Howto fix crappy damp mortar fillet?

[Twisyt]

Hi All,

I am redoing my kitchen - just pulled up the old laminate floor and found this underneath.

Kitchen damp

• Twisyt
• 22 Nov 2010
• 2

Looks like previous 'builder' owner forgot about a DPC

The main concrete slab is dry but it looks like the previous owner put down ~10mm mortar on top of earth when he redid the back door and did noting to stop moisture wicking though into the floor.

I dont have any real idea what the best way is to get this dry. I appreciate any ideas/suggestions/tips.

The best I can think of is to chisel the area out to the depth of the original slab, prime the join with waterproof PVA and infill concrete with a waterproofer (
just got this no nonsence pink admixture. I am worried this may not be enough in terms of priming the join or if I would need a DPC too?

As it is just a small area I was wondering if there was some kind of impermeable product I could use rather than concrete.

My plan was to level the floor with Wickes fibre reinforced latex levelling compound before tiling the floor.

Now I have searched the forum I see that latex based stuff may be weak - I don't know if this would be a problem under tiles and if I should go for something like f ball stopgap 100. I live literally next to a Wickes which sways m buying choices a lot

The whole kitchen is 2m x 4.3m and difference between high and low point is about 10mm.

 

[mac391]

Could be a number of things !!

First, it might not be damp/wet... it's possibly just a different mix thats had too much cement added and looks a different colour. Also, most concrete floors should have an expansion gap around the perimeter, maybe the gap has been filled in more recently ? a bit hard to tell..

Did you mean 100mm mortar as opposed to 10mm ?

Also, if that is a relatively new back door and fitted correctly, its unlikely to be moisture.

 

[Twisyt]

Thanks for the reply.
It is certainly damp coming through the mortar. It was wicking through into the laminate floor and there was an earthy damp smell when I pulled it up.
Now it has been exposed for a few days it has dried out and changed colour.

I did mean 10mm, maybe 20mm - most of the work done by the previous owner has been a bit dodgy. There is no expansion gap on the long sides of the room, I think the single skin brick walls are actually sitting on the slab.

 

[Twisyt]

There are actually slates underneath.
The main slab of concrete appears to be about 30mm thick concrete on tarred paper.

Working purely on guess work I primed with waterproof PVA and, put down a little patch of DPM, primed again, then filled in with 1:1:1:0.5 concrete, sand, PVA, water.

Seemed to work.