plywood deck covered by grp

[pawel]

In my old Colvic 24 deck is made from plywood rainforced by grp. It causing the problem becouse when cracks apiring on top coat of fibreglas water going under and wood is rotting . Is any way to prevent grp to crack and haw to drye out the wood Thanks

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[William_H]

You seem to have problems with your deck. GRP on plywood is never very good especially if the GRP is thin. I don't know the boat type but can only suggest you use an angle grinder to cut out the GRP where the wood is rotten to allow you to dry out the wood or cut it out as necessary. Cut away also the GRP that is obviously not contributing to the deck strength because it is cracked.The fix is to put on more layers of fibreglass and resin over the whole deck or at least those parts under stress from people walking on it so that the GRP is the structural strength and the wood is purely a mold to hold the GRP while it hardens. We are talking about a thickness of 3 or 4 mm or more depending on the loads and the support underneath. This will represent several layers of woven rovings or the thickest glass mat. Unfortuneately this makes the boat heavier above water line which may or may not bother you. You might like to price a carbon fibre mat for the GRP as this is a lot stiffer for the thickness and weight but more expensive of course. Ideally for sticking to wood epoxy resin is best however if the GRP is made thick enough then the adhesion to the wood doesn't matter and the cheaper polyester resin which most hulls are made of will do. I wouldn't get too stressed about removing the rotten wood just dry it out then try to saturate it with resin perhaps with a solvent to help carry it in and with heating to make it more able to penetrate. You might also consider stiffening the deck from underneath as presumably flexing of the deck has led to the GRP cracking. If you havn't done fibreglass work get a book or someone to help you but after you get over the sticky mess you will enjoy it. Regards will

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[kds]

I am afraid that I would not agree with the solution. GRP/plywood and GRP/GRP bonds are very disappointing if there is to be any movement - as you will get in a deck.
Building up the sort of thickness you are talking about to keep it stiff will add a lot of weight on top of the existing weight.
You should really bite the bullet and use epoxy and compatible cloth - it will allow for flexing.
Sorry.
Ken

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[snowleopard]

polyester resin is not a glue and will not form a bond with wood. it may look ok for a year or two but will inevitably separate. there is no alternative, you will have to strip it all off. once you're back to bare wood and dried out you can then use epoxy/glass or even teak planking.

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[Plum]

Your GRP sheathing is most likely to be Polyester resin based which is very poor at adhering to wood which is the root cause of your problem. Because of this poor bond it is no good putting anything on top. You need to remove the old GRP from the plywood, elininate all rot, and replace with EPOXY (not polyester) resin and a single layer of woven glass mat (not chopped-strand mat). Companies like SP Resins and West Epoxy do good free literature on sheathing and will advise on glass mat weight (thickness).

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[pawel]

Thanks to evrybady for good advance
It's fourth winter then I'm struggling with cracks on that deck and now aftre many times of cutting GRP , quick draying wood under and patching with ordynary resin I'm finking abound replacing the entire deck, but I'm fed up with combination GRP plywood. Is any alternative material strong and long lasting for decking, for instance sheets of PVC or plastic, existing beams are still in good condition.
P. S. SP epoxi seems to really work. Pawel

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[chippie]

While polyester over plywood is less than ideal, epoxy resin over glass cloth and ply is very common and long lived if done properly. It is a job that is not beyond the commited amateur. On a deck such as this the glass cloth is only to provide abrasion resistance rather than strength. The resin provides waterproofing and paint provides uv resistance and antiskid.

Wooden Boat magazine has a forum with lots of detail on doing such work.

<P ID="edit"><FONT SIZE=-1>Edited by chippie on 01/04/2004 00:48 (server time).</FONT></P>