Glue up of Wall Art

[Amy Gilron]

I am making a (framed) wall art picture composed of over 100 pieces (7mm thick) and to be glued onto a ply wood substrate (7.5mm). The completed pieces ( 2 sizes) will be 60x60 cm and 30x30 cm. I have a few questions concerns:
* I am trying to figure out how to glue this up, and have come up with 2 options: vacuum press ( I am not set up for this at the moment) and clamping on sand(just read about this on the forum). The sand option looks easiest at this moment, though I have not done this before. From what I understand, I can make a shallow tray, fill it with about an inch of (sifted) sand cover with plastic sheeting ,and after gluing up the picture(it is in a temporary frame) invert it onto the sand, place another caul on top and clamp. Have I missed anything?
*Next question is about glue- since there are so many pieces, applying the glue and placement takes about 40 min. I have titebond, or I can use slow set epoxy. Which would be best given the open time constraints? Or is there another type of glue that I could use? After gluing and clamping, is it necessary to pin the pieces( or at least some of them?(some are very narrow)?
*I know that when applying veneer to a substrate, veneer must be applied to both sides to prevent warping. In this case since the wood is solid wood pieces, should I consider adding additional wood to the underside after gluing? I thought about applying a lattice work of 4-6 pieces of wood about 10mm thick on the back to keep it from warping somewhat. The final picture will be dadoed into a 3-4cm thick frame. Anyone have a better idea?
Thanks in advance for any tips, info, advice. AG

[Jamie Buxton]

I've never heard of this sand technique, and from your description don't see what its advantage is. In your description, I see two issues with your process. First, how are you going to invert a picture with 100 parts in it which are not fastened securely? Won't everything just fall out? Or if the parts are fastened securely enough to invert, aren't you done? And second, after you get it inverted on the sand bed, how are you going to clamp it? Getting clamp pressure to the middle of a large object is one of the reasons vacuum bags are so popular.

How big is this picture? And do the 100 parts form a continuous layer, or are there some gaps between parts?

[Erik Loza]

OP, I'm having a hard time visualizing the concept. Can you share a drawing or rendering of some sort? My dad often did wall art with offcut scraps and it was as low-tech as low-tech can be. Just wood glue, since there was no real weight to any of the individual pieces.

Erik

[John TenEyck]

I would do it flat on your workbench. I'd start with the same thickness of wood as you plan to use for the show side, but not blocks, rather just simple boards a few inches wide. You could pre glue them into a panel first. Lay that down on the bench, with a sheet of plastic underneath, then apply a layer of epoxy to the plywood, turn it over and lay it on the panel. Now apply another layer of epoxy to the top of the plywood and then arrange your blocks on top. When that's done I'd put a layer of plastic over it, then a layer of thin foam to help evenly distribute the clamping load, followed by a sheet of 3/4" plywood. Then put some gallon cans of paint on top. Epoxy doesn't need or want a lot of clamping force.

If you use System Three T88 epoxy you'll have at least 45 minutes working time.

John

[Richard Coers]

Any time you glue hardwood to plywood, you will get an issue with seasonal width changes in the solid wood, and none with the plywood. If you don't want any cracking in the solid wood, only put a bead of glue in the center of the board. Complete glue coverage will cause issues. Personally a 23 gauge micro pinner would be something I would seriously consider.

[Brian Tymchak]

Seems like a bead of construction glue in the center of each piece would be sufficient bonding since the only load on the bond will be the weight of the piece itself. Then a board on top of the whole piece and some weight on top for 3 or 4 hrs should do it.

[John TenEyck]

Any time you glue hardwood to plywood, you will get an issue with seasonal width changes in the solid wood, and none with the plywood. If you don't want any cracking in the solid wood, only put a bead of glue in the center of the board. Complete glue coverage will cause issues. Personally a 23 gauge micro pinner would be something I would seriously consider.

That has been proven to not always be true. Some well respected folks are making exterior door panels with a plywood core, fairly thick hardwood glued on both sides, and then skinned with two layers of veneer. Maybe there would be a problem w/o those surface veneers, however.

