How long to let glue dry before priming

[Rob Blaustein]

I'm edge banding plywood with a 3/4" strip of solid wood. As always, I'm in a rush--if I use a PVA glue, how long would I need to wait before flush trimming and priming with an oil-based primer?
--Rob

[Chris Padilla]

I dunno...what's the bottle say? ;) I'd be specific about the exact PVA you are using. Titebond I sets up pretty darn quick (this is the red cap one) but as you go down the line of Titebonds, I believe they want you to keep the clamps on longer and longer. Titebond also has a Molding and Trim glue that sets up even faster than TB I but it isn't easy to find.

[Rob Blaustein]

Hmm, I guess I could have actually read the bottle--I'll do that shortly. I have TB orig and III. Either way, I think I'm stuck at this point and will have to clamp tonight and prime in the AM.

[Peter Quinn]

I'd go 24 hours minimum, preferably 48, and possibly as much as 78 hours depending on environmental conditions. Good chance your gonna get a little creep as the glue moves from set (when you can pull clamps, @30min) to cured (when full strength is achieved, about 12 hours) to dry, which should not be confused with the above terms and often takes little longer, usually around 48 hours. I've had minor sight lines occur where the wood shrunk just a bit because I primed too soon (about 15 hours later). Didn't affect joint strength, but now I have to look at that hair line for the rest of my life!

I've decided not to rush any more projects unless I can get a confirmed report that tomorrow is my last day here on earth. Then I'll just cancel all projects and have a beer!

[Chris Padilla]

Peter brings up a good point: when one glues with PVA, one is adding moisture in a specific location and the wood is bound to swell from the added moisture. Only when the MC is back to normal should one do anything.

I've seen folks who used biscuits to glue-up boards for a panel get the biscuits telegraphing through. There is a lot of glue around a biscuit and so the wood swells. If one sands to soon, one could end up with slight depressions in the wood when the wood goes back to its regular MC.

[Rob Blaustein]

Interesting points. It's not strength I'm after here but aesthetics--that panel edge will be pretty visible on one side. The telegraphing biscuit issue seems to be uncommon from what I've read--I almost got the impression that it was an 'urban legend'. My biscuit joiner wasn't around so I ended up using the Domino and loose tenons to line up the edge band. Not sure if there have been reports of telegraphing with those.

[Chris Padilla]

Looking in the right light and angle, you can sometime see the slight raised bumps and/or depressions.

Look at any wall in the right light and angle, and you can usually see every stud in the wall. Same thing here to a certain extent.

[Peter Quinn]

One of my jobs at a mill work shop was making stair treads, 3-5 board glue ups typically, edge glued planed but not joined 5/4 to match flooring species. These weren't going out finished, but they were going out real nice.

We would glue, leave in clamps for 1hr, pull clamps and sticker over night. Next morning we would plane to final thickness plus .025", then sticker and let um sit till the customer called for delivery. Before shipping they got 2 passes per face through the wide belt, and they always needed it. You could feel what was smooth as a baby's but right off a spiral head planer treads had developed hairline creep at most joints. We were using titebond III, which takes 78 hours to fully cross link I'm told.

There's a real interesting old thread about this over exact issue over at wood web by Dr. Gene I think (hate to reference another site, but Dr. Gene knows his science when it comes to wood). I think its worth putting a few days age on those edge bands before you flush trim for paint grade, because hairlines in paint grade are very hard to hide.

[Charlie Plesums]

when I use hardwood edging on plywood, I do not use biscuits or other alignment crutches... plain carpenter's glue (Titebond I) is ample. If I trim/sand flush in the first 24/48 hours, I can later feel the joint... appears to be shrinkage of the plywood rather than creep, so I assume it is moisture - there is a lot of water in the glue that goes into the wood before it evaporates.

[Chris Padilla]

I do not use biscuits or other alignment crutches...

Perhaps for plywood, which is usually straight, one may not need such "crutches" but they can be handy on boards that aren't as straight as we'd like them to be. If I use biscuits, I use them for alignment/straightening and I do NOT glue them...in panel glue-ups or edgebanding plywood.

For some casing work I did at my house recently, I glue-up the casing on the floor and each miter gets a heavily glued biscuit. Then I install the casing. Picture frames also get a heavily glued biscuit at the miters.

[Charlie Plesums]

Alignment crutches.... sounds like an unintended slam. Sorry to anyone offended.

