Tile Guru Vaults: Tile Preparation / Getting Ready To Tile

So it’s time for a fresh new look in your home, and you’ve chosen to use tiles to transform your kitchen, bathroom, hallway, living room, dining area, bedroom, conservatory or en suite. If you’re taking on the tiling job yourself, then before you get started, you need to make sure your surfaces are correctly prepared. Below are some questions regarding tile preparation. If they don’t answer your question, ask me directly on technicalhelp@wallsandfloors.co.uk

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Q. I have a newly laid screed. How long will I need to leave it to dry before I can tile it?

A. As a general guideline for cement screeds, the drying time required will depend on the thickness it has been laid. 1mm per day for the first 75mm and 0.5mm per day up to 10mm. Screeds of a thickness greater than 100mm will take considerably longer.
Anhydrite screeds dry at a similar rate. However it is very important that the screed is tested for the correct relative humidity before tiling (0.5% RH).

Q. Can I tile over existing floor tiles?

A. You can fix tiles over existing tiling, but first you need to check that they are firmly bonded to the substrate, then clean and degrease the tiles. Make sure a flexible adhesive is used.
If the existing tiles are loose, they will need removing and any necessary preparation will need to be done prior to the new tiles being fixed.

can I tile onto existing floor tiles

Q. Can I tile over existing wall tiles?

A. It is possible but you will firstly need to make sure that the substrate under the existing tile is capable of holding the weight of two layers of tiles (please see below for further guidance). Secondly you would need to make sure the existing tiles are solid and that there is no danger of them coming loose. If the existing tiles are loose, they will need removing and any necessary preparation will need to be done prior to the new tiles being fixed.

Q. Is there a weight limit when tiling a wall?

A. Yes there is. Here is a general guide to some of the most common substrates and the maximum recommended weights for tiling:

wall tiling table

Q. What preparation is required for newly plastered walls?

A. All new plaster must be allowed to dry for up to 3wks (dependant of thickness. This time is reduced for skims). If you are using a ceramic tile less than 300x300mm in an internal dry area, ready mixed adhesive will be fine. If the tile is larger than 300×300, porcelain or natural stone, you must prime the surface with an Acrylic Primer (such as BAL APD) and use a cement based adhesive. For wet areas such as a shower, above a bath or a wet room, the walls must be tanked first. But remember, the weight of the tile and adhesive combined, must weigh no more than 20Kg/m2. Please contact out Technical Helpline for further information.

tiling onto plaster wall

Q. What is an “Expansion Joint”, and do I need one?

A. An Expansion Joint (also known as movement joint) is a trim, mainly used in floor tiling. They are designed to absorb heat induced expansion, absorb vibration and allow movement due to ground settlement. They are required for any area over 40m2, where the perimeter joints are more than 10m apart. They must also be used where two different substrates meet, and are also recommended in doorways that have tiling either side.

Q. What is a Decoupling membrane, and do I need one?

A. A Decoupling membrane (or matting), protects tiles from lateral (sideways) movement in a floor. They normally have two layers, which separate as the floor moves. As an example, a tiled concrete floor starts to crack. Without the matting, the tile also cracks. With the matting, the bottom layer will stretch or split and separate from the top layer. The top layer will then bridge the crack and keep the tiles intact. The matting is recommended for use on newly laid screeds and timber floors, in underfloor heating situations and any other situation where the floor where there is any danger of movement. They are not a substitute for Expansion Joints.

Q. What is Tanking, and do I need it?

A. Tanking is a waterproofing system for wet areas and showers. It forms a completely waterproof barrier between the tiles and the substrate, ensuring that no moisture can penetrate the background which would inevitably cause problems in the future. It is essential for wet- rooms and showers, but please ask for advice if you are tiling any other intermittent wet areas.

Q. I have a very large tiling project to do. How do I work out what I need?

A. If you have any plans for the relevant areas, please email them to TechnicalHelp@wallsandfloors.co.uk. We can assist you in working out quantities as well as advise on the correct preparations required. Please note that plans can vary from true measurements, so it is recommended that the measurements you provide are verified by your tiler before ordering.

Q. I am about to tile a bathroom, what should I be thinking about?

A. Preparation is the most important as wet areas require tanking. You need to make sure that where water is constantly in contact on both the wall and the floor, that the background is protected from excessive moisture. Due to the amount of water present, it is also recommended that a floor tile with an anti-slip finish is chosen.


Q. Can I tile direct onto a wooden floor?

A. Most wooden floors require bracing with either a minimum 15mm WPB Plywood, cement based tile backer board or underfloor heating insulation panels. Each screwed down at 300mm centres. This is to reduce the flex in the substrate and make a suitable surface to accept tiled flooring. Floating floors are not a recommended substrate for tiling.

Q. What is causing cracks in my floor tiles?

A. The most common cause for tiles cracking is substrate movement. On a wooden floor you may find that either the flex is too great, or there may be movement between the board joints. Concrete floors can also have movement caused by settling shrinkage or extreme changes in temperature. Wall tiles can also be affected, but in all cases, preparations can be done to prevent the possibility of this happening. Another cause for cracking is stress above voids in the adhesive where full coverage has not been achieved.


Q. What considerations should be made when taking on a tiling project?

A. You need to start by assessing whether the substrate is suitable for taking your chosen tile. Preparations and requirements required may include tools, insulation, bracing, waterproofing, de-coupling membrane to cater for lateral movement, expansion joints, adhesives, primers and aftercare etc. We highly recommend contacting our Technical Helpline so that you may discuss your project from the ground up so that we can advise the best solution.

Thank you for reading! I hope these FAQ’s have answered your queries. If not, ask me your question directly! Send it to technicalhelp@wallsandfloors.co.uk or ask me on twitter or Facebook @wallsandfloors with hashtag #TileGuru.



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