How to tile onto a screed with cracking

What can cause a cracked screed?

There are many reasons why a new or old screed may have cracks appear.

Cracks typically form in new screeds because the excess water evaporates from the surface at a faster pace than it is replaced by the residual water, trapped in the concrete slab. Or at stress points such as doorways and corners. This can be caused by not enough or too much water added during the mixing process or simply poor mixing.

When underfloor heating is used, water evaporates at a more rapid pace, increasing the risk of cracking.

What can you do?

As with any screed issue, you need to find out why the floor needs a screed repair in the first instance and then to treat the cause rather than the symptom.

Always seek expert professional advice before repairing or tiling onto a cracked screed.

How to tile onto a damaged screed

Once you have the all clear from a flooring expert that the floor will not crack or damage further, or have had all the recommended repairs carried out, then you could consider using a crack suppression mat such as Flexbone 2Easy or Excel Bond.

If your surface has cracks from lateral movement or gaps up to 3mm that need bridging then a decoupling mat could be the best solution.

Shrinkage/movement cracks can, when tiles are applied directly to a cracked screed, cause crack-induced tension to transmit through the screed to the tiles, causing them to crack and/or debond. A crack suppression mat is a designed to compensate for lateral movement and prevent tile failure and cracking.

Using BAL Flexbone 2Easy

If you’re tiling a dry area and are using the Flexbone 2Easy matting system then read our complete guide on using this product on a anhydrite screed. The handy guide talks through both installing the BAL Flexbone 2Easy and then laying your tiles on top of it.

Using Durabase CI++ or Excel Bond

If moisture is a concern, the Excel Bond and Durabase decoupling matting are both 100% waterproof, they prevent moisture coming through the substrate avoiding damage to the tile adhesive. Either are a good alternative to the BAL Flexbone 2Easy which cannot be used in wet areas.

With DURABASE CI++, shrinkage stresses are absorbed between the concrete and the tiled surface. It can be laid over existing cracks and used to bridge gaps between substrates of up to 3mm.

Depending on the flooring construction and the specific site conditions, edge joints with a width of approx. 5–10mm (or larger as required) must be produced.

If the matting is being used in a wet area (bathroom, wet room etc.) then don’t forget to use DURABASE sealing strips to ensure all the mat joins are water tight (you can use these same strips with the Excel Bond matting).

We recommend you use Excel Bond Rapidset Flexible Grey to adhere the matting to the substrate.

Using a 4x4mm serrated trowel, apply the Excel Bond mortar to the substrate and push the matting into the adhesive.

Never use a larger notched trowel, otherwise the decoupling effect of the CI++ matting will be impaired. It is essential that the entire surface of the backing fabric of the mat is embedded into the adhesive (loose laying of the CI++ Mat is not possible).

Work in the matting using a pressure roller or other suitable tool.

Laying your tiles

To lay your tiles on top of the CI++ matting, we’d recommend using BAL Flex Fibre Plus.

Tiles can be laid immediately after adhesion of the Durabase CI++ matting using the thin-bed procedure and thin-bed mortar which fulfils the requirements of the surface covering.

Here it is advisable to smooth out any mat depressions and first apply the adhesive using the straight edge of the trowel to ensure all the voids in the matting are completely filled with adhesive.

Then using the notched side of the trowel, continue to tile as normal. The notching size of the trowel must correspond to the tile format for tile laying, you can find more information on trowel sizes in our trowels guide.

The tiles must be embedded across their entire surface into the adhesive. In terms of working times, it is also possible to wait for the adhesive layer used to fill the voids to harden before trowelling/laying the tiles as normal.