We're putting ceramic tiles down in the kitchen.
The previous two layers of vinyl tiles are up to reveal a reasonably smooth (though sloping- 2cm lower at one end than the other over a 4m span) concrete floor covered in a thin layer of black sticky gunk. I suspect this is an attempt at damp proofing using bitumen. The house is around 100 years old and the concrete floor is probably original, and probably has no other damn proofing.
I've cleaned it up and put a coat of PVA down to take away the stickiness so we can actually walk around in there for the moment. Now I'm trying to decide what to do next.
Some sites say the bitumen should be completely removed before laying tiles, while others say it's there to stop damp and shouldn't be removed. We're probably not going to put under-tile heating in, which seems to be what a lot of the sites advocating removal are assuming (fairly obvious; the heat mats may melt the bitumen.)
So there's two questions; first, do we need to remove the bitumen before using tile adhesive? If so, how? and should it be replaced with something? Second, what are people's opinions on whether I should get rid of the 2cm fall or not? The floor looks smooth enough to tile on; it was good enough for the vinyl afterall, and the fall is away from the dining room door which may be an advantage in the event of a spill. The only thing that concerns me is whether it will give me any problems when I come to install kitchen units- most probably from Ikea. I'm hoping the telescopic legs on the units will mean it's not a problem but it's good to check.
-- Dr. Craig Graham, Software Engineer Advanced Analysis and Integration Limited, UK.