Thread: Red Gum slab

Originally Posted by mspil

G'day all,
At the Wood show last weekend, I purchased a slice of red gum, approx. 800mm x 500mm x 50mm. The upper surface has been somewhat flattened, while the lower is rough sawn. Unfortunately, it has a concavity in the upper surface, with the centre point being roughly 12mm lower than the edges. Does anyone have any ideas for getting it back to flat? At the moment, I have it upside down, resting on two bearers, positioned across the shorter sides, with a quite heavy bucket of gravel sitting at the centre. It seems to have come back about 3 or 4mm under this treatment. Any better ideas?

I assume it's already dry? If so, the short answer is your chances of flattening it that much by brute force without cracking it are highly unlikely to none. If it's green I would weigh it down some more and monitor what it does and hope and pray it does not crack while it dries.

But being concave is only part of the problem. With redgum, its movement over a year is usually more of a worry. Some pieces don't move much while other's yo-you back and forth for decades. I don't know what you plan to do with it but after it is dry I would leave it up to a year in the room you plan to use it in and measure how much it moves before you think about using it. I have seen pieces that size move from 12 mm convex to 12 mm concave over a year. Even if you can lock it down onto something when it is flat, over time it will flex and pull apart anything it is built into.

After you have assessed how much it moves then think about if and when you might have it flattened. Flattening when it is in the middle of its movement cycle is obviously the best time.

try to find someone with slab master/ woodwhiz or something similar. dress and sand both faces, you'll obviously loose the 12 mm in thickness unless you don't mind the edges on the underside not being completely dressed then u save a couple of mm. That shouldn't cost more than 40-50 bux. Seal it shortly after with your choice of finish same amount of coats on both sides and extra on the end grain. Whatever the application is make sure you to include couple of braces into your design coming up as close to the edges as possible. Coach screws are the easiest to use because you can slowly tighten them in the future if timber will decide to move on ya again, however traditional joinery will work just fine as well.
This is a quick way, otherwise BobL is right on the money.

I've tried to flatten various timber slabs by plonking tonnes(literally!!) on them and keeping them wet and so on without much success. And the ones I've flattened came back sooner or later. Re-dressing and sealing is the one I had the most success with.

Good luck,

Alex

Thanks, fellers for that advice. The slab is dry. I will have no time to do anything with it in the short term. The long term plan is to make a coffee table with it. So it looks as though the plan will be to leave it as is for the moment, see what happens, and then get it faced when I am ready to work on it.

If it doesn't straighten out you will be left with a thin slab,after it has been dressed.Pity it wasn't a bit thicker..'you can take it off,but you can't put it back on'!! The perils of buying 'bowed' slabs.