|Home » Forums » Architectural Woodworking » Message||Login|
You are not logged in. Consider these WOODWEB Member advantages:
wood movement - up or down8/14
we're in the process of finishing a rather large wood countertop and it has cup rather severely. it was flat yesterday when i sprayed the bottom side and now has about an 1" of cup over 100" (looks terrible). it will come down to almost flat when persuaded, but i'm not sure what the correct remedy is. Humid-wise, yesterday and today are the same.
should i finish the top side this evening (like planned), or keep the clamps on it for a day or two in hopes of flattening it out?
Most likely the clamp trick won't work.
Are you saying this counter is 100" wide "across the grain"? Depending upon wood species you could be in for as much as an inch of seasonal wood movement if this is the case.
If it is the 100" across the grain, and you put finish only on one side.........even for 1 day........you are lucky it only cupped an inch.
Spraying the 2nd side may begin to flatten it out but it will depend upon the direction of the cup.
If the edges of the unfinished side cupped up (unfinished side face up) then the cupping is due to expansion on the bottom side caused by absorption of moisture from the finish. In this case spraying the top side will push moisture into the wood on that surface, hopefully forcing the wood back in the direction of flat.
If the cupping on the top unfinished side is down at the edges (unfinished side still face up) then the cupping is due to the moisture in the air expanding the unfinished surface. In this case there is very little chance that spraying the top will flatten it out as the bottom is already sealed and the moisture in the air cannot get into the wood surface.
sorry guys. i was in such a hurry that i left out some important details.
100" x 70" x 2.25" end grain maple
it was slightly (1/4" or less at lowest point) cupped up and this progressed to 1.25", from point to point on the 100" direction. it was also cupped up (unfinished side up) approximately .75" from side to side (70" measurement). assuming moisture was leaving, we wet the block with wet towels and within 5 minutes both directions had come down significantly. we let it dry, finished our sanding, screwed the block to 2x8 rails on the bottom side, and it is back to mostly flat in both directions. i sprayed two coats of sealer to completely seal the block on the top side this evening and we seem to be out of the woods. we'll keep the block on the rails until it is installed.
my thoughts are that the block is now wet and will need to dry out but with all sides evenly coated it should dry out on evenly (and, hopefully, remain flat) since all paths to release moisture are the same (finished). this is unlike what happened earlier today with the bottom finished and top unfinished.
Did you use a water based sealer? Did you drill oversized holes in those 2x8s? That will be a necessity. If it is screwed through small holes and the top tries to move, it will likely crack. Drill some big holes, at least 1/2", and use fender washers under the screw heads.