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Simple Slate Floor Tile Installation Guide for the DIY

by Carolinas Home Stone Stone Fabricator & Installer

This simple guide outlines the basic principles of fitting and maintaining natural slate stone flooring tiles, but does not constitute a fully in depth document due to the extensiveness of this topic. We have attempted to present 'best practice' when installing natural slate flooring products to achieve the desired effect, whether a seasoned professional or an absolute beginner.

For more detailed technical reports, reference can be made to British Standard BS5385 1994 Wall and Floor Tiling. Remember to read carefully the manufacturer's instructions on any packages of adhesives, grouts and sealants. Please follow the golden rule of tiling and keep everything meticulously clean and dry.

SUBFLOOR

The solidity of the subfloor onto which tiles are intended to be laid, must be suitable for the purpose intended. The floors' surface must be level, dry, clean and free of any dust, grease or loose material. This is for both interior and exterior floors.

Sand & Cement Screed

When installing onto sand and cement screed, each 20-30mm of screed takes approximately 1 week to dry properly or longer if adverse weather conditions prevail. Fresh screed will shrink during drying which can create cracks. This may cause tile splitting if not properly dry prior to installation.

Timber Floors

Timber floors if suspended, must not flex and the extra load weight of the natural stone tiles must be accounted for. The most common method of preventing movement would be to affix 18mm WBP plywood over the floor and screw down firmly at 140mm intervals.

A flexible adhesive and grout must be used when fixing onto timber floors. Internal installation onto existing Glazed, Clay, Stone, Vinyl, Linoleum etc. In a perfect world all floor coverings and adhesives will have previously been taken up and surfaces properly cleaned, but if this is not the case and existing flooring is in good repair, then natural stone tiles may be fixed over the existing flooring subject to all grease residues being removed.

Cork & Wooden Existing Flooring

Cork and wooden flooring should be fully removed. Any bitumen left on the floor should also be removed.

Damp

Before installation, damp proof membranes should be checked for existence or effectiveness and installed or replaced if necessary.

Unleveled Floors

A floor with minor bumps and hollows can be leveled by applying more or less adhesive to the underside of individual tiles during installation. In the case of a very uneven floor, a leveling compound should be used.

Under floor heating

It is possible to lay natural slate stone tiles in situations where under floor heating is utilized.

PLANNING

It is advisable to plan your tiling from the corner furthest from the primary entrance. To obtain the center line, measure and mark the middle of opposing walls AB and CD. Join these points with string to locate the center point.

From the midpoint of the center line lay down tiles without fixing them, allowing for joints, to see where the last whole tile will end. Mark a line at a right angle alongside the last whole tile. Locate starting point along the new line in the same way as before to see where the last tile will end.

Now mark the sideline at a right angle alongside the last whole tile. Now check that the line comprises of a perfect right angle, and that the sideline runs parallel to the center line.

Grout Joints

According to personal taste, this can be between 5mm and 10mm.

FIXING

Make sure tiles and sub floor are clean and dry.

It is recommended that a PVA bonding agent is applied to cement screed floors, or an acrylic bonding agent is applied to timber floors.

Mix Tile Adhesive or Rapid Set Adhesive, making sure that only sufficient is mixed for use, as unused material should be discarded. Do not add further water. Apply adhesive to a floor area of around 1m² using a notched trowel. Do not exceed more than 6mm depth of adhesive. Do not screed more adhesive than can be tiled in 20 minutes.

Fix in starting position (see planning) and press tiles firmly into place. All tiles should be firmly pushed down allowing no space for air underneath. Place the next tile adjacent, and so on, allowing for grouting space.

Clean any adhesive from the surface of the tile with a clean damp cloth as soon as possible. Set adhesive will prove very difficult to remove. Clean all tools immediately after use. Once the main area is completed prepare the perimeter and adhere pre-cut tiles, as long as the adhesive is adequately cured.

