Fiberglass advice

[ar1g3]

I cut the transom open today. It was about time this job got carried out.

The core is so rotten you can just scrape it away with your fingers, like dirt. Strangely, the core isn't a single piece. It's made out of 4 pieces puzzled together. Tomorrow I will scrape away all the plywood and then I'll let it dry out.

 

[ar1g3]

I got most of the old core out, took no effort at all. A putty knife was all I needed. Here is all that is left of it:

I discovered that the inner skin is very thin. It's basicly one or two layes of chop strand matting, and that's all. I already removed a part that was damaged beyond repair. But I'm thinking of taking the whole inner skin out just to make the job easier. What do you guys think? I also don't think the epoxy will bond very well with the old inner skin, as there's quite a bit of wood fibers stuck to it.

From what I can see the inner skin's sole purpose is to keep the core in its place, it isn't structural.

 

[PaulRainbow]

Whatever, you will need to get that inner transom clean and keyed. Trim the hole you have cut as big as it needs to be to get rid of any damage, no need to remove the whole thing. Clean all of the wood fibre from it, taper the edge of the hole from both sides and abrade both sides of it. Abrade the entire area where the ply was, every little bit that you can see or get to.

Cut a piece of ply a to cover the hole, from the inside. This can be a section of the ply you intend to use for the core. Cover one side of it with polythene sheet and wedge it over the hole. From inside the cockpit, apply as many layers of mat as you need to fill the hole.

Once dry, but not fully cured, remove the ply and add a couple of layers of mat to the aft surface of the inner transom, coming all of the way to the edges, along the inner hull and the inside of the outer transom.

Stick all of the ply in the void with plenty of epoxy. Put a couple of layers of mat over the whole outer transom. You will obviously have cleaned and abraded the entire transom, the corners and along the hull a little way, plus you will have drilled all of those holes out a little and tapered them from both sides. Use 60 grit paper for abrading.

Now you need to skim the inner and outer transom with filler and fair, with the paper on a block.

 

[lw395]

What is the total thickness of core and outer skin?
If the inner skin is floppy, you won't easily bond the ply to it.
The inner skin needs to be quite strong to gain any sandwich effect from the core and outer skin.
I suspect you will need to work from inside the boat to get this right.

 

[TQA]

Do not remove the inner skin. You risk losing the shape of the stern. Also you need to fit a spreader brace inside the stern. A 2x4 with wedges up against the inner skin will do the job.

Do not worry about the odd wood fibre left on the inner skin. Remove all the loose stuff and sand flat with 40 grit. The epoxy will stick just fine. I have always used epoxy for this sort of repair but I have seen polyester resin used with success.

 

[PaulRainbow]

Do not remove the inner skin. You risk losing the shape of the stern. Also you need to fit a spreader brace inside the stern. A 2x4 with wedges up against the inner skin will do the job.

Why ? There will be a solid ply/epoxy core in the transom.