3M Colorquartz™ Garage Floor Coating
WHY COATINGS FAIL
When polymer coatings and overlays fail, over three decades of floor statistics show that surface preparation of the concrete substrate is one of the primary causes. The most often culprit is called laitance. It's a milky-white to light-gray alkaline substance that consists of water, cement, and fine aggregate particles. As the water evaporates and the substance cures on the top of the concrete, these particles form a paste-like consistency. Laitance occurs when water bleeds to the surface of over wet concrete, and becomes thicker by overworking the concrete during the compaction and finishing process. The thickness of laitance is also influenced by the type and amount of admixtures, and the quantity of water that is in the concrete mix or placed on top of the concrete slab to complete the finishing process. It can very from a very thin film up to 1/8 inch when cured.
A BONDING ISSUE
When laitance is cured, there is a very brittle, weak layer of cementitious material that is poorly bonded to the concrete mass below. Simply defined, adhesion of concrete is the state in which two surfaces are held together by interfacial forces which consists of mechanical bonds. The bonding mechanisms of an inorganic material such as concrete are very complex. Cementitious materials do not bond well together, and it becomes even more complicated when an organic polymer such as an epoxy or polyurethane is required to adhere to inorganic material.
It is the consensus of most major international concrete associations that laitance must be removed before applying coatings or overlays when they will be exposed to natural environments such as freeze-thaw or wet-dry cycles. The same applies when protective polymer overlayment is exposed to stresses such as impact or sheer on either exterior or interior concrete surface.
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