ENVIRONMENTAL EFFECTS ON APPLICATION AND CURING OF COATINGS

 

Summer has once again returned to Canada. The potential for warmer temperatures and elevated relative humidity is just around the corner. Parts of Canada can experience prolonged periods of warm moist air that have the potential to significantly affect the application and cure properties of resin flooring and wall coating products.
 

Every Sikafloor® or Sikagard® Product Data Sheet details critical application information such as minimum and maximum ambient air and substrate temperatures, relative humidity and dew point restrictions.  So why are these environmental details so important and how do they affect your day in day out operations? To answer that question the following article is a quick overview of some of the most common summer time weather issues that can affect our business.
 

Ambient and Substrate Temperature

Based on firsthand experience, we all understand that ambient and substrate temperature can affect cure rate and mixed viscosity that directly alters application characteristics.  Typically colder temperatures delay cure and increase viscosity, inversely warmer temperatures accelerate drying rates and decrease viscosity.  During summer months, it is not uncommon to have a >10°C temperature change morning to afternoon.  On a project that is not fully enclosed, without a functioning HVAC controlled environment, wide fluctuations in temperature during application and cure will produce inconsistent results in final appearance such as lap lines and variable texture.  Adjustments to your application technique may be required as the day progresses to compensate for quicker set times and lower viscosity.


Relative Humidity and Dew Point

Understanding the effect of relative humidity and dew point on the other hand remains a mystery for many installers.  We cannot see moisture vapour making it much harder for the installer to recognize it as an issue until it is too late.   We all know that early water contact with an uncured resin will contaminate the surface causing a variety of surface defects.  As relative humidity (moisture vapour) in the air increases the potential for conversion to liquid water increase as it approaches the dew point.  So what is dew point and how does it affect your project?
 

Dew point is calculated based on a combination of ambient air temperature and relative humidity.  Defined as the temperature at which the saturation moisture (100% RH) of the air is reached.  As long as the air temperature remains above the dew point, the air is unsaturated; ie, it is capable of holding additional water vapour.   The amount of water vapour that air can hold increases dramatically as the temperature increases. Example: if a specific volume of air at 0° C can hold a cup of water, that same volume of air can hold a half a litre of water at 10° C, a litre at 22° C and 2 litres at 33° C.  When the limit is reached for the prevailing temperature, the air is said to be saturated.  If the air cools or comes in contact with a colder substrate then the overloaded air gives up some of its excess moisture.  The dew point is reached, condensation then converts moisture vapour into a liquid water.   A concrete floor temperature is almost always a few degrees colder than ambient air temperature, so when summer time humidex readings begin to appear, it becomes critical to monitor the dew point on high humidity days. Sika recommends that an applicator measure the dew point at least three times per day.   The coated surface temperature must remain a minimum of 3°C (5°F) below the dew point temperature to prevent condensation from forming on the uncured product.  

During periods of high humidity, it is good practise to review job site environmental conditions on a daily basis before application proceeds.  If unacceptable or you believe condition will deteriorate as the day progresses, delay applications until environmental conditions improve.  If you start and the dew point is reached before the surface cures, you must check the cured surface for contamination and or defects before proceeding with subsequent coats.  Typically, additional preparation steps will be required or in extreme cases complete removal. Contact your local Sika Canada Technical Service person for specific recommendations on a project to project basis.

General Overview of Sikafloor and Sikagard Coating Technologies

High Solids Epoxy resins are generally capable of application up to a maximum 85% RH as long as the dew point is not reached, with no minimum RH required.  High
humidity and/or the presence of liquid moisture (water) can cause irregular surface defects such as poor uniformity in gloss, void formation, discolouration, adhesion problems and water marks (see Example 1).


Example 1:  Dew point contamination / water spotting

Technical Corner - Dew point contamination / water spotting

Left picture: moisture contaminated cured epoxy coating with a drop of fresh water applied 10 days later. Right picture: water removed after 5 minutes results in the surface appearing dull with a cloudy whitish stain


Multicomponent Polyurethane coatings are typically more sensitive to moisture than most epoxies. They are only capable of application up to a maximum of 75% RH as long as the dew point is not reached. Along with the common epoxy defects listed above, excess moisture will tend to produce micro bubbles in the film that reduce clarity in clear top coats.


Polyaspartic products experience similar defects to multicomponent polyurethanes, however they require moderate humidity (>30% RH) to cure on schedule with a maximum 75% RH upper limit.   The minimum RH requirement exists because they are partially depending on moisture in the air to fully cure.  Low humidity during application and cure will result slower strength development and reduced physical properties.


Water borne epoxies, polyurethanes and acrylic products all require moisture to evaporate from the film during cure to achieve the desired properties. When the RH is high (>70%) evaporation slows, extending curing times, creating the possibility of skinning over trapping moisture in the film. Extreme care must be taken when applying water borne coatings in an enclosed space with little or no air movement.  Initially acceptable conditions can change quickly as water evaporates from the resin creating a local increase in relative humidity that will soon reach an unacceptable level.  The air must be able to absorb the moisture vapour generated by the evaporation process in order to ensure proper cure of these products.  High humidity during cure will result in discolouration, variable gloss and a softer feeling less durable film. 


Sika Canada’s Technical Services Department can provide applicator training on how to measure ambient and substrate temperature, relative humidity and calculate the dew point.   Contact your local Sika Technical Sales Representative for additional details.

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