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Weather and related site effects on liquid membranes


When products are designed and tested for performance, this is done at a set of specified conditions. The standard conditions for laboratory testing are normally set at between 20 and 23 degrees Celsius and 50-55% relative humidity.

In reality, though, the temperature or humidity on site rarely is as in the lab.

To ensure the waterproofing system performs as intended, below are some recommendations to avoid any issues, especially when the temperature and humidity are varying.

Some of the problems
Variances in conditions can affect the waterproofing membranes significantly. For example, a dark substrate in direct sunlight can be ten degrees Celsius higher than the temperature of the air. Being this hot means the waterproofing membrane won’t set and cure as under lab conditions. Likewise, similar failures occur with excess or lack of moisture in the air or in really cold temperatures.

In fact, when the air temperature is below ten degrees Celsius, certain physical changes and chemical reactions when it comes to drying and curing, won’t work. For example, for materials containing Portland Cement (part of cement-polymer liquid membranes) and epoxy resin, the reaction ceases at around five degrees Celsius.

In hot and dry weather, a water borne liquid membrane can lose its water both through evaporation and the substrate. If this happens too quickly, it can lead to holes and voids. This is not acceptable for a membrane. If the day is cool and humid enough, potentially, it may not cure at all, leaving it soft on the inside. And if it freezes when it gets below zero degrees Celsius, then ice crystals can destroy the structure.

Likewise, heat can rapidly speed up the drying and curing process and often can even trap in moisture, by creating a crust but leaving it soft internally.

Wind, airflows, humidity, fog, snow and rain all have their own issues when it comes to using liquid membranes and can severely affect the future performance of the applied waterproofing coat.

Water falling onto waterborne and cement-based membranes can mean they don’t dry properly and potentially can be washed away. Substrate moisture can also lead to bubbles and blisters. Even geography can play a part in how the material reacts. For example, near the coast your surface may be more likely to have a damp sticky film which can interfere with adhesion.

Some solutions that are proven
It’s hard to avoid or control temperature and condition variables. Scheduling works in expected weather extremes should be avoided; however, the following measures can be put in place:

Hot weather

  • All work should be avoided in the heat of the day. Instead, works should be scheduled for evening, early morning or night. The substrates will take some time to cool after extreme highs.
  • Shade the working area(s).
  • Keep all products stored in cool conditions and out of the direct sun.
  • Do not add water to products that are not intended to be diluted.
  • Mix smaller quantities at a time to reduce self-heating.

Cold weather

  • Keep all products stored out of the cold, especially products not intended to be frozen.
  • Warming materials to around 35 degrees Celsius can help but they will go to the substrate temperature rapidly when applied.
  • Use heated tents or enclosures around work areas.

High humidity and wet weather

  • Installation when rain has recently fallen, is currently falling, or is expected to fall soon must be avoided where possible.
  • Check the weather forecasts.
  • Use tents or protection to cover areas to be worked on.
  • Remove water that has accumulated from rain and allow the area to dry.
  • Use fans or driers and ventilation to remove moisture and lower humidity.

Damp substrates

  • Use the correct moisture barrier as a membrane or membrane’s primer.
  • Make sure that below grade drainage is adequate.
  • Prevent water getting into building elements in the first place (protection of parapets.
  • Test for moisture content.

Other important things

  • Several thinner coats of most membranes are better than one or two overly thick coats. This allows more effective drying and curing in general.
  • Aim for the correct film thickness and use the right product for the application.

Click here to read the complete Technical Bulletin.