicone side, you will see it get through the silicone coating into the threads. Yes, you can see a colour change in the threads when this happens. Now try drying that fabric.
• For some time a HH rating of 1,500 mm has been judged by some vendors as ‘adequate’. This may be so for the fly of a tent, although I would prefer at least 2,000 mm. It is NOT adequate for a groundsheet, which can easily get pressures several times that across it. Kneel on your groundsheet on very wet soil and you may get wet knees.
• Recent attempts to degrade industry ratings to 1,000 mm should be seen solely as a degenerate attempt to make things cheaper. Any weight savings due to the thinner coating would be very small, and the increased weight of your wet gear will nullify them quickly. On the other hand, some vendors are offering gear using a Si/TPU coating with ratings of >2,000 mm or more. These specifications are readily available from some coating mills, and the vendors using such fabrics are the good guys.

My 2c.
Cheers

• When a fabric is silicone-coated and is being torn, the ripstop threads do not add significantly to the tear strength, if at all. Photographic evidence exists.

So then any difference in tear resistance between the RBTR .9oz Membrane SilPoly PU4000 and the 1.1oz SiloPoly PU4000 is due to Membrane being a 15d fabric and the 1.1oz SilPoly being 20d? The ripstop adds no benefit for tear resistance because the material is Sil/TPU coated?

I’ve coated 3 tent flys with a 5:1 ratio respectively of odorless mineral spirits and clear GE Silicone II caulk.  Ratio is by VOLUME.

Rolling it on (exterior of fly) with a small, low knapp brush and lightly wiping off excess with heavy duty blue shop towels gives and excellent additional hydrostatic head to the fly.

For floors (exterior) I use a 5:2 ratio of mineral spirits to silicone caulk. Evidently I didn’t need to coat my SCARP 2 or Moment DW as Tarptent has improved the HH of their flys but I did it before I knew about the improvement. On the earlier Contrail it made a definite difference in driving rain storms. No more mist-thru.

I use the basic three step method.

1. Buy a can of silicone waterproofing spray
2. spray at fabric
3. repeat as needed

there are two types of odorless mineral spirits

one is watery and doesn’t work – it says “not a flammable liquid” on the side

the other is very similar to regular mineral spirits and works fine

if you can get non odorless mineral spirits that’s probably better

Ethan,

I sent you a PM reply, if you don’t get it use franco@tarptent.com

Never used the odourless or the vegetable spirit but from comments I have read from some that have done so it did not work or not as well as the standard (smelly) stuff.

I use the basic three step method.

1. Buy a can of silicone waterproofing spray
2. spray at fabric
3. repeat as needed

<div class=”likebtn_container”> I asked Richard Nisley about this particular process and he told me that using a silicone spray doesn’t increase HH.  It may help to maintain what HH you do have though.</div>

  
<div class=”likebtn_container”></div>
 

Thank you all for the very helpful replies. Lots of excellent data and experience. Well, after reading through this thread and related threads on Richard Nisley’s research on the best non-cuben shelter materials as well as silpoly, it seems going with a well-constructed material and a good coating method both matter, and that it’s difficult to raise the HH much or for very long by coating.

While RSBTR Intruder Multicam Arid is the best stealth pattern for places I’d most often use it, it has a listed low starting HH of around 1000.

@Richard do you think you could test it if I sent a sample? How large a piece would you need?

Justin at RSBTR added: “I just got done talking to Kyle about the difference in the treatment. The Intruder Sil is a 95/5 Sil/PU mix.”

http://ripstopbytheroll.com/products/1-1-oz-silpoly-pu4000 looks promising based on Richard Nisley’s tests, although there’s little experience with the new material. Wish it were available in Multicam Arid. Olive Drab silpoly pu4000 is the closest, but will stand out quite a bit against light dry ground or gray rock.

It’s good to hear Lightheart Gear’s Woodland Camo material is high HH and durable – it would be my choice for use in NE forests, and it’s less shiny than it appears on the material product page (just search for photos of a tarp or tent made from their material). However Multicam Arid will work better over a wider range including the Western US and South.

Thank you Sam for sending those materials to Richard and thank you Richard for testing. Really ups our understanding and hopefully also spurs shelter makers to use the best available materials.

Might be of interest

http://www.dtic.mil/dtic/tr/fulltext/u2/a439385.pdf

Ethan,

I have already started the process to test some of this material (1.1 oz Intruder Silnylon – Multicam). I will post my results to the forum.

So then any difference in tear resistance between the RBTR .9oz Membrane SilPoly PU4000 and the 1.1oz SiloPoly PU4000 is due to Membrane being a 15d fabric and the 1.1oz SilPoly being 20d? The ripstop adds no benefit for tear resistance because the material is Sil/TPU coated?

That has been my experience. The plain weave without ripstop usually has a higher HH and is more abrasion-resistant as there are no large threads sticking out.

Cheers

Ethan,

Today I tested the RBTR 1.1 oz Intruder Silnylon – Multicam. The following is 5mm FOV micrograph:

Its virgin HH averaged 949 mm H2O and so you should coat the fabric before using it for a shelter in heavy rain. The areal density measured 1.59 oz/yd2 and the thickness averaged .076mm.

You live in CA and the mineral spirits sold in this state are very low VOC. It will take up to three days for the tarp to dry after coating it using this solvent. I tested GE SS II mixed with CA MS in a 6:1 weight ratio. It provides >3,500 mm H2O virgin, >3,500 after 5,200 wet flex cycles, 1,757 mm H2O after 10,400 wet flex cycles, and 1,757 mm H2O after 15,600 wet flex cycles. The areal density increase is ~.04 oz/yd2.

There are lots of unique DIY formulations people use to coat silnylon tarps but, other than the tests I did, I have not seen measurements of the areal density increase and HH in the virgin and various aged states.

Its virgin HH averaged 949 mm H2O

That’s hardly even ‘waterproof’. Unacceptable, since there are many far better fabrics out there.

Cheers

Thanks, Richard! How did you arive at 6:1 for a formula? I used to just use the same cup size so this was by volume. Weight will be significantly different.

James,

I coated both microscope slides and 1′ square silnylon panels with a VERY LARGE combination of different solvents, concentrations, and silicones. After drying, I measured in the virgin HH and also the aged HH in 5,200 cycle wet flex increments for every combination.

The dilutions for solvents, were all by weight. It was simple to just put some silicone in a container of known weight. I then did the same with the solvent in another container of known weight to exactly match the mix ratio (I could pour back some solvent if I added too much to the 2nd empty container) and then slowly I added the proper amount of solvent to the silicone while stirring vigorously. Dilution ratios included 48:1, 12:1, 6:1, 3:1, 2:1, and 1:1. The higher dilution ratios all failed miserably during the first 5,200 wet flex aging cycle. 6:1 was highest dilution CA MS and GE Silicone ratio that would maintain > 1,500mm HH after wet flex aging on 5,200 iteration cycle (simulates a couple of weeks of wind and rain).

Roger,

You said, “Unacceptable, since there are many far better fabrics out there.” As usual you are absolutely correct.

Unfortunately there is no other source in the US or internationally for the Multicam pattern on a 1.1 oz nylon base, that I am aware of. That leaves Ethan with a mandatory recoating requirement if he wants to use that pattern.

Excellent info Richard!  Thank you very much for doing the research and reporting on it.