N3237 repairs

[Peter Snowdon]

My boat has a couple of small areas where the plywood has swollen and lifted ( one on the floor near the centreboard bolt and the other on top of the back tank where it joins the centreboard case). I want the boat to be sound for next season but short of cutting the ply out and replacing with new I'm really not sure how to go about it. Both areas have been stripped of varnish and left to dry out.
   Any information or ideas on how to go about this would be appreciated.

[Tim Gatti]

Hi Peter - two things you will need to try to ascertain
1. How and where has the water got in - from above or below
2. How much damage has it done

It may just be that it's the result of surface water penetrating a weak or split area of the ply surface, perhaps due to frost or flexing of the ply with usage. However, if it seems to be seeping in from elsewhere then you must try and find the source of the incursion or any repair you make will be temporary!

To check on the extent the ply has been affected by the moisture I've  used a very fine pin or needle to probe the area around the damp spot.  If the wood has softened it will be obvious as the needle will sink in more readily, enabling you to get a reasonable estimate of the depth and area affected.

Your next step will depend on the size of the problem.

If you are sure it's just a surface veneer that lifted, then you might be able to get away drying and warming it with a hair dryer then injecting some thin epoxy under the veneer once it's all thoroughly dry and then place weights on it while the epoxy sets.Then sand off and revarnish.

However, if the damage is more extensive you will need to remove all water damaged timber as it will have been denatured by the water incursion. Unfortunately with plywood, the outer veneer can appear fine but the inner veneers, which are sometimes softer and more porous, can soak up water which then travels laterally through the ply, affecting a much larger area than was first apparent.

I use one of those  hand-held narrow belt sanders (Black and Decker or Makita) and very carefully sand away the ply layer by layer until I get back to sound wood. Or you can use a very sharp chisel

So be warned, you may end up with a much bigger hole than you bargained for but don't lose heart - once you are back to sound wood you can start to affect a repair.

You may have to scarfe in a piece of ply with epoxy to replace the material removed. Or if it's a small and shallow area and you are not too bothered about appearance, you could just bodge it i.e. fill the depression with epoxy suitably thickened and coloured, then sand off flush and varnish once it's gone off. You might need to embed some glass fibre mat in the epoxy for strength.  Whatever you do it will be very difficult to create a completely  invisible mend, particularly as you probably won't be able to match the veneer on your deck ply cos it's around 25 years old.

Hope that helps. Good luck

Tim

[Peter Snowdon]

Thanks for your prompt reply Tim, I think I'll go for the top layer of ply that's lifted! (Sounds the easiest to repair). I'm about to turn her over to strip & paint the bottom so it will have at least a couple of weeks to dry out. Some of the ply on the floor is slightly darkened but it seems quite dry & solid. The ply on the back tank also seems solid but has lifted on the seam, I guess it's from years of helms standing on the tank through the tacks. I'd really like to get it smooth again without having to replace the ply, there's acres of it across the back of the boat!  
Once again thanks for the info,
 Regards, Peter S.