Tiling a floor-Do I need decoupling? Primer? Self levelling?

[RRRRRR]

Hi- I have a kitchen floor to tile- 25sq. m.
Two areas are newly screeded on jabfloor insulation where rotten old wooden floor was, and two areas original cement where quarry tiles were. Now for the questions....
1/. The new screed is solid, but powdery on top with some loose sharp sand stones as we've been walking on it on boards for almost a year. I guess I must vacuum then seal it. It has a DPM and is dry, so can I use PVA or should I use a specialist product?
2/. Is self levelling essential? In the past I've build up adhesive and a spirit level on each tile.
3/. If self levelling is essential, can I do a 3 soft sand/ 1 cement/ 4 water/ 1PVA to save money, or any recommendations of make/ type?
4/. I believe I need to encourage the SLC to go to low spots etc. as it won't do ALL the work for me. How do I mark where the low/high spots are when I push the SLC around?
5/. I guess I need a decoupling membrane as the old floor joins with the new in several places, but could a flexible adhesive with flexible grout take the place of decoupling matting?
6/. If I need the matting, is there a quicker way than doing primer, then SLC, then adhesive for matting, then adhesive for tiles, as I only have about 50 years of life left?
Any help very gratefully received. Thanks.

 

[Richard C]

Two areas are newly screeded on jabfloor insulation where rotten old wooden floor was, and two areas original cement where quarry tiles

Is the screed over the jabfloor insulation a floating floor?

For unglazed quarry tiles, you need an SBR bonding primer; glazed tiles can be more difficult & really need an SBR slurry bonding coat.

1/. The new screed is solid, but powdery on top with some loose sharp sand stones as we've been walking on it on boards for almost a year. I guess I must vacuum then seal it. It has a DPM and is dry, so can I use PVA or should I use a specialist product?

DO NOT use standard PVA on any tile base, it remains water soluble & will reactivate if it gets wet; use an acrylic/SBR tile primer/bonding coat.

2/. Is self levelling essential? In the past I've build up adhesive and a spirit level on each tile.

It’s best to have the tile base as flat as possible. Building up with adhesive can be done but has its limits; normally a solid bed would be 2-6mm but can be up to 12mm in small localised areas. With large format tiles a flat base is even more important or, if you’re inexperienced, it’ll be all over the place even with careful use of a spirit level. As you have several different requirements an appropriate SLC may be the answer to them all.

3/. If self levelling is essential, can I do a 3 soft sand/ 1 cement/ 4 water/ 1PVA to save money, or any recommendations of make/ type?

No, you can’t lay a conventional sand/cement screed less than around 40mm thick, it won’t last 5 minutes & will take 1 day/mm to cure & dry out before you can tile it. You need a specialist SLC/screed something like this;
http://www.ardex.co.uk/smoothing_levelling.asp

4/. I believe I need to encourage the SLC to go to low spots etc. as it won't do ALL the work for me. How do I mark where the low/high spots are when I push the SLC around?

It’s called an SLC & when mixed correctly, will find its own level with little effort or perhaps some encouragement using a sponge float.

5/. I guess I need a decoupling membrane as the old floor joins with the new in several places, but could a flexible adhesive with flexible grout take the place of decoupling matting?

Can you answer as above; is this a new floating floor? If it is or the new floor has different expansion characteristics/rates then you could have more of a problem. If it’s old/new flooring of the same type you may need a decoupling membrane but, unfortunately, a flexible addy & grout will not take the place of one; you may, however, get away with using a latex based SLC & tiling over that but consult the manufacturer. You will definitely need to use a flexy addy/grout when tiling over an SLC

6/. If I need the matting, is there a quicker way than doing primer, then SLC, then adhesive for matting, then adhesive for tiles, as I only have about 50 years of life left?

Unfortunately there are no shortcuts if you want it to last

 

[RRRRRR]

Hi Richard C-
I can't thank you enough for such a fantastically helpful reply. It gives me faith in human-kind again! I shall read and re-read until its all sunk into my rapidly slowing brain. As for your question, 'Is it a floating floor?' I'm not a specialist, but the new floor was dug down to solid chalk with no hardcore as Mr. Building Control said it was solid, DPM sheet, then concreted, 100mm Jabfloor then 75mm-plus screed. The DPM comes up behind the skirting. Whether that's a floating floor I'm not sure. Oh, and the tiles I'm planning on are porcelain I think (colour all the way through).

Thanks again, another Richard

 

[Richard C]

Whether that's a floating floor I'm not sure.

No you’re OK; you haven’t got a floating floor. Due to their construction the top part can move independently from the slab & for obvious reasons can be difficult to tile. How long has the base been down? You need to allow 1 day per mm thickness for the screed to dry before over tiling!

As it’s not an extension it shouldn’t move so no expansion joint should be necessary but I would use go with a decoupling membrane or check out if a latex SLC would be sufficient. I’ve also noticed that BAL have some new SLC’s in their range one of which may be suitable;
http://www.bal-adhesives.co.uk/products
I haven’t checked them out yet but if you contact BAL they will advise.

Oh, and the tiles I'm planning on are porcelain I think (colour all the way through).

Some porcelain tiles can be susceptible to staining & need sealing before laying & even re-sealed before grouting, some come ready sealed; use any addy colour appropriate for your tile colour. Others are fine & can be laid as they are so check which you have with your stockiest or do a water test. You will need a wet diamond wheel cutter, porcs can be difficult when using a manual cutter.

Floor tiles must be laid on a solid adhesive bed, use either a thick bed solid bed trowel or a large format trowel.