Advice on building a bar

[Pete Costa]

Apologies in advance for a lengthy post. My neighbor has asked for help on his pandemic project - a large built-in bar for his basement. It's an L shape, approx 7 ft by 14. He has built a solid base structure of framing studs and plywood (glued and screwed). He wants to wrap all of it with African mahogany - veneered plywood and battens on the sides and solid 5 inch wide boards for the top (for total of 20 inch width). This is where I'm supposed to provide support, but this is pretty far beyond anything I've ever done. I know that I need to allow for seasonal movement as well protecting all parts of the boards from the inevitable spills, etc. a bar top experiences. I also realize the glue up will be a bear of a challenge. Here's my current thoughts, welcome any and all suggestions.


- First challenge is that he wants single, continuos length boards on each side of the L. We let the wood it acclimate in his basement for a week or so, and then milled it in my shop. I only have a 6 inch long bed jointer, so we squared an edge first, ripped to width, then flattened a face best we could. Flattened is a very relative term given the length of these boards. All still have some bow and least one board has a significant localized kink in it (more on that below). Finally we planed them all to 3/4 thick and sent them back to his basement. The planed surface will be top side




He originally wanted to have the two parts of the L shape meet in a big miter. I explained how those joints might open up significantly with seasonal movement. We decided instead to do an overlapping pattern where board 1's end grain buts against board 2's side and board 2's end grain buts up to board 3 (which is parallel to board 1). I'll use a full width tenon across the end grain to go into a groove on the mating sides. I "think" this is the best option to minimize visual impact of movement, but am not sure. We are near max seasonal humidity, so at least we should be a max board width.



- Getting the boards to lay flat will be tricky to say the least. I'm going to use biscuits referenced off the top face and Titebond three (color is right and it's waterproof). I'm not sure if I should glue up 4 boards at once and then attach to the plywood base or get one board attached and then glue/attach the rest individually. I'll probably try to convince him he needs to buy a bunch more clamps to pull this off, which I will happily store for him once we're done :)


- In either event, I intend to solidly connect the center of the glued up panel to the plywood base from below with screws and construction adhesive. I'm hoping that the adhesive will have some flex to it so boards can move a bit. The outer edges will be secured down with construction adhesive and screws with slotted holes to allow for some movement.


- I'm hoping that between gluing up the boards to each other and securing the glued up panel to the base, we can resolve the remaining bows or twist in the boards. For the one bad kink, I may cut a series of kerfs across the bottom to allow it to bend flat more easily.




He wants to finish the bar with polyurethane. We'll do the bottoms and end grain before securing it to the base and then do the top once everything is in place. I need to make sure the construction adhesive can attach to the poly.



So what am I getting wrong or just plain missing?


Thanks,
Pete

[Richard Coers]

Absolutely don't use adhesive between the plywood and hardwood. If his basement gets damp in the summer, that top could expand 1/4". Also biscuits are not the greatest for alignment. When I wanted something really accurately aligned, I put a slotting bit in a router and run a groove the length of the board. Then glue in a spline and bring up the other board. That guy must have a ton of drinking buddies! 21' of bar is a ton!

[Doug Garson]

I think you should rethink the big miter joint, by having end grain mate with side grain you are creating the differential expansion you were trying to eliminate. If you do a miter, you have end grain mating with end grain so at the joint, both pieces expand and contract in the same direction (along the diagonal) and since they are the same wood they should expand and contract the same amount.

[Bill Conerly]

I have numerous thoughts about proper breaking in of this structure. Invite me over upon completion and I'll share them.

[Pete Costa]

Thanks Doug. As I understand it, as the board width shrinks with lower humidity and the length essentially stays the same, the angle of the miter will change, opening a gap at the inside corner. Your question does spark another concern. We can generally ignore wood movement parallel to the grain because it's a rounding error for normal lengths, but this is not normal. I'm going to go pull out Hoadley's Understanding Wood, but has anyone dealt with this before? Do I also need to allow for for movement in the long direction as well?
I think you should rethink the big miter joint, by having end grain mate with side grain you are creating the differential expansion you were trying to eliminate. If you do a miter, you have end grain mating with end grain so at the joint, both pieces expand and contract in the same direction (along the diagonal) and since they are the same wood they should expand and contract the same amount.

[Pete Costa]

The ironic part is that I don't drink!
I have numerous thoughts about proper breaking in of this structure. Invite me over upon completion and I'll share them.

[John C Bush]

I think you will start right after the glue-up!!

[Frank Pratt]

If I understand correctly, you are proposing a herringbone pattern where the 2 legs meet at the 90*. That will not work with regards to wood movement. It's gonna be crack city every time the humidity changes. A 45* miter can work. The seasonal angle change will be very small & can be allowed for by securing the top in a way that will allow for a little movement.

I've done 2 solid wood kitchen countertops with a 45* miter & both have stayed perfectly tight.

[Doug Garson]

I guess the question is, if you have a board with a 45 degree end does it stay 45 degrees as it expands and contracts with moisture changes? If it does the miter will stay tight, I think it will but not sure, just an opinion not based on first hand experience, hopefully someone with first hand experience will comment.

Looks like Frank was answering my question while I was asking it.

[Patrick Walsh]

Spline and tight locks.

Not my design, architect. So I don’t wanna hear about how ugly it is or why did you do it like this or that...

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[Christopher Giles]

Patrick is correct. That's the way we do it in commercial cabinet work. The KISS principal is the way to go.

[Frank Pratt]

I used biscuits, counter top bolts, and epoxy.

[Kevin Jenness]

A miter or staggered joint will work as long as you allow for the change in angle resulting from seasonal changes in RH. In a basement that may be negligible, but ignoring the possibility may cause problems down the road.

In this case a 4% decrease in moisture content with an initial 20" width of African Magogany will result in a change of 1/16" to 1/8" depending on grain orientation according to the Woodweb shrinkulator. Assuming rift grain, if the 14' leg is fixed at the long edge and the miter remains tight the far end of the 7' leg will rotate in about .4". If the two legs are fixed the miter joint will want to open up about 1/8" at the inside. If the joint is well glued, splined and bolted it may hold together but there will be significant stress, so it would be wise to allow for some rotation of the pieces.

Another way to make the joint is a 90 degree splined butt joint glued for part of its length at the outside and allowed to float at the inside. That will allow for the overall shape to remain square while allowing for seasonal movement. It also would allow using 12' 4" boards for the longer leg which would be easier to joint than 14-footers.

[Frank Pratt]

A miter or staggered joint will work as long as you allow for the change in angle resulting from seasonal changes in RH. In a basement that may be negligible, but ignoring the possibility may cause problems down the road.

A staggered joint will not work without opening up with changes in humidity. The gaps will be small, but on a bar top you want no gap that can fill with junk. A mitered joint will work without opening, but with very slight changes in the angle of the miter with humidity changes. That angle change must be allowed for when securing the top to the base.

Draw it out on paper & think about how the wood moves & you'll see.

[glenn bradley]

I agree with the 45. Spline for alignment and some countertop bolts (https://www.google.com/search?client=firefox-b-1-d&q=counter+top+bolts).

[Roger Feeley]

Put the flip-up entry at the corner and don’t fight the fight.

[Pete Costa]

Thanks all, I'll let you know how it turns out.