Sealing Bulkheads

I have glassed-in bulkheads in my sea kayak. The bulkheads are glassed-in on one side and sealed with some type of hard (and not very plyable) sealant on the other side. I did some leak tests recently and the bulkheads leak ever so slightly (on both sides of the bulkhead). They appear to be bomber glass jobs, but they do leak slightly. Do you have any recommendations for a type of sealant I could use on the non-glassed side of the bulkhead that would seal those for good. This on a 22 foot expedition sea kayak that I use for long coastal tours, sometimes in rough surf. In short, the boat takes a pounding and I’m sure with over 800 pounds loaded in the boat that the bulkheads tend to flex thus creating my small leaks. Thanks for your help!

I’m not sure if it’ll stand up to the conditions you talk about (or if it even sticks to glass) but I’ve had some success with just plain ol’ silicone. I’ve only used it on foam bulkheads in poly boats but so far so good…If it does work, it should have the “flex” you’re looking for. 800 lbs? How long are you out for? Safe travel.

sealing the existing bulkheads
Most people are NOT good enough at fiberglass work to do a proper job of repairing the bulkhead seam if it leaks. Your best option might well be to use one of the many good adhsive sealants made my either 3M or Sika. This product will remain reasonably flexible as well as strong and watertight.

Roughen the area all around the seam with sandpaper and wipe it clean with acetone. Carefully apply masking tape on both the bulkhead and the hull and deck all around the edge. Put the tape about 3/4" away from the seam on both the bulkhead and the hull and deck. Squeeze a big fat bead of the Sika on the seam, and then using a tongue depressor and a latex gloved finger evenly spread and smooth out the sika until there is a nice radius of it all around the bulkhead. Pull the tape off and it will look neat and clean. Wipe off any excess with acetone. Warning: This will be very messy unless you are very thoughtful and careful in performing all these moves, so take your time and be neat.

sealing bulkheads
That’s good feedback - thanks for the recommendation. Do you recommend I try and remove the existing sealant or just rough it up and seal over it?

you might want to contact the manufacturer of the kayak and find out the type of sealant they used. Sometimes sealants will interact in ways you do not want. When you call them have the number of the boat or when the boat was made as manufactures sometimes change sealants.

prepping the surface
Remove the existing sealant as necessary. If it comes loose, then remove it. If it is still sticking well, then leave it. The Sika or 3M will stick to it as well.

By the way, I have found that while silicone is easy to work with, it does NOT stick well in the long run. Just look at the way it behaves in your bathtub seams! Use a polysulphide or polyurethane instead, which is what 3M and Sikaflex are.