Resinious Floor Toppings

Protecting Concrete with Resinous Floor Toppings: An Owner’s Guide

by R.A. Nixon and R.H. DeWolf, Corrosion Probe, Inc.

Editor's Note: An earlier version of this article was presented at the SSPC 91 National Conference in Long Beach, CA, held Nov. 10-15, 1991.

Floors in today's plants are an integral part of many operations. Concrete floor slabs serve as pieces of process equipment in many cases. Concrete floors contain and support processes and equipment. They even facilitate process liquid spill control to the plant’s sewer system. Floor slabs can be expensive to replace or maintain if proper care is not taken to protect them from the deteriorating effects of today's aggressive manufacturing processes.

An earlier paper, entitled "Assessing the Deterioration of Concrete in Pulp and Paper Mills" (November 1988 JPCL) addressed mechanisms of concrete deterioration. While specific to pulp and paper process applications, the article covers most types of concrete deterioration in industrial facilities. Repair materials can enhance the serviceability and restore structural integrity and functionality to concrete floors. Once repaired, the concrete floor requires future protection using protective toppings, coatings, or overlays.

In industrial facilities, one recurring and costly problem is the failure of flooring repairs and protective finishes. Delamination, cracking, chemical attack, and mechanical wear are often observed after only a few months of service. These problems can threaten structural integrity, personnel safety, and the continuation of process operations, so they result in expensive rework for facility owners.

This article will discuss the major causes of these floor system failures and their prevention in new and existing industrial facilities. The information presented herein pertains predominantly to thick film (1⁄8 in.-1⁄4 in. minimum [3-6 mm]), trowelable floor topping materials and polymer concretes.

Assessment Revisited

For a more detailed discussion of assessment, see the November 1988 JPCL, pp. 48-57. The initial phase of any rehabilitation project is assessment. What is causing the deterioration and what other influencing factors must be taken into account for a proper repair?

Concrete is normally a very durable construction material when properly mixed and placed. Concrete deterioration in industrial facilities occurs in many forms and from a variety of mechanisms. Careful evaluation must ensure that all influencing factors are taken into account when designing a repair.

First, the remaining structural integrity must be considered. Money spent repairing or coating a slab that has limited or no structural strength is money lost. This error is compounded by the future and short-term need to replace the slab anyway.

Once it is determined that the concrete has recoverable integrity, the mechanisms of deterioration must be considered. The most obvious mechanism is reaction with strong industrial process fluids such as acids. Other mechanisms of deterioration include pH reduction of the cement paste, carbonation, sulfate attack, abrasive wear, microbiologically induced chemical attack, excessive deflection, loss of support, corrosion of internal reinforcing steel, and caustic attack.

Once the mechanism of deterioration is accurately determined and influencing factors are defined, appropriate technology can be applied to protect and repair the concrete. Often, rehabilitation with resin-based toppings and polymer concretes is employed. These topping materials isolate the concrete from the local environment with a chemical-resistant protective barrier.

How to Avoid Concrete Floor Topping and Repair Failures in an Industrial Facility

Nearly all floor repair/topping failures are caused by one or a combination of the following problems: improper material selection, improper design or construction of the concrete substrate, inadequate surface preparation, lack of correct construction detail treatment, or improper application of topping/repair materials.

The remainder of the article offers the owner a checklist on how to repair and avoid floor topping failures.

Proper Material Selection

Improper material selection often results in problems with floor topping systems.

Unremovable staining, chemical attack, topping disintegration, and floor system mechanical failures occur due to using the wrong topping material (Figs. 2 and 3). Below is a checklist for averting such problems.

Select materials that resist the physical, thermal, and chemical exposure conditions. Compare exposure conditions with the thermal and chemical resistance data on the products under consideration. Have independent exposure testing conducted if the chemicals used are not specifically listed by temperature and concentration (percent) on the product manufacturer’s resistance charts.

Carefully evaluate floor topping materials for their physical properties. They must be thick enough and offer sufficient compressive strength and wear resistance for the actual physical exposure conditions. Find out what the point loads and dynamic wheeled traffic loads will be first. Then check these against the product data sheets.

  • Select topping materials that meet substrate requirements, i.e., adequate thickness for rehabilitated floors. A 1⁄8-inch thick (3-millimeter) topping alone will not be sufficient for repairing floor degradation that exceeds 1 in. (25 mm) in thickness losses.

  • Select topping systems that can be installed within the available outage or shutdown timetables (if pertinent).

  • Select materials that produce the appearance desired. Review large size sample coupons, several feet square. Do not make selections based upon 4 in. (10 cm) by 4 in. (10 cm) coupons.

  • Select materials that offer variations in texture so that cleaning and non-slip characteristics can be balanced in the field. Trial areas should be installed so that decision-makers from the facility can select the texture they desire. The selected trial area can then be used as the standard on the job.

