In this guide we answer the simple question of ‘can you tile over tile?’

Tiling over the existing tiles may be considered a shortcut, but it can be a practical option for those wanting an efficient kitchen or bathroom redesign. There are several important things to consider before you start your project.

• The existing tiles must be soundly bonded to the walls. If the old tiles de-bond from the wall and fall off, then so will the new ones so make sure the old tiles are well fixed. One way to check is to gently tap them. If it sounds very hollow then they are likely not well bonded. Pay particular attention to wet areas which are more likely to have problems.
• The existing tiles need to be clean and free of grease or other contaminants which could affect the bond of the adhesive used for the new tiles. Use sugar soap or a suitable degreaser to clean the surface before tiling.
• One thing to consider is the aesthetics. Tile over tile can be noticeable around the perimeters of a room such as coving, door frames, shower fittings and especially if the room is only half tiled. This is unlikely to be a problem unless you chose to finish off the top with a tile trim, you can’t put the trim behind the original tiles so this may leave an unappealing finish.
• Determine the original substrate before tiling. Most background substrates such as plaster and plasterboard have a recommended weight limit per m². Skimmed plasterboard can only take around 20kg/m². If you have a bumpy white tile (20×25) along with adhesive and grout, you will have a weight of approx.14kg/m² on your bathroom wall. With this in mind, you’ll only have an allowance of 3kg/m² for tiles after adhesive and grout which if surpassed may cause structural failure – this will limit your choice of new tiles. If you are looking to use larger, heavier tiles, you will likely need to remove the old ones first.

UNDERSTANDING THE VALUE OF TILE ADHESIVE

When embarking on a tiling project the preparation is key and using the right tools for the job is essential!

For preparing your space for tiling, you can read our guides on preparation, these guides cover how to plan your space, levelling your surface and preparing various types of substrates ready for your tiles. The next step then is to talk about how to fix your tiles.

Choosing the right adhesive for your specific tiling job can sometimes be a little confusing, in this article we breakdown the technical jargon and provide you with the key points on how to choose the right adhesive for your job and why sometimes it’s worth investing a little more for a better finish.

CEMENTITIOUS TILE ADHESIVE CLASSIFICATIONS

When looking at a cementitious adhesive, various letters are used to help describe the products added efficiencies, we’ve mapped them out for you.

C = Cementitious

1 = Normal characteristics

2 = Improved characterises (usually this means its flexibility, referring to additional polymers or such like to improve the performance of the adhesive)

T = Reduced slip (so how effective is the product’s grab, aka keeping the product on the substrate)

E = Extended opening times (how long can you work with the product)

F = Fast setting (how quickly after application can you grout your tiles)

S1 = Deformable (in conjunction with all the above features, this adhesive also has added flexibility, a deformability of between 2.5mm & 5mm)

S2 = Highly Deformable (this product has high flexibility, a deformability of above 5mm

To put these letters in a bit of context, if you’re tiling a wall with large format tiles, you’d need to look for an adhesive that is C2T as a minimum, as this has reduced slip. If you’re tiling a floating floor, you’ll need a C2TES1 as a minimum (as it depends on how much movement is in your floor).

If the product you’re looking at has a ‘D’ (for Dispersion) classification, then this is not a powdered adhesive (aka ready mixed) and not suitable for a project that requires the properties of a cementitious adhesive, for example, large format tiles or flexibility.

WHY CHOOSE A S1 OR S2 ADHESIVE?

Although typically more expensive than the standard C2 adhesive, S1 and S2 adhesives are designed to cope with movement within a substrate and ultimately preventing the final surface (aka tiles) from de-bonding or cracking. If a non-flexible adhesive is used and movement or vibration occurs within the substrate the adhesive is likely to crack or fail, resulting in a damaged floor and tiles lifting.

All materials are subject to some form of movement, most commonly expanding and contracting with changes in temperature therefore for a long-term investment like tiles it makes sense to secure your project by reducing the risk of tile failure.

Even in substrates you would normally expect no movement, such as concrete, over a few years they can continue to cure creating even the slightest movement. This is often why you see cracks appearing in floors some years later after being laid. But this issue can be prevented by investing in your preparation and the right adhesive.

