Marine Plywood

[ondarvr]

Re: Marine Plywood

Hmm.. under what circumstances will epoxy crack, and how long will it take?

News to me

While epoxy is stronger than polyester it still succumbs to the stresses of temperature and humidity on the wood, add to that the normal flexing of the boat and while it does last longer, it will still crack. The glass is what saves both products and makes them usable. It also depends on the type wood, some types check a great deal adding to the stress.

 

[83mulligan]

Re: Marine Plywood

ondarvr. what's your reccomendation for treating marine ply for decks? Will a few coats of polyurethane instead of just resin or resin and glass protect it?

 

[ondarvr]

Re: Marine Plywood

I'm not sure what the polyurethane is supposed to do, I think straight epoxy would be much better. I always use some type of glass.

 

[83mulligan]

Re: Marine Plywood

wouldn't the polyurethane seal the wood from moisture. It's 3/4" so i don't think it needs the structural support.

 

[Mark42]

Re: Marine Plywood

wouldn't the polyurethane seal the wood from moisture. It's 3/4" so i don't think it needs the structural support.

Clear polyurethane is great for hardwood floors, but does not hold up outdoors very well. It cracks and peels with the slightest expansion of the deck. Best to put mat and poly resin down.

3/4" is very heavy, and probably not needed unless there are great spans between stringers. Most boats use 1/2 or 5/8 ply. Add a layer of resin and mat and it will be even stiffer and probably outlast the reset of the boat.

 

[Mark42]

Re: Marine Plywood

Are there treated and non treatedmarine pllywood? I checked today and one place had marine plywood with six layers but not treated. Another has what they called treated marine plywood. Of course the one without treatment is 3/4" thick. The other is 1/2" Would you have to treat the untreated?

Yes there is pressure treated marine plywood available. Untreated marine rots fast when wet. So either be 100% sure it is sealed water tight, or go with regular pressure treated.

 

[wallybme]

Re: Marine Plywood

Well I did some more research on this subject today. I was at Lumber 84 who said that they carried marine plywood. As I looked at the sheet it marked MAR AB with five ply layers for the 1/2 inch and nine for the 3/4" On the 4' side it said "marine". What was visible were a few football pieces. I also look at some at another lumber yard wit marine type without the football pieces.

 

[MUDWISER316]

Re: Marine Plywood

What plywood would be best for use on a alumimum boat being P/T plywood will cause corrosion. would exterior plywood be the same as P/T but dried out.

 

[fishrdan]

Re: Marine Plywood

Well I did some more research on this subject today. I was at Lumber 84 who said that they carried marine plywood. As I looked at the sheet it marked MAR AB with five ply layers for the 1/2 inch and nine for the 3/4" On the 4' side it said "marine". What was visible were a few football pieces. I also look at some at another lumber yard wit marine type without the football pieces.

I'm in LV too and bought my marine ply from 84 Lumber. Their marine plywood is "virtually" void free, but I did find a few spots that had small voids,,, big enough for a screw to pull through the face though . Overall I'm satisfied with it. What are you working on, fiberglass or aluminum boat?

You mentioned "marine type" plywood without the boat patches from another lumber yard, is this the Arauco plywood from Lowes? If so, it's not good for marine use as the type of pine used is more susceptible to rot than other types of wood used in marine plywood. If you are covering it with fiberglass and keep it 100% water tight, then it might be OK as it uses the same glue as marine plywood. When I bought plywood for my Crestliner rebuild I considered using Arauco, but decided to spent the extra to get true marine plywood,,, extra $200

What plywood would be best for use on a alumimum boat being P/T plywood will cause corrosion. would exterior plywood be the same as P/T but dried out.

AQC treated plywood is your enemy on an aluminum boat, but CCA treated plywood is fine. CCA is what aluminum boat manufacturer's use, but it's hard to find. AQC looks green, CCA looks yellowy-orange. I've heard of people putting a barrier (heavy tape, rubber strips, paint) between AQC plywood and aluminum to prevent corrosion...

 

[wallybme]

Re: Marine Plywood

I'm in LV too and bought my marine ply from 84 Lumber. Their marine plywood is "virtually" void free, but I did find a few spots that had small voids,,, big enough for a screw to pull through the face though . Overall I'm satisfied with it. What are you working on, fiberglass or aluminum boat?

I was at Lumber 84 and the marine type did have some football shape pieces in the upper veneer. According to the previous thread it was suggested that the marine type would not have these football shape pieces. I was also at Austin's and they had the marine plywood without the football shape pieces in the veneer.
I am working on fiberglass.
Did you coated yours with glass?

 

[marquette]

Re: Marine Plywood

besides the color differance is the PT stamped AQC or CCA?