Articles on Residential, Commercial and Industrial Coatings

Articles on Residential, Commercial and Industrial Coatings

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Concrete Coating Surface Preparation

By the amateur the question is always asked, why is concrete coating surface preparation so important prior to the application of a floor coating system?

Whether you are new to flooring, a specifier, architect or potential customer, understanding the importance of a properly prepared concrete floor prior to the application of an impermeable lining is paramount, especially if it saves you money in the long term. Without correct preparation, concrete coatings will fail resulting in bubbling, blistering and delamination of the lining from the concrete substrate.

Sometimes, the correct concrete coating surface preparation is simply overlooked by both experienced and inexperienced flooring contractors; it may even be the case that the customer wants to cut costs, not understanding the reasoning and importance of correct surface preparation.

To ensure the coating properly adheres to the concrete substrate, a flooring applicator must take into account a number of considerations, which will result in a long lasting, durable, versatile concrete floor coating.


The Concrete Slab

newly laid concreteThe age of the concrete substrate itself can be the first issue especially if newly laid. Concrete is formed by mixing cement, sand, stone and water, as the moisture evaporates the mix cross links leaving hardened concrete in its place.  This curing process normally takes around 28 days, issues arise when coatings are applied to slabs that are still curing, leaving laitance on the surface..  The next issue is excessive moisture.  5 % moisture in the slab is the recommended maximum to which an applicator should be going ahead and coating the concrete slab.  There are tests that applicators can carry out to ensure the moisture content is at an acceptable level and will not cause problems further down the track.  With regard to laitance, this has to be water blasted off the concrete before profiling.


Surface Preparation and Profiling

Concrete PreparationThe third issue is the actual surface preparation.  This is often the most important part of any successful coating or resurfacing application.  The surface profile must be prepared prior to coating, which allows for strong adhesion and reduces the chance of failure.  The NACE  International standard “Surface Preparation and Coating of Concrete” defines a surface profile as “the roughened surface that results from abrasive blast cleaning or power tool cleaning.  For commercial and industrial indoor jobs, shot blasting is another method to prepare the surface. For residential indoor jobs; scrubbing with detergent, acid washing, neutralizing, rinsing and wet/dry vacuuming is another method of surface preparation when mechanical surface profiling is not easily achieved. After profiling, the surface must be clean from dust, dirt, grease or any loose or foreign material that can interfere with bonding.


The Weather & Concrete Coating Surface Preparation

rainy weatherFailure can also occur when a coating is applied under the wrong ambient conditions.  For example, when epoxies either outside or inside are in the curing process they have the ability to draw in moisture caused by high humidity.  Note that humidity should be no higher than 80%, if higher you run the risk of the coating failing.

Tip:  To gauge if a surface is suitable for coating it is necessary to determine the Dew Point, this can be determined by cross-referencing the Ambient Temperature with the Relative Humidity and only lay coatings when the substrate is a minimum of 30C above dew point.

Other issues for coating failures can include:

  • Poor coating thickness
  • Pigments and resins are not blended well enough
  • Abrasion, impact or mechanical damage

Added to the above Murphy’s Law will often apply, if something is going to go wrong, it will go wrong.  Thankfully, if it happens while the coating is being applied you have the ability to correct there and then.

So remember, concrete coating surface preparation is the most important part of any flooring project.  Without it, even the best flooring applicator may experience a coating failure. The cost to repair or replace can be expensive, not to mention the down time involved including customer dissatisfaction  – nobody wants that no matter what line of business you are in.


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