  • Select materials that comply with relevant volatile organic compound (VOC) regulations. These regulations vary from state to state.

  • When selecting floor topping materials, review the odors given off by the resin system to ensure the health and safety of area or building personnel.

  • Do not use the same floor topping everywhere in the building just because it will all look the same. Use the right product for the specific exposure conditions. For example, line containment areas for chemical overflows and spills with a protective coating or lining system that resists extended exposure to the full strength chemicals. Isolate this area from the unexposed adjacent floor areas.

    Proper Design and Construction of the Concrete Substrate

    If everything else is done correctly, floor topping systems might still fail due to substrate inadequacies. Here is a checklist for avoiding commonplace substrate problems.

    Ensure that attention is paid to drainage and compaction of soil for all slab-on-grade portions of the facility to be built or repaired.

    Be certain that well draining sub-base soils are specified or provided and that diversions of run-off water and water table elevations are considered. Hydrostatic water or moisture vapor problems in slabs-on-grade frequently cause floor topping failures. Blistering-type modes of failure often occur when hydrostatic water problems are present.

    Check to make sure that routine quality assurance measures are in place during construction to enforce proper compaction of sub-base soils. If soils are not properly compacted, settlement of the slab-on-grade will result in slab cracking. This, in turn, will cause cracking of the floor topping materials.

    Ensure that the quality of new concrete is optimized.

    The water-cement ratio should be as low as possible while still ensuring good workability. The slump of the concrete need not exceed 31⁄2 in. to 4 in. (9 cm to 10 cm) for floor slabs. This is the slump before the addition of super plasticizers or high range water reducers. This will minimize shrinkage-related cracking and increase the impermeability of the concrete.

    Do not use lightweight concrete in areas where heavy and frequent wheeled traffic will be typical.

    Be certain the concrete is properly placed and consolidated without the addition of more water.

    Be sure the concrete is properly cured to avert unnecessary cracking. Curing for approximately 5-7 days is preferred. If curing agents or sealers are used, be certain they can easily be removed by surface preparation. And make sure they are compatible with the topping/repair materials selected.

    Be sure the concrete is poured, consolidated, and finished properly without the use of additional water. Finishing should include screeding for proper pitch to drains, floating, and steel troweling as required to produce a uniform, tight surface that meets flatness tolerances. Steel power troweling to a burnished, hard finish is inappropriate and undesirable if a floor topping is to be applied. Hard, power-troweled concrete brings cement fines to the surface, producing a thick layer of cement paste or cream. This layer of cream must then be wholly or partially removed to achieve proper topping adhesion. This removal is expensive and unnecessary when toppings are to be used. Overfinishing is therefore wrong.

    Underfinishing, such as broom finishing or mere float finishing, is improper if a topping is to follow. Broom or float finishing leaves irregularities and undulations in the concrete. Variations in the thickness of the cement paste or concrete matrix create problems for final floor flatness tolerances, pitch for drainage, and surface preparation for the floor topping. Underfinishing adds unnecessary costs to the repair or topping operation.

    Review the structural design for floor slabs.

    Make certain that adequate expansion joints are provided for thermal expansion.

    Make sure control joints are provided to control cracking in the slabs. Control joints should be sawcut. Be certain joint locations do not intersect walls and doorways.

    Check to see that joints are placed at logical transitions, such as where one floor finish meets another.

    Do not allow the use of "zip strips" or other construction joint isolation materials. These will have to be removed for proper floor topping installation.

    Column footing isolation joints should not intersect walls or doorways if possible.

    Make sure the cove base to be used, if applicable, is terminated at a height on the facility walls so that it can be easily cleaned and sanitized. Do not allow it to end at the first concrete masonry unit (CMU) mortar joint in masonry buildings. The cove base should terminate onto a flat wall surface, and the top of the cove should be chamfered (back towards the floor).

    Ensure that steel embedments in the concrete are carefully set at elevations conducive to good floor topping transitions. Embedded angles and plates at trench drains, circular floor drains, loading dock platforms, and elevator entrances should be set slightly above the finished concrete elevation. This distance must take into account the specific thickness of the floor topping and the extent of concrete removal during surface preparation. Also, the elevations of such embedments should be uniform from one end to the other. Otherwise, floor system installation costs go up.

    Carefully review the grouts or flash patching materials specified for settling or leveling penetrations and metal embedments in the slabs. Make certain they will be compatible with the selected floor topping.

    Check to see if expansion joints have been designed to occur at perimeter walls in the facility. If this occurs, the installation of a cove base requires careful attention along such walls. Placing a rigid cove base over an expansion joint will result in subsequent cracking of the cove base.

    Make sure as much equipment as possible can be removed and reinstalled to accommodate future floor topping maintenance.

