Best way of repairing a weak kayak deck

I have an older fiberglass kayak, but the deck has become weak compared to the material elsewhere on the boat. I have once spot that is very damaged I am removing and replacing with epoxy resin instead of polyester for the added strength. I would I go about strengthening the desk? I was thinking of adding support underneath but am not sure what the best method is. I was planning on redoing the gel coat on the deck anyway to remove gel coat cracks since I have to paint my new patch anyway, should I add more resin near the spider cracks?
I am somewhat new to fiberglass work, here is a video of my boat and the weak deck if you would like to see.

Hell she’s rubbed clean through!
First off, I don’t think it needs to be stronger than original. Something rubbed that, a lot.
As for repairing it, I would sand it out say… six inches outside the damaged area, put a thin layer of resin, cloth and more resin on top, maybe on the underside do the same but go resin, cloth, resin, cloth and resin. The underside doesn’t need to be pretty.
After she sets you get to start sanding and making the top smooth. Forget about gel coat, just paint to match.

The white patch of fiberglass you see I sanded down because I wanted to assess the damage before deciding wether to cut it out or repair it. That area is damaged to the point it can’t be patched and it needs to be removed and replaced. Its the rest of the deck which feels more flexible than it should be (though not as bad as that sanded area. Im looking for the best way of reinforcing it from the inside as it definitely has lost strength and I want to prevent the new gel coat I put on from spider cracking again.

I’d put one big piece of mat on the entire deck. It will stiffen it up immensely. You can use West system EPOXY with the mat take care to wet and roll in properly.

I have done 4 of my 5 CD kayaks on the bottom seat area huge difference. I did two layers one about 4" bigger on first mat layer. One should be plenty for the deck.

Don’t cut that section out unless it’s rotted out, that will just create a lot more work that is unnecessary. Also, keep in mind that the bigger piece of glass you lay down - the bigger pain in the ass it will be to make sure that it’s all laid correctly, so I would personally do sections at a time. Especially if you’re new so then you can get an idea of how resin and fiberglass work together. Lay down a piece that is a little bit bigger than that patch, and then each layer after do an extra two inches around it. Flip the kayak upside down and that will make it easier too. I would probably lay a section or two of glass over that rubbed area and then add a larger mat across the whole deck inside the cockpit. Make sure you sand all the rough edges down before you lay another layer. I use vinylester which only needs a catalyst and wets out the fiberglass much better than epoxy and is a fraction of a cost of epoxy. I order my stuff from Express Composites in Minneapolis. You can get measuring cups and popsicle sticks, brushes, anything you need. They have inexpensive gelcoat too, just make sure to talk to Tim.


Resin and Catalyst:

I would consider a layer of carbon fiber cloth on the inside.
I was using CF and epoxy to reinforce and stiffen boat hulls forty years ago…
Lots of info has to be out there…

My suggestion would be to do some research on youtube for videos and instructions on how to proceed with these types of repairs. If you have to ask how to do it, you’re not ready to do the job right the first time.

There have been lots of comments on this site over time on how to do the job. I think you might be able to find some very useful suggestions from experienced folks. I would also look up working with composites on Google, or whatever search engine you use.

Absolutely do not cut out any portion of the deck even if damaged. If you feel that reinforcing a discrete area will suffice and you can access that area from the interior through the cockpit, then I would apply an interior patch.

You could use a variety of materials for the patch, fiberglass (E or S), aramid, carbon fiber. But you really don’t want to make the repaired area much stiffer than the surrounding deck as this will create a stress riser along the edges of the patch.

If you feel you need to stiffen the entire deck you won’t be able to access the entire area from the interior. In that event I would remove all the gel coat from the exterior until you can see the fibers of the underlying structural fabric, then lay on a blanket of lightweight cloth. S fiberglass in 4 ounce/square yard weight would be best. Then fill the weave of the cloth, smooth, and paint.

Stiffness is mostly a function of thickness. A coat of resin won’t provide much thickness or stiffness. A very thick coat of resin would be much weaker than a thin layer of fabric impregnated with resin.