Best joint for window sill panel

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BlackMerlin

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Hello,

I'm planning to make a simple internal window sill to sit on top of the previous sill (old clay tiles). I've got 190mm oak boards and have made sills out of them for most windows but I've got one window with a big recess that needs a ~300mm sill. My plan is to glue two oak boards together like you would do for a normal panel and trim as needed. I'll then use CT1 to glue the panel on top of the tiles. This has worked well with the other sills and provides a level of flexibility for the wood.

The way the window is positioned I expect people will end up siting on the sill quite a bit and I'm wondering if just gluing the two boards together will be enough considering the forces that might be applied to the individual boards and the flexibility of the CT1 adhesive underneath. Is there a better joint I should use? I was wondering about a half-lap for example. Tongue and groove would be another but I'm not sure I can manage that as an amateur with just a router.

What would you suggest?

Many thanks!
 

Ollie78

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Biscuits, domino's, loose tongue ( router a groove in both sides and glue in a bit of wood full length ).
Be very careful if using a sealant to fix it. Just do a couple of dabs or stripes. If you use a load of sealant it will warp the board.
Do not seal it all along the front especially.

I like to use a couple of t slots in the window board and flat headed screws in rawlplugs in the sub cill. Screw them down till its just right to push the board on.

Ollie
 

Inspector

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I disagree with Ollie78 recommendation of "Biscuits, domino's, loose tongue ( router a groove in both sides and glue in a bit of wood full length )." A properly glued long grain joint (boards side by side) is as, or stronger than solid wood. All the extra goodies will do is aid you in keeping the joint aligned when glueing. They work great where end grain and long grain are joined and the choice is yours if you want to use them but modern glues are stronger than the wood they hold. I don't disagree with any of his other recommendations.

Pete
 

BlackMerlin

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Thank you both! That's super helpful. I've heard the "modern glues are stronger than the wood they hold" argument before, just wasn't sure if it also applies in this use case.
 

John Brown

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Thank you both! That's super helpful. I've heard the "modern glues are stronger than the wood they hold" argument before, just wasn't sure if it also applies in this use case.
I've heard that too. I used to know a builder/carpenter who asked why, if the glue was stronger than the wood, we didn't build houses entirely from glue.
 

Steve_Scott

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I’ve just made a sill out of ash jointed with dominos for peace of mind and alignment and it’s doing fine…. Other than warping where I trimmed to fit the reveals and omitted to reseal before fitting. I’ve convinced the lady of the house it’s intentional to discourage people for putting drinks down on it.

I guess the point I’m making is the jointing mechanics isn’t the critical factor! Hopefully you have more success!
 
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