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How to fix cupped drawer bottoms so they'll stay flat

Posted by dilettante (My Page) on
Wed, Nov 28, 12 at 19:07

I recently bought a small Eastlake washstand that needs a little TLC. Normally, I try to walk away from fixer-uppers, but it was perfect match for my Eastlake bed and dresser (even down to the wood, which is chestnut), and it just screamed out to me. It was also dirt cheap, so I was willing to take it on.

The most serious problem is that the bottoms of the two narrow drawers are seriously cupped. The drawers are only 9" wide, and the gap between the bottom of the drawer and the back of the drawer is about 3/8" at the widest point, so the cupping is significant. Oddly (to my mind), the top drawer, which spans the full width of the washstand, doesn't have this problem.

What is the best way to fix this? I tried steaming the concave side (the top) of one of the drawer bottoms, and the wood straightened out easily, but the cupping returned when the wood dried. I didn't put any weight on it while it was drying because I was afraid of damaging it and decided I'd better get some expert advice before doing anything else.

Could one of you experts please explain (in detail) how to fix these so that they'll stay fixed? I know they shouldn't be nailed. Assuming that steaming is the way to go, how long should I steam them (just until they straighten out, or a while longer)? Would using weights while they dry help them stay flat? How much weight can I safely use without cracking the wood, and how long should I leave the weight in place?

The drawer bottoms currently have no finish of any kind. (The finish on the exposed wood is shellac.) Would putting a finish on them help keep them from cupping, and if so, what should I use?


P.S. Obviously, I could just replace the drawer bottoms, but I'd only do that as last resort.

Follow-Up Postings:

RE: How to fix cupped drawer bottoms so they'll stay flat

I would remove the drawer bottoms, and follow the procedure below. You can also clamp it between two pieces of 3/4" plywood, and after a few days remove it from the clamps.

Wood warps when moisture loss on one side is greater than on the other. To straighten a warp, add moisture to the dried-out side. Place the wood cupped side down on damp towels in strong sun. Place some light weights on top of the wood during the flattening process.

RE: How to fix cupped drawer bottoms so they'll stay flat

While wood can warp when one side is wetter than the other, when the moisture equalizes, which it will, it will return to its natural state.

The problem is due to either or both of these:
- Reaction wood -- twisted grain or wood that was grown under stress such as on a hillside.

- Differential expansion / contraction rates of radial (from the center out) and tangential (around the growth rings).While these number vary by species, it's generally on the order of twice as much tangentially as radially.This is why logs usually split and open a "pie piece" shaped split.A way to explain this is that the curves in the annual rings tend to flatten out.

My opinion is "in the end, the wood has the final say."I've not seen a successful way to "unwarp" something permanently.My recommendation is to use plywood or fabricate new drawer bottoms from quarter-sawn wood.

Here is a link that might be useful: See figure 4.3

This post was edited by bobsmyuncle on Thu, Nov 29, 12 at 14:20

RE: How to fix cupped drawer bottoms so they'll stay flat

Thanks, Sloyd. I'm not sure if I can slide the bottoms out without breaking them. They're not nailed and don't appear to be glued, but they don't seem to move.

Interesting link, Bob - thanks. I may end up replacing the bottoms, but I want to at least try to fix them myself first before paying someone to do it. After all, they must have started out flat. I don't care if they're not perfect, I just don't want the drawers to stick. Around here (Boston area), I'd probably have to pay far more to replace the bottoms than I paid for the washstand itself (which would explain why it was so cheap).

RE: How to fix cupped drawer bottoms so they'll stay flat

After you get then straightened out, seal them so they can't absorb moisture. That helps keep them flat.

If they still warp, replace them.

RE: How to fix cupped drawer bottoms so they'll stay flat

If you want to keep the bulk of the wood (for historical purposes?) you could rip the bottoms into several slats, re-square the edges, glue them back together and then plane the whole thing flat. You'll need to add some new wood to replace the wood lost to the saw kerf and the bottoms will be thinner than before.

Have to admit that for furniture to use I'd replace them with old wood or with baltic birch ply, depending on how fussy you want to be about it. You can try the steam and clamp method (nothing to lose), but I'll bet they will warp again.

RE: How to fix cupped drawer bottoms so they'll stay flat

Lazy, what could you use to seal them? Would shellac work?

Rwiegand, if steaming and clamping doesn't do the trick, I'll have someone else replace them, with old wood if possible. Even though this is a relatively easy job (as furniture repair goes), I don't have the skill or the tools to tackle it myself. (The only power tools I own are a drill and a palm sander - no saw of any sort.)

I'll try steaming, clamping, and sealing first and see how it goes. As I said, they don't need to be perfect, and I'm hopeful that, once straightened, they'll be reasonably stable now that the washstand is in a stable environment.

Thanks to everyone for all the suggestions!

RE: How to fix cupped drawer bottoms so they'll stay flat

"seal them so they can't absorb moisture"

There is no finish that can stop the movement of moisture in and out of wood.

The wood has 24 hours a day, 365 days a year to com to equilibrium with the relative humidity of the air around it.

All finishes do is slow the movement.

It it is warped at equilibrium, it will warp again when it reaches equilibrium.

RE: How to fix cupped drawer bottoms so they'll stay flat

Exactly what I was going to say, Brickeyee. Besides, many finishes you don't want to put inside casework or you will smell it for years.

Same reference, figure 16.3 Moisture Excluding Efficiency (MEE) of various finishes.

RE: How to fix cupped drawer bottoms so they'll stay flat

I'd try removing the bottoms and then re-installing them upside down(gravity helps). Weigh them down and then depending on the thickness , either drive tack nails through the backside of drawer (groove or no groove) or if its thin like luan ,I'd attach a small peice of wood to the back inside of the drawer to hold it down in place. Replacing the bottoms could be more work because of the thickness difference ,you would either have to enlarge the grooves or shave down the bottom to fit.

RE: How to fix cupped drawer bottoms so they'll stay flat

Sorry, i just read the part where you can't remove the bottoms. I 've redone alot of drawers of older pieces, and I usually do find small tack nails drivin through the bottom edge of the side pieces to hold the bottom in place. There may be only 1 on each side, and there very hard to see.
Or you could reverse what I said above and turn the drawer over , weigh down the bottom so its in place , tack nail it from the backside or place a small piece of wood on the underside of the back side piece to hold it in place.

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