Fixing, Oak window boards.

[Ollie78]

I have a job to make up and install some solid Oak window boards, picked up the sawn boards today.
The client is having all the windows changed this week and wants to replace the nasty MDF window boards with solid Oak. I have no issue making up the boards but have a concern about the potential for cupping as some are 220 wide ( 28mm thick ).

I am thinking of pre finishing them all around to prevent uneven moisture content, probably osmo oil as they want a nice satin finish to match other stuff.

I am flipping between just sitting them on a couple of lines of polymer sealant but not sealing them totally. Or, drilling and screwing them into the brick or block and then plugging the holes with tapered plugs.

Not sure I want the look of the plugs or the extra finishing needed but dont want them to cup. I am hoping I will be sliding them into the gap left by the originals and this will help pinch them to stop movement.

I don`t want to cock it up as its prime Euro Oak and not cheap.

Any ideas ?

Ollie

 

[Spectric]

Are they one piece boards or made from several planks? Joining several smaller planks and keeping the grain direction opposing I was told will help prevent cupping. Also leaving the timber in the building to climatise before fitting may help.

 

[Ollie78]

They are one piece, I think (hope) the thickness of 28mm will help, I considered kerfing the underside maybe ? I plan to leave them in the property for at least a few days before installing them.

Ollie

 

[RobinBHM]

I have a job to make up and install some solid Oak window boards, picked up the sawn boards today.
The client is having all the windows changed this week and wants to replace the nasty MDF window boards with solid Oak. I have no issue making up the boards but have a concern about the potential for cupping as some are 220 wide ( 28mm thick ).

I am thinking of pre finishing them all around to prevent uneven moisture content, probably osmo oil as they want a nice satin finish to match other stuff.

I am flipping between just sitting them on a couple of lines of polymer sealant but not sealing them totally. Or, drilling and screwing them into the brick or block and then plugging the holes with tapered plugs.

Not sure I want the look of the plugs or the extra finishing needed but dont want them to cup. I am hoping I will be sliding them into the gap left by the originals and this will help pinch them to stop movement.

I don`t want to cock it up as its prime Euro Oak and not cheap.

Any ideas ?

Ollie

You could put some stress relief grooves in - usually 3 grooves about a 1/3 of the depth running full length.

You could put 1 screw near each end, say 50mm - that should hold them down and would be less visible

 

[Cabinetman]

I asked the same question about six weeks ago but the boards were 500 mm wide and I decided that it was best to run away and not accept the job (not my normal sort of work) I don’t think the thickness of the boards will have any effect on whether they cup or not, but saying that kerfing as you call it will probably help, and I would kerf/ groove them quite deeply – it will never be seen- probably leave only six mil ungrooved and as you say three or four grooves across that sort of width. Ian

 

[JobandKnock]

I think that the environment they would be going into is one where temperatures and RH can fluctuate wildly, so I'd be looking to install with screws and cups to control the tendency to cup, because even MR-MDF can cup. I'd also seal the bejasus out of them.

 

[RichardG]

Does it have to be solid oak, could you use a quality veneered panel?

 

[Doug71]

I'm guessing the new windows won't be wood with a nice groove in the back to slide a tongued window board in, that used to make life so much easier when fitting window boards?

If they don't cup they still might dry out in width, they often can't move at the front because they are lugged around the reveal so when they shrink the back of the board pulls away from the window leaving a small gap.

Knowledge is a dangerous thing as you just start over thinking things, in the past I would have just fitted them and moved on, now like you I would be procrastinating over it trying to work out every possible outcome from how I fitted them

I'm sure you will make a good job however you fit them and the wood will just do what it wants anyway.

 

[Adam W.]

They will cup unfortunately, unless you use quarter sawn, sorry for the bad news.

They will also shrink, as you'll drive the moisture content down in that position if the sun gets on them.

 

[J-G]

I considered kerfing the underside maybe

That was my first thought.

 

[xy mosian]

I can see why you would avoid using screws through the boards. How about kerfing the underside and re-inforce that with screws into keyhole slotted plates, also on the underside? That would hold the boards down, hopefully flat, and allow for movement. The frame edge could be glued so that any width movement would affect the under cill wall overhang, hopefully un-noticed.
xy

 

[JobandKnock]

But how would you get an a accurate fix into, say masonry? Because of the constraints of the window reveals the only way to install it would be so that it pushed in from the room towards the window and onto the screws, but I feel that accurately locating 4 or (for wider boards) 6 or even 8 screws with sufficient a accuracy into plugs in masonry would be nigh on impossible, and that's before any fiddling about you night need to do because the reveals aren't square

 

[xy mosian]

But how would you get an a accurate fix into, say masonry? Because of the constraints of the window reveals the only way to install it would be so that it pushed in from the room towards the window and onto the screws, but I feel that accurately locating 4 or (for wider boards) 6 or even 8 screws with sufficient a accuracy into plugs in masonry would be nigh on impossible, and that's before any fiddling about you night need to do because the reveals aren't square

If there is no vertical play in the final fit, without screws. Then change mirror plates, keyhole plates, for long dovetail slots. If the choice is to use dovetail slots, I use the term as descriptive, then worries about strength could be eased by using steel edges. Or even a preformed channel let into the underside of the board.
As for accurately positioning the screws then how about drilling the masonry fixing holes first. Use some sort of marker, screw with scratch edge etc., to mark the underside of the board. remove the board and then fit the fixing plates.
xy

 

[The Bear]

I replaced the window boards in my house about 4 years ago when I had new windows. These were 40mm thick solid oak. No grooves on the new windows to fit them to. I put 3 coats of matt oil based varnish on all surfaces. Then stapled EML on the bottom with heavy duty hammer in staples (not flimsy staple gun jobbies). There was enough room after chopping the old ones out to slide the board in and bed it down on a bed of cement. The back of the board had a thin line of clear silicon to "stick" it to the bottom of the window frame, but not enough to ooze out. No plugs, they will always be seen. It important to pre finish them if oak as you'll otherwise end up with some pretty horrid water stains when you patch the plaster.
No movement, would do it this way again.

HTH
Mark

 

[Ollie78]

Thanks for all the suggestions. Quite a few ideas there.

I am leaning towards doing some kerfs along the underside, this seems a pretty popular plan.
I have gone off the idea of fixing from the top if I can help it, mainly so it looks nicer, but I did think that if doing fixings right through this could cause splitting if big shrinkage occurs.

I have to go and look at the job again once the windows are in and see what I have to fix to etc.
I have a Keyhole router bit somewhere and I am considering using two slots with this (more on long boards) then if I use a suitably shaped screw in a wallplug I should be able to slide the boards in from the front. Maybe a couple of blobs of Sikaflex or similar as well.
Perhaps even doing two fixings per slot, hopefully this will be enough to prevent too much cupping but allow a bit of seasonal movement without splits.
Maybe even wider slots with a washer or something ?

If I had access to the complete area from above (if you see what I mean ) I would have gone for something like buttonfix or something but I think they are going to need to be slid into place from the front.

Thanks

Ollie