floor screed again

[sm_jamieson]

I've now surveyed the floor area I have to screed, and it turns out
most of it is above 50-60mm, so unmodified screed would be OK there.
Only one area about 6m^2 is down to 30mm, and I'd use the half-
strength SBR mix there, i.e. SBR = cement / 10 (total liquid approx
20kg for 50kg cement).
I have some glass fibres from a previous fibre-cement project that I
could use in places.

Total volume is 1.8m^3 so SBR for all this would cost a fortune and be
over-engineered.

1. I've seen mixes of sharp sand to cement 1:3 and 1:4. Any reason to
make it stronger than 1:4 ? This has some bearing on the amount of
SBR. Also, what ratio for the unmodified area ?

2. I will use some SBR to stabilize the base before screeding. Would
it help to also use SBR in the bonding slurry, even if it's not in the
screed ?

3. Where interfacing between an SBR section and non-SBR, anything to
watch out for ?

3. If I put some glass fibres in the mix (perhaps over one area where
2 slabs join), how should the mix be modified to accomodate.

All this seems long-winded, but its what DIYers have to do to make of
for experience :-)

Cheers,
Simon.

[Jim K]

did you consider good ole PVA?

"Q2. What is the minimum depth for bonded screed?
A. Bonded screed can go to a 10mm in thickness screed, as long as it
is bonded chemically (epoxy) or laid with SBR/PVA bond and SBR/PVA
modified screed mix. If the screed is to be cement bonded then 30mm
should be the minimum depth."

http://www.adhf.co.uk/html/body_screed_faq.html

(as googled - no association etc etc)

Jim K

[sm_jamieson]

I was put off it by the previous discussions. Its not actually that
much cheaper, about 60 quid for 25 litres SBR, 50 quid for PVA.

>
> "Q2.  What is the minimum depth for bonded screed?
> A.   Bonded screed can go to a 10mm in thickness screed, as long as it
> is bonded chemically (epoxy) or laid with SBR/PVA bond and SBR/PVA
> modified screed mix. If the screed is to be cement bonded then 30mm
> should be the minimum depth."
>
> http://www.adhf.co.uk/html/body_screed_faq.html
>

So you need SBA in the screed and the slurry for it to be effective
bonding the two it would appear.

Thanks,
Simon.