DPC onder threshold

[brianivor]

I would be grateful if someone will advise me how I can deal with securely fitting a tile threshold on top of an uneven 50 year old DPM (a bit like roofing felt.)

A DIY enthusiast, I have just cut a doorway through a 9 inch solid internal wall from my garage into the house and am fitting a FD30 fire door and frame with fire approved door furniture and seals etc.

The concrete garage floor is almost flush with the DPC in the wall and I want to fit 13mm thick floor tiles in the door gap, which would be 27ins wide x 9 ins deep.

The top surface of the DPM is lumpy and uneven so I was wondering whether I could remove the DPM in the gap and level the threshold below where the DPM rested.

If I do this, can I just paint a thick coat of bitumen sealing compound across the gap (sealing it to the remaining DPM either side of the wall cut-out) or will I have to fit a new piece of DPM?

Whatever your advice, the bit that concerns me most is - can I just bed the tiles on top of the new DPC with ordinary mortar or should I use something which sets less brittle?

Sorry to be so long winded, but I wanted to describe the situation fully.

 

[^woody^]

The bitumen will act as the DPM, so you wont need an additional piece.

Then you would just use tile adhesive, and only use mortar (sharp sand, not building sand) if these are quarry tiles

 

[brianivor]

Thank you Woody,
A nice short detailed explanation - unlike my question!