Are all exterior plywood glues created equal?

[will w.]

I,ve been looking for some actual 3/4" ply for a transom. My local Hdepot doesn't have anything that isn't 23/32 except for interior grade. I did find marine grade made by Jonesburg in 3/4 at Menards the next city over. The subject of which plywood to use for boats has been discussed mant times over and it appears the general consenus it that any ply with an exterior glue should be ok to use on our boats especially since most here are applying a protective finish.

While on Menards site I decided to look for an cheaper alternative ply in 3/4 that uses exterior glue. I did find some. While looking at the specs on this ply, I noticed it had a downloadable PDF under the documents bar, so I checked it out. The glue has formaldehyde. Looking around the net for formalehyde Vs aluminum, I found the little snippet posted below. I could find the chemical make-up of the marine grade glue, whhich was made by a different company, but I wonder if the MG ply is the same make-up?

Links and snippet below. Sorry if this has been discussed in the past, this was just minimal searching, so there may be more info available.

http://www.menards.com/main/mobile/...di-panel/p-1470076-c-13337.htm?freeFormRowId=

http://www.chemicalforums.com/index.php?topic=20111.0

 

[tpenfield]

Why won't 23/32" be acceptable for 3/4" ??? :noidea: I don't see 1/32" making a difference . . .

"exposure1" "exterior" and "marine" grades all use the same glue, according to the APA. Exterior is generally acceptable for marine use . . . Marine grade has better wood quality in the laminates.

 

[will w.]

I need a full 1.5" for a transom. Multiply that short measurement x2 and it isn't good. Transoms need a good snug fit.

 

[Woodonglass]

will w.,

The waterproof glue used in Ext. Grade Plywood and Marine grade are the same. The main difference between the two are the type of wood used in the plys, the quality of the plys (MG has less voids) and the number of plys. The Arauco brand of plywood has been found to have about the same amount of plys and very few voids and uses the same glue for about 30% less in costs.

By the time you coat the 23/32 plywood with resin, CSM, Resin, a Layer of 1708 Fabricm Resin and a Final layer of 1708 + the PB to adhere it to the outer skin, You'll prolly be a bit over the 1.5 " thickness and that's OK too!!! The Actual final thickness of the transom is NOT as critical as you might think. + or - 1/8" - 1/4" is the norm.

 

[zool]

Why won't 23/32" be acceptable for 3/4" ??? :noidea: I don't see 1/32" making a difference . . .

"exposure1" "exterior" and "marine" grades all use the same glue, according to the APA. Exterior is generally acceptable for marine use . . . Marine grade has better wood quality in the laminates.

yep Ted. 23/32 is 3/4 in actuality, its only 23/32 at its thinnest point, absent of any humidity....

 

[will w.]

Thanks for all the tips. My original intent was pointing out what was said about formaldehyde becoming an acid that eats aluminum, which is one of the contents of PW glue. With more thought, it really doesn't matter, all PW has it. I just question if this formaldehyde adds to the corrosion we see in these aluminum boats.

I ended up with the MG as it was .734'' thick. Could have got the other for what Woodonglass said, around 30-40% less cost. I did find Arauco, but only in 1/2'', oops i mean 15/32''.:lol: This wood is for an aluminum boat where the framing in built for a 1.5'' transom. Maybe I'm wrong, but it seems that anything less would warp the transom skin when tightening the thru hull fasteners.

 

[jbcurt00]

Will
You still have to seal the transom w/ something, and glue laminate the 2 sheets together. I seriously doubt you'll miss the 1/32 or 2/32 at install............ or need it

Might look thru several dozen Starcraft tin boat builds posted here, where most have used 23/32" exterior grade plywood with no ill effects

 

[MTboatguy]

I have rebuilt 3 aluminum boats and never had any ill affects from using Home Depot and Lowes Plywood, there is just not enough of a difference to do anything.

 

[will w.]

You guys are right, I work with tenths thru thousandths everyday. I think it was clouding the picture for me. .062'' isn't much at all across the width of a boat and like you fellas pointed out, minus the coating/sealer from .062''. Now if i wasn't so stubborn, I could have saved myself $30. Better keep that one to myself.

 

[Woodonglass]

If it was only a $30 dollar difference I would have bought the MG too!!!

 

[gm280]

Oh yes the 1/32" inch thinner plywood issue. Which means for every 31 sheets they manufacture, they get one free. It is how the lumber industries tries to squeeze out every penny in profits they can. That measurement has even prompted the router companies to manufacture dado router bits for those 1/32" smaller sizes. You normally buy a straight cutting router bit set with 1/4", 3/8", 1/2", 5/8" and 3/4" sizes in the set. Now they market all those sizes as 7/32", 11/32", 15/32", 19/32" and 23/32" incremental sizes to accommodate the plywood thicknesses now. And for the record, while the lack of 1/32" inch building transoms doesn't make any difference, it certainly does in furniture and cabinet making cuts... Once you laminate two sheets of plywood together and coat the front and back sides, you will have a thicker transom then 1.5" for certain. And that is even if you don't use CSM or 1708 fiberglass materials either.

 

[tpenfield]

I was thinking that the sanding operation was leaving the plywood slightly under thickness, so from a legal sense they say 1/32 under the 'standard size' . . . Maybe so :noidea:

I guess I'll take my micrometer out and check some plywood that I have lying around . . . of course, moisture variations could easily go + or - on the spec'd thickness.

 

[MTboatguy]

That is the reason, I don't build cabinets boxes out of plywood anymore, due to variances in the plywood.

 

[minuteman62-64]

Oh yes the 1/32" inch thinner plywood issue. Which means for every 31 sheets they manufacture, they get one free. It is how the lumber industries tries to squeeze out every penny in profits they can. That measurement has even prompted the router companies to manufacture dado router bits for those 1/32" smaller sizes. You normally buy a straight cutting router bit set with 1/4", 3/8", 1/2", 5/8" and 3/4" sizes in the set. Now they market all those sizes as 7/32", 11/32", 15/32", 19/32" and 23/32" incremental sizes to accommodate the plywood thicknesses now. And for the record, while the lack of 1/32" inch building transoms doesn't make any difference, it certainly does in furniture and cabinet making cuts... Once you laminate two sheets of plywood together and coat the front and back sides, you will have a thicker transom then 1.5" for certain. And that is even if you don't use CSM or 1708 fiberglass materials either.

I always thought the change was to accommodate metric sizes - resulting from the more and more global economy. However, just converted 21/32 and it comes out to 16.6 mm. OK, back to one free sheet out of every 31

 

[will w.]

I think tpenfield is correct, they make us pay for the sawdust. If you bought wall studs per board ft', you would be paying for a full 2x4''. The PO of my home laid down marble tile which was bustedn up when i bought the home. He screwed down that orange plastic sub flooring then filled the screw heads with tile cement. I tore the floor up good when i removed this mess and had to replace a section of base floor. It was a nightmare trying to match the thickness with todays standards.

Anyway, + or - a few thoudandths' it has got to be better than this.:lol:


While at it I couldn't stand not to paint the transom. I sanded down to bare aluminum, wiped with mineral spirits, then wiped with dry cloths until I couldn't pull anymore aluminum dust from the surface. Hope that wasn't a mistake as i see many use vinegar diluted 50% with water. After the wipe down i did two dusting coats of ZC half an hour apart. Two coats of rustoleum industrial aluminum primer after the ZC and thats what you see. It has been a rather messy rush job as I,m trying to finish by sat afternoon, hence the mess and lack of pics.Its kicking my butt not adding a sheet of aluminum to the transom within the splash well, but I'll get to that at a later date when time permits.