WHY CHOOSE A S1 ADHESIVE

A S1 adhesive has increased deformability when compared to a regular adhesive. It has added flexibility, a deformability of between 2.5mm and 5mm.

A S1 adhesive will therefore safeguard against tile adhesive failure by coping with smaller types of movement.

WHY CHOOSE A S2 ADHESIVE

Similarly, to S1 adhesives, S2 products are designed with flexibility in mind. The difference being the amount of deformability the product allows. Typically, an S2 allows for 5mm or more deformability, for example the BAL Fast Flex allows for movement of up to 20mm, one of the best available.

S1 adhesives can be used for most tiling projects, however those that have more movement and/or vibration an S2 product should be used. Those circumstances are typically

• Tiling directly onto tongue and groove floorboards
• Floating floors

It is essential that any existing timber floor is stable, clean and in good condition with adequate ventilation beneath to prevent atmospheric moisture distortion. It should be sufficiently rigid and stable, as any unsupported movement in the subfloor can cause tiles to crack, and the floor should be able to support the additional weight without any deflection (bounce in the floor).

Once movement has been resolved, timber floors that require strengthening ready for tiling can be overlaid using a suitable, flooring grade, 15-18mm thickness WBP plywood (to be primed on the underneath and sides, not on the top side).

Where floors require further strengthening, you may wish to fit additional noggins within the joists beneath the subfloor or floorboards.

Please note plywood should ONLY be used as an overlay and not fixed directly to floor joists.

Tile spacers are key to creating a uniformed grout line for a professional finish,

Regardless of the type or style of tile (porcelain, ceramic or stone) a minimum of 3mm tile spacers should be used for floor tiles.

Depending on the tile, the spacer required can go as high as 10mm. Most commonly a 5mm spacer is used, especially if you’re using indoor to outdoor tiles.

The tile type, size and substrate will dictate what tile adhesive to use, here we breakdown the differing types of adhesive suitable for different projects and how to apply them.

How much tile adhesive do I need?

The amount of tile adhesive you need depends on the depth of the adhesive bed you spread across your area. We’ve listed what each adhesive covers per tub to give you a rough indication of how much you will need for your project. The deeper your adhesive bed, the more adhesive you will need.

READY MIXED ADHESIVES

BAL Green Star is a simple, but effective ready-mixed tile adhesive perfect for fixing ceramics up to 30x30cm, mosaics and some natural stone in dry or wet interior environments. It’s suitable for domestic areas including showers, kitchens and bathrooms and shouldn’t be used for porcelain tiles, power showers or wet rooms. Each 15kg tub will cover approx. 6m² in a dry area and 4.5m² in a wet area. It cannot be used for floors.

BAL White Star Plus is a non-slip, water resistant ready-mixed adhesive suitable for showers, kitchens, bathrooms and wet rooms. Suitable for ceramic tiles no bigger than 30x30cm and porcelain 15x15cm. Each 10L tub will cover approx. 6.6m² in a dry area and 5m² in a wet area. It cannot be used for floors.

For ceramic tiles bigger than 30x30cm and porcelain 15x15cm, a powered adhesive is recommended.

BAL All Star is a high strength and highly flexible ready-to-use tile adhesive for walls. It’s non-slip and water-resistant, recommended for ceramic tiles and porcelain up to and including 60x60cm. This amazing product innovation is exclusive to Topps Tiles and available in 100% recycled packaging. Each 10L tub will cover approx. 6.6m2 in a dry walled area, 5m2 in a wet walled area (using a 6mm trowel).

POWDERED ADHESIVES

BAL Rapid-Flex Fibre Plus is a non-slip cementitious tile adhesive for walls and floors formulated with BAL Fibre Strand Technology (FST) for improved flexibility, strength and grab, suitable for dry, wet and interior, exterior including showers, swimming pools and total immersion. Each 20kg bag will cover 10m² in a dry area, 8m² in a wet area and approx.5m² on a floor.

