MikeG.":2h3s2z5k said:
If it is warped (ie twisted), then I'd say forget it.
Actually Mike that's not quite true because:
1. Warp is really a general term indicating distortion of some sort in a plank. The following sub-categories more precisely describe warp.
2. Cupping across the width is a concavity across a board's width.
3. Spring, crook, or edge bend means the edge of the board is not straight.
4. Bowing shows as an end to end bend along the length of the wide face of a plank, and cast is another name sometimes used for this condition. Another sometimes seen form of bowing is multi-bowing (a series of waves) through improper stacking of the wood during drying or storage where the bow is induced by poor stickering, particularly when the wood is wet and flexible, i.e., stickers aren’t set vertically exactly one above the other.
5. ‘In winding’ or twist. Differential shrinkage, usually in all three planes- tangential, radial and longitudinal, causes the plank to resemble a propeller. Very often a contributory cause is reaction wood, either compression or tension wood, or juvenile wood. Another common cause of the fault is spiral grain.
6. Kink is a sharp deviation from straight along the edge: commonly caused by an edge knot.
As to fixing the cupping in this worktop, others have already suggested possible strategies, but here's what I normally do, and it's a more aggressive technique than some already described.
Sit the board convex side down on a flat surface. With the concave side now sat upwards get a water wet rag and sponge this side generously. Monitor the cupping over the next hour or so. Similarly, you can sit the concave face down on a flat surface over wet newsprint in a warm area. Again monitor to observe progress towards flat.
When the board has (hopefully) flattened sticker it up horizontally on stickers set about 500 - 600 mm apart running across the grain that are 20-30 mm thick so the air can circulate all round. Monitor the board for a while and tweak as needed. You can also put an extra layer of stickers on top of the top board, if there's more than one, put a piece of plywood or similar over the stickers and apply pressure, e.g., weights, cramps, blocks, whatever.
If there are several boards to stack (regardless of needing to remove any form of warp) always align the stickers vertically to minimise the chance of inducing multi-bowing as described above - multi-bowing isn't usually induced in wood that's dry if the stickers aren't perfectly aligned and storage is short-term, i.e., two or three days, but any long term storage really should be done with precisely vertically aligned stickers. Slainte.
