How to fix this window board to prevent cupping?

[aingram]

Hi there
I'm going to make a window board out of a piece of 40mm x 150mm x 1400mm flat sawn american white oak. I bought the wood from a builders merchant, the wood was in an outdoor open warehouse so a similar environment to where it is now. The window in an outdoor kitchen, it an open building but largely sheltered from rain. The underside of the board will get moist from the blockwork, the top will get dry from the sun coming through the window. Please help on what measures I should take to avoid cupping. My intention is to blackjack the blockwork where the board will sit. I'll also biscuit the board to the window frame. I intend to strap the board to the blockwork underneath with two of the pieces of metal shown. Will orientation the growth rings help? Growth rings like"u" or like "n".

thanks in advance, Andrew

 

[profchris]

You won't stop it cupping as humidity changes. So instead, plan to minimise it.

1. Let it acclimatise thoroughly before final dimensioning. If 'outdoor kitchen' means the space isn't fully enclosed, then it's in the right place to do so. I'd watch it for a few weeks, tracking humidity via eg the BBC weather app so you can see how much it moves. If a lot, I'd use it for something else. If OK ...
2. Pick a medium humidity day for final dimensioning, so when it moves it does so in both directions. Maybe 60% would be about right, but note your highs and lows while monitoring.
3. Grain orientation as an n will look less obvious if it moves, but pens etc might roll off. However, there's nothing on my own kitchen sill which rolls.
4. In a year or so it will move less (though still move), so if it can be removed and flattened again, that would be useful.

 

[johnnyb]

I would overthink it if it were me. Bang it on see what happens.

 

[Inspector]

Or use plastic deck boards that match the final colour as close as possible and keep the oak for a nice project. I know, a heretic suggestion.

Pete

 

[Bingy man]

Just wondering what’s happening with the brick walls and the window opening . Are they going to remain as bare brick or will they be plastered or dry lined . Same question with the floor ( slabs ) it seems as though this will be a high humidity area unless that building is insulated , heated and adequately ventilated there will always be potential issues with damp and moisture. Any type of plastering , or floor screeding will produce even more moisture until the building drys out . For these reasons maybe as @Inspector says use plastic or composite which is easier to fit with modern grab adhesives..just my opinion though ..

 

[Jacob]

Plane the board thinner, saw kerf the underside say half way through at 1" intervals, fix down with screws, add half round nose to the front to get back to the original size.
Had to do that with my last project - 18" wide boards were in situ waiting too long to be fixed and they all curled. Managed to pull them down flat.
Yours look quite narrow so may not be such a problem

 

[pip1954]

Could you try fixing pieces across it to help to keep it flat you could let them in it or just screw them to the underneath, also would it be a good idea to varnish top and bottom before you fit it,you could even bread board the ends as well to help keep it flat
Cheers
Phil