BAL Flex Fibre Plus is ideal for large tile formats, it has gel rheology – maintaining its structure – plus excellent non-slump and non-slip properties. This particular adhesive is perfect for walls and floors, formulated with BAL Fibre Strand Technology (FST) for improved flexibility, strength and grab. Suitable for dry, wet and interior, exterior use including showers, swimming pools and total immersion. Each 20kg bag will cover 10m² in a dry area, 8m² in a wet area and approx. 5.3m² on a floor.

For a sustainable and more eco-friendly option, Regener8 is a great adhesive available in S1 rapid and standard setting bags of 20KG (white and grey).

Always mix the tile adhesive as per the instructions on the bag. Most adhesives are available in either white or grey. Generally, when using a lighter tile or grout you should use a white adhesive, and vice versa.

GEL ADHESIVE

Kerakoll think, develop and produce innovative solutions that focus on the environment and on improving both health and quality of life. They use eco-friendly and naturally breathable building materials that offer quality results for tiling. Their unique H40 gel adhesive is formulated into three types, Gel, Advanced and Extreme depending on your tiling requirements.

Kerakoll’s H40 Extreme is a highly deformable and workable hybrid gel adhesive that has been tested for extreme conditions and uses. The formula features fast bonding, is easily spreadable and stress resistant whilst always remaining fluid and thixotropic. It is ten times more deformable than generic S2 adhesives with the highest level of long-lasting performance.

Don’t know whether you need an S1 or S2 adhesive or want clarity on why S2 adhesives are worth the extra investment?

WHAT SIZE TROWEL FOR FLOOR TILES

It’s important to select the right type of trowel for the job. As a general rule for which size trowel to use, follow this generic banding:

• Mosaics (10x10cm or smaller) – 3-4.5mm
• Large format tiles (20×20-30x30cm) – 8mm
• Floor tiles (30×30-40x40cm) – 10mm
• Large format tiles (40x40cm+) – 12-20mm

WHAT SIZE TROWEL FOR WALL TILES

• Small format tiles (10x10cm or smaller) – 3-4.5mm
• Small/medium format wall tiles (10×10-30x30cm) – 6mm
• Large format tiles (20×20-30x30cm) – 8mm

HOW SHOULD I APPLY THE ADHESIVE?

On Walls

Starting from above the timber baton and centre line, start to spread the adhesive on the wall holding the notched trowel (depending on the tile size) at a 45° angle and drag across the wall. Spread evenly right up to the timber baton and set out line, ensuring that the notches are in the same direction. Only cover a small area at a time, about 1m², as the adhesive will dry on the surface.

Place the tile on the bed of adhesive, resting on the top of the timber baton, when in position, twist and slide into place to ensure the adhesive sticks properly. Insert a tile spacer in between each tile and wash down the surface and clean the joint as you go along. If you are tiling brick bond then a T-Spacer is recommended.

On Floors

Starting at the furthest point away from your exit, use a bucket trowel to apply a suitable amount of adhesive onto your notched trowel and spread the adhesive across the floor. A larger notched trowel (8mm+) is needed for floors to ensure the tile has 100% coverage and no hollow spots are formed.

Similar to walls, comb the adhesive across the substrate at a 45° angle, dragging across the floor and spreading evenly to cover a 1m² area at a time and making sure the notches are all in the same direction.

Large Format Tiles

Large format and some natural stone tiles need to be ‘back-buttered’, this is where a thin layer of adhesive is applied to the back of the tile before fitting onto the substrate. For larger tiles it ensures a good contact with the adhesive spread on to the surface you’re tiling. For natural stone, in particular travertine, this method will fill the voids that can be found on the reverse of the tile.

Apply a thin, even layer to cover the whole of the back of the tile with the straight edge of your tiling trowel. Whilst the adhesive is still wet, firmly press the tile into the already trowelled adhesive on the tiling surface.

Repairing cracked floor tiles is possible however, if a tile presents a crack or is broken, we’d always recommend replacing it to ensure it is safe. A broken tile can be a trip hazard and create a sharp edge that can be dangerous.

The exception to this would be if you’re working with a natural stone such as travertine, over time it can naturally pit, similar in how to fix a chipped tile without replacing it, fill in the gaps using a matching-coloured epoxy grout.

If you need to fill in a cracked tile, read our dedicated article on how to fix a cracked tile by replacing it.