polyurethane varnish on ripstop

**rocketrobinhood** · 05-05-2010, 07:48

Does anyone know any reasons why i can`t just paint polyurethane varnish onto ripstop to make it waterproof? I`ve got a bunch of leftover hi quality PU from another project and about 14 yards of ripstop that i'm trying to figure out what to do with.

**Hawk-eye** · 05-05-2010, 07:49

Cause it'd crack and peel .... would be my first thought. Not the way to go.

**RootCause** · 05-05-2010, 07:57

Varnish creates a film on top of the surface it's coating, to provide a UV and water-resistant coating on top of a material that is relatively rigid but responds to changes in temperature slowly.

Fabrics are much more dynamic: the stretching, rolling, flapping, and crumpling that a tarp is subjected to will crack a PU varnish coating almost immediately. On PU-coated fabrics, a different formulation of PU is used- one that adheres to the individual fibers rather than makes a film over the surface of the fabric.

Does that make sense?

But if you're at a loss as to what to do with the ripstop, I'd be glad to take it off your hands!

**gargoyle** · 05-05-2010, 08:16

Ripstop can be waterproofed....pu varnish is probably not the way to go about it tho? I may be wrong, but anything I've pu'd before (that was fun to say,

) has checked, peeled and flaked off, when exposed to the elements. And I dont think a pu treated piece of fabric would be very soft, the word crunchy comes to mind.

For waterproofing your fabric, mix mineral spirits and silicone together, and soak the fabric. Stirring the fabric constantly, to ensure consistant bleed thru of solvent, ring it out after a few minutes, hang to dry, 48-hrs approx.
Do it a well ventilated area, away from sparks, flames...etc. Wear rubber gloves. No smoking.
Regular 100% silicone, from the tube.

Mix 4 or 5 parts min. spirits, to 1 part silicone, mix, stir blend, puree, the silicone till it is COMPLETELY dissolved. A 5 gallon bucket, a power drill and a bent up chunk of wire coat hanger make for a good mixing bowl. <MIX COMPLETELY> Use your hands or a stick/broomhandle to stir fabric, power drill would not be good.

Your fabric will feel a little sticky afterwards, so sew everything up first, then dunk it.

**bugfree** · 06-08-2010, 23:06

doint ruin a good thing,there are alot more options to go for do a little research and it will pay off.

**gargoyle** · 06-09-2010, 08:27

Originally Posted by bugfree

doint ruin a good thing,there are alot more options to go for do a little research and it will pay off.

Bugfree, if you have more options..please do tell? I'm curious what research you have?

We are open to new ideas?

**trouthunter** · 06-09-2010, 10:33

In my experience as a wood worker I would agree that polyurethane coating intended for use on various wooden structures / projects is rigid when dry and often cracks if the substrate it is applied to cracks or moves. So application to nylon fabrics would be a non starter. You need something pliable which is why the tent / tarp industry uses what it does.

gargoyle,

The method you describe is something I haven't tried yet myself, although I have read from multiple sources that it works quite well.

I am curious if you (or anyone else) know of any information where it has been used on backpack material such as Cordura which traditionally has been waterproofed with Urethane?
I'm curious because the Silicone method is much more DIY friendly it seems.

Thanks.

**gargoyle** · 06-09-2010, 12:14

I've done the seams on my tarps with the mixture, works great. I have not done a full size tarp yet, just passing along the info. There have been a few folks on here that dipped a full-size tarp and had good results.
As far as cordura, I don't see a reason why it would not work. Cordura is basically the same as 30d rip, just a lot thicker.