[pct-l] seam sealing a taped-seam sil-nylon tarp/fly?

[Ron Moak]

Matt,

>> Why shouldn't a urethane sealant be reapplied to the nylon tape?  Perhaps
I'm missing something here, but wouldn't the solvent found in the new,
applied sealant simply dissolve the old sealant until it evaporates? <<

The polyurethane sealer does not dissolve the old sealant. So if your
polyurethane has started to degrade, adding additional sealer won't solve
the problem. You can apply additional coating to tape and it'll probably
stop the leaks. However, if the tape and sealant have degraded, you soon see
leaks in other areas. 

>> The seam tape is most likely nylon of some sort and should be chemically
permeable with a polyurethane sealant. <<

Unlike silicone coating, polyurethane doesn't soak into the fiber. That is
why you frequently see it flaking off of old tents like sunburned skin.
Silicone not only soaks into the fiber, it actually strengthens it. This is
why we can get away with using 30 Denier fabrics where we've traditionally
used 70 Denier. With coating the 30D fabrics are stronger. 

>> Shouldn't the outside seam side be re-impregnated with silicone sealant
if the tape leaks?  <<

I believe that's what I said. Since seam tape is applied to the inside seams
of tents, on silicone / polyurethane coated tents, the outside will be
silicone coated. This is the side to apply the new silicone coating.
However, this is a new coating since the factory doesn't seam seal this side
of the fabric. 

The idea is that you're going to the trouble of seamsealing the tent, just
do it once and be done with it. This is best done with silicone. With
polyurethane, you're just kicking the can down the road.

Ron