    Make sure all Portland cement concrete and masonry cures for a minimum of 28 days prior to floor topping installation (if possible). Otherwise, consult a professional for advice.

    Carefully review the construction schedule for the sequence of equipment installation. This sequence is critical for the installation schedule of the floor topping system (Fig. 4).

    Adequate Surface Preparation

    Most floor topping failures are the result of inadequate preparation of the substrate. Below is a checklist for avoiding inadequate surface preparation problems for your floor repairs or protective toppings.

    Ensure adequate surface profile or anchor pattern.

    Resinous and even inorganic floor toppings or overlays on concrete rely on mechanical bonding for long-term, good adhesion (Fig. 1). This is accomplished in 2 ways on concrete substrates.

    First, concrete is a porous, heterogeneous composite. Its pores or capillaries aid in the adhesion of the floor topping. Adhesion is improved via the use of highly penetrating primers, preferably of the lowest possible viscosity. The greater the depth of penetration, the better the adhesion will be. But concrete porosity alone does not produce adequate surface profile.

    Mechanical adhesion is also achieved in the concrete substrate by roughening or profiling the concrete. The peaks and valleys formed by roughening the concrete provide an anchor pattern to which the floor topping can bond. This profile can be created by mechanical methods such as scarifying, air abrasive blasting, water jetting, planing, and shot blasting. Acid etching is also used to roughen concrete surfaces.

    Many people continue to recommend acid etching as a method of profiling concrete substrates. While acid etching can be an effective surface preparation method for thin film coatings, it generally does not produce sufficient profile on concrete for thick, trowelable floor toppings or polymer concrete overlays. Additionally, it can cause problems of safety, waste disposal, and contamination of the substrate, which occurs when acid salts are not completely removed after etching, and which often leads to coating or topping failures.

    Shot blasting has become the most accepted method of preparing concrete floors for thick film toppings. This method of preparation is recommended because it has proven to be very successful for floor toppings.

    Achieving sufficient profile is of major importance to floor topping adhesion. After many years of experience involving over 150 floor topping projects, the authors strongly recommend that profile should be increased with increasing topping thicknesses. Surface profile guidelines are given in Table 1 for resinous (organic) flooring systems.

    Be certain the concrete is sufficiently clean. The degree of cleanliness of the concrete substrate is also critical for long-term adhesion. Surface preparation must produce a substrate that is free of loose cement paste, laitance, dust, dirt, grease, oil, paint splatter, and otherwise deleterious substances.

    Substrate cleanliness means also that there are no non-visible contaminants on the concrete. Simple tests can be performed to insure soluble salts and other contaminants are not present.

    Contaminants can be effectively removed using high pressure water jetting and other methods. Contaminant testing should be performed prior to and following mechanical surface preparation. This way, the extent of contaminant removal and cleaning can be anticipated and planned.

    Curing agents or sealers can cause floor topping failures if they are chemically incompatible with the topping resin. These failures are normally manifested by failure of the resin to cure properly or inadequate bond of the floor topping to the substrate. Solving this problem generally involves more extensive concrete removal.

    Ensure the dryness of the substrate.

    The concrete must also be dry with no standing water or wet or overly damp areas. While some floor topping resins are more tolerant of dampness than others, as a general rule, the concrete should not be damp or wet when resinous floor systems are applied. Among the several tests for presence of moisture, the most effective is the Plastic Sheet Method. The standard for this test is ASTM D-4263, "Standard Test Method for Indicating Moisture in Concrete by the Plastic Sheet Method."

    The degree of cleanliness required of concrete to be coated includes removal of visible and non-visible contaminants and assurance that the concrete is sound and dry.

    Correct Construction Detail Treatment for Trowelable Floor Topping Systems

    Frequently, floor topping failures begin at terminations, transitions, and other construction details (Fig. 5). The following is a checklist to help avoid such problems.

  • Placing seamless floors over construction, expansion, and isolation joints is wrong. Generally speaking, a joint in the concrete substrate should be a joint in the topping. If the topping covers a joint, it must be specially treated first.

  • Active cracks must be treated prior to floor topping application. Placing the floor topping over active cracks results in cracking of the topping once the crack moves thermally. Assume all cracks to be active unless testing is performed to indicate otherwise.

  • Leading edge terminations at embedded steel plates, angles, and trench drains should include installation of a nosing detail (Fig. 6). The nose area should be built from the topping material or a compatible polymer concrete or grout.

  • Leading edge terminations at bare concrete or at alternate floor finishes require a sawcut and a nosing detail.

  • Finish floor topping elevations and door clearances must be addressed. Make a mock-up or door model for checking clearances.

  • Floor topping terminations at circular floor drains require an uninter- rupted transition. The drain must be set at the right elevation. In addition, a transition nosing detail is required for the topping.

