Visit our Popular Forums

RainDog · 01-02-2014, 16:24

I am rebuilding cockpit locker lids. They are about 41 x 17 inches. Thick fiberglass with a plywood core. The core got completely saturated. Is there any reason to use marine, or even exterior, ply for such an application? Or is any old 3/4 inch ply adequate. In theory it will never get wet and only needs to support the wight of a human. The glass on either side is 1/4 inch thick.

boatpoker · 01-02-2014, 16:30

Quote:

Originally Posted by RainDog

I am rebuilding cockpit locker lids. They are about 41 x 17 inches. Thick fiberglass with a plywood core. The core got completely saturated. Is there any reason to use marine, or even exterior, ply for such an application? Or is any old 3/4 inch ply adequate. In theory it will never get wet and only needs to support the wight of a human. The glass on either side is 1/4 inch thick.

If the plywood will never get wet, how did the old plywood get saturated ?

Nicholson58 · 01-02-2014, 16:34

I use epoxy and microballoons as filler. Us Composites for both. 635 thin resin. The strength is around 3000 psi compressive and the density is about 23#/ft^3.

Fiberglass , Epoxy , Composites, Carbon Fiber - U.S. Composites, Inc.

I used this for wet deck repair of balsa and for the entire filled core of my rudder with carbon fiber skin. Rudder photos here.
Member Galleries - Cruisers & Sailing Photo Gallery

I vowed never to have to repair the same area twice

bobconnie · 01-02-2014, 16:34

Seems to me if it got soaked once bad enough to need replacement, it will probley get soaked again! But Minuret(spl) had a real good way to make up fiberglass boards for just this type of use! look back at his rebilding post and see what he did ! sure worked for me on the deck and locker lids on the ketch we just sold!!

Cheechako · 01-02-2014, 16:46

The small additional price for exterior ply is worth it. I think the only difference is the glue and you want moisture resistant glue. All ply has some moisture in it, trapped in there it could be an issue.

RainDog · 01-02-2014, 16:47

Quote:

Originally Posted by Nicholson58

I use epoxy and microballoons as filler. Us Composites for both. 635 thin resin.

Sounds expensive, but I guess it is still cheaper than buying a whole sheet of marine ply.

bletso · 01-02-2014, 16:56

Quote:

Originally Posted by Cheechako

The small additional price for exterior ply is worth it. I think the only difference is the glue and you want moisture resistant glue. All ply has some moisture in it, trapped in there it could be an issue.

No marine ply, in addition to the glues, has no voids between the layers. Regular exterior or interior ply can have some rather large voids between the layers. Here is a site which has some info. Marine Plywood by Homestead - Douglas Fir

Some technical specs can be found at http://plywood.boatbuildercentral.com/help.php

You should certainly be able to source marine ply in your area or up in Houston.

RainDog · 01-02-2014, 17:02

Quote:

Originally Posted by bletso

marine ply has no voids between the layers

My understanding is that is what you are paying the very steep premium for. I just cannot imagine it matters in this application, but perhaps I am wrong?

bletso · 01-02-2014, 17:10

You still haven"t answered bobconnie. How did water get there in the first place? If it happened once, chances are it will again, just maybe with the next owner.

Idylles15.5 · 01-02-2014, 17:23

To replace core use Meranti BS 1088 marine plywood. It is made for underwater use and will not rot. It is lloyds rated and stamped. Another product would be Sapelle marine grade which also has no voids and the glue lay up used is both water proof and Boil proof. You could also try divinycell foam board, but you would have to use a thick piece to get the same rigidity. You need a rigid core in the application you are attempting to repair. Layer upon layer of glass with eventually split and crack unless you make it a half in thick, which in not only a waste of your time and materials but money too. You look at the price of a quart of West hardner and epoxy. You'll get plenty of Ideas on here, but please listen to me.

You can buy a 4x8 sheet and have the remainder for future projects.

bletso · 01-02-2014, 17:29

If you use meranti, you can get partial sheets from http://www.boulterplywood.com/MarinePlywood_4.htm a 3/4 X 2 X 4 is only $44.00. I found their shipping to be very reasonable. A 2 X 4 sheet will ship UPS. They are great people to deal with.