External Tiling

Exterior tiling is exposed to more aggressive conditions than interior tiling. The effects of sun, wind, rain, and frost combine to shorten the life of an installation, by exposing it to a continuous onslaught of a number of mechanisms.

Common issues and queries you can face

Porous adhesives and grouts

Adhesives and grout are porous

Most cement-based products including grouts and adhesives are porous to some extent.

They have minute voids left by the evaporation of un-combined water or by gaps between the aggregates.

These pores allow water to permeate through the grout into the adhesive and substrate.

Expanding

Water expands on freezing

Water expands on freezing and in doing so in a confined space, generates enormous forces. In cold climates the cumulative effect of repetitive cycles of freeze (expand)/thaw (contract) causes rocks to fracture. This action, known as frost shattering is part of the mechanism for weathering.

For tiling this has several implications:

  • Pores in the grout will be vulnerable to frost damage.
  • Any voids behind the tile provide a possibility for water to gather and then on freezing, push off the tile.

Large changes in temperature

Exterior situations undergo large changes in temperature

Interior tiling situations tend to be maintained at more or less constant temperatures. Exterior installations, however, are exposed to much larger cyclic temperature swings.

  • With changes in temperature different materials expand and contract at different rates.
  • When they are fixed rigidly together this causes stresses to build at the interface between the materials.
  • If the stress gets high enough it can exceed the force that binds the two materials and delamination occurs.

Solutions

Use polymer-modified cement-based adhesives

A cement-based adhesive must be used for exterior work. Whilst standard cement-based tile adhesives are suitable for exterior use, highly polymer-modified adhesives offer enhanced bond strength, reduced porosity and therefore better resistance to frost & greater resistance to movement (thermally induced movement is inevitable particularly for walls). Tiles recommended for exterior use will often be fully vitrified and these also require a higher specification for the adhesive.

Fixing the tiles

We recommend weber.set SPF or weber.set rapid SPF for exterior walls and floors, both of which are highly polymer-modified. Alternatively, weber.set WF and weber.set rapid can be modified by the addition of weber AD230 or weber AD250 admixtures.

It is very important that a solid bed of adhesive is achieved behind the tiles to prevent water collecting and this is easiest to achieve by back buttering the tiles in addition to spreading adhesive on the wall. It is good practice to occasionally remove a tile during fixing to ensure that the appropriate contact is being achieved.

If tiles are large, heavy or being fixed above first-floor height (3 m), they must also be mechanically fixed. Contact our Technical Helpline for more details.

Construction requirements

Any movement joints in the building structure must be carried
through the tiling layer and intermediate flexible joints included at suitable intervals.

Grouting

As with adhesives, highly polymer-modified grouts are more durable due to their reduced porosity, higher strength and resistance to flexing. stoneset fine wall and floor grout and weber.joint wide flex are highly polymer-modified and weber.joint wall and weber.joint wide can be modified by the addition of weber AD230 admixture.

Ensure that the joints are completely filled with grout and tool the surface to obtain a closed surface texture. Protect the top edge of the highest row of tiles from water ingress.