I am making a kitchen table for my niece out of wood from her grandfather's barn. She wants a granite top, and I have some questions about how to best build the top.
The wood is 8/4 air-dried red oak which is 80 - 100 years old. I was thinking about making a trestle table with a top consisting of a wood edge 'frame' around a granite slab. The wood frame around the granite would be joined with 'Greene and Greene' style finger joints (screwed together and plugged with pillowed ebony plugs). The house was built in 1848, and the kitchen is very small so the table can only be around 24" X 48" max dimensions.
I had considered setting the granite top on a piece of plywood set into a dado in the frame, but I am worried about the air-dried wood shrinking against the granite and cracking the joints, or expanding and making a gap around the granite that would catch every crumb that came near it. Any suggestions on how to assemble the top to avoid both of those problems would be appreciated.
I have basic power tools, a table saw, a router, and a good selection of hand tools, but I will be building the table with mostly hand tools.
Second in the process of giving you good information about doing this project we will likely have some more questions for you so please check in on occasion.
The first one that comes to mind is how wide will your oak frame be?
I was going to try to keep as much thickness as possible - the edge of an 8/4 board after planing would be the 'up' side. I was going to try to keep the depth of the frame as narrow as possible. The granite will be the standard kitchen counter top thickness (around 1" ?) and the plywood will be 3/4". Allowing 1/2" under the dado for support would mean the side could be as narrow as 2.25". Making the sides 3" thick might make the box joint fingers look better (1" fingers instead of 3/4") but I would probably have to make a mock-up to decide.
Your basic question is about the wood movement of the frame stock surrounding the granite slab.
This should really not be any problem at all. Especially if your 8/4 red oak mills out finished to 1-3/4"+ thick and this is the top of your edging. If there is any movement at all, the oak is going to attempt to move across the grain (vertically in your case) and with 2-3/4" to 3" wide material, it won't be noticed and won't move away, or towards, the slab enough to create any trouble. Any movement across the 1-3/4" quarter sawn edge is so negligible it won't affect anything either.
Things that you must be aware of:
Most of the counter top granite we have seen is 1-1/8 to 1-1/4" thick.
This top will be extremely heavy even at 24" X 48" in size. Depending on the thickness, we estimate this slab will weigh about 135 to 165 LBS.
We agree that a trestle table base is a wise decision and should be built to support this weight with out any tendency to rack. This could make your whole table weigh in at about 250 lbs or more!
A crumb gap is a problem, both for crumbs and dirt, but also for spilled liquids that can spoil... like milk! Knowing what the edge finish on the slab is going to be, would be very beneficial in determining the best way to attach the framework.
If the stone is cut perfectly square with a sharp, crisp, untreated edge, you could attach the oak frame like two jointed boards. Flush, tight, and on a smooth plane. If the granite has any profile, or even a small round over like 1/8", this will add to gap problems. With this small round over, you might be able to attach the oak 1/8" below flush (so the granite sits 1/8" proud of the framework) to accommodate a tight fit and a good seal.
We think, with wood movement not being a problem, that gluing the oak directly to the granite will be a good option to permanently seal the gap. Another option is to purposely leave a gap and grout the joint.
You will probably want to make the top slab, oak frame, and support substrate, as a removable assembly from the trestle base for ease of handling/moving this heavy table.
Thanks John. I have never worked with air-dried lumber and did not know what to expect in the way of wood movement.
I am having the granite cut with a square unfinished edge, so a wood/granite glue joint may be the way to go. Do you think finishing the wood and using epoxy would be best? Finishing first would definitely make the rounded 'Greene and Greene' finger joints easier to work on.
The trestle base will have no problem with the weight of the granite top - the 100 year old old oak is stout! I had planned to make the base removable from the top assembly for easy transport, and so it would fit through the narrow doors in the old house. I may even use a tusk tenon stretcher so that the base can be broken down also.
Jeff, I have replied in a copy of the body of your text below:
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Thanks John. I have never worked with air-dried lumber and did not know what to expect in the way of wood movement.
I am having the granite cut with a square unfinished edge, so a wood/granite glue joint may be the way to go.
We think you should definitely check with your granite people to get the thinnest available slab. It will certainly help with the table's weight. You should also get your slab into the shop and build your plywood substrate and framework around the slab to insure a perfect fit. Building the frame first and then getting the slab cut to fit (and hoping it will), can be disastrous!
Do you think finishing the wood and using epoxy would be best? Finishing first would definitely make the rounded 'Greene and Greene' finger joints easier to work on.
The three best adhesives recommended for stone to wood are 1) silicone based adhesives, 2) a product like Liquid Nails "Marble", or 3) epoxy. The fact that you will be attaching the oak frame to both the plywood sub, and the edge of the granite slab, epoxy may be your best choice there so you can assemble this joint using one adhesive only.
To finish first or afterward should depend on your choice of finishing process, and your comfort in applying it. At least with stone, it is easy to clean up any finish contamination from the surface. If you feel you could remove the stone slab after you have all your wood components fit, and glued up, (by using glass cups, or even carefully turning it over) you could build it, remove the slab, "finish" the oak frame, then re-install the slab with your epoxy or silicone as a sealer to complete the job.
You certainly want to carefully dry fit everything, including the stone slab, and have everything going together correctly before glueup.
The trestle base will have no problem with the weight of the granite top - the 100 year old old oak is stout! I had planned to make the base removable from the top assembly for easy transport, and so it would fit through the narrow doors in the old house. I may even use a tusk tenon stretcher so that the base can be broken down also.
It sounds like you have the base well thought out!
Wood/Granite table top
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