Gluing thinner plywood sheets to get thicker stock

[Steve Lansdowne]

I'm considering using epoxy to glue pieces of 4 mm marine plywood together to get 8 and even 12 mm thickness stock. This is for a canoe project and would save me the cost of buying a whole sheet of thicker wood of which I only need a bit. Any advice on whether or not this is possible and any cautions from those who have tried this?

[NormMessinger]

Well, I've done it several times. The results seem to be satisfactory but one never knows for sure. The transom on Prairie Islander is two pieces of 1/2" plywood plus a veneer of teek. I used a mastic spreader, a plastic dealie with knotches in the edge to spread the thickened epoxy on the surface which of course was first coated with neet goop. I didn't thicken quite as much as usual, just enough so the ridges would stand up a bit because I wanted to be sure the goop spread.

A piece of plastic went on the carpet in the family room then the two pieces of plywood then a whole slug of those long sand bags they sell for weight in the back of pickups in the winter. I got just a little squeeze out all around and when I trimmed to size I found no voids.

The veneer went on the same way except it went on the plastic covered carpet first then the cured plywood sandwich and a quarter ton of sandbags. No bubbles, ripples or unevenness resulted. Good Job Norm!

Other laminations were not so large so clamps usually suficed.

[mmd]

Another method to apply clamping pressure is to lay the ply down on a sheet of plastic bigger than the ply, lay up your laminates, and place another piece of plastic over all, sealing the plastic edges with two-sticky-sided carpet tape, except for a small hole where you stick the nozzle of your shop-vac in. Seal the plastic around the nozzle with tape and turn on the shop-vac. Presto! Home vacuum-bagging. A 3 psi drop in pressure inside the bag is easily attainable, which exerts a clamping pressure of over six tons over the ply surface. Use your old shop-vac, though - this is kinda hard on the poor critter's motor bearings.

[ihrig]

Not hard on the shop vac if you use 5 minute epoxy!

[Beowolf]

Norm...

You were able to do large laminations in the family room!?! Our wives need to get together sometime. [img]smile.gif[/img]

Jeff.

[John Blazy]

Just ten minutes ago I laminated three layers of 5 ply quarter inch stock to itself for a bulkhead/frame member, one of hundreds in my lifetime. The issue to remember is that you will not need to worry too much about strength because almost any glue with moderate pressure will do well because the stress loads usually never exceed the strength of the bond due to such a large surface area bonded. That said, the best glue is low viscosity polyurethane like Gorilla glue, because it will expand into any voids from unclamped or lightly clamped areas like sandbag weight. It pays to roll it on for uniform coverage. I think epoxy is overkill in this type of bond. PL Premium polyurethane construction adhesive (identical to 3M 5200 at a fraction of the cost) also works well for thicker plywood.

[NormMessinger]

Originally posted by Beowolf:
Norm...

You were able to do large laminations in the family room!?! Our wives need to get together sometime. [img]smile.gif[/img]

Jeff.

Phyllis's motto is: "My house is clean enough to be healthy and dirty enough to be happy."

[Steve Lansdowne]

Thanks, all.

[Steve Martinson]

PL Premium polyurethane construction adhesive (identical to 3M 5200 at a fraction of the cost) also works well for thicker plywood.[/QB]

I suspected that as well. Actually PL polyurethane caulk smells just like 5200 and behaves the same. Anyone else been using PL Polyurethane Caulk?

Steve

[NormMessinger]

What does the PL stand for? Is that the brand? Is it carried by national chain stores such as Lowes? When one looks at the shelves with calk and construction adhesives there is probably seventeen dozen, give or take, choices.

[Russell Sova]

Yep, I used PL polyurathane on the boat I'm building right now. I tested it by clamping two pieces of wood togther with PL in between. After a month I put it under a downspout for a week wherein it rained almost every day. I couldn't pry the pieces apart even with a large srewdriver and hammer. You have to wait at least a couple of weeks for the tube glues to obtain max strength. I've seen others talk about their tests on these glues but I'm not sure how long they waited to let the glue steup.