  • Cove base heights and terminations require careful planning.

    Figures 7-11 show some correct methods for handling floor topping construction details.

    Proper Application of Topping Materials

    Improper floor topping application can result in topping failures. Below is a checklist of items to help avoid such problems.

    Be certain the material is mixed properly. If it is not, the topping material will not cure properly. Improper mixing may also lead to staining or discoloration in resinous flooring materials (Fig. 12). Streaks of darker and/or lighter tones may remain in the finish.

    If an inadequate resin-to-filler ratio is achieved because of poor mixing, the system may never develop the chemical resistance or physical properties designed into the formulation.

    The best way to ensure proper mixing is to provide independent quality control inspection of the floor topping installation.

    Check to ensure that the floor system is installed at the specified thickness. If the contractor installs the material below the specified thickness, it may not provide the wear resistance or load spreading capacity required for the service conditions (Fig. 13). Also, the thinner topping may not isolate the substrate from chemical exposures.

    If the floor topping is applied above the specified thickness, it may not cure properly throughout the film or films. And broad irregularities in thickness will compromise both performance and aesthetics.

    Use only contractors with tradespersons experienced with the product specified. Carefully evaluate the contractor’s project references, which must be similar to your project. Also, request resumes on the contractor’s application tradespersons.

    When checking job references, call the plant and talk to someone in the facility other than the named reference. For example, if you were given the Maintenance Engineer’s name, ask for someone in the Production Department where the work was done. Later, talk to the named reference person as well. Then compare responses. It is worth the effort.

    Be certain all prepared surfaces are properly primed with the topping systems’ primer prior to trowel application of the basecoat.

    Make sure you monitor the finishing operation early in the installation work. Good finishing work can make all the difference between a good-looking job and a mess.

    If topcoats are included in the system specified, make certain they are applied according to the manufacturer’s recommendations.

    Check to make sure that the contractor’s staff follows the recoat limitations and minimum ambient conditions for topping system application. These requirements will be well defined by the product data sheets.

    If substrate temperature, air temperature, or humidity at the time of application fail to meet the minimum requirements, improper or insufficient cure of the topping may result.

    If minimum and maximum recoat time limitations are not followed, intercoat delamination, cure problems, or eventual cohesive bond failures may occur in the topping (Fig. 14). For example, solvent entrapment can result if a base coat is topcoated too early. This entrapment can promote blistering of the topcoat, and delamination will develop. If the maximum recoat limitation is exceeded for a successive coat, a cohesive chemical bond may not form between coats. This could produce topcoat or intercoat delamination in the topping.

    Before allowing traffic or activity on the finished floor, be certain the finished topping system is cured for the minimum length of time at the appropriate minimum ambient conditions. Failure to ensure adequate cure time will result in damage to the topping.

    Conclusion

    Avoiding floor repair/topping failures in industrial facilities requires careful attention to details. This article does not cover every possible detail involved with floor topping/repair systems. It does, however, point out the major causes of floor topping failures and show you how to avoid them.

    Ensuring successful floor topping work is the job of the engineering consultant, the material supplier, and the contractor. But the owner can play an active role in avoiding potential floor topping failures by using the information contained here as a roadmap for the project.

    Preparation of detailed and thorough specifications and drawings is essential. An experienced flooring contractor is needed. Quality control inspection of the topping work is as important as inspection of the structural work in a building.

    It is critical to remember that floor topping design must start with the structural concrete and mechanical design in a facility. The substrate can be correctly designed and built to accommodate successful floor topping installations.

    Randy A. Nixon is founder and president of Corrosion Probe, Inc., a consulting engineering firm. Over the past 7 years, Nixon has specialized in rehabilitation and new construction for pulp and paper plants, chemical facilities, and animal research and pharmaceutical facilities, particularly in the areas of protective wall, floor, and other structural finishes. Nixon started his career in 1976 in facilitiesconstruction/maintenance positions with Georgia Pacific Corporation. He subsequently worked in protective coatings/concrete rehabilitation for a specialty contractor. He founded Corrosion Probe, Inc. in 1984. He can be reached at Corrosion Probe, Inc., 230 Shore Road, Old Lyme, CT 06371; 203/434-8212.

    Rick H. DeWolf is currently the Manager of Projects for the Southeast Region for Corrosion Probe, a position he has held since September 1989. DeWolf was graduated from Alfred University in 1978 with a Bachelor of Science degree in Ceramic Engineering. After a short stint in the Army, he joined Westvaco Corporation’s Luke, MD fine paper mill in 1978. He worked in a series of technical positions, including Materials Quality Assurance Coordinator. In this position, he acted as an in-house consultant for the design engineering department.
    DeWolf can be reached at Corrosion Probe, 5302 Cross Creek Cove, Acworth, GA 404/924-4969.