Levelling a very damp cellar floor

27 Mar 2016
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United Kingdom
I've got a cellar approx 20ft x 6ft, with ceiling height of about 6ft. The house is Victorian and the cellar floor is made of bricks embedded edge downwards into the soil. There is no damp proof membrane in the cellar and the floor is permanently damp.

I wanted to level the floor, mainly because the soil and general crap gets dragged into the house every time I retrieve something from the cellar. So a few weeks ago I mixed up about 8 bags of Bostik Cemoplay Deep levelling compound:

This worked a treat, piece of p*ss to lay and looked great... for about 5 days. Then the levelling compound expanded and raised the screed in huge boils, some standing 7-8 inches off the original floor. These boils have now cracked so the floor is a mess of broken chunks. I know you're supposed to put expansion joints into solid floors, and I didn't bother, however we are not talking a bit of expansion, this was serious bulges all over the floor. I assume because the floor is permanently damp and the product I used is not suitable.

I'm prepared to have another go - was the issue with the type of product I used? Should I use a different levelling compound, or put an additive in? Or should I use an entirely different material, e.g. concrete? The requirements are: thin (I don't want to lose ceiling height because it is already a stoop), easy to level (hence levelling compound mixed up nice and runny), cheap (this is just a storage room) and to create a non-dusty solid surface (the purpose is to stop crap being dragged into the house).

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If the SLC was blown by damp pressure (not expansion) so soon after laying it then your only hope is to dig out and lay a membrane and concrete floor.
Be aware that this solution might (its only a possibility) force damp up the surrounding walls and create further problems.

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