As most of you know, I have a very crappy front room floor, half of which
is "screeded" with a very weak mix.

A few weeks ago I soaked 10l of SBR mixed with 30l of water into the floor
until it could take no more (20m2).

Yesterday, I was patch-screeding to fill in the deeper holes where I'd
removed loose screed. I had to chisel a little bit more out to clean up the
edge of a hole, so I took the chance to see what the SBR had done.

Result - on a 1/2" thick lump 3" back from the edge, there was a strong SBR
film on the top and the rest of the lump was consistently tough all the way
through. I don't think much SBR had made it to the concrete below, but the
previously friable screed is now pretty solid. Took a reasonable amount of
SDS effort to shift it. Not as much as a strong screed but a lot more than
would have previously been required.

I'm more than happy pouring scunge on to of that lot. I shall do a test pour
of a small amount to check Stopgap 900 adhesion to the SBR film (it's not
something F Ball have tested) but as 900 is an acrylic mix, I don't expect
any problems.

I also mentioned previously that the humidity had dropped sharply in the
room after the SBR set (we know there is no DPM). I did a very crude
measurement the other day. Room humidity was 45% (Oregon weather meter). I
put the Oregon on the floor and covered with an upturned metal bowl
overnight. In the morning, max humidity under the bowl had registered 65%.

That would seem to indicate that the SBR had not blocked the vapour flow but
has probably slowed it considerably. I only have one Oregon, so for all I
know the room humidity might have gone up overnight too, I would have
expected a seriously damp floor to register 80% at least.

Cheers

Tim