Damp patches

[grahamclive]

My boat, a 1960 Holman design has been stored ashore under a sturdy leak free tarpaulin since last October. Given that my winter overhaul gradually turned into a more serious refit than anticipated and that this has been the wettest summer I have ever known here in Cornwall, in June I took the opportunity of putting the boat in the yards shed.
My cabin sides are of teak about 7/8" thick with tongue and grooved joints and as they had looked a bit like a piece of garden furniture I have stripped all the sikkens exterior woodseal off with a view to using a clear varnish to do the wood some justice. By this time the timber had plenty of opportunity to dry out.
Since stripping, whenever we get excessively wet weather, various areas of the stripped timber, particularly at the joints come out in wet patches. These patches then dry off again when the weather clears. I am reluctant to varnish over these areas until I have determined why this is occurring.
My own view is that someone has treated the wood around the joints with some form of leak proofing chemical which has left a hygroscopic residue. Does anyone have any similar experiences and suggestions for remedial action?

 

[Peterduck]

I wonder if there was a time in the boat's history when there were bare patches where you now find the wood is hygroscopic, and that salt from spray had soaked into the wood? Salt is, of course, very hygroscopic and very handy to boats, so it must, in my view, be a strong contender for the 'villain' of the piece. Perhaps a 'tongue test'?
Peter.

 

[Kukri]

That would be my working hypothesis, also.

 

[meldrum]

I am currently restoring my 44year old water witch and I too have come across similar problems on other parts. My thinking is that it could be what the other contributers have suggested but I have also found that initially I covered her with an all encompassing heavy duty pvc tarpaulin in an attempt to dry her out but found that every morning and evening when i worked on her,condensation appeared on the underside of the tarpaulin and obviously must be the moisture from the boat drying out and condensing on the sheet and then returning to the wood. (self defeating) I then extended the sheeting to prevent rain getting in and left the ends open to allow air flow, this seems to have cured the problem. A good tip I was given by a boatbuilder was if you wished to dry old wood out to acheive the required moisture content for using epoxy or other modern coatings was to
play a heat paint stripping gun over the wood for a while (avoiding burning or scorching) before applying the coating.
Hope this is a help.

 

[ccscott49]

You could try washing the bare wood, with fresh water, this would help to dissolve any remaning salt (I agree with the others) then allow to dry properly, would be better if you could get some heat into the area, with a fan heater or whatever, but of course a tad expensive.
There is a clear waterbased epoxy type treatment available, which you could put on to seal the timber, before varnishing.