How to fix wood blocks to GRP?

Zagato

Zagato

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I am fitting out a boat from scratch and want to fix blocks/battens of wood to the GRP so that I can screw things into them e.g. shelving, strapping points etc. Do I need to glass in the blocks or will something like Silkaflex or Gorilla glue work - they need to be strong! Doesn't matter what it looks like as they will be covered - thanks
 
Eyore said:
Fiberglassed in would be the proper way to do the job.
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Absol-blurry-lutely! Neither Gorilla Glue nor Sikaflex are likely to give sufficient structural strength for the twisting, bending, flexing cyclic loads imparted by a sailboat working in a seaway.

Epoxy fillets with glass tape over is my suggestion - and that is informed by 'The Gougeon Brothers On Boat Construction', something of a 'bible' on this topic.
 
I have used car body filler for lightly loadedthings. Simply glssed over whn more highly loaded. It has the advantage that it sets quickly, esp if warmed a bit
 
I've been experimenting with one part polyeurathane vs two part epoxy. Mostly because of price and ease of application
So far no failure in either. The main benefit of the polyeurathane is that it can be used on uneven substrates and where there are high levels of vibration as the glue foams slightly to give a vibration resistant join
Best one....only time will tell
 
Zagato said:
I am fitting out a boat from scratch and want to fix blocks/battens of wood to the GRP so that I can screw things into them e.g. shelving, strapping points etc. Do I need to glass in the blocks or will something like Silkaflex or Gorilla glue work - they need to be strong! Doesn't matter what it looks like as they will be covered - thanks
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I actually experimented with some of the adhesives like "sticks like sh*t" which I had floating about. I used small strips of timber 1" Wx 6"L x 1/4" thick, cleaned up the GRP and spotted a blob which gave near 100% cover. All pulled off with firm pressure applied by hand which surprised me as I had have a crockery shelf glued with the same stuff in the galley and it was very firm after a good pull test. However, this winter I am refitting the galley and that crockery shelf just pulled away, again with firm pressure. As others have said, Epoxy glue, or glassing in. It is worth pointing out that all the original joinery is attached to battens that are glassed in place and that is still there, secure, after 40 odd years. I now use Epoxy glue in this refit.
 
oldbilbo said:
Absol-blurry-lutely! Neither Gorilla Glue nor Sikaflex are likely to give sufficient structural strength for the twisting, bending, flexing cyclic loads imparted by a sailboat working in a seaway.

Epoxy fillets with glass tape over is my suggestion - and that is informed by 'The Gougeon Brothers On Boat Construction', something of a 'bible' on this topic.
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And you can have it for free!

http://www.westsystem.com/ss/assets/HowTo-Publications/GougeonBook 061205.pdf
 
My boat has GRP "top hats" to screw into which are a retrofit by a previous owner from what I can tell but work very well. Major benefit is I'm not worried about wood rotting and being hard to replace - always think of future owners when you do these things.

As for glue, Epoxy seems to stick anything to anything :)
 
+1 for epoxy. I've mixed up the resin and hardener and then painted a thin coat on both surfaces to permeate. Then I thicken the remaining epoxy with microfibres until it's like toothpaste and "butter" the wood on it's sticky side and press it on to the hull (which, of course, was abraded first with 40 Grit paper)! Only problem is that if your outdoors it might not go off very well in this weather.
 
When my hull was originally built many years ago all of the reinforcement strips were glassed in using CSM and polyester resin. In some cases it was wooden pads and in places of high loading such as where the jib tracks were or where the mast passed through the deck the pads were aluminium about 6mm thick.

The join between the pads and the underside of the deck will be held in compression by the screws holding the fittings on the deck.

There is much less of a requirement to use epoxy for that task as the strength of of the joint is less dependant on the adhesive used.

But for any extremely highly loaded pad I would never consider anything but epoxy with the appropriate fillers.
 
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Despite others comments I have successfully used Sikaflex 292, that's 292 not 291. I bonded timber battens direct to fibreglass for plywood head linings. The test batten I tried first split under sideways hammer blows before the adhesive failed. Prepared with 40 grit and cleaned with thinners first. Was important to clamp or wedge in place until it had gone off. That, in fact was the most difficult part of the job.
 
I also used sikaflex to fix battens for head linings and they still hold after 6 years of uk and med temps, also used them on camper van conversion which seems to be a normal construction method.
 
lustyd said:
No, I was told it was a standard GRP term - just a top hat shaped piece of glass where the rim sticks to the hull, forming a sort of n shaped ridge of whatever length you need. Imagine glassing over a piece of wood but without having the wood in there, not sure how it's done :)
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Ah yes, I know what you mean now.
 
lustyd said:
No, I was told it was a standard GRP term - just a top hat shaped piece of glass where the rim sticks to the hull, forming a sort of n shaped ridge of whatever length you need. Imagine glassing over a piece of wood but without having the wood in there, not sure how it's done :)
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Usually the top hat section is formed by actually glassing over something. In the past cheap boatbuilders have used all sorts of things including cheap softwood, cardboard tubes, bits of pipe, etc. If you are just using the top-hat to form a purely stiffening stringer, the best thing to use is probably sections of closed-cell PVC foam. If you are making an attachment point for screwing in something well-dried decent wood is pretty good.

Epoxy bonds better to old GRP but costs more and is nastier to work with, also not all glass mats work well with epoxy. Ordinary resin and glass mat/tape/cloth is cheap and does well enough for most jobs, if you clean and abrade the bit you are bonding to.
 
I've used 'no more nails' to stick a rubbing strake onto a tender.
It survived a lot of abuse and was still good 4 or 5 years later when I sold it.
Hot melt glue also has its uses!
 
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