Last night I cleared off the work bench and went to work on the leaking down from the used Montbell bag I purchased last month. It’s early, but I’m feeling pretty good that I managed to get the seams sealed up.
Examining it a bit closer, it looked like most of the problem was occuring at “double seams” where two pieces of lining, such as the main top and bottom pieces, were being butted up against each other, and the thread had stretched a bit, creating just enough gap for small pieces of down to leak out. There also were a few places where the material/seam separated at what I would call stress points in the bag. Interestingly, there was no leakage from the exterior fabric.
I should have taken some pictures, but essentially I ended up using a small craft brush and painting a thin line of diluted silicone solution along the seam. The fabric would quickly absorb the solution, but the “thicker” suspension would then be left on the seam to seal it and dry. The result is a thin line over the seam that is just a little darker than the fabric. I didn’t notice any tackiness from the silicone, and any stiffness along the seam is negligible.
Since I had the bag laid out, I used the opportunity to spread the fill around the baffles a bit. I suspect that the bag has been washed recently, which caused some of the down to clump up. It was amazing how much the bag lofted after doing fluffing it up.
My next project with the bag is to test the water-proofing. The Ultralites are supposed to have enough DWR treatment to last 100 washings, but I want to make sure that things will be OK if I get into wet conditions. I don’t expect the bag to be like new, but I do hope to get it pretty close to the condition of my Montbell #3.