Dinghy resin and varnish

[Gordon]

Over winter and spring 2008/9 I gave my mirror dinghy a birthday. Having replaced a square in the floor towards the aft end I then decided it would be a good idea to give the whole floor a coat of epoxy resin. "last for ever thought I"

The dinghy spent 6 months of 2009 outside covered with a canvas cover. After some heavy rain a small amount of water got in remaining there for a couple of weeks at the most.

I was surprised to see that the resin had been attacked in places when the water had stood and was reduced to white powder There were a couple of similar spots on the deck as well.

The mirror has spent the last 12 months in my garage at home and today I was full of enthusiasm to have a closer look at the resin. The inspection revealed some opaque patches and closer inspection suggested that it was away from the wood Chipping and scraping away reveals that I can peal the resin off even where it appears to be stuck.

So the question is did I make the mistake of resining over varnish, even though it was roughed first, and what to do next

I have scraped/pealed it off from the lowest part of the hull ie inside batten as far as the thwart The resin it still looking good behind the thwart I am reluctant to try to remove it all as it would take hours and hours.

Any idea why the resin was attacked and did not stick?. Have I got to get it all off and varnish instead. ? Was it bad luck and can I get away with just re-resining where I remove the old stuff.

The resin was a new tin of SP 106 The temperature was cold at the time and I put the boat cover over it with a 60 watt bulb burning for a couple of days. Boat was nice and dry having been in the garage for some months and the resin dried hard and was three months inside after the resin was applied

Possibly difficult to answer but has anyone any ideas please

[Guest]

Some people may disagree on here ( ), but IMHO it can be difficult to get a good bond between epoxy resin and "old" wood, especially ply. Once it has been exposed to the elements and water for a time, wood takes up a certain amount of mositure, especially dinghy hulls.

On the other hand, when used on new wood, it can stick very well indeed, and seal the wood better than any other surface treatment.

Many racing dinghy enthusiasts that use DIY plywood craft coat the panels with epoxy thoroughly after carefully selecting marine ply that has the lowest moisture content they can find, because it can be as much as 50% lighter, and will stay that way, once sealed.

Many subsequently epoxy sheathed boats have failed to achieve the desired result, because once the water can get between the wood and the skin, the rotting process is accelerated.

[DaveS]

So the question is did I make the mistake of resining over varnish, even though it was roughed first

Unfortunately, I think the answer to that has to be a definite yes Gordon, as varnish is not a suitable substrate for expoxy resin, or styrene based resin (as in fibre glassing.

It would have been better to have removed the varnish with Nitromors or similar, and then left the hull to dry out in the garage over the winter.

However, given that Nitromors will attack the resin that bonds the fibreglass tape to the seams, it has to be used with care.

About 5 years ago I bought a Miracle dinghy in which to teach my eldest grandson to sail. The hull was in good condition, but the varnish and paintwork was long overdue for some serious attention.

Rather than just rub it down and repaint and varnish, I stripped the entire boat back to bare wood with Nitromors, and started from 'scratch'.

Here's a couple of photos of the stripped back boat, and the finished job.

BTW, the grey paint in the bottom is not to cover up bad wood, as there wasn't any, but was anti-slip deck paint which was applied over the varnish.

Dave

[Guest]

WOW very nice

Jonny

[Gordon]

Dave

That varnish looks magnificent. Yes I have a feeling that all that epoxy has got to come off.l My fear is as strowager says that it will harbour the moisture.

Fortunately the polyester resin I used to bond in the repairs has soaked into the wood and is really strong It is a case of what I thought was a good job finished now requires hours more work

Thanks for the input guys