Warped wooden worktop - any solution?

[glenfield2]

I bought a couple of iroko wood block worktops a few weeks ago, trimmed them to size, sealed all round with several coats of Danish oil then left them on the kitchen units unsecured over maybe two weeks around Christmas. Just gone back to the job and both are bowing significantly across the widths which will clearly be an issue when fitting sink and hob.
They are on a boat I’m refitting (on dry land) so pretty cold inside but weather tight.
Anything I can do to rectify matters? Would it be worth trying to gradually pull them flat?
The amount of bow varies but at worst if the rear is flat down the front edge is lifted maybe 6-7mm.

 

[Cabinetman]

Hi I thought at first you were going to say that they were bowed the other way, and I thought it might be the Danish oil on the top expanding that surface, but obviously not. It isn’t that but just curious did you oil both surfaces?
Another thought is that if you only oiled the top this may have stopped moisture in the atmosphere reaching the top surface but it did perhaps get into the bottom surface which made it expand, purely a guess.
As they are made from blocks it is extremely unlikely that they are reacting in the way that piece of solid wood would, so really all I can suggest is that they have either got damp on the bottom surface which has made it expand or dried out more on the top surface – have they been in the sun? Ian
Edit, how to rectify it depends to some extent on what caused it.

 

[EddyCurrent]

A bit like maths equations, you can do whatever you want to one side provided you do the same to the other. Applying veneer to one side only can have a similar effect.
I once saw an idea where kerfs were cut into the lower surface allowing the wood to more easily bend in the required direction, then filled with thin strips of glued in wood or epoxy.

 

[Doug71]

Were the tops getting much air to the underneath as in do the cupboards below have doors on?

If so maybe the top side has dried out as it's getting air to it but the underside is drying slower as it's getting no air to it as it's over the sealed cupboards if that makes any sense?

 

[stuckinthemud]

Seems likely one face is wetter than the other, if there's no rush, I would let the timber equalise, the warp should disapear

 

[Sgian Dubh]

The amount of bow varies but at worst if the rear is flat down the front edge is lifted maybe 6-7mm.

6 or 7 mm cupping across a width of perhaps 600 mm isn't a great deal.

1. Can you take out the cup (cross grain warp), with the concavity facing up simply by pressing down at both outer edges?
2. If so, screwing the top down to the cabinets front, middle and back should be enough to pull them flat at installation time, with an allowance for cross width expansion and contraction via slot screws, or similar, at the mid-point and at one edge, with the expansion allowance probably best to occur at the back.
3. To check if you can flatten the pieces you might find you have to clamp or temporarily screw one edge down to the top of your cabinets, concavity upwards as at 1 above, then clamp or temporarily screw down the other edge. If that works, then go back to bullet 2. Slainte.

PS, in the interests of accuracy in describing warp in wood, a long grain deviation from straight (warp) along the length of a solid wood panel, where the concavity/convexity follows the panel's length is described as bowed or bowing. Cross grain deviation from straight, i.e., a concavity/convexity across the width is described as cupped.

 

[toolsntat]

Might be as simple as turn them over and leave for 2 weeks.
Check em regularly and if they hit the flat spot again, work, seal and fix em sharpish....
Cheers Andy

 

[glenfield2]

Thanks for all the advice. How was it stored? Cut to length and width then sealed with two, maybe three coats of Danish oil each side and at least four on edges. Haven’t done any cut-outs for hob and sink yet.
They have been sat on the kitchen units and covered with those black corrugated protective sheets you lay on floors etc. Maybe this was a cause of the problem - the top surfaces sweating under them?
The boat is cold (very cold at the moment) so there’s some damp around even though it’s fully weatherproof.
PS and, yes, sgian-dubh, I’ll get my terminology right next time - they are indeed cupped.

 

[eribaMotters]

Sounds like you are oiling correctly, or a least it's fair to say I do the same. I have not fitted many kitchens, but those I have done have Iroko surfaces, about 8 from memory. I have never experienced cupping of more than a couple of mm over a 650mm depth. Moisture content being a cause should be less of a problem in the cold weather as humidity levels are lower than in the summer months. I think your comment about the top surface being covered with black sheet may be the culprit.

Colin

 

[stuckinthemud]

Moisture content has bern really high around here moisture condensing on roads and pavements, on any cold surface, would think a cold black surface would be an excellent condenser...