Pressure treated plywood in aluminum boat

[ozenine]

Hi all, do not want to open this can of worms but will still do lol
I am replacing a transom on 1999 crestliner and was thinking of using pressure treated plywood. In the past this was a big no-no, as chemicals in treatment ate up the aluminum.
I have been researching MicroProSienna treated plywood and it says in the manual that contact with metal is same as contact with untreated wood. Contact with aluminum is possible but not where it is constantly wet (not sure why they have this disclaimer - I have reached out to them today any will let you know if they will respond).
What do you guys think?
Marine grade plywood is 210 dollars a sheet in my neck of the woods, exterior is 40 and micropro is 60.
I need 2 sheets for the transom and 5 sheets for the floor.

 

[cyclops222]

NO NO NO You can paint or seal regular plywood. And not have any worries. Do it the right way. 1 time.

 

[airshot]

My experience with the newer treated plywood ( within past 20 plus years) is that good exterior grade will last just as long or longer than pressure treated if sealed up well. All the pressure treated lumber I bought when my house was built 24 years ago, is now rotted away, while the untreated is still stabil. Just seal it up good and don't take the chance on unknown treated lumber.

 

[ozenine]

Existing transom is 5/8 x 3 ply. I was thinking of exterior grade with epoxy in between sheets and covered eith epoxy. Not sure how much width it will add and if the whole sandwich will fit.

 

[airshot]

Just the wood 5/8" ? Most transoms are 1 1/2" or thicker overall. Will you have wood on inside and outside ? Clamp on or bolt on outboard motor?

 

[cyclops222]

All fairly new motors MUST ? Should have bolting holes for securing motor to the boat. My hand clamps loosen by themselves in a few hours.

 

[ozenine]

Just the wood 5/8" ? Most transoms are 1 1/2" or thicker overall. Will you have wood on inside and outside ? Clamp on or bolt on outboard motor?

Sorry, was not clear it is 3 sheets of 5/8. Motor is bolted.

 

[ozenine]

All fairly new motors MUST ? Should have bolting holes for securing motor to the boat. My hand clamps loosen by themselves in a few hours.

The motor is 90hp. It is bolted

 

[Scott Danforth]

Exterior plywood, titebond III, and some Iinseed oil will last longer than treated plywood and it won't eat your aluminum hull

 

[cyclops222]

Did we convince him ?
I hope so.

 

[RMClark]

At the risk of piling on...

I looked up the MicroPro Treated product on line. I found this on their fastener and hardware page:

"When using MicroPro Sienna Treated Wood in ground contact and/or high moisture applications, it is recommended that spacer materials or other physical barriers are used to prevent direct contact of the treated wood and the aluminum products. A ¼” space must be maintained between the treated wood and the aluminum product. Another option is to use a polyethylene barrier with a minimum thickness of 10 mils between the treated wood and the aluminum product to prevent direct contact."

If it was me, and it was over the past few years as I redid decks on my aluminum boat, I'd use exterior grade ply in thickness of choice. I used fiberglass resin to coat all of the ply before installation, paying particular attention to edge grain.

 

[ozenine]

Did we convince him ?
I hope so.

Hahaha, you did. Will do exterior acx plywood with fiberglass resin over it.
How many coats do I need and is there a particular type that you can reccomend?

 

[JASinIL2006]

If you are not planning to encapsulate the wood with fiberglass cloth, poly resin by itself might not be your best choice. When used on wood alone, it is prone to cracking.

A better choice might be to treat the wood heavily with Old Timer's Wood Sealer (see here for formula: https://forums.iboats.com/threads/carpet-glue.757215/post-5774053) or epoxy. Either would provide more protection than polyester resin alone, IMO.

 

[Scott Danforth]

Old-timers formula, straight linsead oil, or simple rustoleum oil based

For the exterior plywood ACX, or cheaper BCX

 

[ozenine]

If you are not planning to encapsulate the wood with fiberglass cloth, poly resin by itself might not be your best choice. When used on wood alone, it is prone to cracking.

A better choice might be to treat the wood heavily with Old Timer's Wood Sealer (see here for formula: https://forums.iboats.com/threads/carpet-glue.757215/post-5774053) or epoxy. Either would provide more protection than polyester resin alone, IMO.

This looks awesome. I am planning to redo the floor and use vinyl flooring glued with either carpet glue or contact cement. Do you know if this sealant leaves dry finish?

 

[JASinIL2006]

This looks awesome. I am planning to redo the floor and use vinyl flooring glued with either carpet glue or contact cement. Do you know if this sealant leaves dry finish?

Others will hopefully chime in, but I think it works fine on surfaces that are to be carpeted with contact cement or glue. If you're really concerned, you can use straight polyurethane as a top coat. That will dry hard for sure.

Just be sure to give it a good 72 hours or more to soak in and cure.

 

[briangcc]

As its mineral based it may take some time to completely cure. If you can still smell it, give it more time.

 

[ozenine]

As its mineral based it may take some time to completely cure. If you can still smell it, give it more time.

I think I will try a transom first. It does not have to be glued upon. And then will make a decision re floor. I think I will start the new thread with restoration. Hoping to start digging into it next week.