The adhesive must be given a minimum of 24 hours to dry, or in accordance with manufacturer's instructions, prior to sealing and grouting.

CUTTING

A flat bedded diamond cutter (water fed) is required for the cutting of all natural slate stone tiles (available at nation-wide Hire Centers). The correct cutting blade must be used & this will depend on the type of stone being used. (Advise the hire center).

This process will necessitate the re-cleaning of the tile, as dust is unavoidable.

GROUTING

Internal & External

Before grouting all adhesive must have dried properly. Normal drying time is 12-24 hours, unless fast set adhesive is used then a drying time of 4 hours is normally adequate. Thicker beds of adhesive and cooler temperatures will all slow down the drying times. Make sure all joints are clean and dry.

When adhesive has set, clean the floor by very lightly wiping it with a large sponge to remove any dust that will inevitably be on the tiles. Do not soak the floor with water. The floor must be fully dried before any sealer can be applied to the floor.

We recommend the floor be left for as long as possible to dry to ensure the tiles have fully dried out, to prevent any moisture being sealed in during the sealing process.

A layer of a recommended SLATE PROTECTOR, (Please call for our advice if unsure), this will vary according to the product being laid & should be applied with a small sponge roller, this will act as an impregnator and stop the grout from staining the tiles.

One coat should be applied depending on the porosity of the slate.

Leave to dry for 30 - 60 minutes or until fully dried before grouting.

This undercoat treatment absorbs into the slate reducing its porosity, helping to protect against staining.

We advise the joints to be filled by a spreading or 'slurry process'. The tile surface must be kept as clean as possible.

Grout must be pushed down firmly and all joints well filled, as no air should be allowed to remain in the joints. The more grout used means it will set harder. It is essential that excess grout is removed with a damp cloth or sponge continually.

Leave to dry for a minimum of 24 hours.

After grouting, ensure that the floor is both perfectly clean and dry.

To clean off any really stubborn grout residues, which may be particularly difficult to remove from highly textured slate, cement & lime film remover should be used. Please call us for advice as it will affect the appearance if the wrong remover is applied. (Very important).

The overall strength of the floor is dependent on the quality of grouting, which must support all the tile edges.

SEALING

Natural slate stone tiles are virtually maintenance free when sealed correctly. It is strongly recommended that all natural stone floorings are sealed and allowed to dry before use.

Prior to sealing ensure that all areas are clean and dry otherwise dirt and damp will be sealed in.

Apply the recommended SEALANT 24 hours after grouting and apply using a small Sponge Roller. Do not pour sealant on, an even spread will create a better appearance. It is advised to work on an area of 1m² at a time. We suggest 1 application depending on porosity of the slate. Leave to dry for approximately 2 hours. Repeat the application if required. Leave to dry for approximately 24 hours depending on room temperatures.

Exterior Installation

Natural stone tiles are porous hence when laid outside there is a risk that moisture will be absorbed and the tiles may be susceptible to frost damage if extremely cold temperature persists. By using the correct sealer the risk of damage is minimized.

MAINTENANCE

The above sealants protect the slate by forming a barrier against dirt and stains but are not a stain proofing system.

All Sealer's on the market will usually protect stone flooring for between 4 - 8 hours, It is vital that acidic liquids/foodstuffs be wiped up straight away, i.e. Red Wine, Orange juice, Vinegar, Oils, Tea, Coffee, otherwise they may stain the floor. It is vital that the protection is maintained. Harsh cleaners will erode the finish and should not be used.

The appropriate recommended MAINTENANCE CLEANER will both clean and prolong the life of the protective surface finish applied. We recommend the floor be cleaned with a light brush & not a Hoover as this may scratch the surface of the tiles & we also recommend the floor be mopped once a month depending on the foot traffic.

When mopping try to clean out the mop bucket as often as possible as highly textured slate will hold dirt & grime more than any smooth finished products.

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