[Russell Sova]

Norm, I went out and checked the tube and it doesn't say what PL stands for. It's made by OSI in Mentor, Ohio right here in Lake County. It's sold everywhere including Home Depot.It costs a couple of bucks around here.

[Steve Martinson]

PL is a brand name. They make several construction adhesives and caulks. I'v been very pleased with their building construnction adhesives. www.stickwithpl.com

[ 08-09-2003, 08:16 PM: Message edited by: Steve Martinson ]

[NormMessinger]

I checked the local Ace Hardware, PL300 construction adhesive and PL400 floor and panel, or something like that but no PL polyurathane as such. Perhaps they both were but it was not mentioned on the label that I noticed. $2 and $3.50 respectively. So what specifically does the label on what we are talking about here say?

[Steve Martinson]

Those are other PL products. They make many. Look for PL Polyurethane. They market it as a sealant for windows, doors and siding.

[NormMessinger]

"By Jove, I think he's got it...."

[John Blazy]

Hey Norm, Steve (sounds like I'm on 'This Old House') and Welcome Russel, from my neck of the woods:
I just very well may be the top salesman of PL Premium Polyurethane construction adhesive, at least in my mind. I've been using/buying it by the case since the eighties when it came out, carried by very few lumberyards (the one's in the know), and I tell everyone that walks into my shop about it. Most of my professional colleagues use it. It is truly a miracle adhesive - specifically the pure adhesive, not the sealants, although the sealants are awesome.

I've veneered with it (macassar ebony), bent laminated boat parts, glued steel to glass (not fiberglass), glass to wood, aluminum to wood, PVC to plywood (pre-prime with solvent cement and bond to the PL wet-on-wet for a full weld).

When I was in the high-end cabinet and furniture business, I learned that the PL urethane literally welds itself to melamine faces - something no other glue can do, and my case construction was exlusively PL butt joints - stronger than screws, biscuits, dadoes or insertion dowels (did press tests to prove it).

Nowdays, there's almost as much of it on my boat as there is epoxy (framing & buildups).

Stronger, yet half the cost of Gorilla Glue, though higher viscosity.

Do I sound like a PL geek?

[Steve Martinson]

John,
Do you use PL below the water line or where UV can get to it?

btw. Menard's stores stock PL products.

[ 08-11-2003, 08:36 PM: Message edited by: Steve Martinson ]

[John Blazy]

Niether. I love PL, but nothing beats epoxy. I glass/epoxy all the joints in the ply and layed 38 oz of biaxial/CSM onto the bottom. Much interior build up cleats, gunwhales, solid wood braces and such are all done with PL, and bulkhead-to-hull joints are done with both.

I have to glue some aluminum backing plates to the build-up rabbets I just epoxied in for the glass bottom cutouts in my boat and I will use PL for this, as its bond to aluminum is superior to epoxy. I also plan to seal in the Lexan with PL polyurethane window sealant between the rubber gaskets, because its paintable, yet as elastic as silicone.
Some guys have done stitch n glue with PL, but thats just a little too crazy. I make sure that sunlight never gets to my PL joints, either.

[Tomcat]

Whether or not epoxy is overkill depends on how one will load the joint. Plywood certainly can fail, for instance when used in boards. Since epoxy is cheaper and easier to use, and gives better results, I am not sure why I would use construction adhesive, but obviously it is case sensitive. A good test would be to suspend a bucket of sand from a belt sized sample of each with about a 2 square inch ovelap, and just come back periodicaly to see which drops to the floor. Another neat test would be to laminate some multi layer samples, and catilever them with weights, see if either sample is stiffer. No fair if the PL sample is thicker.

If you try the shop vac trick, be sure to use about four 1/4" holes in the hose, to ensure that the motor gets air cooling, the motor will burn up if you don't, while they go through thousands of cycles if just a little air is let in. Idealy use a vac gauge, or the palm of your hand to sense when a certain number of holes cause a big drop. 4 x 1/4" holes has always worked with the small vacs, which are all you need.

One limitation is that these vacs usualy won't bond the last inch of the ply, I rarely use that, it's usualy cut off anyway, but it usualy won't press down. The inside however is sublime, you can't beat it.