Masonry Magazine April 1993 Page. 42
Correcting the Level of Floor Surfaces
Design professionals are faced more and more with the need to improve floor flatness and insure that floors are level within tolerances.
By JACK COVER
Technical Sales Manager
W. R. Bonsal Company
Design professionals are faced more and more with the need to improve floor flatness and insure that floors are level within tolerances. In the following we explore Portland Cement based floor products used to patch and level floors for many different flooring conditions. The flatness of level tolerance most commonly used is ¼ inch in ten feet. How well this tolerance has been adhered to in the past is questionable. (The origin of this tolerance is an American Concrete Institute Specification that in 1990 was deleted.) Better methods of determining flatness along with contractors that have begun specializing in this field, and new fluid applied cementitious materials are greatly improving floor flatness.
Key to any floor correction is preparation. Concrete that has been frozen, rain damaged, has a camber problem or has been only rough screeded, needs careful consideration. Petrographic analysis can be very useful in determining the extent or depth of damage caused by rain or frost. This is critical since a visual inspection will probably not reveal the depth of the damage.
Self-leveling overlays are in many instances a need born out of a problem of one kind or another. Knowing the condition or integrity of the concrete is vital. The money spent up front to determine these conditions can save thousands of dollars and tremendous aggravation down the road. Core samples provide a finger print of the concrete and can reveal such problems as air content, chloride and sulfate conditions, compressive strength, alkali reactivity, aggregate distribution, and reinforcement placement. If the concrete is a bonded surface, (that is another material has been attached to the surface of the concrete such as quarry or ceramic tile, or terrazzo), the bond test can indicate how well those materials are adhering to the substrate. If the results are favorable, removal of those materials may not be necessary.
Portland cement self-leveling materials in combination with epoxy primers can be applied over such materials.
Caution must be exercised to remove wax, sealers and other materials that would interfere with bond when using any cementitious topping. Materials such as "cut back" adhesives are also difficult to remove. Grinding, sandblasting or sanding is usually unsatisfactory. A ¼ inch thick application of self leveling material with its accompanying primer can be be applied without removal of the "cut-back" adhesive. The bond strength of the "cut-back", however, will be the limiting factor of successful applications.
Wood substrates may also receive Portland Cement self-leveling underlayments and wear toppings. Application involves covering the substrate with building paper and mechanically attaching galvanized metal lath. It is important that the substrate be sound and capable of supporting a design load with a maximum deflection of 1/360 of the span.
Sealed or painted surfaces require explicit preparation techniques such as shot blasting, grinding, sandblasting or scabbing prior to application. Typically, the cementitious topping is installed at an average thickness of ¼ inch or more. The depth is depen-
ENR/July 19, 1990-Still Eyeballing Floors for Flatness? Shame on You Say Many Experts.
42 MASONRY-MARCH/APRIL, 1993
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