The Brew Cabin

I am completely new to all this, so apologies right away!

I am looking to lay sandstone flags (2ft x 1.5ft x 1-1.5 inch) in my kitchen. The kitchen currently has a concrete base.

I have some questions!

I am looking to put underfloor heating (electric) under the flags, but am struggling to get a straight answer as to the best type to use, how effective it will be, and the best way to lay the flags.

So, now for the questions!

1. What am I best to lay the flags on (I was planning on sand & cement). Is this OK?

2. What mixture would I use, and would it be wet or dry?

3. I have been told to paint the back of the flags in PVA bond, or SPA bond. Is this a good idea?

4. I have been advised to use a 6mm cable type system, by Cozy Heat. Any advise/experience?

5. What do I use to point the flags, can I use the same mix?

6. I am planning on using impregnator (by HG I think) to seal the flags, is this a good idea?

Sorry for the questions. I am keen to get this right, and I am keen to do it myself, rather than get someone in!!

Cheers

Mark

Hi,

the usual spec for UFH with stone flags is to lay them on a bed of semi-dry mortar, around 10:1 with just enough water to make it damp. I'm not sure what the idea is of using PVA on the backs of the flags, unless some eejit thinks it would make the flags 'stick' to the mortar, which is not even necessary!
Movement joints are not normally required, unless this is a very large project.

As for the cable system, all I can advise is to follow the manufacturers instructions to the letter and it all usually works. Usually.

Point the flags with a stronger mortar, a Class II (say 4:1), and tool it smooth. Allow the flags to stand for at least a week before applying the HG Gunk, so that the moisture level in the bedding/jointing can stabilise, and then be prepared to rub, rub, rub to achieve the desired effect.

Good luck! :)

Thanks TonyMcC

I think the idea behind the bonding was 2 fold. Firstly to make it stick better, but also to waterproof? From what you say this sounds a bit like a pointless exercise?

Another question, if my room is 19 metres square, how much sand and cement will I need to order. Is there some sort of equation to allow me to estimate?

Also, when you mention 'Movement joints' what does this mean?

Last one, is there any particular tips to motaring, as I am worried I might stain the flags? Should the impregnating be done before or after the pointing?

As before, any help welcome

Cheers

Mark

There's no real need, or there should be any need, to make the floor waterproof. The concrete base is/should be waterproof, and the flags themselves, once properly laid, are as near as dammit waterproof, so forget the PVA - it's just an unnecessary expense.


So, quantities - this depends on bed thickness, which in turn depends on the flags you're planning to lay all a being a regular thickness....but, assuming you'll be using a bed that's an average of 35mm thick, then the equation you need is simply one for volume, ie, area multiplied by thickness, and then use the info on the Concretes and Mortars page to calculate your requirement in kg or 40kg bags or 1kg agg bags etc.

As a rough guide, I reckon you'll need summat like 150 kg of cement and 1200kg of grit sand, plus maybe 80kg of building sand for the jointing.

Next, movement joints. If you've only 19m2, it's unlikely you'll need one, but, for completeness, there's some detail on them on the Concrete page and on the Resin Bonded Aggs page.

And finally, the jointing. If you've no confidence in your ability to point the flags wityhout staining (see Mike's very long thread in The Craic) then you might want to use GeoFix or another polymeric sand. You can read more about these expensive products on the Alternative Jointing page.

And finally, just before I go to bed, leave the 'impregnating' until the very last, at least a week after laying, so that the mortar bedding has a chance to stabilise.

I'd be most interested to hear your experiences while laying this floor, as, I'm sure, would many readers of this forum, as UFH is becoming more and more popular and it's something I've only installed a few times myself. Your insights could be invaluable, as would any piccies you manage to take. :)

Thanks very much, your advice will be heeded and put into practice.

I will indeed let you know how I go on, and I am taking lots of pictures, so I will do my best to post some.

Keep up the great site, it is most valuable.

Cheers

Mark