Pressure treated transom board??

New guy here!
Redoing a 16/48 lowe line flat bottom. I ordered 2-3/4" sheets of marine ply wood for the front and back deck but planed on using a pressure treated 2x10 for the transom. I got it all cut out and put a layer of spar urethane on it. Then i read on here that pressure treated wood is bad for aluminum!! Dang it!
Do i need to get some more marine plywood for a new transom board or can i just put a couple more coats of spar on the treated 2x10 that i have ready to go?
I did notice some corrosion on the transom. some spots ate out but not all the way through and one spot a little smaller than a dime ate all the way threw. Could it be the old transom was treated plywood? It was all rotten mush when i took it out. Hard to identify.
I wire brushed all of the corrosion areas down to bare metal, wiped w/ acetone and primed w/ rustolem self etching primer. Should i have done anymore? Still can i guess.
Thanks

I wouldn't use the pressure treated stuff.

What you need is Exterior grade plywood. It has the same glue as marine ply but cost much less. Several layers of exterior plywood glued and screwed together for the transom. 3/4" ply is heavy 1/2" might be all you need for the deck.

Pressure treated will still rot. They had it in mine when I bought it. Everywhere it touched was pitted.

It's bad for your boat, just don't use it. Better to do it right the first time.

lckstckn2smknbrls said:

What you need is Exterior grade plywood. It has the same glue as marine ply but cost much less. Several layers of exterior plywood glued and screwed together for the transom. 3/4" ply is heavy 1/2" might be all you need for the deck.

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3/4" is all i could get. Checked every local lumber yard. Finally home depot said they could order it. Didnt have half inch though. $65 a sheet. Only other place that could get it was $90

Yeah. The other thing to keep in mind is that dimensional lumber ie a 2x10 is not going to give you nearly the strength that a couple layers of plywood will for your transom.

Figure out your thickness and then get some hardwood plywood and layer it up. Some people use contact cement, others have had success with gorilla glue for gluing the layers.

To get the correct thickness I used four layers of 1/4 inch oak plywood. Laminate the layers (gluing them together) and then do your three coats of spar urethane.

BoCoMo said:

lckstckn2smknbrls said:

What you need is Exterior grade plywood. It has the same glue as marine ply but cost much less. Several layers of exterior plywood glued and screwed together for the transom. 3/4" ply is heavy 1/2" might be all you need for the deck.

Click to expand...

3/4" is all i could get. Checked every local lumber yard. Finally home depot said they could order it. Didnt have half inch though. $65 a sheet. Only other place that could get it was $90

Click to expand...

Return the marine ply use exterior grade ply.

lckstckn2smknbrls said:

BoCoMo said:

lckstckn2smknbrls said:

What you need is Exterior grade plywood. It has the same glue as marine ply but cost much less. Several layers of exterior plywood glued and screwed together for the transom. 3/4" ply is heavy 1/2" might be all you need for the deck.

Click to expand...

3/4" is all i could get. Checked every local lumber yard. Finally home depot said they could order it. Didnt have half inch though. $65 a sheet. Only other place that could get it was $90

Click to expand...

Return the marine ply use exterior grade ply.

Click to expand...

x2, I paid for marine ply. The exterior grade would have been good enough at less than half the cost. I used 3/4 inch for decking and my boat is heavy. But it doesn't move when I or my 300lb friends step on it.

lckstckn2smknbrls said:

BoCoMo said:

lckstckn2smknbrls said:

What you need is Exterior grade plywood. It has the same glue as marine ply but cost much less. Several layers of exterior plywood glued and screwed together for the transom. 3/4" ply is heavy 1/2" might be all you need for the deck.

Click to expand...

3/4" is all i could get. Checked every local lumber yard. Finally home depot said they could order it. Didnt have half inch though. $65 a sheet. Only other place that could get it was $90

Click to expand...

Return the marine ply use exterior grade ply.

Click to expand...

I cant return it. It was a special order.
Asked around today for exterior plywood and none of the lumber yards around here have anything thats not pressure treated.
I did luck out though. Called a guy i know who works on boats and he happened to have 2 sheets of 1/2" marine plywood at his house. $35ea. I wasnt arguing.
So ill use the 1/2" for front and back deck and use 2 layers of the 3/4" for the transom. Thats gonna leave me w/ a full sheet of 3/4" left over now. Oh well ill find something to do w/ it.

The chemicals in ASQ pressure treated lumber are highly corrosive to aluminum:

https://www.loghomebuilders.org/the-corrosive-problem-acq-treated-lumber

The others are right about the 2 layers of 3/4" plywood for your transom, it'll be stronger than dimensional lumber and won't hurt your aluminum.

Plywood weighs about 25 lbs. per 1/4" thickness. Your boat will only be about 50 lbs. heavier with 3/4" decking, not as much as a cooler of beer and ice.

I like 3/4" for decking, it makes for a strong build and a solid feeling deck.

What about the corrosion on the transom? Will it keep spreading or will sealing it off stop it?

BoCoMo said:

What about the corrosion on the transom? Will it keep spreading or will sealing it off stop it?

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That's another thing about using PT lumber, it has so much moisture in it that it has to dry for months before a sealer will penetrate and bond properly. If you try to seal wet lumber the sealer will just turn milky and peel off.

Im talking about the the corrosion on the aluminum behind the transom bored. I wire wheeled it down to bare metal and then primed it. Will that stop the corrosion from spreading?

Did you use a stainless wire wheel/brush on the transom to clean it up before priming or was it a plain steel?

If you cleaned it down the metal and then cleaned that off with acetone you should be fine.

JMichael said:

Did you use a stainless wire wheel/brush on the transom to clean it up before priming or was it a plain steel?

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It was a $5 wire wheel brush for a grinder so im assuming it wasnt ss

BoCoMo said:

JMichael said:

Did you use a stainless wire wheel/brush on the transom to clean it up before priming or was it a plain steel?

Click to expand...

It was a $5 wire wheel brush for a grinder so im assuming it wasnt ss

Click to expand...

It will not matter as long as you cleaned all residue off with acetone...

That i did..

Got the ply wood cut out and glued together today. Used liquid nails. It was the only stuff that i could find that was waterproof. Gonna let it set overnight then start on the spar urethane.
Thanks for the help.

I think you are the first I have seen here use the liquid nails. Should work though. Main thing is that the layers are held together good...bolting it to the transom is going to help keep it nice and tight too.

Don't forget pics!

I think Gorilla Glue is waterproof after it cures.