Researching Waterproofing Options

I'm making my son a Green Pepper raincoat from this pattern. I've used this pattern before as a winter coat. This time it will just be the fabric and a lining. Because of that, I want it to be waterproof even at the seams. There are several products out there that claim to waterproof a seam. I bought them and tried them out.

I'm a science teacher. I like experiments. I like being methodical. Yes, I'm type-A in a very big way. So, I made four samples and tested the waterproofing ability of each product. First up, Seam Sealer 3. It's a water-based product that claims to "put an end to leaky seams and joints." This product is super easy to apply with a dauber cap and dries quickly with little odor.


K-Tape is a "universal repair tape that can be used on all smooth synthetic fabrics, fleece, and vinyl." It's 18" by 3". For this sample, I cut it to a width of about 1/2". This is a very easy product with which to work. It's just like masking tape that stretches. I did notice that if you stretch it when you apply it, the fabric will gather as the tape shrinks back to its regular length.



Seam Grip is like rubber cement. It smells similar and had a similar consistency. You use a brush to apply it and you should be in a well ventilated area. It "permanently seams, bonds, and repairs tents, outerwear, and gear." This one has to cure for 8-12 hours. If you want to glue two things together you apply a light coating of Seam Grip to both surfaces, let them dry for a few minutes, and then stick them together. Sound familiar? Rubber cement uses the same directions.


Here they are together. I had high hopes for the K-Tape but I think Seam Grip won out in the end.

Here they are after a good washing. I wanted to see how they held up under a washing cycle.

After washing the seams on the Seam Sealer 3 sample started to peel up. And, I think it's actually okay. It's not a glue, it is supposed to soak into the thread itself and make the thread waterproof. It's kind of like Fray Check.

The Test: I pinned all the samples and applied about 3mL to each sample. This fabric (Nylon Burlington DWR) is so waterproof, it was hard to stop the beads of water from rolling off. The bottom, my control, is a sample with no sealant on it. On all samples, I tried to concentrate the water to the seams. Like I said, that was hard to do because they wanted to roll off.

This is what it looked like an hour later. Notice the control sample has visible water spots along the seams.

These were pinned to a cardboard tube to test for water leakage. Of all the samples, the only one to leak was the control (ignore my goof-up at the top).

Overall, how did they do? Well the easiest to apply was the Seam Sealer 3. You just dab it on. I think the most effective one will be the Seam Grip. It acts like a silicone caulk that moves with the garment. I think it will be the best overall. I may use the tape for a large area though. If I decide to embroidery something on this coat, I will probably tape it inside with the K-Tape and use the Seam Grip around the edges of the tape.

Helpful? I figure someone out there has gotta be into outerwear like I am. :)