Window Board Secret Fixing

[Garden Shed Projects]

Hi can any one offer any tips for secret fixing a window board. I have one to fit at 3600mm x 350mm in my extension and am thinking gripfill or similar but wondered if there was any innovation or technique I am not aware of. The walls and reveals are already plastered.

Any ideas greatly received.

 

[Phil Pascoe]

Gun polyurethane - ensure you have weights to keep the board in place and that it can't shift from level. The stuff expands. Get rid of all dust and damp down the surfaces. No second attempts.

 

[johnnyb]

Hybrid silicone? gripfills OK but not used loads these days(I've not used it for over a decade) gun grade pu foam which is what phils saying?
Hybrid silicone is used for everything
Plumbing decorating sealing gluing but it's real sticky messy muck for sealing stuff not recommended. Normal silicone works fine to.

 

[niall Y]

One way to do this mechanically, is to rely on a fix at the back of the window board, using a bare face tenon along the length of the window board, inserted into the groove on the inside of the window sill.

The front is fastened down using Galvanised strap or angle brackets screwed to the underneath of the board, and to the wall beneath This is more convenient to do before plastering, but it is a simple enough operation to house the straps deep enough into the plaster and fill after fixing.

EDIT.
For a really neat fix, the sides of the window board can be partly recessed into the reveals, cutting the tops and bottoms of the housing with a multitool, before chiselling out the waste, and filling after the board has been installed.

 

[RobinBHM]

As Phil says gun adhesive.

But if it’s going on cell on type blocks then I would vacuum them then coat with something to seal them first.

If the windowboard is mdf it’ll hold but if it’s solid timber you need mechanical fastenings to stop cupping


https://www.screwfix.com/p/dow-inst...57l9lc75k7Xc74AQeGAaAtELEALw_wcB&gclsrc=aw.ds

 

[Chubber]

+1 for multi tool using a scrap of board thinner than the window board by the thickness of the blade if you are working off a flat plane surface?

 

[Ollie78]

Use a t slot cutter to put a few of slots in the board from the back edge to about three quarters of its width. Do a small test bit to the same depth.
Mark the positions on the substrate and install some pan head screws in line with the slots using appropriate plugs or whatever, 2 per slot, front and back.
Use the test bit to check the height of the screws and when its just right slide the board in. You want a little bit of resistance but not loads.
I am assuming a solid wood window board, I have done it on loads of Oak ones and some Utile, might need to be careful on MDF as its quite weak.
Use a bit of stixall or other hybrid polymer as well if you feel like it.