I received a bunch of short pieces of mahogany from a friend. I thought I’d try to make an outdoor side table for my daughter. The design of the top would be a lattice of 1″ by 1″ pieces and I’d join the lattice by using half lap joints (I’m not sure if that is the correct term). My question is: would the gridwork hold together in an outdoor setting with the rain and humidity or would the wood expansion just blow it apart? If that technique won’t work, is there a better way to make the lattice that would survive? The top would be about 20″ x 20.” – Michael Krajeski
Tim Inman: This is a project doomed to failure, in my view. Why spend so much time joining and fitting fine wood to just put it outdoors where it will destroy itself? There’s my bias. I’d rather encourage you to make a table for your daughter which can be expected to live indoors where it can become a family heirloom.
Chris Marshall: Michael, I’ll offer you a bit more hope.
Wood movement can have surprising results – and often the effects are not what you want — but on 1×1 lattice pieces, I think your side table project is going to work out fine, even when it’s exposed to the elements. The fact of the matter is, the narrower the cross grain area is, the smaller the amount of wood movement will be.
According to a handy wood movement app I have on my phone called “The Woodshop Widget” ($4 for either Apple or Android devices at woodshopwidget.com), the amount of expansion or contraction on a piece of flat-grain African mahogany 1-in. wide is just 1/64-in. (with relative humidity starting at 20 percent at 30 degrees—winter–and shifting to 80 percent humidity at 95 degrees—summer). And if your mahogany is quarter sawn instead, the amount of wood movement is even smaller. So, those half-lap joints will surely tighten and loosen some seasonally, but the results won’t be explosive. You may not even notice much change … little gaps that open during dry spells and close when the humidity skyrockets.
Mahogany, by the way, is a great choice for an outdoor project like this! Good on you for wanting to use it for a project your daughter needs, wherever the table is intended to live.
A table that sits outside is not going to last as long as one that never leaves the living room. There’s no question about that. Sun and water are harsh adversaries for outdoor projects. But, it will still last a very long time. Seal the wood with a penetrating stain that has a UV inhibitor in it to help slow down the degradation by sunlight. And have your daughter store the table out of the elements when winter comes.
I say go for it, and have fun building it.