Flooring and Carpeting Limestone Tile Installation, nine dots, water tubes

Flooring and Carpeting Limestone Tile Installation, nine dots, water tubes

Flooring and Carpeting /Limestone Tile Installation

Expert: Gerard Veenendaal — 4/2/2008



I have provided additional information at the end of this email.

I just had 600 sq ft of porous white/beige-coloured large format tiles (24″x24″x3/4″) installed over a gypcrete floor (the floor has water heating tubes embedded in it but I don’t think this has any bearing on my question).

The floor was off more than 1/4″ in many places but the tiler said he didn’t have to level or flatten the floor first, against my wishes. Then he proceed to install the tile using a grey mortar. When I asked if he maybe should be using white mortar he replied that the stone was thick so it wouldn’t matter. Then I noticed he was trowelling the floor with the mortar, then placing about nine ‘dots’ or lumps of mortar on the surface and then installing the stone. He did not backbutter the tiles before placing them. The stone and mortar has now had 4 months to dry (and remember the floor is also heated due to the water tubes_). Now you can see the dots of grey mortar telegraphing through the stone and staining the surface. It is so obvious where the mortar has adhered, because of the staining, and there is probably less than 50% adhesion.

I know realize he did everything against standard installation practice for this type of tile. He now claims that he has never heard of light coloured limestone requiring the use of white mortar, so the staining is not his fault (but he admits he does use white mortar when he installs something like Carrera marble). He also claims that his method of installation would never result in the tile cracking and he’d guarantee that (a guarantee is worth nothing to me as it should be installed properly in the first place and he might not even be around when it comes to honouring the guarantee). He also says backbuttering is not required nor would it have helped. Finally he says that using white mortar would have produced the same result!

I am going to have this ripped out and re-done. My questions are:

1. What is the proper method of installing large format porous (or not so porous) white limestone tiles?

2. Do you use white mortar as a rule?

3. What is the proper method for applying the mortar to the floor. Is the ‘dot’ method an approved method?

4. Should you backbutter first before installing each tile?

5. Should you seal the surface of the tile first before installing it to protect it from any mortar adhering to it?

6. Should you seal the underside of porous tile before installing to decrease the chances of staining the tile even when using white mortar. I am asking because I have even heard that even white mortar can stain some white limestones? Or would is this not advisable as it could result in the tiles not adhering to the mortar?

Additional Information:

The limestone has a honed finish. There are no cracks in the tiles. The tiles are not impregnated or sealed yet as we wanted to make sure they dry out. The heating was started up two years ago. The gypsum floor was installed a little over 2 years ago (yes, it was a long renovation) and the water temp running through the pipes is 86F or 30C with the surface of the floor being about 80F or 27C. There is both a slab sensor and an air sensor, the slab sensor is set at 86F/30C and the air temperature at 70F/21C. If you tap the tiles where there is staining they do not sound hollow, but if you tap them where there is no staining they sound hollow (which is how I know the grey mortar has telegraphed or ghosted through).




Hi Leon,

I do still miss the exact name of the stone, limestone is a familyname for at least 500 specific types of stone, all with their own specific properties.

I will try to reply to your question in general.

1 and 2:I understand that the stone has been installed in a mortarbed of at least 2 inches. If your stone is transparent you should use a white mortar. If not: a grey mortar can be used as well, but. the mortar should be designed for use on marble and limestone. Buttering and floating is the best method.

3. I do not prefer the «dot» method for more than one reason:

The floor heating is not as effective as it should be, heattransmission will only occur through the dots.

The floor will be noisy, when you walk on it with leather soled shoes.

The tiles may tear, when you drop a hammer or a bottle on it.

The joints may tear.

4. Yes

5. Depends on the porosity of the stone. If very porous: probably. If not: No

6. Absolutely not, it will prevent adhesion of the mortar

The fact that you see «imprints» of the mortar on the tiles may mean that the floor has been installed in a mortar NOT specified for limestone, or the mortar may have been to wet. Salts from the mortar may have transferred into the limestone.

Between installation and start up of the floorheating should have been 3 months drying time.

Floortemp is OK, should not exceed 35C

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