A few years back, a demo at a woodworking show by one of the old masters included an alignment trick that I find works well when gluing up panels... Align and clamp at one end, then move to where the next clamp would be and get it aligned and clamped, and the next, etc., working down the joint. With the far end "open" it is fairly easy to align. The joint comes together fast, easy, and remarkably precise. For really squirrelly boards, I may put clamps twice as close together while doing the initial alignment, then remove the extra clamps to use as I get farther down the joint.

I use similar techniques adding "1x2" hardwood edging to plywood, which I find is not as straight as the hardwood.

I do have a biscuit jointer, and use it, but no where near as much as the ads say, nor as much as I did when I first got it.

[Rob Blaustein]

I use similar techniques adding "1x2" hardwood edging to plywood, which I find is not as straight as the hardwood.


Just curious Charlie--when you edgeband with this technique do you try to apply a slightly thicker edgeband and trim it to match the width of the plywood (say with a router), or do you shoot for an exact match and align using the method you describe for panels of the same thickness. Also, is your final dimension 1 1/2 inches of additional solid wood edge or do you cut it down some once attached?
--Rob

[Chris Padilla]

Rob,

How much edgebanding one applies depends on one's desired outcome. Do you want the plywood to look like a solid board? If so, rip the edgbanding to very thin such that the glue line nearly disappears. Do you want to put a nice edge on the board? Keep the edgbanding thick enough to accomodate your desired edge treatment. Did you screw up cutting the plywood too short? Edgebanding might save you!

As far as matching it to the thickness of the plywood, I ALWAYS make it wider and trim to fit using a flush trim bit in a router table with a tall fence. I think it is very difficult otherwise to get it nice and flush. Remember that plywood thickness varies all over the place.

[Rob Blaustein]

Do you want the plywood to look like a solid board?

Yes in this case since I'm painting and hoping to avoid seeing the paint line.


If so, rip the edgbanding to very thin such that the glue line nearly disappears.

Did you screw up cutting the plywood too short? Edgebanding might save you!

Unfortunately, the answer to this question is also Yes::(
I think I'll actually have to edgeband both edges with 3/4". Either that or shell out another 75 bucks for another sheet of MDO which I'm not keen on.

[Charlie Plesums]

Just curious Charlie--when you edgeband with this technique do you try to apply a slightly thicker edgeband and trim it to match the width of the plywood (say with a router), or do you shoot for an exact match and align using the method you describe for panels of the same thickness. Also, is your final dimension 1 1/2 inches of additional solid wood edge or do you cut it down some once attached?
--Rob

I was thinking in terms of putting the edge on a shelf - nominally 1x2 or 3/4 by 1 1/2 (or 1 1/4). The 3/4 thickness is enough to add strength, and the 1 1/4 to 1 1/2 height adds stiffness. That board is straighter than a piece of plywood, so can help straighten the shelf.

For a larger answer... if I am just trying to hide the edge, the heat activated edgebanding works fine.

If I am trying to make a wear-resistant edge (such as the edge of kids furniture or a bed rail) or will be adding a machined profile, I add 3/4 inch or more, and trim flush with the plywood.

There is an absurdly expensive machine for trimming the wood flush with the plywood - a lipping planer. Works good most of the time, but in addition to breaking the budget, a flicker in your concentration can destroy your workpiece. But when it is good, it can trim as fast as a saw, ready for final sanding.

[Rob Blaustein]

Rob,

If so, rip the edgbanding to very thin such that the glue line nearly disappears.

Just wondering Chris, do you do this after you glue on the edgeband or do you first rip a narrow strip and then glue that on (ie making your own thin edgebanding). If the former, then I guess you can't use biscuits for alignment and brads instead of clamps.

[Chris Padilla]

I've always left my edgebanding relatively thick (~1/2 - 3/4") because I either like it for added strength on a shelf, or for wear purposes, or because I've added a nice bullnose or ogee shaped edge to it.

I've SEEN edgebanding ripped thin and it really does work to disguise the glue line assuming the grain of the plywood flows along with the edgebanding.

I don't see any reason why you couldn't rip thinner edgebanding and glue it up as long as you are careful with the thinner material (useing cauls and such) so you don't damage it. It might be safer/easier to rip it after glue-up, too, but that all depends on your stock dimensions.

I've had great success simply gluing on edgebanding...even 2"+ thick edgebanding (had a little "cut the plywood too short" problem one time....). I've never used anything but glue, TB II most of the time.

[glenn bradley]

My bottle says clamp for 30 min. and don't work the piece for 24hrs. That's what I do unless I don't need the clamps. Then I just leave them on.