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Tiling uneven surfaces

It is important, both for appearance and for safety, that the finished tile surface is flat with no tiles standing higher than the others. Providing ‘normal’ tiling practices are followed, this is straightforward on flat, level substrates. If the substrate is however not flat, then a number of problems can arise.

Problem

Increased difficulty in achieving a flat finished surface on the tiles

A serrated adhesive spreading trowel, when used at a constant angle, enables the even distribution of adhesive onto the substrate. If the tiles are all bedded with a similar force they should be at the same height with only minimal unevenness. However, if the substrate is not level, this is much more difficult to achieve and there is more chance that some edges will be standing proud.

Extra time required to fill multiple holes

Localised deep holes may result in a bed thickness that exceeds the specification for a thin-bed adhesive. Patching such holes can be time consuming if there are more than a few of them.

Combination of problems

In some instances, for example when tiling over a layer of existing ceramic tiles, the above mentioned problems may be combined. Some tiles may need to be removed because they are unsound, whilst others may have been imperfectly fixed and exhibit some variation in height.

Some natural stones are not a constant thickness

Uncalibrated natural stones are stones that have been split along natural fracture planes rather than machine cut. The result is a stone that varies in thickness, both from within each stone and from piece to piece. These types of stones require an adhesive that can be applied to greater thickness than normal.

Solution

Use the appropriate flexible adhesive

There are a number of possible solutions depending on the condition of the substrate. A levelling compound will give a smooth surface but this does not help with uncalibrated stone, where a high-build adhesive must be-used. Deep holes should be filled first with a repair mortar.

Solution 1: Use a levelling compound

A levelling compound can be used to smooth out irregularities, holes and gaps between existing tiles etc. and provide a flat and level surface for tiling. Ensure that the surface is clean, dry and sound. 80% of a painted surfaces must be chipped. All existing tiles must be firmly adhered. Thoroughly prime with weber.prim Plaskey WB250 and weber.ad Key-it WB117.

Pour the appropriate levelling compound to the required thickness using weber.floor Self Levelling Screed WB270 floor from 1 to 20 mm. Make sure that any movement joints in the substrate are carried through the screed and tiling layer. Fix the tiles using a Weber cement-based adhesive as appropriate for the type of tile. Allow the adhesive to set fully and then grout the joints.

Solution 2: Use a thick bed adhesive

If the tiles/stones are uncalibrated, a thick-bed adhesive must be used. This will also allow for some irregularities in the substrate. Ensure that any loose or unsound material is removed. Fix the tiles with weber.set Ultra-Flex thick bed adhesive, which can be built up to 25 mm thick. Allow the adhesive to cure for at least 24 hours before grouting the joints.

Solution 3: Use a patch repair mortar

For occasional deep holes in an otherwise flat surface, a repair mortar may be the best option. Ensure that any loose or unsound material is removed and that the area is cut square and not feathered. Fill the hole(s) with weber.floor 4602 Industry-Base Extra compound and allow to cure. Then fix the tiles using an appropriate weber.set tile adhesive. Allow adhesive to cure fully before grouting the tiles.

Solution with the following weber products

Solution 1

weber.prim Plaskey WB250

Cement-based primer and surface preparation.

weber.ad Key-It WB117

A latex-based liquid primer and keying agent specifically formulated for use with weber.prim Plaskey WB250 onto gypsum and cement surfaces.

weber.set Ultra-flex

A highly deformable, fast setting, high strength cement-based tile adhesive for all types of tiles.

weber.floor 4602

A rapid setting, fast-drying underlay screed for industrial use.

weber.floor Pro

A rapid-setting, fast-drying economically priced underlay screed.