DAMPPROOFING, SEALANTS & ADHESIVES
our living areas and should be well constructed,
functional and as usable as the internal spaces
that we occupy. To ensure this, the tile coverings
used should be durable, hard-wearing, of suitable
slip-resistance and capable of withstanding all
types of weather.
Recent estimates suggest that more than 50%
of all coverings (including timber) on balconies
and terraces, are damaged in Northern Europe,
mainly due to poor installation and incorrect
selection of systems.
The challenge historically has been that
poorly constructed assemblies have resulted in
visible tile/surface damage which can include,
tiles cracking, efflorescence, stained or patchy
tiles – all of which can be influenced by excess
water residing within the assembly for long
periods of time. To expand on this, when
water ingress and retention is combined with
fluctuating temperatures; the outcome can prove
destructive to both the covering and potentially
As water penetrates the surface and permeates
through the grout joints and then adhesive
capillaries into the lower levels of the assembly,
Without proper drainage, sunlight and heat
can cause water particles to rise to the
surface creating effloresence
the water begins to pose a serious risk to the
covering and the structural integrity of the entire
assembly supporting the tiles. Significantly,
thick screed systems will retain more water and
subsequently can take longer to dry, leaving the
opportunity for this water to become a problem
and affording more time for low temperatures to
adversely affect it.
Any water that reaches the primary
waterproofing cannot escape quickly. This puts
more reliance upon the waterproof membrane to
be functional, as no provision is made for water
to drain away efficiently, allowing it to sit and find
weak points in any primary waterproofing layer.
British Standards provide guidance on the need
for removing water away from the tiled surface
and the various layers within the cement-based
assembly quickly and efficiently. Not only for the
purpose of reducing the risk of damage by frost
and freeze/thaw cycles expanding trapped water,
but also for the prevention of void formation/
propagation, efflorescence and lime bloom which
can materialise through grout joints and at main
water exit points.
BS 5385 Part 3 2014, 22.214.171.124 Balconies and roof
terraces states: “The formation of soluble salts can
occur when water becomes trapped for prolonged
periods of time within cement-based systems.
“It is important that balconies and terraces
should therefore be designed and constructed as
to allow water to drain free and effectively.”
To ensure that moisture staining does not
become an additional problem in the future, it
is crucial to specify the right products. It is vitally
important to remember that water-sensitive tiles
and slabs should not be used externally.
The correct combination of products and
• Appropriate drainage assemblies – structures
with effective and working falls, drainage and
often with reduced thickness.
• Suitable backgrounds – non-absorbent, rigid,
fully cured and dry, unaffected by temperature
fluctuations and preferably cementitious.
• Correct selection of adhesive and grout – rapid
setting/low water demand.
• Tile/slab selection – with low porosity, breakproof,
suitable for external use i.e.
Traditionally, external tiles have been
fixed directly onto cement:sand screeds, into
cement:sand mortar beds, thick drainage screeds,
loosely laid gravel bed and sometimes by using
cement-based pedestal systems.
While each has their own benefits, such as
ease of use and lower cost, they do not always
deal with water effectively. For example, while
traditional cement:sand screeds, thick drainage
screeds and gravel all absorb large volumes of
water and are prone to the problems highlighted
above, whereby water can also travel back up
through the screeds, gravel beds or adhesive
pedestals, causing water-sensitive and absorbent
tiles and slabs to become stained.
The use of a ‘passive capillary’ drainage
screed is the answer. Cavity rich, with lots of
capillaries, the water drains through quickly and
efficiently and offers reduced risk of shrinkage
and deformation. When combined with a
quick-setting cement for fast-track installation,
drainage mortar seems to be the ideal solution.
However drainage screeds alone will not solve
the problems. The use of a drainage system
which includes drainage matting, drip/drain edge
profiles, drain grates and guttering, can provide
a solution for the rapid and immediate drainage
Water is drained down through the screed and
transported away from the assembly by means
of a drainage mat situated below the screed and
over the primary waterproofing system.
New to the UK market, the passive capillary
drainage screed/drainage membrane represents a
complete new system for tiling externally but one
that provides complete protection for tiles from
MAY 8 | BUILDING PRODUCTS
Full drainage system with drainage mortar, drainage
mat, drain grates and edge profiles