Where the old kitchen's come out, me and the builders have dug out 1" quarry tiles and there's another inch or so of bedding sand/cement between tiles and concrete.
Concrete has no damp proof membrane it turns out, though is nice and dry.
Before laying new tiles, how should I screed it? I assume for 50mm, sand/cement is the stuff to use - but what mix? And is it worth PVA'ing the concrete or painting on a liquid DPC membrane? I'm going to use some paint on membrane in the wetroom shower anyway.
50mm is quite thin for a semi-dry screed ... If it were me I'd use a fibre reinforced screed .... you can own mix, a 4:1 mix would be OK, buy buying bags of the fibres to add to the mix ... FIBRIN is one well know make.
If it is not a huge area you could use liquid self leveling screed, but pricey if a big area.
I would go with a paint on DPC just to be sure, and then a fairly strong mix (4:1) sharp sand / cement screed to make up the 50mm. Possibly with a latex self levelling to get a nice finish on the last couple of mm (depends on how neat your screeding turns out).
John Rumm coughed up some electrons that declared:
Thanks John, Rick.
Now that the builders have cut the old bedding off, back to the concrete, I see that I have only about 35mm depth - bedding was less thick than I thought.
Most of it is very stable except for a few patches round the edges. Do you reckon I'll still be OK with sand/cement on top of a painted membrane or should I be looking at something like:
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It looks good but at 85 per 25l it's not cheap.
The final finish isn't critical - it's going to get more floor tiles (stone or ceramic) stuck on, so mostly flat and stable is the main aim.
That's too thin for unmodified cement/sand screed, so yes, you need to polymer modify it (ought to be able to get SBR a bit cheaper than =A385/25l if you shop around), or else you are in range of the higher- build 'self-levellers' (again, at a price).
would stick to a chemical dpm, the self-levelling manufacturers (not that different) get very fussy about which of their products can be used over chemical dpms.
snipped-for-privacy@mailbolt.com coughed up some electrons that declared:
floor areas are fairly small and I could set some battens[1] in at intervals to use as a levelling guide (especially for wetroom, where I need a carefully set fall in the right directions).
And admix+cement as a primer. I'll phone them nearer the time and enquire about compatible tanking paints, but given the current quarry tiles were a bitch to shift and them were stuck on with some rough old sand/cement mix with voids everywhere, I don't see this job as having serious problems - just trying to avoid silly fubars...
I suspect tanking paints are overkill[2], except in the wetroom, where it would definitely be a good idea to prevent water seepage getting into the building structure.
[2] In the bathroom and bedroom, despite not having a DPC under the floor slab, we've never had damp and I doubt we ever will as the house is on a hill and there's a lot of hardcore underneath. However, if it's cheap and easy, might as well. I'm not expecting to add tanking to the rest of the screeded floors prior to laying tiles. If I stick any wood down I'll take the manufacturer's advice on membranes.
I would say that is too thin for a screed over something flexible. (i.e. over an insulation board). However, onto a concrete base I can't see you having a problem with a thinner screed.
I used one of the other mixers (the £5 job) for mixing up two-part felxible tile cement. I didn't use the SDS, I used a Bosch "blue" drill with a two-speed gearbox running at 300rpm. It seemed to do a decent job without any problems.
They're for the Makita mixers I think, or something equally beefy. Plaster is worse in some ways because it can suddenly thicken and put a hell of a strain on the motor
If you're talking about the 2 part latex screed, the solids don't absorb the liquid as cement would, so I don't think thorough mixing is crucial, but "screed" can mean pretty much anything.
stuart noble coughed up some electrons that declared:
I was thinking mostly about sand/cement + admix. I would have chucked this stuff in a regular mixer, but the admix instructions on at least one admix say not to do that as too much air gets entrained.
When I do the latex cement (water mix type from Wickes), I stick the required 5L in a big mixing bucket, tip in the bag of powder and just use a medium sized paddle in my 18V combi drill. Works very well I find. (I do plaster in the same way). It would not cope with large mixes of mortar though.
Been looking at the grand budget spreadsheet today and decided time for extravagance needs to be over or costs will go the way of a government contract!
Think I'll get a paddle for the SDS on the basis that it'll mix plaster and tile gloop (need lots of both and it's a cheap Aldi grunt drill so I don't mind abusing it).
If it can cope with cement screed, well and good, otherwise I'll mix by hand, the old fashioned way... If nothing else, it'll turn the dry mix over OK which is half the work...
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