We are putting new oak flooring down in our foyer, replacing ceramic tile that we never liked. We've decided that we would like to have an inlaid medallion of our own design in the middle of the floor, and I'm now looking for advice on execution. The medallion will be a square, 29" on a side, but set in a diamond orientation to the floorboards and the room. Each individual square on the perimeter is 1"x1", and I have a choice of making the whole thing out of 1" building blocks (except for the diagonals) or out of the largest practical rectangle or triangle. Because is will be part of the floor, it will need to be tough, and probably will have to face at least one sanding/refinishing cycle in its life. It will be made up of four different woods (I know that's a lot, but it is an accent, not the whole floor). The drawing illustrates the design. The black will be ebony, the red will be either padauk or bloodwood, the yellow will be yellowheart, and the "tan" will be some very tight grained white oak that is not 1/4 sawn and does not display rays. The effect being sought is one of color, and the boards were chosen for color and subduded grain patterns.

I'm looking for the best strategy for doing the medallion. In each case, I will be resawing and cutting the wood into smaller pieces to be assembled like a mosaic, probably onto a baltic birch backing, although I could conceivably make all the pieces 3/4" thick and not use a back at all. I see a number of choices that I feel comfortable attacking but each of which might present some problems.
1. Cut all the pieces 3/4" thick. This would present the most durable surface but would likely present the most difficult assembly and installation problems. It would probably also mean dropping more $$$ on ebony.

2. Resaw the pieces to 1/4 finished thickness and mount them on 1/2" baltic birch (closest dimensions for each to match thickness of surrounding floorboards). This would give me enough thickness for durability, but has me worrying about wood movement. (more discussion on wood movement issues below).


3. Resaw the pieces to 1/8" or 3/32" or less. This might minmimize movement issues, but would introduce thickness issues, both in terms of standing up to refinishing and in terms of matching the surrounding floor. It would likely force me to put another layer of something with the baltic birch, but there's no way I could face duplicating the design on top and bottom of the medallion.

So, a couple of questions.
1. If I go with 3/4 thick pieces, do I
a. edge glue the pieces together?
b. Do I try to alternate the grain direction of the individual pieces in an attempt to minimize movement in any direction? Keep in mind that the design will require a significant number of pieces running at 45° unless I cut a lot of the pieces on the diagonal (and probably have to get more wood ).
c. Do I, god forbid, try to tongue and groove each piece to the others, and try to install them directly on the floor (with nails? )

2. If I go with 1/4 thick pieces, same first two questions as for 3/4 plus
a. Do I glue the pieces to the base?
c. Edge glue AND glue to the base?
d. Do I have to worry about balancing the top and bottom, even though the whole thing will be sitting on OSB subfloor?

3. If I go with 1/8 or thinner pieces, same questions as for 1/4" plus what do I about the fact that a floor sander will probably go through it if I ever refinish the floor?

Summary: Which approach would you recommend, and how would you address the movement and durability issues of each approach? Also, will minimizing the number of pieces help or hinder the wood movement issue? If I minimize them, the largest single size will be two pieces of 1"x7" of yellowheart. That would still leave 106 pieces of 1"x1" but 204 pieces of 1"x3" of ebony and yellowheart, with various other sizes adding up to a grand total of 568 pieces. As you can see, that a TON of pieces.

Also, what glue should I use, TBI, II, III, or plastic resin which has tons of open time which I will probably need here, construction adhesive, etc., etc.
?

Do it the way everyone else does when they are complex. Use the 1/4" over the 1/2" plywood and glue it to the plywood. Remember, even though flooring is 3/4" thick, it only has about 1/4" of surface for sanding until the tops of the tongues are exposed so you really only have a 1/4" of hardwood to sand. So your 1/4" mosaic medallion will have as much sanding surface as the surrounding floor.

I'd build it on the plywood back like a complex chessboard. Use a jig to cut the pieces EXACTLY the same to make assembly easier. You can use some larger pieces as well if you wish instead of a series of squares. Dry fit as you go. Consider building a frame that will hold the whole thing together while you dry fit it. Easy to do since it's a square. Once it's all built and you're ready to mount it on the backer board, use Bostick's Best urethane adhesive. A 2 to 3 hour open time approx. No need to glue each piece to the next; just glue to the backer board. Use another frame to assist in assembly After assembly, place some large piupe clamps on both sides of the frame to exert side pressure and tighten everything up till the glue cures. Leave alone for 24 hours minimum. After that, sand the surface somewhat so all the pieces are fairly flush. Then fill any cracks and voids with filler for that particular wood. 4 different woods=4 different colors of filler. NOTE: No one seems to worry about expansion on smaller to medium sized medallions. You are basically making a miniature parquet floor. Anyway, that's how I would do it. Anyone else?

Gary, thanks, that's very helpful. I've got a question about the glue you recommed. The open time sounds great, but what kind of clamping pressure is needed? Also, does it expand like Gorilla glue and other poly glues? It wouldn't be a deterent, just wanting to be prepared. I don't have a vacuum press so I'm faced with some sort of custom made veneer press or a ton of cauls. Not having to edge glue solves a lot of problems of the glue up, but is glue oozing up between the pieces something I should be prepared to handle? If it's oozing up while in the press or under cauls, it would be much harder to handle. (On the other hand, I guess that's what scrapers are for. Also, by the time I get to that point, I should have my new drum sander that would help the cleanup as wel. )
I was planning on a frame so your suggestion there fits the bill nicely.

Butch

Bostick's Best is a urethane flooring adhesive. It does not expand as it dries. I'd use an 1/8" x1/8" square notched trowel. The adhesive is very tacky and has good "green grip" meaning you need to place things where they go. I wouldn't woory about it oozing out. Install pieces tight to each other as well as possible. You won't need downward pressure; the glue will suck the pieces down. Just have a little pressure on the sides to keep pieces tight and aligned. You can tape pieces together as you go (tape on top of pieces) to hold in place till glue dries.

Gary, this is really helpful! Many, many thanks!
The project will take a while to get completed (probably not before the end of March or mid April, but I'll be sure to post pictures of the project.
Butch