On 28 Dec, 13:09, stuart noble wrote:
Tim S wrote:
Hi again,

Quick recap - got to make up a floor with about 25-35mm screed. The current
surface is solid, but it's a bit of a "farmer's concrete" special, meaning
it was made with small round pebbles and in a few patches the pebbles are
not well attached. ie they're attached but it doesn't take much to loosen
them.

I suspect if we go digging the less well attached pebbles out we'll get to
earth fairly quickly. No vapour barrier either. I should add, that the
floor's been fine under quarry tiles so I don't see any need to go
replacing it - I just want to make sure the screed gets a good bond.

How does this sound:

1) Soak the floor in a stabiliser.

2) Prime the floor with SBR/cement slurry

3) Screed with 4:1 sand/cement + SBR

4) Paint damp proof membrane on top.

5) Finish (ceramic tile or engineered wood depending on location)

?

=====

What would be good for 1): Liquid SBR? I think PVA will bite the dust due to
the fact there's no vapour barrier.

Also, any good recommendations of a paint on DPC membrane?

Many thanks

Tim

If there's no damp, you shouldn't need SBR at all, but it would be an
extra precaution, at least for the stabiliser.
SBR doesn't mix well with sand cement mortars. It has a tendency to go
its own way and leech out if you leave it standing for any length of
time. Pva mixes in better and the mortar is easier to use because of that.
You could just use sand/cement for the screed and paint SBR on when it's
dry. It's penetrates like crazy, which is better than creating a film on
the surface

ISTR that SBR mixes can be made (as long as enough SBR used) to be
waterproof in themselves - that's one of it's main uses isn't it? I
used it to construct two hearths that were previously damp being laid
on earth - worked well enough for me...

cheers
jim