Fiberglassing over wood

[Cheechako]

Always coat the wood with resin first and let it saturate.
Never use finishing resin as it has wax in it.
The resin should stay tacky for adding fiberglass to it.
Many attempts to build complete boats with glass over wood were made decades ago, they seldom worked out well with poly resin.

Bulkheads laminated to glass with poly worked ok, but you can see a lot glass pulling away from a bulkhead on older boats sometimes.

Not a huge fan of Epoxy for all things, but if you want to bond glass to wood, I would use Epoxy.

[Cheechako]

Originally Posted by Fore and Aft

I hardly see any glass tabbing failures on plywood bulkheads. But when it comes to polyester/fibreglass on plywood that’s on the exterior of a boat I have seen some shocking failures.
Cheers

Yep, this is what I was saying. Although, there are many examples of glass pulling away from ply bulkheads out there. But I suppose that is not a "failure" because it's not 100% pulling away.

[coopec43]

Originally Posted by Cheechako

Yep, this is what I was saying. Although, there are many examples of glass pulling away from ply bulkheads out there. But I suppose that is not a "failure" because it's not 100% pulling away.

When I "tabbed" my bulkheads in I drilled 2 inch holes around the perimeter of each bulkhead, tapered the edges of the hole then fiber-glassed from one side to the other. I've googled and I don't think anyone else does that though?

You may be able to see the indents in the photos.

[Benz]

Originally Posted by coopec43

When I "tabbed" my bulkheads in I drilled 2 inch holes around the perimeter of each bulkhead, tapered the edges of the hole then fiber-glassed from one side to the other. I've googled and I don't think anyone else does that though?

You may be able to see the indents in the photos.

That's very thoroughly done. I have yet to see a production boat that went that far. I've heard it suggested, but never seen anyone bother.

[Chotu]

Originally Posted by coopec43

When I "tabbed" my bulkheads in I drilled 2 inch holes around the perimeter of each bulkhead, tapered the edges of the hole then fiber-glassed from one side to the other. I've googled and I don't think anyone else does that though?

You may be able to see the indents in the photos.

That’s really cool. Was that in the plans? That’s actually mechanical fastening. Using composites. Brilliant stuff.

[Fore and Aft]

The other good thing about polyester tabbing is that you can use flow coat in all your lockers. That’s a great hard wearing paint.
Cheers

[CHM]

I have used fiberglass on wood without any issues regarding adhesion and have been very satisfied with the results.

[Hasbeen]

We did a lot of work on polyester & glass sheathing of wood years ago. We wanted the harder more impact resistant glass on center boards & rudders for high performance boats. Epoxy & dynel fabric were damaged by impacts with flotsam in the water. Glass withstood impacts much better if done correctly.



Working with the raw material supplier we experimented with many grades but found the main requirement for successful adhesion was the water content of the wood when glassed. For high adhesion the wood had to have a free moisture content between 6 & 10%.


We had to install a kiln to dry our center boards & rudders to this content as it was always higher than desired in Sydney Australia. We never had a case of the glass pealing off the timber once we controlled the moisture content.

[NormanMartin]

Our technique is to use MAS Epoxy which thins with alcohol.
Sand surface, clean with alcohol, squeegee on a couple layers of epoxy, sanding and alcohol wipe between coats. Finish with epoxy and glass, etc.
May be worth a call to Jamestown Distributors as they provide good customer service for clients.

There is a guy on you tube with a video on this subject, too.

[rla]

Have a look at 'Life on the hulls' on You Tube.
Ross is building a large cat and is a very experienced GF user, as he owns a Kayak building business. his methods and reasoning are to the highest standards and knowledge. He tries to use foam board rather than wood but has to have main bulkheads of plywood.

[Benz]

Originally Posted by CHM

I have used fiberglass on wood without any issues regarding adhesion and have been very satisfied with the results.

At issue is not whether to use fiberglass or not; it is which sort of resin to use with your fiberglass. Some say that polyester resin sticks just fine to wood, while others say that epoxy sticks so much better it's worth the extra money. Either will be reinforced with fiberglass, at least in this discussion.

[coopec43]

Originally Posted by Benz

At issue is not whether to use fiberglass or not; it is which sort of resin to use with your fiberglass. Some say that polyester resin sticks just fine to wood, while others say that epoxy sticks so much better it's worth the extra money. Either will be reinforced with fiberglass, at least in this discussion.

Thanks for that. That was exactly the point of the thread.

[gulfislandfred]

Use styrene to thin polyester resin, and tolulene to thin epoxy resin. Git Rot is a product, made with epoxy resin and tolulene, sold to penetrate and "cure" rotten wood (don't get me started - false hope is as mild a comment as I can muster). It does soak into wood.

Epoxy sticks and holds better. The only disadvantage to using all epoxy is higher cost. There are some high end custom boats built with epoxy resin, sometimes carbon fibre, and, often, structural foam, which doesn't absorb water, and adheres to both polyester and epoxy resin better than wood.



Bulkheads are sometimes made with structural foam, or Nomex (basically epoxy saturated paper - used on aircraft) core, with aluminum or glass/epoxy skins. These are carefully engineered.

Perhaps the strongest laminated structures in the boat world are carbon fibre masts and spars, which are usually made with epoxy resin saturated carbon fibre.

[topcar]

Acetone is for CLEAN-UP ONLY. To get a good bond into the wood it is necessary to thin the resin with styrene monomer. About 10% should do it. In an ideal world you should also add about 5% of promoter to get the thin resin mix hotter so it will go off. Promoter is the best but it can be substituted for by adding extra catalyst. Normal polyester catalyst ratio is 1% but as the mix is thinner, heat build-up needs a boost so try 2–3% catalyst. Paint in a couple of coats to get a good penetration and seal of the wood. There will now be the usual tacky finish and you can build up layers of glass as normal.Start with a resin-rich light (300g)chopped strand layer. Add some waxed styrene (or flowcoat which already has the wax) to the final layer of glass.

[coopec43]

Originally Posted by topcar

Acetone is for CLEAN-UP ONLY. To get a good bond into the wood it is necessary to thin the resin with styrene monomer. About 10% should do it. In an ideal world you should also add about 5% of promoter to get the thin resin mix hotter so it will go off. Promoter is the best but it can be substituted for by adding extra catalyst. Normal polyester catalyst ratio is 1% but as the mix is thinner, heat build-up needs a boost so try 2–3% catalyst. Paint in a couple of coats to get a good penetration and seal of the wood. There will now be the usual tacky finish and you can build up layers of glass as normal.Start with a resin-rich light (300g)chopped strand layer. Add some waxed styrene (or flowcoat which already has the wax) to the final layer of glass.

I just looked at your profile and it is blank so I don't know what your experience is to back-up your advice.

If you look at comment #16 and #17 you'll find a guy who advises against adding acetone or styrene.(He has 45 years in the game! )

"Adding styrene to new resin to get a better bond to wood seems like a good idea up front, but the chemistry starts working against you rather quickly. Adding more than a very small amount of styrene (2% or so) can have a big effect on physical properties, this includes water resistance and crack resistance, plus the penetration into the wood is only marginally better".

https://www.boatdesign.net/threads/p...styrene.57039/