Silpoly rainshell seam sealing advice please

Hi Matthew

Silnet is $$$. Exploitive.

Thinned silicone, from a cartridge, is not all that good for fabric. I explain below.
What some of us have been using with very good results is small tubes of Permatex Flowable Windscreen Sealant, undiluted. I use it. But there are quite a few others brands now, and if you seal the tube up quickly they will last a long time.

Explanation: there are thousands of different formulations of ‘silicone’ (really). The ‘silicone’ which comes in cartridges is OK for what it is designed for, but it is not designed for use on fabrics. I find it better to buy the small tubes of ‘silicone adhesive’ (as opposed to ‘sealant’) as it sticks much better to the silnylon coating and does not need diluting. The Permatex stuf works more as an adhesive.

Further explanation: diluting cartridge silicone has real problems. Most industrial solvents contain a few percent of water, and the cartridge stuff is quickly catalysed by water. It is designed that way. So what many have found is that by the time they are ready to spread diluted cartridge silicone on whatever, it has already gelled in their mixing pot and started to cure. It is just the wrong stuff. (Fine for bathrooms and gutters, pumped straight from the cartridge, of course.)

HTH, Cheers

Thanks, Roger.

So silicone is the correct thing to use on Silpoly?

I see references to silpoly being silicone treated on one side and polyurethane. How would I know if that was the material? I suppose I could put a little dab on the fabric and see if it sticks or not…

Hi Matthew

It’s complicated. Part of the complication is that a really accurate technical description of the fabric and the coating is not always available, or perhaps that the marketing dept does not have enough technical knowledge to be able to keep the spin accurate, or perhaps the coating plant in Asia did not tell the customer exactly what they were buying. Some of the ‘coating plants’ in Asia are a bit ‘backyard’.

One ASSUMES that the word ‘silpoly’ is meant to be a contraction of ‘silicone’ and ‘polyester’, as with silnylon. If the fabric has a coating on only one side, the coating is likely to be just PU.

But quite a few silpoly fabrics actually have a silicone coating on one side and a PU coating on the other side. There are several reasons for this dual coating: a silicone coating (applied first) strengthens the fabric very significantly while a PU coating makes it significantly weaker; a good PU coating gives a higher HH than a silicone coating; and you can use a stock acrylic seam-seal tape on the PU face.

More recently some coating plants have been experimenting with a silicone/PU mix. I am not sure why they are doing this as it sort-of nullifies the benefits of each coating. Perhaps it is just a marketing thing? Dunno.

Anyhow, how can you distinguish between silicone and PU? The appearance of the coating will generally tell you which is which, provided you know what they should look like (in some detail). A far simpler and usually more reliable method is sticky tape. Take a bit of good brand sticky tape and rub it down onto the surface. Leave it for a minute and then try to peel it off. If the coating is PU, this will be hard; if the coating is silicone the tape will peel off fairly easily. I have actually seen 3M9485 tape rip the PU coating off the fabric in one case.

Personally, I prefer a silnylon, although I could live with a silicone/Pu nylon fabric. I would put the PU face on the outside, with a seam-seal tape over it (on the outside). For straight silnylon I would use a siloxane tape, as I have on a number of tents I made and sold.

But why nylon? Because in a howling storm the elastic nylon will absorb more shock than polyester. I admit this is based on a couple of very simple lab tests and I have not tested it in the field. Also, the elasticity of the nylon means that the tent will accomodate slight sewing errors much more easily. For the same reasons I do not use Cuban on my tunnel tents.

Some bias is evident here: the gently mild ‘Sierra Summers’ don’t apply here in the Oz Alps. All-night 100 kph storms are a fact of life here. Sleet at the peak of summer, and hailstorms 2 hrs after a clear blue sky … we get them. Part of the fun, but with gear implications.

HTH, Cheers

Thanks again, Roger.

I have some 3M 9482 transfer tape. I’ll see how both sides of the jacket respond to that tomorrow.

3M9482 transfer tape has a moderately thick acrylic adhesive with a high bonding energy. It should work well on a PU coating, but it will NOT work on a silicone coating. That would be a waste of time.

Note that you will need to select a PU-coated fabric to act as the carrier or backing for this. I have not seen many PU/PU coated fabrics, so the tape on the exterior surface will probably be a bit obvious.

What one would normally use for the outside surface of a PU-coated fabric would be a clear single-sided tape or a clear thermal bonding tape (or a liquid PU sealant from a tube). The seam would then be only a ‘little’ visible.

Cheers

Roger, I am officially confused.

1) This is an existing rain jacket. It’s not a tent and I’m not making a new jacket. I want to seal the seams on it.

2) I’m trying to figure out what it is made out of so that I can try to seal the seams.

3) I was planning on using the tape in an inconspicuous location to try and figure out if each side has silicone on it (releases easily) or if there is PU on the inside (release would be difficult).

Once I determine the likely coating on the fabric I will ask about strategies for sealing it.

