best preparation for over laying 20-40mm stone over suspended subfloor

[jonnyc]

I have quoted for a job where the antique reclaimed marble will vary between 20 to 40mm.
bedding marble on a solid substrate is no problem but this floor will be laid over a suspended subfllor in an old manor house.
Room size is approx 100.00 sq mts.
I cannot fix marble over ditra on top of plywood because they will only allow max 10mm bed regardless of how thick the tile is.
It was too late in the day today to contact hardibacker but does anyone know the max thickness of bedding material over 12mm boards or is there a better method.
I am assuming that the subfloor will have minimum 18mm plywood or more, supported under all sides by noggins/ joists

 

[Concrete guy]

Are the tiles a consistent thickness or do they vary from 20mm at one end to 40mm at the other like a split slate?

 

[Spud]

Jonny does the floor have brick piers built under neath to support the joists ? if not how wide are the joist spans

 

[jonnyc]

Are the tiles a consistent thickness or do they vary from 20mm at one end to 40mm at the other like a split slate?

tiles vary between 20 and 40mm thick.the reclaimed floor is black/white chequerboard.
i have no problem with bedding them
i think that the white might be average 20 mm and the black 40mm.
what i need to find is a sub floor prep that allows for bed depth variance.
this is a very prestigious project in a very fine period property and there may not be a guaranteed method of fixing .
i have had this before on similar projects some yeras ago but maybe there are new options I am not awrae of

 

[jonnyc]

Jonny does the floor have brick piers built under neath to support the joists ? if not how wide are the joist spans

gary . to be honest i have very little info at present.
i had a fixing enquiry a few weeks ago recommended by a stone shop .
i put some basic figures together and highlighted potential problems with sub floor prep but it would seem that the project is gathering pace
the property is a classic fine country house of the highest order,
my initial dealings have been with the new owner and i dont think he understands the importance of joist widths etcc.
but it does seem that this floor could happen

 

[Concrete guy]

I did a similar job in large house in Purley some years ago. The product there was split slate 600 x 400 and the varience in thickness was a similar amount.

I glued and screwed Aquapanel cement board to the floor and taped the joints, but this was back when you could buy Aquapanel in 2400 x 1200 sheets, so that kind of ages me a bit.

I sorted the tiles into batches of appropriate thickness and in areas where 20mm edges were meeting 40mm edges I used extra pieces of aquapanel glued and screwed to make up large discrepancies in tile thickness.

I bulked up the rapidset adhesive with sand. I think it was S16 and Ardion 90 plus sand. The whole thing was very rigid. But it was supported on brick piers, and the joists were simply enormous.

 

[rainsco]

sounds like an interesting projekt. looking forward to the pics. do you check if there is more thickness of mortar possible on the ditra-drain?

 

[jgrant]

The maximum thickness of the marble is 40mm so overall you are going to have something like 45mm tile and adhesive over 100sq m. Density of marble is 2,800 Kg per m3 and presumably cement is similar, therefore the weight of tile and adhesive per sq m is 126Kg (ish!) or 12.6 tonne for the whole floor. Ouch! I hope the engineer has down some calculations or otherwise the house owner should walk round with a crash helmet on.

 

[jonnyc]

yes ita a load of weight for sure
i actually calculated that if bedding material same weight as stone then it would be 112.50 kg per sq mt based on marble weighing 50 kg per sq mt @ 20mm thick.
you then have to add on the weight of 12mm hardie backer.
i really need more info on exiating subfloor but the actual fixing is not a worry.

 

[jonnyc]

sounds like an interesting projekt. looking forward to the pics. do you check if there is more thickness of mortar possible on the ditra-drain?

no i havent checked that yet.
very nice job though rainsco.
think you would enjoy doing this as well.