Warped oak window boards

[craig1234]

I am building an extension with solid oak window boards. Prior to plastering I oiled the boards (hoping to seal them), nailed the underside to provide a key and then bedded them onto mortar.
However, the boards have all warped to varying degrees with a couple resembling ash trays!
My questions are:
1.As I have a further 4 boards to fit, what should I do differently to try to prevent warping when I install these
2.The fitted boards have warped such that on the top side, both front and rear edges are raised producing a dip in the centre along the entire length of the board (although it is worse in the middle).
I intend to remove some of the warp in situ by "planing" the rear edge of the board. However, due to the proximity of the window frame to the warped area, I can't get my electric planer close enough to the edge to use and a manual planer is proving to be very hard work! Can anyone suggest an easier method/tool to use or do I just have to persevere with the manual planer?

 

[Burnerman]

Leave the timber in the proximity of the installation for as long as you can for it to acclimatise.
Any treatment is best applied to both sides of the timber to get a balance, and don't attach them until they've been planed flat.
Planing oak by hand Your muscles will put Popeye to shame
John

 

[Harbourwoodwork]

How wide are the boards?
Did you seal both sides and how many coats?
Do the window boards fit into a groove in the window frame?

 

[craig1234]

Firstly in reply to John, the boards were acclimatised for well over a month and showed no sign of warping before I installed them. It may be coincidence but the board that I paid special attention to when fitting had two good coats of oil but has warped the most.

Harbourwood, the boards are wide at 300mm - some are single pieces of wood but others are joined - I spoke to the manufacturer prior to purchase and was told that at this width the boards are more resistant to warping if two pieces of timber are used!. I sealed (or rather oiled) both sides - some had a single coat whilst others two - more coats doesn't seem to have helped the problem.
The boards but up against the PVC window frame - no groove

 

[Harbourwoodwork]

Firstly in reply to John, the boards were acclimatised for well over a month and showed no sign of warping before I installed them. It may be coincidence but the board that I paid special attention to when fitting had two good coats of oil but has warped the most.

Harbourwood, the boards are wide at 300mm - some are single pieces of wood but others are joined - I spoke to the manufacturer prior to purchase and was told that at this width the boards are more resistant to warping if two pieces of timber are used!. I sealed (or rather oiled) both sides - some had a single coat whilst others two - more coats doesn't seem to have helped the problem.
The boards but up against the PVC window frame - no groove[/quot
screw the window boards bed on mastic if needed and pellet the holes the ones that are bedded on mortar will have to come off cleaned up and dried out and should go back to original shape,pre oiling beforew fixing is a good practice ,but oil doesnt take much effect until at least 3 coats ,Iwould go overkill on the coats the window area is a very demending area for a natural product condensation
heat cold plant pots ,sunlight and rads, belt and braces would be the approach.

 

[jockscott]

Personally , I wouldn't have put nails into the underside of the board, then bedded this into mortar. I'd have made the mortar bed as flat and level as possible and allowed it to dry. Then plugged and screwed the board to the sill. Water/moisture and timber don't really mix. I'm not surprised they bowed.

 

[noseall]

Personally , I wouldn't have bedded this into WET mortar.

Neither would I.

This is how we do it.

 

[PeakOakFrames]

The moisture difference between the wet mortar on the lower surface and the drier air on the upper surface is the cause. Not much option but to pull them off and start again.
To plane out the cupping would be better done with the window boards out and you may find that they will end up so thin that they need replacing. Sorry to be the bearer of bad news.

 

[Dave54]

Agree with the others on what's caused the problem and what to do about fitting the rest.
You might find that if you take the board off, and wet the cupped side well it will dry flat (tish) You would preferably need to put it on a flat surface, with battens every few inches on both sides to support it, and a flat board (a piece of ply or something, I wouldn't use the other oak boards) on top with some weight on it.