On a smal test section, I would try using the normal method of diluted seam sealant on the outside (very diluted, so it can flow into the seam), or the Permatex stuff mentioned above. Never tried the Permatex stuff, but it sounds interesting.

Is one side less slippery than the other? If yes, then that would be the PU coated side. If no, then it’s all sil coated.

This thread covers all your options:

https://www.hammockforums.net/forum/showthread.php/142569-Silpoly-seam-sealing

That’s a good idea about tape.  When I lay out fabric I tape the corners to pull out any wrinkles.  With silpoly or silnylon the tape barely sticks

silpoly is good for tents because when you set it up taut, it won’t stretch overnight and be loose in the morning like nylon.  For a jacket that doesn’t matter.  Nylon a little stronger for the weight.  But the difference is small – silpoly would work fine for jacket.

I have silicone on hand for gutters, so it’s easy to just dilute it (10:1 with mineral spirits).  A lot of people swear by Permatex.  Easier to not have to dilute it.  Probably cheaper if you just want a small amount for seam sealing.

@Matthew: sticky tape is your guide.

@John: I was talking about fabrics in general, and what external tape would look like on a jacket.

@Jerry: The problem I have with the cartridges is that once I have opened one, it goes off in a couple of months. On the other hand, the Permatex and other adhesives in a tube seem to last for over a year or more.

Cheers

Ok. Thanks for all of the responses. It looks the same on both sides so I’m guessing it has silicone on both sides. I’m too tired to get motivated to do a spot test tonight. Maybe tomorrow.

Matthew,

Luke’s Silpoly was from RBTR. If it looks the same on both sides then it’s positively Sil/PU blend in which case you’ll want to just use standard silicone. I have Silpoly PU4000 on hand and can tell you that the PU side looks totally different. There’s no way you would mistake it for standard Silpoly. In summary, no need to test. It is silicone both sides and will seal with any standard silicone. I would recommend running into your local auto parts store and grabbing a tube of Permatex Flowable Silicone per the above. It works great.

Excellent. That is very helpful, Hoosier. Both sides appear identical.

Question, how do you recommend applying the Permatex? I’m assuming I should hang the jacket on a hanger, put a thin bead along the seam and then work it in with a small artist’s brush. Does that sound right? Any tips?

Find rather plump and gullible stooge.
Fit jacket to stooge with arms outstretched.
Apply sealant directly to seams from tube, via small nozzle if poss.
Press into seam with (one only) finger).
Feed stooge occasionally while the sealant dries.

Tents are easy: they just sit there. Jackets are harder.

Cheers

If you seal a seam with fabric loose, then stretch the fabric (by putting up tent or putting on jacket), the seam sealing will split open right at the seam junction

if you erect tent or put jacket on stooge, that will stretch the fabric, then seal the seam.  Seam sealing won’t split

if you put jacket on hanger such that it stretched fabric, that would work, then you don’t need a stooge

I don’t have a plump stooge. Maybe I’ll just stuff it full of towels and work one part of the jacket at a time.

Thanks again!

stuff it full of towels
Yeah, that should work. Done tightly enough it should handle Jerry’s concerns.
It’s why I often use siloxane tape instead.

Cheers

Balloons work well. Especially the long ones in sleeves and trouser legs.

Balloons … Now that is brilliant.
Admiration.

Cheers

Yeah, I like that idea.

Sorry for the delay, I just saw this thread.

GE 100% Clear Silicone (either I or II) is a good brand and highly recommended. You can get this in large 24floz tubes, small 10floz tubes for guns, and smaller 2.5floz,1floz and even smaller tubes for single use. Silicone caulk IS an adhesive. All 100% Clear Silicone caulks are. Sometimes a manufacturer will add things to enhance some property: color, mold resistance, adhesion, paintabilty, etc. None of this is needed or wanted for rain jackets/tarps/flys/backpacks or other waterproof backpacking gear.

It includes a chemical inhibitor to prevent “drying”…actually “setting up” or “vulcanizing” the rubber like compounds is more correct, indeed some companies market a “room temperature vulcanizing” (RTV) product that is perfectly correct to say and 100% advertisement mumbo jumbo. When this chemical gets damp (usually by absorbtion of water vapor from the air) it breaks down the inhibitor allowing the caulk to set. This can take from 3-48 hours (sometimes longer) depending. Sometimes, you can find an old sealed tube that is hard. The inhibitor is not real stable and can break down with age.

