Bedding oak windowboard on tile adhesive

[Albumen]

Hi folks.

I'm doing my bathroom. I've got an oak window board to go in. The reason I chose it was that I just wanted a hardwood windowboard, and that's what Howarth gave me. It's in an area that might get a bit of wetness, hopefully not too much.

But I like the look of it so am going to try to keep it as is, without painting it. The walls are plastered and the trough in the window is too low to use so:

1. Are there any 'invisible' fixings I could use? I'm aware that window boards are usually held in by the trough in the window and plaster, but none of that is possible in this case. If I have to drill a couple of holes and fill with the best matching filler I can find it's not the end of the world, but I'd rather not. It's a really nice looking bit of timber.

2. What are the best clear waterproof finishes for oak?

3. The (plastered) sill slopes back a bit. If anything I'd rather have the windowboard sloping forward, so any water that does collect runs off. Rather than pack it on hardboard or whatever, is there anything to stop me bedding it on tile adhesive (BAL single part flexible, as it happens). It's meant to be water resisitant, flexible and so on. As I said, this window sill SHOULDN'T get any water, but I think it will, and I hate the idea of a void where water can collect and do it's evil work.

4. Oh yes, I remember hearing about only using a certain sort of fixing with oak. Can't remember what though. I'll be using ss screws probably.

Many thanks.

 

[joinerjohn]

The best fixing would probably be to drill, counterdrill and screw, then cut some timber plugs to fit into the holes in the top.
Sealing wise, perhaps polyurethane varnish or something. Oak will have to be well sealed in a bathroom environment. You'll probably have to give it a couple of coats underneath too (before fixing)

PS use either brass or SS screws for fixing. If you use ordinary steel screws, the tannins in the oak will react badly with the steel and discolour fairly soon.

 

[Albumen]

Thanks for the reply.

I think I've worked it out, as often happens when you've just explained your problem.

Forget the 'wanting to avoid a void underneath' OCD that I have. This window sill will get a little splash when people forget to use the shower curtain properly, but won't be subject to much, and will be newly tiles around, so should be OK.

How about this to avoid visible fixings:

I get some WBP ply (got loads). I know 9mm wil take a countersunk screw. I glue whatever packing I need to on to the bottom to get it straight and level as I want. Call this a sub-sill. I screw it down to the brick/plaster sill. I glue the oak windowboard onto that.

There's some pretty tenacious waterproof glues about these days. 'Stronger than wood itself' etic. I've got plenty of my weight lifting weights to put on top and the glue will be spread over 2 large surface areas. And new clean dust-free wood. And this won't be subject to any stress. The only potential forces would be somebody sittin on the edge and trying to tilt it up, and hitting if from underneath with a hammer (?).

I'll have a small strip under the windowboard to polyfilla.

Any drawbacks I can't see?