Technical Note: cts 5a – Tiling onto Timber Substrate

Tiling onto Timber Substrate

Reference should be made to BS 5385 part 4, section 6.3.4.1., section 6.3.4.2 & section 6.3.4.3. the following sections are particularly relevant:: BS section 6.3.4.1 General

‘Timber sub-floors are not the ideal bases for floor tiling, especially where heavy static/dynamic loading is likely in service.

With reference to ‘New Timber Bases’ BS 5385 part 4, section 6.3.4.2 recommends the following:

‘New Timber bases should be constructed with noggings between the joists. Water and boil proof (WBP) exterior grade plywood of 15mm minimum thickness should be screwed to both joists and noggings at maximum 300mm intervals. The lower face and edges of plywood should be sealed against ingress of moisture using preferably non-aqueous sealers, e.g polyurethane varnish, or styrene butadiene rubber, to prevent distortion by changes in atmospheric humidity before being screwed down. All junctions between boards should be supported by noggings or joists.’

In practical terms we would also strongly recommend that particular note be made of the following:

• It is essential that quality WBP plywood be used otherwise it can  lead to problems with tiles de- bonding within a year of fixing.
• Attention should be paid to ensuring that once fixed the plywood  shows no sign of flexing or movement whatsoever. Whilst the  plywood may well be securely screw fixed down, if the entire sub-floor ‘bounces’ when, for example, a person walks along it at a  fast pace, then the floor is unsuitable for tiling onto.
• Tiles should be fixed using a flexible (polymer modified) adhesive;  this category of adhesive is known as C2S1. The category of an  adhesive will be shown by each manufacturer on the bag.