Laying Flagstones evenly

Hello All,

We are having difficulty laying flagstones evenly because these flagstones are a natural, limestone product and the thickness varies by up to 3mm. We are using a builder who is very good in many respects but, maybe, not an expert in this area.

The flagstones are part of a heated/warmed floor, and they need to be laid on flexible adhesive. Our builder knows about varying the amount of adhesive to allow for variations in thickness. I feel that the height variation should be within about 1 - 2 mm. Do you think that this is reasonable ?

We are using a wider grout, about 15mm. to make the height variation less obvious.

Has anyone any views/experience on this ?

All comments welcome.

John N.

Reply to
John Nolan
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Not at all reasonable, even if the flags were exactly uniform.

if the thicknesses vary by 3mm, it's impossible to get them to within 1 -

2mm.

What do you mean by 'flexible adhesive'? - are you using flags as floor tiles? - if you are, and they are indeed natural stone, I would imagine that they would look better naturally uneven than unnaturally perfectly flat.

Reply to
Phil L

varies

maybe,

variation

within 1 -

imagine that

Ah but they won't be able to push the tea trolley over them without spilling the tea

AWEM

Reply to
Andrew Mawson

Get shut of the builder or have someone else fit the tiles. It is possible to fit them perfectly level using what you describe. You do not need to leave 15mm for a gap or have the floor uneven.

Reply to
Clive

Why? You just need more adhesive under the thinner ones.

It rather depends on the surface finish of the flags. If they go up and down by 10mm (as the ones in our last house did), it doesn't make sense to fuss about the height of one edge. If they are riven slate and smooth to .1mm, it's rather a different story.

Reply to
Martin Bonner

I see, so if you lay ten flags and then find one that is thicker than all those already down, how much adhesive do you put under it to get it lower?

Reply to
Phil L

You dont. It is too late then. You sort them out into the varying thicknesses before work starts, then put the thickest ones down first, then, in theory, it is possible to get them level. If the OP's builder hasnt done that, or allowed a suitably thick bed of cement to lay them, then they will never be level. If I was the OP, I'd insist that they were taken up and got level. Alan.

Reply to
A.Lee
[..]

I think that Dave Symes ..'Grumpy Dave'(?).. may have some real knowledge in this area. He may be around in the argonet groups somewhere, eg a.a.voyager or a.a.misc - but he's also seems to be around a lot in zfc-chat..

You could try to raise him there as well, John. I'm sure he would have some helpful comments.. :))

Bill ZFC

Reply to
Bill (Adopt)

I recently laid my own traverine floor. The stones arrived smooth on one face (top) and varying in thickness only very little (+-1mm). I too had to use a flexible adhesive, as they were going onto the screed of a UFH.

The key is the flatness of the screed. It may look flat, but in fact undulate over quite long distances. This means that tiles in the bottom of the dips might be 3mm lower that those on the crests. I wish that I had put down self-leveling, but I didn't. It meant that I had to fill the dips with very expensive adhesive, and sometimes put in little wooden pegs to stop the tiles sinking before the adhesive set. It was quite fiddly.

In the end it isn't perfect (2mm in some places), but as my first (last?) attempt I'm content. However if I had paid someone, I would expect better than I managed.

R.

Reply to
TheOldFellow

Hello Bill, Dave, Phil, Alan and TheOldFellow, (from various NGs)

Many thanks for your responses. Sorry I didn't say it before.

I was given a tip that someone, with potentially useful information, might lurking on some other NGs as above. if you are coming in on this thread, for the first time, and want to know what has gone on before, I can fill you in Yes, I did have some DIY feedback. But, basically, it didn't add to what we knew already.

I hope that I'm not breaking any netiquette rules by writing a piece, for anyone that is interested, that brings together my own experiences, for what they are worth, and those of other contributors.

Basically, you have to find the thickest flag, lay that, and then build up the adhesive under thinner ones, to get the same level.

That might seem obvious. But it is not so easy to do when the sticky labels with the thickness measurement keep coming off and you are laying a special pattern of flags of different sizes. The thickest flag may not be the first to be laid !!