Some companies use some solvent to dilute the silicone. This does NOT change the fact it IS silicone. It is just easier to move around and will penetrate a little deeper into the fine cracks and crevices of a woven fabric. When the solvent evaporates, no harm is done, generally. Different chemicals have different properties of course. Some can speed up the drying process by pulling in water vapour, or inhibit drying by encapsulating the silicone/vulcanizing inhibitor and not letting water vapour in. Anyway, this is what petroleum “dilution” does. Basically, about the same as placing a piece of plastic wrap around a glob of caulk, but on a much smaller scale, of course. Or storing it in a plastic tube…

Your rain jacket should be freshly laundered and rinsed twice. No oils or dirt on it. Then allowed to dry, turning it inside out every 8 hours or so until dry. Dilute the 100% Silicone caulk about 1 part to 1 part mineral spirits (NOT the eco-friendly stuff!) Mix this together. Then mix in another 4-12 parts of mineral spirits. You should do this all relatively rapidly. Once it is mixed it is good for several hours because the mineral spirits will slow the uptake of water vapour by the caulk, it really doesn’t stop it, though. You cannot leave it for more than 3 hours. It will NOT keep.

Using a cheap-o chip brush (around 2″wide, a cheap bristle brush or foam one from WallMart will cost about 79cents) brush your seams fairly firmly, then just smooth them over. A foam brush works with thicker mixes(1:2-5) and is easier to apply, but it will not penetrate as deep. A thinner mix (1:5-15)is easier to apply with a bristle brush and will penetrate deeper, but it will also be messy and “walk” away from where you apply it. On most seams, a thinner mix will actually penetrate deeper into the entire thread rather than just surface coating it. You can apply 2-3 coats of this, if needed. Usually you will not completely fill the texture of the fabric nor interfere with adhesion. I still use an old nylon jacket from over 30 years ago that I removed the tape from (it had gone bad in several places) and coated with a couple coats of 1:10-12 mix. It actually is more flexible than the tape was and packs much smaller, now.  Anyway, do with the seams, then do the seams again after about a 15 minute break.

I also have an old tent with a PU floor (both sides, apparently) that has a seam in it. A few years ago, it started leaking. I simply brushed on a mix of caulk and mineral spirits and it stopped leaking. No, it probably does not have the original 10,000mm head. I usually use this on every trip since it takes about 5-6 hours to get to a trail head…I usually stay at a state park the first night.

OK, Now for a little more chemistry. What happens is the mineral spirits (or white gas/Coleman fuel) will actually form a colloid around the inhibitor/rubber. This restricts the uptake of water vapour. When the mineral spirits evaporates, it leaves the caulk behind where it is free to pick up the water vapour and vulcanize. This is actually an ongoing process, and, you might notice the mix becoming thicker as you use it. After a couple hours, it is likely degraded and shouldn’t be used further. But it should last long enough to seal any seams/threads/leaks you have.

Thank you for the detailed information, James. I have two followup questions, if you’ll indulge me:

1) Would you recommend I launder the jacket using conventional detergent? (This seems like an important step and not one that I had even thought of.)

2) Do you agree with my plan (and the precious advice) to seal from the seams from the outside of the jacket?

Interesting James info (as usual), also Roger (as usual).

You could use a soap intended for outdoor gear

Don’t use regular detergent

Woolite from the store is good, I’ve used that

When you’re applying the sealant you want to work it into the seams.  Into that crack between the two pieces of fabric.  It is better to make it look bad and really work it in, than to just apply it perfectly.  If it’s 10:1 it will be so thin you will hardly notice after it dries.  You could always do one spot first, maybe a less noticeable place, let it cure, see what it looks like

If you have no use for silicone besides waterproofing, maybe the Permatex is just as cheap or cheaper and takes less time because you don’t have to thin it.  I haven’t heard anyone do it, but maybe you want to thin Permatex a little.

If you use caulk, when you first add the mineral spirits, it doesn’t seem to be mixing.  You have to stir it quite a bit to get it to start to mix.  Then stir it a bunch more to get it to fully mix.  Maybe stir it some, let it sit for a minute, stir some more…

Maybe hang the rainshell from a hanger so it will stretch like normal usage.  And stuff something in arms.

Overthinking this : )

Well, it is all synthetic, it doesn’t really matter. Just use very little and rinse twice. Nylon soaks some water, poly does not. They often use different dye media for this reason. Anyway…

Silpoly, in most uses, indicates that it is poly cloth treated with a silicone based coating. So, it doesn’t really matter. I believe the shiny side is due to rollers as it passes through a mill and the other side is simply left open, but I could be wrong on that. I have not purchased any new fabric in a couple years. I am not familiar with what the manufacturers are doing. It might simply be calendared to reduce it’s thickness giving it a sheen on one side…maybe both. Poly cloth is generally a little thicker than nylon. Anyway, it is safe to use 100% silicone on these.

In a few cases, Silpoly Poly or Silpoly Nylon can also mean a cloth with silicone based treatment on one side and a plastic(like PU4000) on the other. Yup, it is confusing. They are just getting around to standardizing on the names and this usage is depreciated.  So, this is getting rarer. Silicone will peel off the PU side rather easily, though it sticks to threads/seams OK.

some detergents have fragrance and other stuff.  The chemicals are harsher, a little harder to rinse out.

better to use a soap intended for outdoor gear, or intended for washing wool clothing