Thread: Glue for Hardwood Plywood Laminating ?

Titebond. That said, I used a laminating glue for a plywood handrail for a spiral staircase last year (below) which was fantastic when it came to grinding and sanding back the rail - which I had to do a lot of. Are you planning on sanding back? It can be an issue with a lot of glues, Especially when some heat is generated. Unfortunately the laminating glue is a very fast fix, but if you have it together and don't drink, and practice with it a while it is no problem. I good way to clamp the sort of stuff you're doing is to use car jacks attached to the top side of a sturdy frame (or whatever) over an even sturdier bench - you get the idea.

For that sort of glue-up, PVA would be fine for internal use.

But...PVA is not the easiest glue to sand, if you are intending to sand the form smooth after laminating. PVA is soft (and softens more on heating) so you can clog sandpaper very quickly if you are getting rid of squeeze out. It's better to wipe the PVA away with a wet rag while the PVA is still very wet, to minimise the amount of glue related sanding!

The general go-to glue for laminations is epoxy as you can use a slow-set hardener that gives you about 30-50 minutes (more if it is a cold day).

But...epoxy is as hard as the hinges of hell when set, and although it sands ok, it is slow going if you can't get to areas with a power tool.

You can scrape it off with a sharp chisel when it has gone sort of rubbery hard (about an hour or so), or wipe off with acetone before that, but you've got an intricate and involved shape, so you might really be pushed for time (and it doesn't look all that easy to get to, even with a chisel).

Note that the glues will change the way the timber takes up/doesn't take up any finishes over the top of of it, so if you were looking for a 100% natural unfinished appearance, the sandpaper will still need an outing.

You'll be as busy as a one-armed paperhanger using pipe clamps and all-thread with that many components. And they'll provide pressure only at the edges, which may be sufficient if the edges aren't too far from the interior.

For more general pressure, consider placing several (6-8) pieces of straight timber fingers lined with food wrap at critical locations of the exterior edges vertically for alignment. Attach half of them to a clone of the pattern below, and the other half to a similar clone above. Make the fingers slightly shorter than the final total thickness. The food wrap provides a bond-breaker against the glue. Also use food wrap to line the pattern clones. Assemble the stack so that the lower set of fingers engages the layers, and the upper set completes the alignment, like two hands praying.

Place a bottle jack on top of the stack to push against a post to the ceiling. Apply whatever pressure you require, taking care to avoid buckling the arrangement. Practice first, of course.

For appearance, Titebond II Dark might provide a close simulation of the glue used in manufacture of the plywood, if that matters.

Cheers,
Joe

thank you all for the helpful replies!

>movay,

yes, i am planning to sand back to a nice silky smooth finish, then use a few coats of feast watson scandinavian oil to finish it off, so ideally the glue i use should be as unobtrusive as possible (and able to take stain i guess)

>master splinter,

yes, i was thinking the same thing about epoxy. its setting time sounds good for the complex setup i have but as you say, getting to some of the inner surfaces to scrape it off would probably be a bit of a challenge.

>joe,

titebond ii dark sounds good, as ideally i'd like the joins between each slice to be indistinguishable from joins within the ply itself.

I hear you re pipeclamps and needing nine arms. The jack idea certainly sounds like a good one. I'm thinking about perhaps joining it in sections, primarily because i want to get the alignment right and if i'm racing against glue set, doing 4 or 5 at a time might be easier to manage.

Actually all of the pieces except for the front & back faces have 8 cnc cut holes going all the way through (and the front & back faces go half way in). Originally i was going to use 30mm long fluted dowels (which i would join sections with), then it was suggested to me to use allthread as it could go all the way through, and could be used with nuts and washers to provide clampage.

But when i did a 2 section joining test with dowels i found that if they were even slightly angled when hammered in, they pulled the alignment of the slices out by 1mm or so. So my current thinking is to glue, align and clamp sections together, then drill through the existing holes to force align them & hammer dowels in as i join sections.

One further question, if anyone has any idea: do i really need to provide internal structure with dowels or allthread ? Or would titebond, properly clamped / pressured provide enough strength ? The total weight of the piece is going to be around 16kg!

thanks!

Matt

If I were building what you seem to be building, I'd be looking at the weight of the whole assembly and looking at ways to reduce it.
I'd also be thinking about how I could make the edges smooth after glue up.

I think I'd build the stack in stages, using a jig and possibly dowel rod to keep all the pieces aligned

Matt

glued up ply will be plenty strong enough -- you don't need to reinforce with allthread

because the inner plies are hidden, you can clamp the inner layers together with nothing more complex than srews

ian,

re weight, yes, thats a good suggestion. Drilling a bunch of holes might be the easiest way to achieve that.

& thanks for the advice re strength & allthread - its horrible stuff to try and use - the thread makes it all but impossible to push through hardwood unless it has space around it- making it essentially useless for alignment.

