Back Buttering – and clay stone installation - tile on tile - Do or not to do?

There are many arguments regarding the doing or not doing the back buttering practice to the tile/stones to be installed.

1. When the tile/stone have some extruded portions at the bottom, say some kind of ribs is provided for mechanical key purposes:

In case if we try to do the application on the substrate alone and then install the tile / stone directly, the bonding coverage will not be 100%. So there will be hollow pockets. Tile / stone may less bonded, they may crack if impact load falls on the hollow bonded surface. Have a look this video for more clarification:

Special thanks to: EdgeStripKits for this video.

2. When the substrate is having undulations at very short interval or when the substrate is non exactly easily accessible for applying the adhesive, use back buttering or back splashing procedure.

3. Tile on tiling: To save the time, manpower and cost, in renovation works / to have the new tile or stone look, tile on tile can be done.

> But, do not tile on over the existing natural stone tiles such as sandstone, slate, etc., as these natural products tend to de-laminate within themselves. 

> Also, you have to know that the floor level will rise and accordingly, the door panel shall be adjusted. 

> Tile on tile shall be done over the good, firm strongly bonded tile/stones only. 

> All glazed top surface shall be grinded to make them rough or apply bonding scratch coat or use adhesive as per manufacturer's recommendation only. 

> Use the adhesive in back buttering passion for sure 100% bonding coverage.

> In internal applications it is possible to apply ceramic tiles over existing or in-situ tile finishes.

> The existing tile surface must be sound with no loose or dummy tiles and the final installation is still reliant on satisfactory adhesion of the preceding one. Mechanical preparation will usually highlight unsound existing tile substrates.

> This procedure does not include certain external applications including high facades & walls, cantilevered verandahs or decks, and tiled driveways as these areas can be subject to high stresses and movements.

> Swimming pools and ponds are not suitable for tile-on-tile installations by these procedures and this is not recommended as a standard practice.

> Pebblecrete surfaces must be removed.

> Where the area to be tiled is a wall, the individual tile weights, and also weights per square metre must be taken into account. The first layer of tiles and adhesive will be loaded by the second layer, but then both layers will cumulatively load up the substrate.

> Shaded external walls and floors with adequate falls to prevent ponding water are acceptable.

4. Heavily loaded area: Tile/stone installation at high traffic area and that too exposed for wheeled traffic, the adhesive will play a role of loading distributing part. So, the adhesive bed shall be 100% present at the bottom of tile/stone. So for sure, back buttering process will help to achieve 100% coverage at the bottom.

How to do the back buttering:

Apply adhesive on the substrate in uni-direction adhesive combing process and then apply adhesive at the back of tile/stone using the flat edge of the trowel as a scratch coat.

As per NTCA Reference Manual: Back butter is defined as, “the spreading of a bond coat to the backs of ceramic tile just before the tile is placed.”

Back buttering increases the bond strength of the mortar to the back of the tile by keying the mortar into the tile surface.

Secondly, it fills the voids created by the embossed pattern on the back of the tile which creates a flat plane. All natural stone products may necessarily need to be back-buttered. Travertine, marble, granite, slate, etc., are natural materials have voids at the surface. By back-buttering these types of tiles, the installer is filling in the voids giving additional strength to the weaker areas. This is again done in the attempt to achieve the original goal, “Set the tiles in such a way to reduce the possibility of failure.”

As per ANSI Specifications, back buttering is not a requirement. ANSI A108.5 section 2.5.3 states: “Average contact area shall be not less than 80% except on exterior or shower installation where contact area shall be 95% when not less than three tiles or tile assemblies are removed for inspection. The 80% or 95% coverage shall be sufficiently distributed to give full support of the tile.”

There are many types of tiles are available in market:

These are interlocking clay tile, do not install them on sand cement mortar with wet on a wet adhesive system or with any type of adhesives. They must installed in an interlocking manner. You may install the waterproofing sheet applied or liquid membrane on a rafter or sloped RCC and then install the wooden or mortar battens and then install the tiles in the interlocking procedure.