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post #1 of 11 Old 08-20-2012 Thread Starter
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plywood type for fiberglass .

after yet another unsucessful motor mount i have decided i need to build a wedge rather then just a stand off .

so here is the question can i use regular plywood from lowes if im going to fiberglass it ? i have a 6 hp 4 stroke and i plan on using 1/2" plywood and wood screws before i fiberglass it .

our lowes does not carry marine plywood .
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post #2 of 11 Old 08-20-2012
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Re: plywood type for fiberglass .

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Originally Posted by Southron Spirit View Post
after yet another unsucessful motor mount i have decided i need to build a wedge rather then just a stand off .

so here is the question can i use regular plywood from lowes if im going to fiberglass it ? i have a 6 hp 4 stroke and i plan on using 1/2" plywood and wood screws before i fiberglass it .
Could you explain this better? What are you doing with the wood screws? Zinc plated or more like deck screws? How many screws and what size?

Are you using ACX or BCX (surely not CDX)? Just one thickness of plywood or more? Epoxy or polyester resin? How many layers of glass over the wood? What weight of fabric?

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post #3 of 11 Old 08-21-2012
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Re: plywood type for fiberglass .

I would use the cheapest ply you can find glass it up use plenty of filler and paint. Hey it seems to work for the big name boat builders

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post #4 of 11 Old 08-21-2012
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Re: plywood type for fiberglass .

Wasn't clear where this is and its purpose but the minimum grade you should use is a ply with exterior glue ac bc exterior are reasonably resistant to exposure and most importantly have few serious voids
cdx is not remotely ok as.current products have been known to delaminate onsite while waiting to be used! Polyester is fine for this then prime and paint or use pigment from the beginning
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post #5 of 11 Old 08-21-2012
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Re: plywood type for fiberglass .

I had thought that most people knew that the 'X' in ACX was exterior but perhaps not. It was my assumption that the OP was talking about exterior grade.

In terms of polyester resin I can't agree with that. There are too many problems. Polyester is not an adhesive. To get maximum strength you need to put on additional layers while the first layer is still tacky. But even if you do it won't stick to the plywood. I would use epoxy. Epoxy is an adhesive and will stick to both the original fiberglass and the new wood. Epoxy is also waterproof whereas polyester is only water resistant. You have to make polyester thick to have a reliably water tight boat. For example the glass on my boat is about 1/4" thick with polyester resin but all the repairs I did were done with epoxy.

I've heard of people building plywood boats with zinc coated screws and then having these screws rust in salt water in one season under a thin layer of polyester glass. It's something to consider.

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post #6 of 11 Old 08-21-2012
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Re: plywood type for fiberglass .

I used plywood as a temporary centerboard refit when I repainted zzZippety Doh Dah. I believe it was 1/2 inch plywood that we cut to shape and glued/screwed together. We then covered it in several layers of epoxy and glassed it.

There is a pic of it right after being epoxied in this post about 3/4 down
Ben Lobaugh Online ZDD: Haul out for refit and painting

Unfortunately I did not get a chance to snap a pic after it was glassed and before it was painted.

FYI - Ben Lobaugh Online ZDD: Lucky sailing this summer
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post #7 of 11 Old 08-21-2012
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Re: plywood type for fiberglass .

you would be better to use a piece of hardwood (oak/hickory/etc) and epoxy coat that....

you can then see what is happening to the wood....

Plywood is going to "squish" over time unless you are using multiply/specialty ply...

the home stores carry 4,5, or 7 layer, up to 3/4"....but that is poor for your purpose from the get go.
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post #8 of 11 Old 08-25-2012
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Re: plywood type for fiberglass .

Why bother with a wedge at all?? Fiberglassing over plywood, who wants to do that?? Take a look at the mount I use on my boat under the modification post. It was easy to make. You don't need to have a power lift. But it is GREAT to have one!
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post #9 of 11 Old 08-25-2012
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Re: plywood type for fiberglass .

I'd use two layers of 1/2" Oak Plywood glued and bolted together then fiberglassed. Buy the small 2'x2' pieces and it'll cost about $18, Cut the perimeter after gluing together so you have no overhangs between the pieces and the fiberglass will uniformly adhere to the edges. Glass cloth doesn't go around the corners well so initially epoxy the whole thing with no glass to ensure watertightness.
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post #10 of 11 Old 08-27-2012
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Re: plywood type for fiberglass .

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.... Take a look at the mount I use on my boat under the modification post. It was easy to make. ...
For reference Spirit 23 modifications
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