Sandmar - Surface Preparation

Sandmar Products Australia Pty Ltd

8/26 Longstaff Rd
Bayswater, VIC. 3153

Phone: (03) 9738-0770
Fax: (03) 9738-0996


Surface Preparation


Aquepoxy®- Surface Preparation Guide

Substrate condition: 

The condition of the concrete substrate to which Aquepoxy® Concrete Floor Finish will be applied has a direct effect upon the quality and performance of the coated concrete. Thus, the preparation of the concrete surface to provide a suitable substrate on which to apply the Aquepoxy® Concrete Floor Finish is critical to achieve a satisfactorily coated concrete surface.

Substrate history:

Wherever possible try to determine the history of the concrete from the owner, builder, architect or specifier. Background knowledge about issues such as the age of the concrete, the compressive strength of the concrete, the type of pre-existing coating, conditions to which the concrete may have previously been subjected (including cleaning procedures, contaminating spills etc) should ensure that appropriate surface preparation is employed.

Surface examination: 

A visual examination of the surface should be carried out to determine whether the surface appears to be sound and free from defects, such as the presence of laitance, existing sealers, curing materials, grease, oil, wax, asphalt, gypsum, efflorescence, and dirt or anything else which may interfere with the adhesion of the Aquepoxy® Concrete Floor Finish onto the concrete surface.

Surface Contamination:

Often, common defects and the presence of contaminants on the surface should be identified since they can negatively impact on the adhesion of the Aquepoxy® Concrete Floor Finish coating to the concrete. Whilst the range of contaminants can be wide, we offer the following suggestions for removal of the following contaminants which, if permitted to remain, would be typically expected to cause adhesion problems.


Efflorescence is caused by moisture being carried through the concrete and is manifested as the appearance of crystalline water soluble salts on the surface. Such water soluble salts can interfere with the adhesion of the Aquepoxy® Concrete Floor Finish and the subsequent treatment of the substrate. Any salt deposits should be removed with a stiff bristle broom, followed by scrubbing with clean water and a final rinse with clean water. However, it is important to recognize that the presence of efflorescence indicates that moisture ingress from external sources has most likely occurred. Such moisture ingress should be prevented from continuing to occur, or else this will provide a hydrostatic pressure which could cause any subsequent coating on the concrete such as Aquepoxy® Concrete Floor Finish to lift off. Where moisture ingress from external sources is recognized to be occurring, and cannot be easily prevented, the services of a qualified building engineer should be sought to determine what courses of action are required prevent to prevent such moisture ingress.

Clay soil:

Contamination with clay soil may occur, particularly on newly laid concrete. As much residue as possible should be removed by mechanical means, and the affected area should be washed with hot water and detergent followed by a rinse with clean water.

Fungal Growth:

Where fungal growth has occurred, the surface of the concrete should be wetted and a chlorine bleach applied with vigorous scrubbing followed by a rinse with clean water. Within a few days a deposit of dead fungal cells will usually be noticeable, these should be removed by further brushing with a stiff bristle broom and repeat of the cleaning process as necessary.

Oil and grease stains:

In particular, these can be very difficult to remove because of their rapid absorption and penetration into the concrete surface. Where a fresh oil spill has occurred, its spread should be prevented by encircling with absorbent material such as sand, dirt, cat litter or sawdust. Any residual stain should be covered with a 5 mm layer of poultice made of 1 part of lime to 2 parts of Mineral Turpentine. This is then covered with plastic sheeting and left in place for 24 hours. After this period, the cover should be removed and the powder scraped off. After a day or so, where any deeply ingrained oil or grease has continued to rise to the surface, it may be necessary to repeat the process. Subsequently, washing of the surface with mild detergent (sugar soap) and water is recommended, followed by a final rinse with clean water.

Chewing gum:

Chewing gum can be solidified by contact with ice cubes followed by removal through mechanical scraping as much as possible. Persistent residues should be treated with a poultice made up of cat litter or similar absorbent material which has been saturated with methylated spirits. After drying of the poultice, the residue should be brittle, permitting removal with a wire brush or scraper.


Laitance is a weak layer of cement, lime and sand fines on the concrete surface, which prior to the concrete curing can rise to the surface of concrete which has been subject to over-watering, has been permitted to dry prematurely or has been subjected to other conditions such as over trowelling. If excessive laitance is present then this weakly bonded zone at the surface of the concrete must be removed by mechanical means such as diamond grinding to provide a sound, solid concrete substrate on which the Aquepoxy® Concrete Floor Finish can achieve good adhesion.

Flaking and drummy floors:

Flaking is where small surface pieces become detached from the surface of the concrete, usually these are flat – hence the name “flakes”. Flaking is caused by inappropriate finishing techniques (usually mechanical), prior to curing of the concrete, where the surface has been sealed and has trapped water which would normally rise to the surface as bleed water. Drummy floors, which may be identified by tapping, are indicative of delamination of the concrete surface. Flaking and drummy floors should be repaired by removal of delaminated concrete by mechanical means as discussed in the section below, followed by appropriate repair to the damaged area where necessary.

Mechanical Properties of Concrete:

Mechanical properties of the concrete such as the compressive strength are important. The use of a concrete hardness scratch tester to determine the surface hardness is highly recommended.

Low Compressive Strength Concrete:

Where the compressive strength is low, due to weak zones such as those caused by laitance, then subsequent removal of the weak zone by mechanical means, e.g. diamond grinding, is recommended.

