Raising level of concrete floor before tiling

[veryfluffy]

Hello -- I am looking for advice on the most reasonable way to raise the level of a floor to be tiled (probably with large natural slate tiles). It's a Victorian house, and we've just knocked together the kitchen, hall and dining room to give an area of about 25 sq m.

I'm lifting the old wood block floor, which is approx 33 mm high, and would like the new floor at about the same level -- a couple of mm lower won't matter though. The base is concrete, almost certainly original. It seems quite sound and very dry. There was some water penetration along one wall, where the old blocks did suffer a bit, but this problem has been sorted.

I'm estimating the the slate tiles and adhesive will give a height of about 15 to 18 mm or so. The question is how to get the extra 15mm. (We are not installing any underfloor heating.) My initial thought after reading the diy forums was to get a screed put on to give a nice solid base, but I wouldn't know who to get to do that, what it would cost, or if there are any disadvantages to that.

My other half, who is an engineering sort and a competent DIYer, wants to use a layer of the green flooring chipboard. We used that before in a utility room, 8 years ago, tiled with ceramic and waterproof grout, and I have to agree it's been brilliant. That floor is rock solid, although it's often getting very wet.

The option that seems to be popular here, though -- which I hadn't run into before anywhere -- is the concrete board. I like the sound of this generally. It would run to a couple of hundred pounds more than the green chipboard, which is obviously not much if it saves £££ worth of slate tiles from being ruined, but it's only 10 mm max and it's a bit harder to get hold of for DIY. I must admit that this project is already way over budget, so I'm not keen to spend more money than we need to. We're doing most of the work ourselves, so there is no question of suing anyone, just blaming ourselves if it goes wrong.

Helpful advice?

 

[Ian]

Good morning. You could use cement boards, hardie backer do one that is 12mm and with the adhesive used to stick it down this will give you 14/15mm total height, alternatively you could use a levelling compound but at that depth you will need 1 bag for every square metre, there won't be a great deal of difference in cost doing it either way.


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[Gazebo]

Good morning,

I would opt for the cement boards or even 12mm marmox boards if you can.

Avoid the chipboard at all costs, might have got away with it once but not best practice.

 

[veryfluffy]

Thanks -- it looks like the cement/tiling boards are the best bet. I also remembered that about 5 years ago there was torrential rain here, the drains outside couldn't cope, and it was running in under the door -- we ended up with a half inch of water in the kitchen. Even if that doesn't happen again for another 20 years, I'd rather not take the risk. The wood floor actually dried out fine (and it's been there for 100 years, so probably seen worse), but I suspect that "water resistant" chipboard might have a bit of trouble coping.

Next question is -- is there any major difference between the various brands? (Marmox, hardie, gaia?) I'm looking at c. £300 to do the room, and I really don't want to spend more than necessary, especially as this isn't about thermal insulation at all. I just want to be able to lay it down, put the outrageously expensive slate tiles over it, and have it last another 100 years if necessary. Do these boards have a life expectancy, or are they really a permanent solution?