Proper surface preparation requires that the following basic needs are addressed:
- Surface profile
- Surface irregularities
It has been stated that 80% of all polymer coating and topping failures are attributable to inadequate surface preparation. If this is true, it is important that key aspects of surface preparation and strict adherence to manufacturer’s recommendations be followed closely.
There is an abundant array of technologies, equipment and methodologies to produce a profile on concrete surfaces. Unfortunately, there are no visual standard universally accepted by our industry as a guide in defining acceptable surface profile. As we have seen in our discussion of the complexities of concrete thus far, there is an overwhelming variety of conditions and concrete’s that we may face with each project. For this reason, there are many ways to approach these tasks.
Regardless of the method employed, we are attempting to provide a surface that will accept the penetration of polymer based products and mechanically bond the polymer securely to the concrete. The type of service the structure will be subjected to, and the type and thickness of polymer coating or topping required, will help to define the degree of profile required.
Surface profile may be defined by considering the view of a cross section through the surface of the concrete. By measuring the average distance from the peaks of the surface to valleys, we can establish a quantifiable dimension, and call that our surface profile. This dimension can be expressed in terms of mils (1/1000th of an inch) in the case of coating applications or fractions of an inch in the case of thicker toppings. Either way, we then have specific measurable relationship between degree of surface profile and thickness of polymer product applicating.
It is reasonable to assume, that monetary constraints and the type of service that the concrete structure will be subjected to, will dictate the type and thickness of protective polymer coatings or toppings that are to be applied. It is also reasonable to assume that the depth of penetration of the polymer into the concrete surface and the degree of surface profile will dictate the strength of the bond and therefore the degree of service it may be subjected to. If we accept these arguments, we can then accept the relationship of surface profile to material thickness and establish a conservative rule of thumb.
For a coating application (defined here as up to 30 mils), the surface profile should be not less than 20% of the thickness of the coating or 5 mils, whichever is greater. For a topping application, the surface profile should not be less that 25% of the thickness of the topping or 10 mils, whichever is greater.
Perhaps the oldest, and unfortunately the most common, form of attaining a surface profile is the use of acids. This method of surface preparation is dependent on the density of the concrete, concentration of the acid and duration of application. The use of acids is dangerous and requires extreme caution. Today’s environmental concerns continue to restrict the use and disposal of chemically contaminated debris, which will increase the expense associated with this method. Neutralization of the acid with alkaline washes and thorough water flushing of the area is a mandatory requirement to insure long-term bond stability. Free chlorides, produced by the use of hydrochloric acid (Hcl), can cause corrosion of imbedded steel and blister off coatings through the process of osmosis, wherein moisture is drawn through the coating by a physical chemical attraction of water to chloride ions.
Also 99% of all concrete slabs poured in Ontario are cured with a cure and seal membrane. Acid will NOT penetrate this membrane, therefore no reaction to the slaked lime in the concrete and no etching.
There are a number of tools and equipment to mechanically abrade and / or chip away the surface of concrete. These range from hand held manually powered tools to electrically or pneumatically driven power tools capable of removing fractions on an inch to inches of concrete surface. Examples of common types available are as follows:
- CANGO (Chips away the surface perpendicularly with a single head)
- SCABBLER (Chips away the surface perpendicularly with multiple heads)
- SCARIFIER (Scrapes or tears the surface from a perpendicular position with star shaped multiple rotary blades)
- PLANER (Scrapes away the surface from a parallel position)
- DIAMOND GRINDER (Abrades away the surface in a parallel position)
Again there are a number of tools and equipment available to perform mechanical blasting of concrete surfaces. This type of surface preparation has become the preferred method for sound uncontaminated surfaces. Contaminated Surfaces required special attention with regard to the environment in which the blasting is taking place, and the proper disposal of contaminated debris created with this method of surface preparation. Consult the Professionals at Epoxy Solutions for their recommendations on the removal of contaminates from you slab. The choice of equipment used is limited to regulatory requirements, availability and job site conditions. Some types of equipment available is as follows:
- ABRASIVE BLASTING (Various abrasive aggregates propelled at the surface of concrete by air pressure)
- WET ABRASIVE BLASTING (Same as above with the addition of water)
- HIGH PRESSURE WATER BLASTING (With pressure up to 30,000 P.S.I.)
- SHOT BLASTING (Centrifugal vacuum blasting utilizing recyclable metal shot in a confined vacuum chamber)
All of the above mentioned methods of obtaining a surface profile will provide the contractor with varying degrees of texture, varying rates of production and a variety of equipment and power requirements.