30 sq m of big slate floor tiles: preparation+ laying!

I am getting very confused and stressed, and we haven't even started. I know this job will be difficult (and may get a tiler in to lay and grout eventually), but in the meantime I would love some advice on at least preparing the floor properly for the project.

Room is 30 sq m. Floor is concrete, probably at least 100 years old, now nice and dry after sorting outside drainage, but very unlikely to have form of DPM. Mostly level, two areas of about 1 sq m that seem a bit low (2-3 mm lowest), and nicks of 1-2 mm but not bigger than 4 mm across.

Floor was (stupidly due to bad advice!) coated with Aquaprufe, which failed to stick in most places, except for on areas where concrete was replaced recently. Everything loose has now been removed, and Construction Chemicals advised that the firmly adhered stuff could be primed with SBR and tiled over. Some products seem to demand total removal of any bitumen though, so this is confusing.

Next I am guessing we need to seal the floor with SBR (diluted 1/3? 1/4?).

Will use self-levelling compound in areas that need it. Easiest for me to get is Norcros Pro 50, but that looks like the fibre-based kind that can only be used with a DPM. These aren't big or deep areas that need filling, so what is easiest to use that will do the job?

The tiles I'd like to use are 900 x 600 gauged slate -- ie quite flat on the bottom side, apparently. Big and heavy, but less grouting. I am aiming for a traditional, rusticky-cottage effect (this is for the kitchen-breakfast room), so mirror-flat isn't necessary.

MrFluffy is convinced we're capable of laying the tiles ourselves. He's done ordinary ceramic floor tiles, and we did small slates on the fireplace hearth. Stressful but successful! They both look great, and no problems, but much smaller jobs.

If we lay them, it will take a while, but is there any problems other than the size and weight of these? I understand I should prime the surface with SBR again just before laying. Then -- adhesive: I don't want rapid set. What's recommended for big slate tiles on concrete? I reckon I do need a thick bed, at least 6 mm. For 30 sq metres I think that means around 20 bags, and it seems around £20 a bag! Ouch! Trowel: 10mm or 20mm?

Seal well before grouting, I know too.

Anyone done anything similar to this? Help?!

the bigger the tile the more level you need your floor BUT 1-2mm nicks you can ignore, and 2-3mm isnt too big a deal given the kind of slate your talking about. best way to check isnt to concentrate on small nicks but to get a long straight edge, lay it on the floor and see how flat it is, peaks and troughs will need to be worked around or levelled.

The best advice i can give you is to pick an addy manufacturer and contact their tech advice line, then use them for self leveller, primer, addy and grout. i sell granfix most of the time and if contacted they will give you written details for your installation and the backup if you need it. I'll happily contact them for you if you wish, but this would draw you toward using granfix products either from me or a local supplier. These days we always use a polymer based adhesive (single part flexi) as it gives better adhesion even on stable floors.

900x600 slate is harder to lay but not impossible - its harder if your working around large variations in subfloor level, you need a solid bed trowel to give a deep bed of addy, slow set is a good choice for a diy'er if you can take your time. you'll need 2 people to lift these into position. Clean the addy off as you go with a wet cloth and seal with LTP or Lithofin before and after grouting.

You will need a decent cutter, but on that size of tile an angle grinder with a diamond dry cut blade can be easier if you can cope with the mess.

You do have to weigh up your stress factor against getting a tiler in, if you take your time i'm sure you can do a great job, but reading your post you mention that slate on the fireplace was stressful, if so might be worth getting a tiler

on a sales note, i can supply the adhesive at far less than £20 a bag, and if you happy for me to quote for the slate i can get you a great price on that too - let me know either by personal message or direct email.

Just one thing, self leveling compound, my mate tried it on a small 9'x9' conservatory and got it totally wrong as he had never done it before, and ended up ripping it all up.

You need to talk to the adhesive manufacturers about a floor without a membrane as I've seen lots of problems with them. The fact that the Aquaprufe didn't stick should set alarm bells ringing.

joe-90 said:

You need to talk to the adhesive manufacturers about a floor without a membrane as I've seen lots of problems with them. The fact that the Aquaprufe didn't stick should set alarm bells ringing.

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That mainly seems to be because it wasn't dilute-primed first, according to instructions, just painted on neat, and the surface was a bit sandy. It's cleaned now -- except for where it won't budge. The floor was previously woodblocks, the bitumen dried out long ago, and 90% of the blocks were absolutely dry and unrotted after 100 years. Main thing seems to be priming with SBR first.

libby lou lou: thanks for warning on self-levelling. Everyone seems to just say "slap down some SLC" like it's easy=peasy and straightforward!

tpt: thanks for that, had a look at your website, might be in touch!

the main thing with self levelling is that it does need some help, and some dont expect that. You need to pour it and then trowel it to roughly the right place, then the 'self' bit finds its own level.