A concrete subfloor can appear completely dry while still being at risk of condensation. If its temperature falls sufficiently close to the dew point, a microscopic film of moisture can form on the surface which may be extremely difficult to see.

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Understanding dew point therefore provides installers with another simple way of checking that environmental conditions are suitable before applying StarFix adhesives, sealers and tanking membranes.

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What Is Dew Point?

The dew point is the temperature at which the air becomes saturated with water vapour and condensation can begin to form.

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Dew point is determined primarily by the temperature and relative humidity of the surrounding air. The important measurement during installation is not simply the air temperature. It is the difference between the dew point temperature and the actual temperature of the substrate onto which the product is being applied.

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The 3°C Rule

As good installation practice, the substrate should generally be maintained at least 3°C ABOVE THE CALCULATED DEW POINT before application begins.

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For example:

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   Air temperature: 20°C
   Relative humidity: 60%
   Approximate dew point: 12°C
   Minimum recommended substrate temperature: 15°C

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A substrate temperature of 15°C or higher therefore provides the recommended 3°C safety margin in these conditions. This margin reduces the risk of condensation forming as environmental conditions fluctuate.

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Why Does It Matter?

A microscopic film of condensation between a construction product and the substrate can potentially interfere with adhesion or affect the appearance and performance of the applied material.

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Depending upon the product and circumstances, excessive surface moisture may contribute to:

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• Reduced adhesion
• Blistering or surface defects
• Uneven curing
• Changes in coating appearance
• Entrapped moisture
• Reduced long-term performance

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The risk is particularly relevant to coatings, membranes and sealers where a continuous bond to the substrate is required.

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StarFix Pedestal Adhesives

StarFix pedestal adhesives are single-component moisture-curing polyurethane adhesives, so moisture plays an essential part in their curing reaction.

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This means that the relationship between moisture and a StarFix pedestal adhesive is somewhat different from that of a conventional floor coating. Normal atmospheric moisture assists the curing process and minor variations in humidity would not normally present a problem. However, this should not be interpreted to mean that visible condensation or a wet substrate is desirable.

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Good installation practice remains to check environmental conditions and ensure that the substrate is suitably prepared and at least 3°C above the calculated dew point before adhesive application.

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Tanking Membranes & Sealers

Dew point control is particularly important when applying StarFix TANKING, TANKING-ZERO, SEALER and SEAL-ZERO. Unlike a pedestal adhesive applied locally beneath individual pedestals, these products are applied across a much larger surface area.

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Condensation or an invisible moisture film across the substrate can therefore potentially affect adhesion, appearance or film formation over a significant area.

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The substrate should be clean and appropriately prepared, and environmental conditions should be checked before application.

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How Do I Check Dew Point?

Modern electronic environmental meters can make dew point assessment very straightforward.

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Before application, installers should ideally record:

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• Air temperature
• Relative humidity
• Calculated dew point
• Substrate temperature

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Many professional dew point meters automatically calculate the dew point once air temperature and relative humidity have been measured. The substrate temperature must then be compared with the calculated dew point.

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   Substrate Temperature − Dew Point ≥ 3°C

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If the difference is less than 3°C, application should normally be delayed until conditions improve.

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Conditions Can Change

A dew point measurement is a snapshot of conditions at the time it is taken. Temperature and relative humidity can change throughout the working day, while the thermal mass of a concrete slab means that its temperature may respond much more slowly than the surrounding air.

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This can be particularly relevant:

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• Early in the morning
• During rapidly changing weather
• In unheated buildings
• Following overnight temperature changes
• Near external doors and openings
• Where different parts of the floor experience different temperatures

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Environmental conditions should therefore be monitored throughout the application where there is a risk of significant change.

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Dew Point Is Not the Same as Subfloor Moisture

It is also important to distinguish between dew point and moisture within the concrete substrate. A dew point measurement assesses the risk of condensation forming on the surface because of atmospheric conditions.

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It does not determine the moisture content of the concrete itself. Where substrate moisture may be relevant to the installation, an appropriate concrete moisture assessment should be undertaken separately.

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Good Installation Practice

Before applying a StarFix product:

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1. Measure the ambient temperature and relative humidity.

2. Determine the dew point.

3. Measure the actual substrate temperature.

4. Confirm that the substrate is at least 3°C above the dew point.

5. Check that the substrate is clean and appropriately prepared.

6. Recheck environmental conditions if they are likely to change during application.

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Where conditions are unsuitable, delay application until an appropriate environmental window is available.

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Need Technical Advice?

Every installation is different.

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If unusual temperature, humidity, condensation or substrate conditions are encountered, please contact the Star Uretech technical team before application.

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We are happy to provide product-specific guidance for StarFix and StarFix ZERO installations.