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 ?

1. 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 ?

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

1. 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."

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.

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

Thanks, Simon.