Manufacturer's instructions vary on this, but (trust me) a silnylon shelter does require seam sealing in order for it to be completely waterproof. If you have ever seam sealed a silnylon shelter, chances are you are familiar with McNett's SilNet Silicone Seam Sealer. You might even have followed the directions on the package, as I have, and ended up with a very goopy, thick bead of SilNet along the shelter's seams. It's certainly waterproof, but it's also unsightly and unnecessary to apply such a thick layer. There is a better way.
All that is needed is a thin layer of silicone to properly seal the seams, and a thin layer is nearly invisible when it dries. SilNet can be thinned with mineral spirits to improve its flow and ease application. Backpacking Light Associate Editor Will Rietveld showed me this technique, which he learned from Tarptent's Henry Shires, and it has worked wonderfully on several of my shelters. It also greatly increases the coverage you can get out of a single tube of SilNet. For example, a pyramid shelter generally requires two tubes of SilNet when applied according to the instructions. By thinning the SilNet, one can cover the eight seams with less than half a tube.
Your next question might be, "Won't applying thinned SilNet reduce the seam's water tightness?" I have not found that to be the case, and suggest the opposite is true. Thinned SilNet penetrates the stitching in the seams in addition to coating the surface. I have also seen conventionally applied SilNet tear along sections of seam that were not taut during application, a situation caused when the seam's stress transfers from the stitching to the sealer. This does not occur with thinned SilNet. It should also be noted that applying thinned SilNet is much easier and less time consuming.
ARTICLE OUTLINE
- Introduction
- Recommended Materials and Equipment
# WORDS: 890
# TABLES: 1
# PHOTOS: 7
Member Exclusive
A Premium or Unlimited Membership* is required to view the rest of this article.
* A Basic Membership is required to view Member Q&A events
Discussion
Become a member to post in the forums.
> Yes, you can thin PU adhesives and sealants down, but
> what the best solvents are is something I haven't
> researched much. I am fairly sure solvents such as
> Xylene would work fine, but this class of stuff is not
> normally available outside a chem lab. Instead I have
> used pressure to force the PU sealant into the surface.
I got Xylene at the local hardware store. Lowes I think.
Sorry Gary – I missed your posting. I think I was away walking at the time.
Can you put Atsko DWR over PU sealant? Yes.
Whether it will bond very well is another matter, but that hardly matters. After all, if there is a layer of PU sealant there it will block the water 100% anyhow.
Can you put PU seam sealant over DWR? Yes.
Use some pressure to force the PU into the thread in the fabric as a fair bit of the bond it makes is purely mechanical in my experience.
You are right in suspecting that the DWR will block surface bonding to some extent. Do not ever try to mix Fluorocarbon DWR with silicon DWR: they are totally incompatible for this reason!
What DWR would a good company use? As far as I know, the only DWR used on fabric these days is fluorocarbon, and never silicon.
Cheers
I've searched but can't seem to find any info on sealing cuben. I have the MLD poncho tarp so assume I need to seal the neck-what should I use?
Any good acrylic seam-seal tape. Yachting seam-stick tapes work well. 3M9485PC tape is excellent. And PU adhesives also apparently are good.
You probably will need to make the tape up yourself using some spare Cuban and whatever adhesive.
Cheers
cheers roger!
I've sealed the floor of my bivy made of silnylon, both inside and outside
It wasn't completely waterproof before
I used generic silicone caulk diluted with "odorless" mineral spirits, 1 part silicone to 3 parts spirits, by weight
outside (surface that contacts ground) didn't work very well, after about 10 nights it started peeling off. I finally "helped it" and got most of it off. The flakes of sealant were a bit of a mess.
inside (surface that contacts my sleeping pad) is good after maybe 100 nights. much more waterproof than before I sealed it
I've used McNett seam grip on PU coatings a number of times. YOU HAVE TO REMEMBER TO COAT WITH POWDER AFTER IT DRIES TO PREVENT STICKING AGAINST ITSELF!!! I keep forgeting this and it makes a complete mess when you do this :) I scrape off some Gypsum board like used for walls in houses which doesn't smell. Silicone doesn't have this problem.
That stuff works very well (on PU). I repaired a pack where a mouse had chewed a hole and it worked really well.
In case someone hasn't already noted – if you don't want to use mineral spirits, you can thin silicone sealant with alchohol – e.g. methanol or any alchohol stove fuel – e.g. the gas tank additive HEET. Isopropanol (IsoHEET) might work too but I haven't tried.
As with mineral spirits, it takes nontrivial agitation to get it to dissolve smoothly. Try shaking in a sealed mason or salsa jar. The alchohol evaporates quickly, which is both a pain and speeds 'drying' of the finished work. I've had good permanent sealed seams on silnylon using alchohol-thinned hardware store silicone caulk.
You can use alcohol, but there may be problems. Many silicone sealants cure by absorbing water from the atmosphere. It takes a while to diffuse into the silicone so you get some working time.
BUT, when you dilute silicone sealant with a solvent, any water in the solvent gets mixed into the silicone and sets off the cure immediately. And quite a few solvents, including most alcohols, have some water as an impurity. You may find that the silicone is halfway cured by the time you have finished stirring.
For this reason I have gone away from using the hardware store cartridges of thick silicone, using instead tubes of less viscous silicone adhesive. The stuff in the tubes seems to bond better and the tubes last longer before the remainder sets completely.
Cheers
Become a member to post in the forums.