Tiling concrete floor (under dpc)

[gaz2923]

My 1950's semi has an outhouse, the floor of which looks like it sits below the dpc of the house.

The room is single skin and cold so currently fitting insulating plasterboard to help.

The previous owner had laid this rigid Lino sheets down and when I lifted these the concrete was stained red where they had been and the red transfers to your hands/feet when you touch it.

I am planning to mop it well to get rid of whatever this red is and then tile straight on - comments please as I want the tiles to stay down!

I don't have enough height free (external doors would need replacing) so I can't add anything on top other than maybe bitumen paint. I don't want to dig it down to lay anything either as its 10 sqm

Gaz

 

[chippy5]

a couple of coats of bitumen would help but you would need to coat the walls up to dpc level as well.
that's if the outhouse has a dpc.