Bowing sapele tabletop

My kids are doing remote learning and I needed another table. I reclaimed a table from a curbside. The top was junk but the legs and skirt had something like birds eye hickory.

I had wanted to work with sapele and it was the same price as cherry, so I built a .8" thick top that is about 72 x 32. Now the legs on the table are about 1/4" proud of the skirt, so the top rests only on the leg tops. I haven't attached it to the top so it is just resting on them.

Moving it around on Christmas, I noticed the top had bowed up. I didn't measure it, but it is visible - maybe a 1/4". No splitting or cracking between boards is visible. The top was built out of 3 pieces of wider lumber and finished with waterlox on the bottom and top. Any guesses to what happened? It was finished in mid September and I don't remember seeing a bow in it at that time. I did finish the bottom side of the table top before the top. I don't remember if I did a quick seal of the top before finishing the bottom, so I guess the top could have been absorbing moisture (indoor air conditioned shop).

Thanks!

Mark, take the bow out from below with fasteners that don't impede seasonal movement across the grain. It happens and that's the fix.

Every time a flat board cups, it's from moisture. Either the boards were wet or the top or bottom absorbed moisture differently. Letting glued up panels sit around can create issues if there is not good air flow around all surfaces.

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Originally Posted by Mark Visconti

...the legs on the table are about 1/4" proud of the skirt, so the top rests only on the leg tops. I haven't attached it to the top so it is just resting on them.

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How are you going to attach the top to the tops of the legs?

Turn the top over for a couple weeks on the legs. Perhaps there is directed hot air flow that is drying one side of the top more than the other.

I plan to attach it to the skirt. I will use blocks with loose tenon into the skirt and screws into the underside of the tabletop. The blocks have a cutout so the loose tenons can be pulled out later with a pliers if the table needs to be taken apart. Did this on another cherry table and it worked great when I had to disassemble the top to move the table. That top rested on the skirt, but the block isn't dependent on the skirt and top meeting. We do lift from the skirt when moving tables. If you look along the edge of this table you would be able to see the block thru the <1/4" gap. I guess I should have trimmed the pre-existing legs so that everything is level with the skirt. Thanks for pointing that out!

I too have had issues with Sapele moving on me in a panel of a small jewelry cabinet. I had to scrap the panel and use bubinga instead.

Having said this, my sapele had some wild grain and was probably some reactive wood and is not the norm for sapele. Typically sapele can be very stable, similar to real honduran mahogany. Large table tops similar to yours often have a tendency to bowing and sometimes cannot be prevented without using joinery or other measures. Jim is correct in that I think your only option at this point is to use screws to help pull it down. You may even need to use battens on the underside with screws or sliding dovetail to get this wide table top flat.

I would highly recommend researching table top buttons for attaching your top to the aprons. These do a really good job of accounting for wood movement and is the method I always opt for to attach table tops to a table base, that is if I have aprons to mount to.

I used to have a terrible time with glued up panels till I built a solar wood drier. Now I have a ready supply of dry wood.