If, as we have, your flags are different sizes in plan, as well as thickness, then it is a bit more complicated. I would suggest that the pattern is laid out, sufficient to include the thickest flagstone. If, from experience, you know how thin the thinnest layer of adhesive can be, then you put spacers under the thickest flagstone to mimick the thickness (or thinness) of that layer of adhesive. You then lay the thinner flagstones level with that thickest one. Then, when its turn comes take up the thickest one and lay it properly.

This all may seem obvious, when I've explained it, but wisdom in hindsite is a wonderful thing !

TheOldFellow - uk.d-i-y - said he used little wooden pegs to stop the tiles sinking before the adhesive set. Yes, I had thought the same sort of thing. If I had been laying them myself, I might have used small pieces of slate of different thincknesses for the spacers. Of which we have an abundance.

We didn't have the problems of a slightly undulating screed surface. If the wavelength of undulations were sufficiently long horizontally and sufficiently small vertically, I would not have thought it would matter. As for difference in height of adjacent flags, I have felt an error of up to 2 mm. was reasonable. Our builder suggested a wider grout, about 15 mm. to "mask" this. But, with different sizes of flags, this brings other problems of different grout widths - see below - unless you cut each flag to suit !!

So, we are on a learning curve, but are getting there. We have lost some flags in the process :-( There are other costs, like thicker layers of adhesive being needed. We averaged 3 sq.m. per 20 kg. bag, when we were advised that the spread should be 5 - 6 sq.m. per 20 kg. bag.

Another cost is the amount of grout required and flag cutting. Most of the flags, except the smallest, have been cut to fit assuming zero grout thickness. With different flag sizes this causes problems. It is impossible to get a constant grout width without cutting every flag. This takes considerably longer. So there are extra time costs, as well. For us, it is probably a "one-off", in a lifetime. We have about 200 - 250 flagstones to lay to get half way !

Our flags have nominal sizes in mm of 300 x 300, 600 x 300, 600 x 600 and

600 x 900. Obviously, these last, being much heavier, were much more difficult and also much more expensive if you get it wrong.

Finally, because we wanted coloured grout - brown - we have had to go to a company called Mapei as Bal seem not to make it anymore. We were warned by the Mapei suppliers that we should use white adhesive as the colour of ordinary grey could come through our slightly porous marble flags. Our builder, who normally uses Evostik cement based, polymer modified adhesive was sure that this would not happen with our flags, particularly as they are about 23 mm. thick. But, doubt having been sown in our minds, we felt we had no choice but not to take the risk. After all, we do not have the choice to get it wrong. The Mapei adhesive is much more expensive.

No one seems to be quite sure about this point of discoloration. Some felt it could happen with thin travertine, others felt the problem was sometimes translucency. I even managed to extract an informal and free opinion from the Building Research Establishment. They felt that it could happen !!

For both adhesive and grout for UFH, you need flexible material. We are using Mapei Kerqquick white with liquied Latex Plus, for the adhesive and Ultracolour grout.

John N.

Reply to
John Nolan

Traditionally they were laid on soft sand, which has enough clay in it to set stiffish. Or very weak dry mortar i.e.sand plus a bit of lime. Quite easy then to get them perfectly flat. Wet mortar no good as it moves about, or they sink, etc.

Reply to
jacob

I used wet mortar Packed with gravel, bits of hardcore and anything And not weak either. I tried the weak sand crap and it simply compacted away from the flags and left them rocking.

In th end I screwed my eyes up and pretended they were just very large and odd shaped bricks, and laid them accordingly.Just tapped them down to a string line.

If th mortar is too dry, they wont tap, if its too wet, they slump. Ther is a happy medium.

Sand works with concrete slabs of exact thickness, where you can rake a bed level and just plomp the buggers down, but its totally useless for variable thickness sandstone.

Reply to
The Natural Philosopher

And none of this works with UFH, where you need a good thermal bond as well as a flexible connection to take up the differential expansion.

R.

Reply to
TheOldFellow

Then you can just pack them out as you go surely

Reply to
Stuart Noble

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