Not Happy with Silicone Seam Sealer

[manzana]

I am making a (BIG!) tent with a lot of help from this great forum. I got some Mc Nett Sil Net seam sealer at REI last night. ($13 worth). What a waste. My material is silicone-coated nylon so this is the only stuff which will work. Trouble is, it is like rubber cement and very thick. It does does not penetrate the fabric at all. It basically sits in the seam like caulk. It does stretch like it says, but will pop out under a lot of pressure since it really just lays on top of the fabric. My advice is to skip it. My testing showed that a tight seam was very waterproof anyway and would only leak under a lot of pressure- not from rain running over it. Any other opinions are welcome. (I believe the stuff does have value for mending rips, however, so I shall keep it!)

APPLE in AUSTIN

[flyfisher]

You might read the section of Jardine's book or Ed Speer's Hammock book where they talk about silnylon tarps.

This is what I do:

Buy a $3 tube of clear silicone seal from the hardware store. It is used to seal tile joints around bath tubs. I put about a teaspoon of this in a jar lid, and then add about two tablespoons of solvent. I mix this with a small stick and then a small paint brush. Then I use the paint brush to paint a half inch stripe along the seam. The silicone soaks into the small spaces and saturates the stitches. I have not had any leaking with this method with several tarps. The silicone is not thick enough to appear as a separate layer on the tarp. It has not peeled when applied this thin.

Jardine recommends paint thinner as the solvent. Speer recommends white gas (Coleman type) as the solvent. I have used both, and white gas seems to disolve the silicone a little easier and dries quicker.

Note: this is for sil nylon only. I do not recommend it for PU treated nylon. Seam sealer of the standard variety is better for that purpose.

Risk

[flyfisher]

BTW,

I have written this same advice often enough that I decided that it was worth writing it down in an http coded page. If anyone needs the advice again, it is here:

http://www.imrisk.com/seamsealer/seamsealer.htm

Risk

[tlbj6142]

For those that already have SilNet just mix it with some paint thiner (or white gas) until it is nice an runny. I used a staining "sponge brush" to apply it.

I think both www.tarptent.com and www.sixmoondesigns.com have similar instructions.

The real key is to thin it so it runny. Otherwise it (SilNet or $3 tub stuff) is just about unuseable.

[Youngblood]

Flyfisher,

I use the same technique with a slight difference. I put the clear 100% silicone adhesive in a glass jar with mineral spirits and then mix them very easily by using the glass jar (with lid) as a shaker. I use roughly a 50/50 mix, something that is thin enough to easily brush on. I also have had good results using a 1" wide foam brush to spread the thinned mixture. I found that it spreads easier with the foam brush than with a short-bristle brush. (You can always turn the brush sideways if you want a narrower bead of sealer.) I have used empty jelly jars, salsa jars, etc. for the glass containers. It is much easier to apply if the fabric is held taut. Before I refined my technique, it was much, much more difficult and frustrating to apply the sealer, now it isn't much of a problem. Buy plenty of the foam brushes (about $0.50 each?) if you are doing a large project as I wasn't able to reuse one the next day.

Youngblood

[manzana]

That sounds great. The stuff (Sil Nett) is awesome, just way too gummy. It would be perfect if it could be thinned down. Why the heck don't they mention that on the container? I have some serious experimenting to do now...

APPLE in AUSTIN

[Rambler]

Never had a problem with the stuff both from McNett and the hardware store without using thinners. Put down a glob and then spread it with my fingers. $8 hours later rub in some talcum powder. (PS Don't use alcohol as a thinner!)