Tiling onto a concrete slab without a DPC

[MadAlicesDad]

The outhouse/ extension refurb moves on slowly - next job is tiling the floor. I've lifted the old carpet tiles to reveal a nominally sound looking concrete slab, a bit of efflorescence and a smell of damp. There is no DPC and the rubber backed tiles have locked the dampness in - after a day the floor seem quite dry and the smell has gone. However there is one area in the middle of the building next to the internal party wall which won't dry, I suspect due to the very high ground water level with the current amount of rainfall.
I'm assuming it's unwise to ignore it and lay tiles over it especially whilst damp and in an ideal world I'd dig up the concrete, put in a DPC and insulation and lay a new slab. This is not possible, so I'm looking for a compromise, noting that this is an outhouse, not a living area, so I'm not after a 100% fix.

My initial thoughts are:
a) Tank it with a couple of coats of PVA/cement mix, either total floor or just localised to the damp spot; that's how I stopped my garage inspection pit from becoming a swimming pool.
b) Use a waterproof cement/adhesive that can form a DPC over the slab.
c) Because water resistant adhesive is not waterproof (ie it is porous but holds together when damp) can I just ignore the damp spot and tile over it with a water resistant adhesive that allows the damp to escape? (I'm sure the answer to this will be 'no' but there's no harm in asking!)

If it makes any difference, the room is ventilated (trickle vents in windows) and when complete it will be heated.
Sorry for the long post, but any help and advice on what I should do will be gratefully received.
Cheers,
Mike

 

[tictic]

with no DPM you will have problems if you do fix tiles..

have you thought about Altro flooring,i did one similair a few years back.
in a bathroom with no DPM,contacted F Ball..

we used a 2 coat surface membrane(red in colour) first coat across the room second up the room,primed the floor first cant remeber the name tho..
have look at their webpage,i cant remeber the codes(well numbers) thats what they use instead of names..think it was stopgap 65 or 75 i think??..
dont know if you can fix tile adhesive to it or notwell you should i think because you will put a 2 part latex over it proir to any adhesive,worth a punt having a look or give their tech guys a call..

 

[tictic]

http://www.f-ball.co.uk/product_detail.asp?product=F75&catID=damp

found it...