Selected Answers

From Bruce Snyder of Sherwin Williams on January 7, 2016:
Coating concrete is done for several reasons, such ...read more Coating concrete is done for several reasons, such as corrosion protection, waterproofing, and dust suppression, as well as aesthetics. A significant issue that must be considered when coating new concrete is the coating’s ability to handle moisture. Many times, extra water – or “water of convenience” – is used to help in the ease of placement of concrete. This extra water not used in the hydration of the concrete must be given time to come out of the concrete prior to coating with traditional coatings. There are special coatings that allow one to coat concrete prior to 30 days, as well as slabs with MVE (moisture vapor emission) above 3 pounds of moisture per 1,000 sq. ft./24 hours. Although estimates vary in the percentage of slabs that have moisture issues, when an issue occurs, it can be traumatic for all parties involved. Since concrete is very porous, the coating will need to penetrate into the pores of the concrete to help seal the concrete, as well as to help prevent primers and topcoats from having pinholes due to outgassing from the concrete. Based on moisture and porosity, concrete coatings may also need to be applied to surface saturated dry (SSD) concrete. The surface may look damp but can be coated as long as there is no standing or glistening water present on the surface. The coating also needs to be tolerant of high pH (alkaline), as freshly placed concrete has a pH of 13. The specifier must understand what physical attributes the coating needs to withstand, such as foot or wheel traffic on a flooring system, prior to making the correct recommendation. These factors will also help determine the chemistry of the coatings that will be selected.

From Randy Nixon of Corrosion Probe, Inc. on December 31, 2015:
I can only build on the comments from the other tw ...read more I can only build on the comments from the other two experienced gentlemen by adding a few words to the wise based on a number of years of experience. The three things that must go into selecting coatings for success on new concrete are as follows:

1. The coating system must be able to meet the exposure conditions while being capable of curing under the actual field conditions. This will include the all important moisture properties of the new concrete. Products with greater moisture tolerance during cure are therefore desirable for new concrete. This, of course, is provided they can be resistant to any chemical or physical exposures inherent to the specific application.

2. The coating system must be capable of achieving good film quality meaning no pinholes, holidays, or other types of discontinuities. This is particularly crucial for concrete due to its many non-homogenous properties, i.e. “bugholes” or entrapped air voids. This means the system must be capable of filling and surfacing the substrate sufficiently to prevent discontinuities from being created via the outgassing of entrapped air during coating system application. Film quality is simply more difficult to achieve on concrete than on steel. In this same line of reasoning, the coating’s film thickness must be appropriate to assure good hiding properties to avert discontinuities.

3. The coating system must provide adequate adhesion to the concrete. This goes without saying, but is worth repeating because different degrees of cleanliness and wide variations in concrete surface profile can be appropriate for a wide range of coating products. Selecting the coating system which will provide good adhesion as necessary for the intended surface conditions is a worthy consideration.

From Tom Murphy of VP Marketing LLC on December 2, 2015:
This is a great question. I agree with Rodney tha ...read more This is a great question. I agree with Rodney that the selection process starts with determining the performance criteria. The next factor to consider is the surface condition and the surface prep required for the systems selected. The next challenge is the installation conditions and schedule requirements. Now that you have narrowed the field of options, you can determine which fits the budget and life cycle requirements for the intended use and maintenance.

From Rodney White of Independent Consultant on December 1, 2015:
Coatings must be selected to perform in the intend ...read more Coatings must be selected to perform in the intended service environment. Is it an exterior, water-repellent finish for tilt-wall;is it a shower wall; is it a floor surface in a production facility; a clean room in a chip-making facility? These things must be considered before selecting any coating system- for concrete or any other surface, and each has it's own set of "most important factors."