Flagstones - depth of mortar bed

[richardf]

Hi Folks,

I am intending to take out some horrible parquet (sp?) flooring and replace it with some limestone flagstones. I have 40mm of depth available to me and can get limestones 'flags' from around 20mmm depth. I would have preferred the 2" thick reclaimed variety, but it is not an option.
My floor layer wants to put them on a sharp sand/cement mix and is talking about adding PVA to add strength - but I am concerned that the approx 20mm of bedding on top of existing concrete will not be strong enough. One option would be latex self levelling grout - but I'm a bit scared of the price!
Any suggestions would be most welcome
Thanks
Richard

 

[Nemesis]

Lime and sand?

 

[Andrew Bodenham]

What is the substrate that your new flooring is being bedded onto? I presume it's concrete, in which case a cement based bedding woud be compatible. "Strength" is nor really a problem here, as the bedding material will be acting in compression - all it has to do is sit between the substrate and the flagstone. The grouting between the stones will take care of any lateral forces.
I recently bedded some slate tiles onto an existing concrete floor screed using lime mortar, and that seems to have worked fine. The long setting time was an issue - next time I'll consider hydraulic lime rather than the cheaper hydrated.