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