Primer for GRP

[mike_bryon]

Can anyone recommend a product sold for domestic or construction use suitable as an underwater primer for bare GRP prior to anti-foul?
I’ll be lifted in St Vincent and the Grenadines and in Kingstown the capital there are a good many hardware stores but no chandlers. What do you suggest I use? Would a metal or wood primer do the job, what about wall stabiliser?

I asked this on the liveaboard forum but so far no one has suggested an alternative.
Thanks in anticipation.

 

[Bajansailor]

Mike, I have found that ordinary WEST epoxy (easily obtainable in St Vincent or Bequia) works very well as a primer on to bare GRP - scuff up the fibreglass a bit first, apply a coat (or 2) of epoxy, and then put on a coat of antifouling before the epoxy 'goes off' fully, so that there is a good bond between them.

 

[oldsaltoz]

Mike, I have found that ordinary WEST epoxy (easily obtainable in St Vincent or Bequia) works very well as a primer on to bare GRP - scuff up the fibreglass a bit first, apply a coat (or 2) of epoxy, and then put on a coat of antifouling before the epoxy 'goes off' fully, so that there is a good bond between them.

May I suggest you clean the area well then wipe it down with Acetone to remove any contaminants BEFORE you sand, or you will just spread them, I also wipe again after sanding with Acetone to remove the dust and any contaminants that may have been exposed by the sanding.

Good luck and fair winds.

 

[mike_bryon]

Thanks Bejansailor and Oldsaltoz. I know where to buy both epoxy and acetone in Kingstown and will follow your advice. I will be out at Ottley Hall for most of April to have the hull taken back to the GRP among other things then a sail back to the UK for the summer.
Thanks again.

 

[Bajansailor]

Yes, very important re cleaning with acetone before and after!

I was thinking that you were just doing some localised touch up jobs..... do you really have to take everything back to the gelcoat?
Popular wisdom generally seems to say that there is not much point in coating a bare fibreglass hull with epoxy if the moisture readings are still high - and I think they probably would be still high on an older boat, after 'just' a month on the hard, even in this fierce sun.
Or has Dark Horse been epoxied previously?

 

[mike_bryon]

Yes Dark Horse has been epoxied previously and faired too and the anti-foul in places is coming off. This did not use to happen so I decided I would get all the old anti-foul off and prime before anti-fouling once again.

 

[Bajansailor]

Our boat is in a similar situation - she was epoxied 3 years ago, and is now hauled out again - about half of the antifouling (what was left) 'fell off' when the hull was pressure washed, and about half of the rest has been sanded off.
There are still some patches where the antifouling is stuck on tightly.
And there are some areas where small areas of epoxy have come off.
So I am going to prime the bare areas with a couple of coats of epoxy, and then apply a full coat of epoxy all over the bottom, and then get the antifouling on before ithe epoxy cures.

 

[mike_bryon]

That’s useful information thanks Bejansailor. I’ll see how things look after the power wash and hopefully need only treat bare areas where the antifoul has come off. I don’t expect it to be as extensive as you describe. Thinking about it I will try to avoid an all over epoxy coat after only a month of drying out.