I hadn't considered screws but they certainly sound easier! I guess i'd need to make sure they screwed down below the level of the ply surface so they dont hold each slice apart at all though.

I Would do same..
Screw all the pieces together bar the two external pieces obviously..
And PVA would be my choice as well..
Brushed on with a brush for even coverage.
Just remember to start gluing from the middle and work your way outwards so that you are always laying a piece to the top and bottom as you are gluing out so that the forces of the glue are even and not trying to pull one way.
(Hope this makes scene)
Goodluck..

Upon reflection, forget my nonsense about the bottle jack. For some reason, I locked into the notion of gluing it all at once. Sequential gluing would be a lot better, even though somewhat time-consuming.

I think what Strom implies is that the middle layer should be the starting layer for assembly. If you were to start at the bottom layer, the sequential glue drying would tend to curl the assembly. Starting at the middle layer would allow the alternate curlings to offset each other.

The plywood itself is held together with glue, so absent external loads, reinforcement isn't necessary.

For 15mm layers, countersunk flat-head screws 25mm long will reach far enough, but not too far, into the receiving layer, and the heads will sit below the joint. Offset the screws about 15mm so they don't interfere with the next attachment. And pre-drill clearance holes so the screws don't push the layers apart. BTDT.

Only the top and bottom layers will need clamping, and they also need not be done simultaneously. If the piece is very large, the bottle jack might still be useful, after all.

Cheers,
Joe

Originally Posted by joe greiner

Upon reflection, forget my nonsense about the bottle jack. For some reason, I locked into the notion of gluing it all at once. Sequential gluing would be a lot better, even though somewhat time-consuming.

I think what Strom implies is that the middle layer should be the starting layer for assembly. If you were to start at the bottom layer, the sequential glue drying would tend to curl the assembly. Starting at the middle layer would allow the alternate curlings to offset each other.

The plywood itself is held together with glue, so absent external loads, reinforcement isn't necessary.

For 15mm layers, countersunk flat-head screws 25mm long will reach far enough, but not too far, into the receiving layer, and the heads will sit below the joint. Offset the screws about 15mm so they don't interfere with the next attachment. And pre-drill clearance holes so the screws don't push the layers apart. BTDT.

Only the top and bottom layers will need clamping, and they also need not be done simultaneously. If the piece is very large, the bottle jack might still be useful, after all.

Cheers,
Joe

Thats exactly what I meant !!!
Cheers Joe...

>strom & joe,

thanks for the ideas!

* the alternate top/bottom glueing sounds like a good tip, i hadnt thought of that.

* i've gotten hold of some titebond 3 glue, which should give me a bit of time to get things aligned before set, and its colour (light tan) looks pretty compatible with the faces of the ply. I'll do a test on some offcuts tonight.

* as per ian's comment above, i'm thinking to build a simple jig to help align the pieces as i go, especially because this table has so many edges that need aligning- and do it in sets of 4 layers.

* re needing glue, if they're screwed together - i guess if my jig can hold them accurately in place while i drill the starter holes for the screws then i could get away without glue for those pieces.

i'll do some more tests and post again as i go.. thanks for all the help so far!

For consistency of appearance, you might find it better to glue all the joints, so the glued joints don't look so odd. Also, and probably not noticeable by 99.9% of witnesses, alternating the face grain of adjacent layers (as are the inner plies of the plywood) would promote the appearance of a monolithic assembly. By "alternating the face grain," I mean North/South vs. East/West.

If you haven't yet cut the plywood for the final construction, I suggest testing both ways on some scrap to see if this complication is worthwhile. Ditto the question of glue vs. no glue.

Cheers,
Joe

thanks joe,

i have already had the wood cut (you can see it in the photos linked above)

i will certainly do some glue / screw tests on offcuts & see how it looks, cheers for the suggestion!

hi guys

after a few different technique tests, i've finished glueing up my first type table.

pic is here:



Glue used was titebond 3, though i might try something else next time, as the 10-15 minutes assembly time is just a bit too tight for comfort. I might try titebond polyurethane next time, it supposedly has 20-25 min assembly time.

In the end, i assembled it in 2 sets of 8 slices, clamping the whole lot together both times, to ensure it would all align at the end (the danger if pieces are assembled separately). Its not perfectly aligned, but its close enough to correct with sanding. Lessons learned ? Even CNC doesnt produce completely accurate cuts. Margin of error seems to be about 1-1.5mm on this particular machine i used.

Anyway, i'm down to the sanding stage. Just wondering if any of you has any tips on best way to tackle this beast ?

To flatten out the few misaligned (or innacurately cut) slices, on the outside faces at least, do you think a plane would be much use ? The slices that are protruding seem like they would be suited to being planed down. Aside from that i'm also thinking to use a belt or orbital sander for the areas that really need to brought down a lot.

Inside parts will be attacked with a dremel flap wheel/ mini-belt on a shaft attachment plus sanding blocks & elbow grease.

thanks for all your help in getting it to this stage!