Advantages of liquid-applied membranes
After application, and following a curing period, LAMs dry up to form continuous waterproofing
membranes which are fully adhered to well-prepared substrates. These materials offer a number of
advantages over pre-formed sheet membranes:
a) They provide seamless protection, having no side or end lap joints;
b) They can be applied efficiently and quickly in large areas by spraying, or manually in small areas where
access is narrow;
c) Detailing is relatively easy. Unlike preformed membranes which need to be cut, folded, and welded
over upstands and plinths, the liquid material is quickly applied over corners and changes in surface
profile once all the necessary preparations (e.g. angle fillets) have been completed;
d) They are generally cheaper than pre-formed membranes.
The thickness of the waterproofing membrane; why it is important
An obvious advantage of preformed membranes over LAMs is that the thickness is controlled in the
manufacturer’s plant and easily checked on site to see if delivered materials comply with specifications.
LAMs are a different matter, however. Thickness quality control can only be done either by:
- checking the wet film thickness during installation with a thickness gauge
or …
- measuring the dry film thickness after the membrane has cured. (The measurement is
complicated by the uneven surface profile on the substrate-side of the membrane.)
Achieving the right thickness is important for the simple reason that the performance and durability of
the waterproofing membrane depends on it. The values published in a manufacturer’s product data sheet
for, say, water impermeability, crack-bridging, tensile strength, elongation, etc., are obtained from lab
tests conducted on specimens of specific and uniform thicknesses (which must be provided for reference
by designers).
Therefore, where product selection is based on lab-tested performance properties, it makes sense for the
project designer to specify the required dry film thickness of the membrane rather than the material
consumption (which would provide varying thickness characteristics depending on site conditions). This
will become clearer as we examine the subject further.
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