In a recent thread about adding tarp pullouts there was mention of using silicone adhesive to glue patches to the tarp, thus eliminating the sewing of circles in the middle of a tarp. This got to me to pondering the possibility, given that I've avoided adding pullouts for the sewing challange (I usually like to find the easiest way). So here is my experiment. I wanted to test things out before committing my tarp.
Silnylon circles 3, 4, 5, and 6" were cut out for pullout patches. the attachment point are 1/2" nylon webbing, 2" long, backed with some 300D PU coated packcloth. The webbing was box-stitched. The patches were then glued to larger silnylon pieces to simulate placement on a tarp. The silicone was GE Silicone II, straight from the tube. It was brushed onto the patches in a thin layer, leaving it shy of the perimeter by about a 1/2". The silicone was then squeegeed with a plastic card, making a smooth, uniform layer under the patch to the very edge. The excess was removed with a paper towel. Then it was left to cure for a week (then time until I could take up the experiment again).
A carabiner was used to attach gallon jugs of water, then the piece was hoisted allowing the weight of the water to pull on the patch.
The 3" patch easily held 2 gallons of water before showing signs of delamination at the webbing backing. The 4, 5, and 6" patches held 3 gallons with no signs of delamination.
The force of the stress was in line with the direction of the webbing. On the larger patches, the distance from the end of the webbing to the edge of the patch was greater. This was where the most force seemed to be concentrated. The 3" patch was too small in this respect. On future patches, an elliptical or diamond shape, oriented longways with the webbing, would be a good way to maximize the material where the force is greatest. Something about 4" wide by 7" long.
The polyurethane coated nylon backing used to reinforce the webbing attachments did not adhere to the silicone. This was especially evident in the 3" patch, as seen in the last picture. The larger patches did not show this delamination, because the larger surface area distibuted the force better. Using silnylon to reinforce the sewn attachement point should eliminate this problem.
The silicone adhered very well. It was difficult to even partially remove the 3" patch. It actually began to tear the fabric. It this pic, it's clear to see where the PU coating prevented the silicone from adhering well.
Overall I was very pleased with the results. This is definitely how I will attach my pullouts. I'll try a different shape patch before I actually put these on my tarp. This was I fairly quick process to make the patches, and glue them on. It could be done easily in 1-2 hours depending on your sewing skills. This isn't technically a "no-sew" option, but it eliminates sewing a patch on to the side a tarp.
(I couldn't figure out to attach the pics in the body of the post, so they all ended up at the end.)