Gooey-glue gurus needed within ...

[sbaxter]

I have a need to bond two sheets of quarter-inch plywood together in a way that will allow them to be permanently installed outdoors in the open air (but sheltered from rain) in the Florida humidity. I intend to apply several coats of polyurethane to the wood to help protect them, and seal any voids with paintable caulk.

First, is it possible to apply polyurethane before the sheets are bonded together? If possible, is it desirable? What sort of adhesive should I use to achieve said bonding? People tend to say "wood glue" but I presume the marine-grade glue would be preferred. Is it possible to use an epoxy such as JB Weld instead?

If the sheets were thicker I'd consider using screws, but I think that would be more trouble than it's worth in this case.

Qapla'

SSB

[Redgriffin]

First I'd go to your home center and ask them. Barring that I'd use carpenter's glue liberally applied to bond the plywood and clamp it so that the most contact is made let it dry , about 25 hrs and then add about six (6) coats of Polyurethane sanding between coats.

[Andrew Gorman]

JB weld is darn expensive- I'd just use a construction adhesive in a caulking gun over some marine potion. I've never seen a "liquid nails" joint come apart from exposure alone. Seal the thing once it is together to add a some protection to the joints. Just my 2 cents.

[Lt. Z0mBe]

Epoxy could be used but as others have said it would be expensive. If you're wanting something in that ballpark, you might also consider Gorilla Glue. You just dampen each surface with a bit of water from a wash cloth or brush, apply the glue to each surface and clamp everything together. It will not come apart.

As others have said, Liquid Nails is awesome. I would recommend their construction adhesive. It's what contractors use to adhere plywood underlayment to floor joists and that kind of stuff. Spread a good coating of that stuff out, clamp everything together and it also will not fail.

I hope this helps.

Kenny

[Ziz]

Why are you using two 1/4" sheets instead of one 1/2" sheet? Seems like creating work for no reason.

[Rogviler]

Why are you using two 1/4" sheets instead of one 1/2" sheet? Seems like creating work for no reason.

If I remember the previous discussion, it needs to be bent into a curve, which is easier with two thinner pieces.

I'd go Gorilla or Titebond (II or III). Any of those are waterproof, although I would still take great pains to seal the edges with caulk before painting. No need to get too excited about the glue though. I know you're on a budget with the project.

-Rog

[Kylwell]

Gorilla. It's polyurethane to begin with so won't have issue with the urethane finish.

[sbaxter]

Why are you using two 1/4" sheets instead of one 1/2" sheet? Seems like creating work for no reason.

If I remember the previous discussion, it needs to be bent into a curve, which is easier with two thinner pieces.

Close … not bent, but cut into an arc shape on one edge. The reason for using two pieces is that the second piece will be a smaller strip — the front will be 38 inches wide and about four inches tall at the highest point of the arc; the second will be about 30 inches wide and about two inches tall (that one will be a straightforward rectangle). When installed, the second smaller piece will be hidden and give the front the illusion of floating slightly above the surface of the wall.

I'd go Gorilla or Titebond (II or III). Any of those are waterproof, although I would still take great pains to seal the edges with caulk before painting. No need to get too excited about the glue though. I know you're on a budget with the project.

Yeah, there is a budget to mind. I asked about epoxy partly because I have some on hand. I'm not sure I have enough, though. I was thinking JB Weld because so many epoxies have a short working time, and it seems as if some is always wasted because I run out of time with it; JB Weld has a longer working time, so I can be careful with it and still probably use pretty much all I mix at one time. But I can probably get some of whatever glue I decide to use. The shapes of the pieces mean I won't need vast quantities of whatever is chosen. We're talking eight signs, each one having two of these assemblies. I've got enough plywood to make at least one full replacement set of signs, but the additional pieces will mostly just be cut, partially finished, and stored indoors in my office. I'll probably make one or two fully-finished sets in case I need to make an unscheduled replacement.

I have the caulk I need to seal the edges; should I apply the polyurethane and then the caulk? Seems to make sense to me as the caulk is the sort that is cleaned up and smoothed with a damp cloth …

I swear, if I catch some doofus student trying to tear one of these down once they're done, I might apply polyurethane to his or her face!

Qapla'

SSB

[sbaxter]

I'd go Gorilla or Titebond (II or III). Any of those are waterproof, although I would still take great pains to seal the edges with caulk before painting.

I went with Titebond II. I glued the first set yesterday before I left work. As they were (predictably) somewhat bowed, I glued them and then clamped them (using several spring clamps) to flat sheets of aluminum, in hopes that will also flatten them out.

Good tip about caulking the edges — I presume you mean around the edge of the smaller piece where they're glued together? Hadn't thought of that but it sounds like a good idea; thanks! There were fewer voids in the cut edges than I expected, but I'll fill those with caulk as well.

I read the directions, but how long do I really need to leave the pieces clamped to the aluminum? I only have so many pieces of aluminum I can use, and so many spring clamps … when I get to work, the pieces I glued up yesterday will have been sitting undisturbed for about 15 hours …

Qapla'

SSB

[Kylwell]

Wood absorbs best along it's end grain, so it's got to be well sealed for outdoor use.

[TER-OR]

Polyurethane glue, baby.

But beware of urethane finish and exposure to UV from the sun. It will last a few years, but eventually will peel like a ginger's skin. I've got a set of Adirondack chairs to sand and refinish, and those were never in the full sun.

[sbaxter]

Polyurethane glue, baby.

But beware of urethane finish and exposure to UV from the sun. It will last a few years, but eventually will peel like a ginger's skin.

It's too late for polyurethane glue. That ship has sailed.

However, the polyurethane coating is just a start. Following that (at least three coats of it), there will be at least two coats of high-build Duplicolor automotive primer, a couple coats of of a hammered metal paint, at least one more coat of another metallic color (a satin nickel), and possibly a hand-applied wash of a darker acrylic metallic (depending on how I like the results of test applications). In addition, these will be outdoors but in a sheltered location. They'll be shaded most of the day, and will get two or three hours of direct sun at most.

The order of operations I've settled on is this: Gluing first, then polyurethane, caulking, primer, hammered metal paint, second color, and optional wash.

As stated in the earlier thread, there's no doubt that styrene or PVC or some such plastic (or aluminum) would have been the ideal material for this, but budget concerns derailed that idea — at least for now. It is my hope these will last at least five years, and I have enough pieces to do a full replacement set of each sign. If they don't, I hope that they will be so well-received that if the materials fail sooner, TPTB will decide it is worth the expense to replace them with more durable materials.

I'm fairly confident my prep will make them last long enough; I'm more concerned about theft, since I'll be using Velcro to attach them to the walls. Many of my foam board signs have been stolen over the last dozen years or so. To help deter that idiocy, I'll be using a ladder to install these as high off the ground as possible; in the past I've simply put them as high as I could reach while standing on the ground. I hope the the greater height will at least deter the casual, opportunistic thief,

Qapla'

SSB