Guidelines For Applying Two-Component Urethanes To Concrete Floors

General Objective

The objective of this guide is to describe the material and workmanship necessary to produce a high quality, high performance concrete floor coating system for industrial and commercial services.  The painting shall be done according to the manufacturer's instructions and shall be done so as to meet the satisfaction of the project engineer.

Scope

This guide covers the application of MasterCoat 106 primer/sealer and AG111 finish coats.  MasterCoat products are manufactured by PM Industries of West Milford, NJ.

Coating System

A.  Interior Floors

Primer: MasterCoat 106, one coat

Finish:  AG111, two coats

B.  Exterior Floor (or floors requiring maximum chemical resistance)

Primer:  MasterCoat 106, one coat

Finish:  AG111, two coats

Preparation Of Surface

Do not apply coatings over weak, damp or contaminated surfaces.  Test concrete with hammer and chisel.  If it easily breaks or crumbles, it is not sound and coatings should not be applied.  Test for dryness with moisture meters or by plastic patch test.  test for contamination by water spot test.

A.  New Concrete

New concrete must be well cured, free of laitance, dust, form oils, curing compounds and other foreign matter.  Form oil and curing compounds can be removed by Terrazzo machine grinding, sanding with coarse open-grit paper, sandblasting, mechanical blasting or scarifying techniques.  Concrete hardeners should be avoided in new concrete floors which are to be painted.

New concrete floors, free of form oils, sealers, hardeners, and insoluble curing compounds should be etched with a 15 to 20% solution of muriatic acid to produce a slightly granular surface.  Approximate spreading rate for the acid solution should be 50 to 75 square feet per gallon.  Note:  If acid does not foam when applied to concrete and beads up, this is an indication that curing compounds, oil, wax, or other contamination is present.  If this happens, scarifying will be necessary.  Acid should be worked into surface with stiff bristle broom.  When foaming action stops, flush the surface with plenty of water.

In some cases more than one acid etching operation is required to obtain a satisfactory profile.  Each acid etch should be followed with a thorough water flush.  Follow closely the mixing and safety instructions supplied with the muriatic acid.

Upon achieving a surface profile similar to that of medium grit sandpaper, check surface with pH paper.  If reading is below 6, neutralize with a 1% ammonia solution.  Flush with water and check pH again.  If pH is between 6 and 8, preferably 7, pH is satisfactory.  The floor must be thoroughly dry before coating.  Floor should look dry (light gray color).  Moisture can be checked by several moisture detectors on market; however, if not available, a simple method is to tape a polyethylene sheet approximately 2 ft. sq. to the concrete, taping down all edges and allowing to set overnight, then examine for moisture under polyethylene.  If present, allow additional drying time before coating.

B.  Old Concrete

Remove all oil, grease, wax and dirt accumulation.  this may be accomplished by high pressure steam cleaning using a hot caustic solution.  Presoaking floor with a caustic solution prior to steam cleaning is also recommended.  An alternate method to steam would be high pressure (1000 psi) hot water machine using caustic solution.  After thoroughly flushing with clean water use water spot test.  If water beads up on floor, oil, wax, or grease contamination is still present and additional caustic cleaning is necessary.

Chemical cleaners, strippers and solvents may be used in conjunction with the above hot caustic cleaning techniques, if necessary, to remove certain chemical contamination.

Upon completely removing all residual contamination, as indicated by water spot tests, acid etching should be done as the next step prior to coating.  Follow procedures outlined above in Section A for new concrete.

C.  Previously Painted Concrete

Buff or sand floor to remove gloss and loose paint.  Vacuum all dust from floor prior to painting.  Apply AG111 finish to small test patch of old paint for check on lifting.  If lifting occurs, old finish must be completely removed and concrete surface treated as in Section B.  An alternate test is to saturate a diaper with 711 thinner and tape it to the floor for 6-8 hours.  If blistering occurs, the old finish must be removed.

The importance of a thoroughly and properly prepared floor cannot be stressed too much.  It is vital to the adhesion of the paint system applied.

