Polyurethane glue question.

[Bryan Berguson]

Does anyone know if polyurethane glue will bond with cured finishes? I have some finished plywood and I would like to add some spacers to it. I don't want any nails or screws in the way so my only real choice is glue... if that will work. Expoxy will work (I've done it before), but I have about 24 lineal feet x 1.5 inches to glue and don't want to mix that much epoxy (or spread it for that matter).

How about urethane resin glue?

Any help would be appreciated.

Bryan

[Jamie Buxton]

Polyurethane glue like Gorilla sticks pretty well to anything I've ever tried it on. It'll probably stick to your finish. Another glue which you might try is Roo Clear. It is intended to glue melamine. Gorilla foams up as it cures, so you must be able to clamp your pieces together. If you're working in the middle of a sheet of plywood, that may be difficult. Roo Clear doesn't foam, so it would be better in that situation.

[Bryan Berguson]

Thanks Jamie. This will be used in an area that will be difficult to clamp, not impossible, but difficult. I'll check my local supply for Roo Clear.

Bryan

[J. Z. Guest]

Well, you don't always have to clamp. You could use weights.

But do keep in mind that although poly glue will probably stick it OK, you have to think about how you're going to clean up the foam that comes out. If you're trying to avoid using screws because they're unsightly, having scrape marks from cleaning up poly glue isn't going to be desirable either.

If you use epoxy, you don't need to mix or spread that much of it. You don't need to cover every square inch of a large face-to-face joint. Just a blob here and there will do.

[Hank Knight]

Brian,

I don't have an authoritative answer to your question, but my best guess is that Polyurethane would bond if you rough up the surface of the finish with sandpaper. My real reason for posting is to relate a recent experience I had with Polyurethane glue that has convinced me that I will never use it again.

My wife and one of my neighbors are both certified master gardeners. I built my wife a potting bench last year that my neighbor has admired. Several weeks ago, I came across a potting bench that was in disrepair and had been discarded on the roadside for trash pick-up. It was a nice one, made completely of teak with brass hardware. I loaded it in my Jeep and took it home to see if I could salvage it. I found that it had been assembled originally with polyurethane glue and every joint had failed. Otherwise it was in excellent shape. I spent several days cleaning out the old glue and reassembled it with epoxy. It is now rock solid and looks like new. My neighbor is the happy owner of a very nice potting bench that will last a long time.

I have used polyurethane glue occasionally in the past and have always had some vague misgivings about it. When I finished repairing the potting bench, I threw away three bottles of polyurethane glue. It will never darken the door of my shop again.

My $.02

Hank

[Mike SoRelle]

Brian,

I don't have an authoritative answer to your question, but my best guess is that Polyurethane would bond if you rough up the surface of the finish with sandpaper. My real reason for posting is to relate a recent experience I had with Polyurethane glue that has convinced me that I will never use it again.

My wife and one of my neighbors are both certified master gardeners. I built my wife a potting bench last year that my neighbor has admired. Several weeks ago, I came across a potting bench that was in disrepair and had been discarded on the roadside for trash pick-up. It was a nice one, made completely of teak with brass hardware. I loaded it in my Jeep and took it home to see if I could salvage it. I found that it had been assembled originally with polyurethane glue and every joint had failed. Otherwise it was in excellent shape. I spent several days cleaning out the old glue and reassembled it with epoxy. It is now rock solid and looks like new. My neighbor is the happy owner of a very nice potting bench that will last a long time.

I have used polyurethane glue occasionally in the past and have always had some vague misgivings about it. When I finished repairing the potting bench, I threw away three bottles of polyurethane glue. It will never darken the door of my shop again.

My $.02

Hank


I'm wondering if the oily qualities of the teak were what did it in ultimately, even polyurethane construction adhesive (gorilla glue's much meaner big brother) doesn't do well when the surface has even the smallest bit of oil contamination.

[Howard Acheson]

>> This will be used in an area that will be difficult to clamp, not impossible, but difficult.

The question you have to consider is how strong do you want the bond to be? Or, need to be? Poly adhesive will have less strength if applied over anything other than virgin wood. It will be stronger than PVA but not as strong as an epoxy.

Another point, poly adhesive REQUIRE clamping. As they react with moisture they foam exerting quite a bit of pressure toward opening the joint. If foam forms in the joint the joint is significantly weakened.

[Chris Padilla]

Brian,

I don't have an authoritative answer to your question, but my best guess is that Polyurethane would bond if you rough up the surface of the finish with sandpaper. My real reason for posting is to relate a recent experience I had with Polyurethane glue that has convinced me that I will never use it again.

My wife and one of my neighbors are both certified master gardeners. I built my wife a potting bench last year that my neighbor has admired. Several weeks ago, I came across a potting bench that was in disrepair and had been discarded on the roadside for trash pick-up. It was a nice one, made completely of teak with brass hardware. I loaded it in my Jeep and took it home to see if I could salvage it. I found that it had been assembled originally with polyurethane glue and every joint had failed. Otherwise it was in excellent shape. I spent several days cleaning out the old glue and reassembled it with epoxy. It is now rock solid and looks like new. My neighbor is the happy owner of a very nice potting bench that will last a long time.

I have used polyurethane glue occasionally in the past and have always had some vague misgivings about it. When I finished repairing the potting bench, I threw away three bottles of polyurethane glue. It will never darken the door of my shop again.

My $.02

Hank

Poly is touted as being able to easily glue oily woods but I've no experience there. I've used poly on several projects (all indoor stuff) and haven't had any issues so far.

I'm curious how you knew it was glued with poly. Are you sure? Just checking. :)

[Hank Knight]

I'm curious how you knew it was glued with poly. Are you sure? Just checking. :)

Pretty sure, Chris. Small voids in and around the joints were filled with the foam that poly makes when it cures. I've seen it before when I used the stuff. I'm not aware of any other glue that foams when it cures.

Hank

[Curt Harms]

Polyurethane glue like Gorilla sticks pretty well to anything I've ever tried it on. It'll probably stick to your finish. Another glue which you might try is Roo Clear. It is intended to glue melamine. Gorilla foams up as it cures, so you must be able to clamp your pieces together. If you're working in the middle of a sheet of plywood, that may be difficult. Roo Clear doesn't foam, so it would be better in that situation.

I tried it on some prefinished maple ply. It sticks, but not well in my experience. I can't say about polyurethane.

HTH

Curt

[Doug Shepard]

If this were me I'd fit the spacer and tape off the pre-finished ply. Then unclamp the spacer and take a card scraper, chisel, or plane iron to scrape off the finish up to the tape. Then use yellow glue and remove the tape after it dries.

[Bryan Berguson]

I almost bought some polyurethane glue but didn't partially because of the price and also didn't want half of it to be wasted from sitting on the shelf too long. Thought hard about contact cement but the directions on the can said it would react with certain finishes - polyurethane being one of them. I thought about trying some plastic resin glue but it requires lots of clamping. So, looking at my shelves of "stuff", I notice a couple of tubes of Liquid nails construction adhesive... Hmmm, I used a case of this stuff sticking blue board insulation to poured concrete walls and it worked great. I tested it with just enough 3/4" nails to hold it in place on a test peice. Tried prying it apart the next day and couldn't without breaking the plywood. So, I used it... :rolleyes:

The plywood pieces I'm installing are spacers to go under full extension slides. They are mounted resting on the bottom of the carcase so the only "forces" on them would be upward leverage when the drawers are pulled out. I did end up using enough 3/4" nails to keep them in place making sure they were out of the way of any screws. I don't think I'll lose any sleep worrying about them coming loose...

I appreciate all the reply's!

Bryan