Groundsheet material

Have you thought about Tyvek? Pretty cheap, durable and about 2 oz yd. Cuben in the 1-1.5oz sq yd range is out there too, but you're gonna pay a chunk for it.

If not the above – I would prefer PU coated to Sil for the ground sheet due to the non-skid factor.

Ryan

I have thought of tyvek, but I have no idea how waterproof that really is. Has anyone ever tested th HH of tyvek? I don't remember seeing it among the fabrics that were tested a while back.

Unless someone can get me some seriously discounted cuben it's more costly than I'm willing to afford.

If you use a PU-coated nylon groundsheet, and keep the PU face up (inside), it should be more waterproof and more abrasion resistant than silnylon. It is also pretty sensitive to UV, though, and some PU coatings hydrolyze over time. The silicone in silnylon is much more UV and hydrolysis resistant than PU. So, PU nylon might be a better fit for you if you can store it dry and protect it from sunlight, but if it will be wet a lot of the time, and exposed to direct sunlight, silnylon will last longer.

Spinnaker fabric works good.

–B.G.–

I thought spinaker had a pretty low HH and wasn't very abrasion resistant?

Colin, if I make my bathtub with the PU coating on the inside, won't the fabric soak up a lot of water? I would think it would make more sense to put the coating on the outside so that the water is stoped before it even comes into contact with the fabric.

Here's another question. Would it be possible to use a lightweight PU nylon (lighter than the 90g/sqm stuff from extremtextil) and apply an extra silicone coating on the other side? That would probably be lighter and hopefully it would even be more waterproof than heavier PU nylon. The slippery silicone side would be on the outside and the less slippery PU side would be on the inside. Would this just be a lot of work or can I actually get something more waterproof for less weight this way?

While we're at it, has anyone ever tried applying a coating to tyvek? I think tyvek is durable enough, but I don't know if it's waterproof enough.

I know that soft stucture Tyvek 1443R will hold a Polyurethane coating, such as Aquaseal Polycoat. I have never tried coating hard structure Housewrap.

http://www.aquaseal.com/polycoat.html

Tyvek 1443R is by nature water repellant, but when lightly painted with Polycoat it is waterproof & weighs appox 1.4 oz per sq yard. I have used this on bivy bottoms & booties. The coating has held up for over six years of occasional use. However, Tyvek 1443R is fairly fragile, even when coated. I am quite careful in selecting my campsites, but I would not recomend Tyvek 1443R, even coated, for the use you listed at the begining of this thread.
I would suggest considering 70D Silnylon. It weighs appox 2.3 oz per sq yard, but is tough, waterproof & seems to me to be not as slick as the lighter 30D silnylon. BearPaw Wilderness Designs has 70D Sinylon.

http://www.bearpawwd.com/fabrics_misc/fabrics_misc.html#70D

Searching out the most level campsite available makes silnylon floors not much of a problem, imho.

Mark, yes, the fabric side will absorb a bit of water if the coating is on the inside. I suggested this because of your description of your campsites (rocky). PU coatings are more abrasion resistant than silicone coatings, but they can be damaged by sharp rocks.

I think your idea to coat the other side with silicone is clever. I hadn't thought of that. If the silicone is abraded away in a few spots, it will still dramatically reduce the amount of water the whole piece absorbs, and the PU coating on the other side will keep it waterproof. You'd be carrying the extra weight of the silicone coating all the time, to avoid the extra weight of absorbed water that only occurs sometimes, but it might make sense if you can make the silicone very thin.

I think I'm going to do this.
http://jwbasecamp.com/Articles/Silnylon1/index.html

It's a bit of a gamble for me because I'm still not sure how good this will work and I don't know in what conditions the author used his tent, but it's worth a try.