Pressure treated vs marine plywood

[NJBASS44]

Made the mistake of buying and cutting pressure treated plywood for a floor in my grizzley. Just realized the effects copper has on aluminium.

1. If I lay down something like felt paper over the wood will this protect the boat? Epoxy resin?

2. How does regular plywood hold up coated with thompsons water seal or an epoxy resin?

3. Should I just go out and buy the marine grade plywood and not have to worry about the barrier breaking? Any ill effects from marine grade and anyone know how much it costs for a 4' x 8' sheet?

Thanks

 

[jdsgrog]

Re: Pressure treated vs marine plywood

I'm assuming this is for the sole, or floor and/or casting deck. It also depends if you are storing inside or outside. Since it is an aluminum boat, if stored outside and you are concerned about longevity, I'd use marine grade plywood covered in epoxy. If stored primarily indoors, any exterior grade ply (with exterior grade glue) will suffice and cover in epoxy. The main purpose for marine grade is twofold, exterior glue and rigidity. Marine grade has none or at least almost no voids and has more layers. This is why it is recommended for structural elements in fiberglass boats and for transoms. However, in my opinion, exterior grade plywood when taken care of will last quite a long time and AC plywood is much cheaper (about half the cost). If using fir in either grade, you should expect checking to occur. This can only be reduced by using fiberglass cloth.

 

[TojosMojo]

Re: Pressure treated vs marine plywood

Welcome to the forum!

If you epoxy coat some good exterior grade plywood (it should be rated with "EXTERIOR 1" on the ply's grading stamp) it should hold up a long, long time...

Marine grade ply is pretty high, depends on the thickness you need, is it 1/2 or 3/4? Might set you back $95+ for 3/4".

 

[Bob_VT]

Re: Pressure treated vs marine plywood

Exterior plywood is fine for the boat. Marine plywood is exterior plywood w/o voids and smooth finished sides.

Forget the thompsons..... go with poly resin or epoxy resin and csm to seal everything up.

 

[NJBASS44]

Re: Pressure treated vs marine plywood

Thanks guys! It will be for the floor and side boards as the boat allready has a casting neck I am happy with. It is stored outside, I usually cover it but it doesnt always happen.

I think I will go with the exterior plywood coated with an epoxy resin as recommened. The marine grade is expensive especially as I need 2 sheets. Any idea where you can get this for a decent price and how many coats do you need?

If I were to epoxy the pressure treated wood would the copper still have a chance of leaking out?

 

[Bob_VT]

Re: Pressure treated vs marine plywood

PT wood is usually VERY wet and needs to be dried out before use. Epoxy resin is really costly for what you intend...... poly resin is cheaper and works fine. People have used PT wood but I would not risk it. 2 sheets of 4 x 8 exterior 1/2 or 3/4 are fairly cheap at just about any home depot, lowes or lumber yard.

 

[ondarvr]

Re: Pressure treated vs marine plywood

You'd be better off with paint than Thompson's, its junk.

As for the floor there are many options.

Painted wood... cheap and easy. Since its normally fast and easy to put a new floor in a tinny and if it rots you can replace it again. This method may last from five to ten years depending on how you store it.

Good plywood and epoxy with glass. Cost will be higher, it will take longer, requires more skill and if you do it correctly will last a very long time. Although how you take care of it will still affect the lifespan.

You can choose any method between the two also.


How long do you plan on keeping it? Most people don't keep boats all that long, although when fixing it up they think they will keep it forever.

If you sell it, whatever you do will add little or no value, so don't expect to recoup any of the cost or labor.

 

[NJBASS44]

Re: Pressure treated vs marine plywood

Thanks Bob. Any idea where you can get the poly resin? Lowes? Didnt see it on their website.

 

[redeye1962]

Re: Pressure treated vs marine plywood

I have used the PT wood on aluminum and there were no apparent side affects. I used it again (after the wood rotted) covered in a couple of coats of resin. After reading about the possible affects I hope I have done the right thing but feel it will be alright. I have replaced the deck around 3 times and always put carpet on top which was a mistake and the reason I had to replace it several times.

 

[bruceb58]

Re: Pressure treated vs marine plywood

I would use epoxy resin thinned with MEK so it can penetrate into the wood.

 

[ondarvr]

Re: Pressure treated vs marine plywood

Thinning epoxy is not a good idea, plus epoxy without glass will still fail in this type of application.

 

[thrillhouse700]

Re: Pressure treated vs marine plywood

The boat shop that we get our fiberglass from told us not to even bother with marine or PT it will last JUST as long as ABX or even BCX ply if wrapped in fiberglass.