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Laying Marble, Granite and Slate on to floor |
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New Build |
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Laying Marble, Granite and Slate Tiles on to an Existing Timber Floor (Revised 1995)
INTRODUCTION
In domestic situations, particularly bathrooms, halls and kitchens in older houses, suspended timber floors are often encountered, on to which new marble, granite or slate tiles are to be laid. These tiles are generally 305x305xl0mm thick and so called "gauged" to achieve limited thickness variations.
The usual method, which has been adopted in the past for laying tiles in such cases, is to provide a base in 18mm plywood, screwed down with stainless steel screws, to which the tiles are attached with a thin bed adhesive.
In spite of this, in some instances the tiles still crack along or around the joint lines of the plywood when in large panels. With the development of new backing materials and advances in adhesive and grout technology, the following alternative laying techniques have been developed.
In all cases professional engineering advice should be obtained to ensure that the existing joints can carry the increased dead load of up to 0.8 KN/sq m, without excessive deflection. Adequate ventilation must be provided to avoid raising the moisture content of the timber.
PREFERRED METHOD OF LAYING ON TO EXISTING FLOORBOARDS
This will raise the level of the floor by a minimum of approximately 35mm.
The existing floor should be free of contamination. Two layers of sheets should be used; the bottom one plywood and the top one atile backer board of similar plan size but fixed with the long dimensions in opposite directions, so that the joints in the two sets of sheets are never in vertical alignment. The moisture and thermal movement of tile backer boards is minimal.
The material recommended for the lower sheet is WBP plywood to BS 6566, size 2.44m x 1.22m x 12mm thick. For the top sheet tile backer boards should be used. These tile backer boards are available in various thicknesses from 6mm to 50mm. An overall thickness for both boards of 20mm can be achieved which matches existing practice. The two layers of boards should be independently fixed. The plywood should be laid first one way and screwed into the joists with stainless steel screws at 300mm centres. It is good practice to seal all exposed edges and the back (but not the faces) of such boards to prevent distortion by atmospheric humidity changes.
The tile backer board is then fixed in the opposite direction in accordance with the specific instructions of the manufacturer. Tile backer board may require pilot holes pre-drilled to accept screws. In addition, the joints between backer boards must be treated in accordance with the manufacturers specifications. Tile backer boards are non-structural.
For fixing the tiles, a wide range of background membrane systems, primers, adhesives, grouts and additives are available to accommodate various installation situations and bed thicknesses. Manyadhesives and grouts now exhibit an element of flexibility which will accommodate small scale movements in the backgrounds. Tiles must be pressed firmly to the bed to achieve full contact and left flush with adjoining tiles to avoid lips. Thick bed adhesives may be required where the tiles are not gauged.
Traffic should not be allowed on the floor for at least 24 hours after laying.
Proprietary grouts are available in several colours and to suit joint widths ranging from 2 to 20mm.
If the floor areas are large and there can be significant deflection of timber joists due to long spans and/or heavy loading, then even this technique is not recommended, since there is the possibility of cracking the tiles.
MOVEMENT JOINTS
A gap of at least 10mm should be left all around the margins, between the plywood tile backer board, tiled floor and the walls and any columns. A skirting of timber or marble should then be fixed to the wall, on top of the floor, so as to conceal this expansion/contraction gap.Before the skirting is fitted. the gap must be free of any residual mortar,plaster, grout etc.
Internal movement joints should be placed in the floor at 6m maximum spacing but dividing a floor into smaller areas is always preferable. A brass inset strip is an acceptable method of division and can well be made a design feature. If this can be incorporated over a joint between the top boards, this is an
advantage.
The most effective movement joint is created by using a flexible sealant passing right through a joint in the tiles and their bedding and the joint beneath in the tile backer board. The flexible sealant can be a suitable silicone, polyurethane or polysulphide (see SF data sheet).
A brass or stainless steel strip should also be placed across all door openings.
DIRECT METHODS OF LAYING ON TO EXISTING FLOOR BOARDS
If the existing floor is dry, uncontaminated, structurally sound and level, the tile backer board can be mechanically fixed direct to the existing floor boards. Other details of the tile attachment, movement joints and door strips should be as given above.
With some adhesives, on a floor which is dry, sound, level and rigid, the tiles may be directly applied to floorboards which have been cleaned by sanding. The adhesive manufacturer's advice on all aspects of design and installation should be followed.
ALTERNATIVE METHOD OF LAYING WITHOUT FLOORBOARDS
Where the existing floor boards are suspect they can be removed and polythene sheet laid over the area, covering the joists. Expanded metal lathing is then laid on top of the polythene, stapled to the joists and bellied down between the joists. Lightweight aggregate concrete is then laid on this lathing up to joist level. Finally the tiles are laid on a 25mm thick sand/cement bed.
Internal movement joints should be provided at a maximum spacing of 6m.
NOTE
These methods of laying are not recommended for commercial premises or very large floors in residential developments, but only for comparatively small areas up to 40 sq meters in domestic use.
REFERENCES
For the design and laying of Marble, Granite and Slate tiles on timber floors in new work, see BS 5385: Part 5: 1994.
For general guidance on workmanship in natural stone floor tiling see BS 8000: Part 11: Section 11.2: 1990.
For the design of timber elements refer to BS5268.
MANUFACTURERS AND SUPPLIERS
1 Adhesives 2. Tile Backer Boards
Ardex UK Ltd Panelcrete Ltd
Homefield Road Wincham Lane
Haverhill Wincham
Suffolk Northvvich
PRQ anp Cheshire
CB9 8QP CW9 6DE
Building Adhesives Ltd Wedi Tilebacker Systems(UK) Ltd
Longton Road P 0 Box 117
Trentham Rochdale
Stoke on Trent Lancs
ST4 8JB OL11 5WW
Realstone Limited believes that the advice contained in this Data Sheet is in accordance with the latest technical developments and good practice. However, no responsibility is accepted by Realstone Limited, its servants or agents, in respect of the application of this advice to a specific project. |
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