Plywood
- Thread starter Doc
- Start date
- Joined
- May 25, 2003
- RO Number
- 11591
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I had to remove part of the floor in my Carver, and that's what I noticed. there was a layer of fiberglass on the plywood...
In the past most ply did not have water proof glue. Then came the X class designation to show waterproof glue as in CDX. Marine always had water proof glue but the primary difference was marine had no unfilled voids in inner plys. Today to the best of my knowledge all ply uses water preoof glue and marine still has filled voids. Treated ply is often not a good choice if it will be sealed because the treatment may be waxy or wet neither work with a coating.
A layer of glass over ply on one side only seals that side while allowing the other side to breathe and dry.
In a low strength interior area I would use X rated ply and seal it well on all sides with resin. Outside use marine non treated and seal all edges and sides very well. Extra care to seal all penetrations.
A layer of glass over ply on one side only seals that side while allowing the other side to breathe and dry.
In a low strength interior area I would use X rated ply and seal it well on all sides with resin. Outside use marine non treated and seal all edges and sides very well. Extra care to seal all penetrations.
Marine plywood and exterior plywood both have waterproof glue, but the marine plywood is not supposed to have voids in it. Exterior plywood may and usually does. However I've found "Marine Tech" plywood being sold at a "marine" price which definitely DID have voids. Buyer beware!!! Neither one of them is treated.
The layer of fiberglass on the plywood was probably put on by the boatbuilder or at their request.
IMO if it's above the waterline and strength is not an issue, ordinary exterior plywood is fine and a whole lot less expensive. Depending on the use, treated plywood might be better than either, but I understand fiberglass won't stick to new treated plywood.
If you're going to fiberglass the plywood I'd use exterior, and MAYBE seal the back side and edges with resin. If not, I'd use treated; it has held up well on my boat (12 years now, with just paint). However even treated plywood is not rotproof.
The layer of fiberglass on the plywood was probably put on by the boatbuilder or at their request.
IMO if it's above the waterline and strength is not an issue, ordinary exterior plywood is fine and a whole lot less expensive. Depending on the use, treated plywood might be better than either, but I understand fiberglass won't stick to new treated plywood.
If you're going to fiberglass the plywood I'd use exterior, and MAYBE seal the back side and edges with resin. If not, I'd use treated; it has held up well on my boat (12 years now, with just paint). However even treated plywood is not rotproof.
Exactly as Bruce and willie said. I used exterior ply on virtually all the wood I replaced. Depending on where it's going, leaving one side raw allows 'breathing' so it can dry out. I would seal all sides if used on the deck, just in case it stays damp.
Marine ply is used on the hull or where its in constant contact with the water. I have found small voids in all the marine ply I've bought.
Marine ply is used on the hull or where its in constant contact with the water. I have found small voids in all the marine ply I've bought.
mrknowitall
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- Joined
- Jun 16, 2001
- RO Number
- 4979
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- 302
Marine grade uses Douglas Fir. However some other species are now being sold as marine plywood. South American Hardwood??? not sure what they are calling it. Personally, I would never use anything other than marine grade and I have never used the other species. Rot, resin saturation, durability wise I have tried to cut corners and used a cheaper panels and it's never worked in the long run. IMO a treated hemlock panel is garbage... It you want your repair to last you need to use the best materials.
One of the South American hardwoods used in marine plywood is Mahogany. That's usually the face sheet with cheaper grades in between. Good marine plywood has many layers rather than regular exterior grade plywood. I'm not sure exactly what kind of plywood came out of my searay, but the stringers were all water logged and black with rot. It did not have many layers. It was not sealed. HOW you treat the plywood is many times more important than 'MARINE' plywood as there are many grades of marine plywood...and marine plywood will rot just as readily as many species of wood.
White and western red cedar have long been used in boat building but Black Locust has long been known for fence posts because of their rot resistance.
White and western red cedar have long been used in boat building but Black Locust has long been known for fence posts because of their rot resistance.
- Joined
- Sep 28, 2002
- RO Number
- 10314
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- 858
When I re-did the deck in my '88 Four Winns about 6 years ago I coated all the wood with CPES before assembly. From what I can see the wood has held up well and plywood coated with CPES takes paint like Bilgecoat well. It is particularly important to seal edges and screw holes since that is where rot starts.
Like so many things, you get what you pay for. If you have a $20K boat, it would be silly to try to save $50 by using inferior materials in a repair.
I would use high quality marine grade plywood from a reliable source.
Here is one source:
http://www.worldpanel.com/
Their website has some information on the subject and the different materials available.
I would use high quality marine grade plywood from a reliable source.
Here is one source:
http://www.worldpanel.com/
Their website has some information on the subject and the different materials available.