John

[johnny means]

Sounds like you're describing a wood mosaic or intarsia. Wood movement shouldn't be an issue and clamping shouldn't even be super necessary. Picture is not mine, just trying to clarify that this is what we're discussing.

[Amy Gilron]

Hadn't thought about using foam to help distribute the load, good idea.

[Amy Gilron]

"how are you going to invert a picture with 100 parts in it which are not fastened securely? Won't everything just fall out? Or if the parts are fastened securely enough to invert, aren't you done? And second, after you get it inverted on the sand bed, how are you going to clamp it?"
Everything is in a temporary frame and should not fall out if inverted and glued, but...someone suggested using foam without inverting and I am going to try that.
For how to clamp over a long width, taking a 2" x 2" by whatever length you need, and bowing the long edge, is the way to clamp a piece when your clamps will not reach. When you clamp the edges the gentle bow causes pressure in the middle as well and evens out over the whole edge. When I am too lazy to do the bow, I place a thin piece of wood in the center- works the same.

[Kevin Jenness]

More information would be helpful.

Are there gaps between the face pieces? If so, there's no need for a balance layer on the back. If they are tight, you should consider a backer layer oriented the same direction if possible. If the grain direction is random you might consider a checkerboard pattern with varying grain orientation on the back layer. I don't believe intarsia usually has a backer layer but it is good to consider it. If the pieces are fit tightly and you expect a seasonal change in relative humidity then you can expect some swelling of the face across the grain of the individual pieces in more humid conditions. If they are not edge glued contraction would not be a problem. You should allow for some clearance between the perimeter of the panel and the frame dado so the frame joints are not stressed.

Are the pieces the same thickness? In that case using a flat caul plus cambered cauls should work. If there is slight variation then a layer of foam would be in order. If there is much thickness variation you could lay a piece of 6 mil poly sheeting over the panel and shovel sand on top. Inverting the panel for gluing seems problematic with any glue that might run down between the joints.

Do you need to clamp the pieces? If the substrate and face pieces are flat you might get by with CA glue or just placing the face pieces in a layer of epoxy or construction adhesive, or one by one with hide glue- or, as Richard suggested, use a micropinner.

If you share your location, you might find someone here who would be willing to press these for you in a vacuum press.

[Mike King]

Personally, I would go for a vacuum press -- from what you describe, it sounds too risky to have to invert the art and there's still the issue of what would happen when you go to clamp given that the sand would need to displace to accommodate the texture of your piece. The vacuum may also have some issues with conforming to your piece, but it is a bit more controllable in that you can modulate the pulling of the vacuum while observing how your art is adjusting to the pressure.

As to glue, titebond has too little working time for you. Slow set epoxy or Unibond sounds like a better option for you.

Mike

[Richard Coers]

I've never heard of this sand technique, and from your description don't see what its advantage is. In your description, I see two issues with your process. First, how are you going to invert a picture with 100 parts in it which are not fastened securely? Won't everything just fall out? Or if the parts are fastened securely enough to invert, aren't you done? And second, after you get it inverted on the sand bed, how are you going to clamp it? Getting clamp pressure to the middle of a large object is one of the reasons vacuum bags are so popular.

How big is this picture? And do the 100 parts form a continuous layer, or are there some gaps between parts?

She said the panels were 60cm square and 30cm square. About 2' and 1'. I'd think a rub joint in Titebond would work quite well. But as I said earlier, there will be expansion and contraction issues if the solid wood is bedded in adhesive on plywood.

[Amy Gilron]

More information would be helpful.

If the pieces are fit tightly and you expect a seasonal change in relative humidity then you can expect some swelling of the face across the grain of the individual pieces in more humid conditions. If they are not edge glued contraction would not be a problem. You should allow for some clearance between the perimeter of the panel and the frame dado so the frame joints are not stressed.

Good suggestion to leave clearance around the perimeter of the panel and the frame dado.