Plywood or self levelling prior to tiling a large window sill - Tile Advice

[Noreng]

I want to tile a large window sill, about 450mm deep and 7m long. Previously it was covered with veneered chipboard but after 25 years the sun plus moisture from watering plants and condensation from the windows above did for it.

The wall underneath is uneven brick with some wood inserts previously used to screw the wooden sill too.

So far my two thoughts are:
1) Use self leveling compound then tile directly onto this.
2) Install plywood then tile

The wall underneath is being lined with Gyproc thermaline, bonded to the wall with Dri wall Adhesive, so the tiles will need to go over the Thermaline as well as the old wall. This suggests to me that the plywood solution may be better.

Any thoughts?

Edit: Another factor? The sill gets a lot of sun, therefore potential differential heating with the substrate, the thick stone/brick wall underneath. Would this also point to plywood as the best solution?

 

[Gazzer]

Tile backer board fixed with Fast set SPF adhesive and screws.

 

[Colour Republic]

Hi Noreng, how high is the sill? I suppose what i'm getting at is, will you be sitting on it or using as a bench at all?

 

[Noreng]

Tile backer board fixed with Fast set SPF adhesive and screws.

I looked at backer boards and they seemed to major on use in wet areas, this area is dry (well most of the time!) Presumably the advantage is stability?

Any particular makes or thicknesses for the backer board? People may sit on it so it may take a bit of a load from time to time.

 

[Gazzer]

As long as the board is solidly fixed then it will take the weight. Vastly superior over wood.

 

[Noreng]

Tile backer board fixed with Fast set SPF adhesive and screws.

Does that mean set the backer board onto the bricks below with SPF, or attach the tiles to the backer board with SPF, or both?

 

[Gazzer]

Does that mean set the backer board onto the bricks below with SPF, or attach the tiles to the backer board with SPF, or both?

Both.

 

[Noreng]

One last Q.

The brick and cement is old and dusty, I will obviously clean as best I can, but should I prime/seal with anything prior to applying the SPF?

 

[Gazzer]

Yes prime with an acrylic or SBR tile primer not PVA !

 

[peckers]

You could shutter it off and use sand and cement (screed) yourself a new cill, the only thing is is the drying time before you are able to tile it

 

[DHTiling]

Just dot and dab some 12mm plaster board on it...easiest way..

 

[Colour Republic]

I think they might be sitting on it Dave, so they'd have to get a fair bed of drywall adhesive, better be safe than sorry:smilewinkgrin:

 

[Perry]

Dave's right and why use dry wall adhesive just use cement based on plasterboard and tiles easy as says cheaper lol

 

[mags]

I had similar problem in my kitchen but far smaller area, I filled area with cement

 

[Perry]

I had similar problem in my kitchen but far smaller area, I filled area with cement

yes its easy but needs more skill and you have to wait a lot longer plasterboard doesn't need any drying time