SBR saves the day

[Tim S]

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

[Stuart Noble]

The main feature of SBR is its small molecule size compared to pva, so it mimics the behaviour of a solvent based product. The slight downside is that in a mortar mix the bulk of it tends to take off on its own into the substrate, but that's beneficial in a screed . Difficult to get off your hands too, as I'm sure you've discovered by now :-)

[Steve Walker]

Sounds very handy, must buy some - is this the stuff?

[Tim S]

Stuart Noble coughed up some electrons that declared:

That explains a lot.

Yes - I of course patched with an SBR 4:1 screed as it's only 15mm thick.

SS wire scourers work!

In fact scouring the float and trowels is the only way to clean the sodding stuff off. I have a stainless metal bowl that I use for the cement/SBR slurry and that has a layer of SBR+cement that won't come off with any amount of scrubbing and banging - so it has provably excellent adhesion.

It *is* the new PVA for me :)

BTW - What is it like regarding adhesion to it by other things, say a few weeks after it's dried?

It was slightly tacky for a week, but not any more. I was wondering to brush on another thing layer the day before pouring the Stopgap...

Cheers

Tim

[Tim S]

Steve Walker coughed up some electrons that declared:

Yes, but that's an expensive way of buying it (but no worse than walking into Travis Perkins - they *will* ass rape you.

If I can plan forward enough and need more than 5l, I buy from

the average price is 12-15 quid - but delivery varies.

[Stuart Noble]

It's actually classed as a synthetic rubber I think, although it would be at the non-flexible end of the spectrum.

Dunno. It certainly sticks to itself and takes paint well. I use it for shallow repairs to mortar where thin coats wouldn't normally take. I keep meaning to cast a garden trough with it to see how flexible it really is.

[Appin]

The message from Tim S contains these words:

I seem to have escaped that fate over the last 30 years.

Often the cheapest place around here to get sheet goods on site. And they'll deliver free -- even 100 miles away from the depot, provided you're an account holder. Used discerningly, I've found them OK.