Paint Application

Primer

To 1 gallon of MasterCoat 106, add 1 gallon of 106 Reducer. Stir well and apply with short nap roller at a spreading rate of 400-425 square feet per gallon.  Important:  Do not apply to damp surface or when humidity is above 90% or temperature is below 30 degrees F.

MasterCoat 106 should be applied at the above dilution rate so that it will penetrate into the concrete surface without leaving a highly glazed, glossy surface.  It is acceptable to have varying degrees of gloss on the surface, as this is an indication of varying densities of concrete within the slab.  The ideal time to recoat MasterCoat 106 is while it is only partially cured and will still accept solvent bite from the top coats.  This is generally 1 1/2 to 3 hours after application, although temperature of the slab and relative humidity will affect the cure rate.  

IMPORTANT:  Work should be scheduled so that the primer is recoated within 6 hours of application.  Should the primer cure longer than 6 hours, the primed area be abraded by suitable method to remove all glaze and to thoroughly roughen surface before applying finish coat.

Cutting in of edges may be done by brush or detail roller.  It is best to terminate and cut in at expansion joints and avoid overcoating of caulking and joint compounds. 

Metal surfaces should be primed with metal primer.

Finish Coats

The finish consists of two coats of AG111, as dictated by service requirements.  Each coat shall be rolled at a spreading rate of 275 to 300 sq. ft. per gallon.  The first coat of finish should be allowed to dry approximately five hours to overnight prior to the application of the final coat.  The temperature of the slab will affect the drying time of the finish coats, and work should be scheduled accordingly.  Do not apply these finishes when the temperature is less than 30 degrees F.

AG111 two component finishes are supplied in premeasured kits.  After adding Part B to Part A, stir until uniform under low speed agitation.  No induction period is necessary and these coatings are ready for application upon mixing.  They are also supplied at application viscosity, so thinning is generally not required.  Should be necessary to thin, however, specially thinners, available from PM Industries, must be used.

The finish may consist of two color coats or a color coat and a clear topcoat.  The latter is used where a maximum "wet look" is desired or where there is danger of contact with strong oxidizing agents (i.e., battery acid) which could bleach certain pigments out of the coating.

The high gloss of these coatings gives an apparent wet look to them and, therefore, they appear to have a slippery surface.  They, in fact, are not more slippery than conventional floor and deck enamels, but sealing any concrete surface with a coating causes liquid spills to remain on the surface rather than soaking in, and the spilled material will result in a slippery condition when compared to uncoated concrete.

This condition can be somewhat reduced by broadcasting an anti-skid aggregate, usually aluminum oxide, over the intermediate coat while it is still wet.  It should be noted, however, the size of this aggregate and its concentration will affect the appearance and cleanability of the coating.  This aggregate may also be mixed into the intermediate coat and rolled as above.

Cleaning and Maintenance

Urethane floor coatings represent the state-of-the-art system for industrial/commercial floors.  They have far greater chemical, abrasion, and impact resistance than conventional floor coatings--even other two component types. Their long-term beauty and effectiveness can be enhanced with a minimum amount of care and maintenance.

Allow these coatings to cure 48 hours before subjecting them to harsh chemical spills and heavy traffic conditions.  Although they will tolerate light traffic within 12 hours of application, they do need a proper cure cycle of several days to achieve maximum properties.  Also, once cured, it is still not wise to allow harsh chemicals to lay on the surface for prolonged periods and to repair deep cuts that would allow chemicals to penetrate beneath the coating to concrete.

The use of a urethane coating on a concrete floor will reduce routine cleaning to the use of mild detergents, usually a mild TSP solution, unless unusually stubborn spills occur.  These can generally be cleaned with whatever solvent or chemical is necessary to cut them, as urethanes have excellent resistance to solvents and chemicals.  Use brushes with soft nylon or polyethylene bristles and always wet mop in preference to drop mopping of gritty materials.

Finally, urethane floor systems can be dressed with conventional floor waxes and polishes.  These must, however, be completely removed from any areas that may be recoated at a later date.