High Compressive Strength Concrete:

Where the compressive strength is very high (such as in high strength concrete which has a compressive strength of greater than 35 MPa), then the adhesion of a coating such as Aquepoxy® Concrete Floor Finish can be an issue. A mild acid etch followed by a wash with sugar soap and rinse with clean water is recommended. In extreme cases such as a burnished concrete surface, mechanical abrasion by diamond grinding or similar may be required to remove any glazed surface layer and provide a porous concrete surface for effective coating adhesion of Aquepoxy® Concrete Floor Finish. In any case, adhesion testing of Aquepoxy® Concrete Floor Finish on the prepared surface is essential.

Pre-existing Coating: 

Where there is a pre-existing coating on the concrete, it should be understood that Aquepoxy® Concrete Floor Finish will adhere to most pre-coated concrete surfaces although the adhesive bond strength to the concrete will only be as good as the adhesion of the existing coating to the concrete. If the previous coating shows any sign of flaking or peeling, this coating must be removed completely, e.g. by diamond grinding, with appropriate washing of the surface with mild detergent (sugar soap) and water, followed by a final rinse with clean water, prior to application of Aquepoxy® Concrete Floor Finish.

Residual Concrete Curing Compounds & Membranes:  

There are three common classes of concrete curing membranes: Polyvinyl Acetate (PVA), chlorinated rubber and wax emulsions. PVA latex polymers, although the least effective as curing membranes, do not usually need to be removed before Aquepoxy® Concrete Floor Finish is applied. Wax-based curing agents, and chlorinated rubber-based systems in particular, must be removed, preferably by diamond grinding, before application of Aquepoxy® Concrete Floor Finish or indeed any surface coating or flooring adhesive, since these agents generally behave as bond breakers and reduce adhesion.

Importance of Adhesion Test:

Adhesion of the Aquepoxy® Concrete Floor Finish to the concrete surface is critical. Thus, in all situations where the presence of any deleterious surface treatment or contaminant is suspected, and appropriate remedial measures have already been carried out then adhesion to the concrete surface should always be tested (Aquepoxy® Concrete Floor Finish samples are available) on small areas of the concrete surface prior to the general application of Aquepoxy® Concrete Floor Finish.

Age of Concrete – More than 28 days:

Traditionally, the application of coatings onto newly cast concrete has been restricted to the concrete which has been permitted to cure for at least 28 days. This is because drying and shrinkage cracks can occur as the concrete cures. At the same time, to achieve effective bonding, concrete coatings which are based on solvent-based or solventless resin systems such as epoxy resins etc should only be applied onto a completely dry surface, which is unlikely to be achieved before the 28 day period has passed.

Age of Concrete – Less than 28 days:

However in the case of waterborne epoxy resin coatings such as Aquepoxy® Concrete Floor Finish, a damp concrete surface is not such a concern, and Aquepoxy® Concrete Floor Finish can be applied to a slightly damp surface (recently washed) but not when saturated i.e. mop up ponded water before application. It may also be applied to freshly casted concrete which has not been permitted to cure for the full 28 days, so called “green” concrete. In such a case, the coating acts as a curing compound, however it should be recognized that any drying and shrinkage cracks will not be bridged by the Aquepoxy® Concrete Floor Finish and may therefore be evident in the coated cured concrete at some later stage.


Diamond Grinding:

The most effective way to remove laitance and to smooth out surface imperfections in the concrete is by mechanical treatment such as diamond grinding. Diamond grinders use horizontally rotating discs (encrusted with industrial diamonds) to abrade the concrete surface so that it becomes clean, level and smooth. Diamond grinders with full vacuum extraction will significantly reduce the level of dust produced by the grinding process. Diamond grinding which has been effectively carried out completely removes laitance and levels off imperfections on the concrete surface, to provide a flat, smooth surface with ideal property profile ideal for all coatings, Aquepoxy® Concrete Floor Finish. To achieve the best possible result, the services of a trained diamond grinder using appropriate diamond grinding equipment should be employed.


Another mechanical method is that of shotblasting, where tiny beads of shot are propelled at the concrete surface trip to produce a profiled surface suitable for subsequent coating. This method gives a very rough surface and is not recommended.

Acid Etching:

Acid etching is not recommended, because it may not necessarily remove all laitance and the presence of any residual acid could interfere with adhesion, curing or subsequent performance of the Aquepoxy® Concrete Floor Finish. Also, acid etching does not remove petroleum-based or vegetable oil contaminants and can produce variations in surface sheen, which may become visible later through the Aquepoxy® Concrete Floor Finish.


Detergent Washing:

To remove surface oil and grease (and any water soluble contaminants such as efflorescence) the washing of the surface with mild detergent (sugar soap) and water is recommended. High pressure water washing with or without sugar soap detergent is highly recommended. Ensure that puddles of wash water are vacuumed up and that no residue is left behind on drying. A final rinse of the cleaned surface with clean water is recommended to remove any cleaning agent residues.

“Water drop” Test:

A "water drop" test can be used to determine if a surface is clean. Water beads on surfaces contaminated with sealers, curing compounds, oil, and grease.

Solvent Cleaners Not Recommended:

In general, except where necessary under the specific cases discussed above, the use of solvents, degreasers, or adhesive removers should not be used to remove contaminants from porous concrete since the use of such chemical methods may drive the contaminant deeper into the pores of the concrete, and may later migrate to the surface before application of Aquepoxy® Concrete Floor Finish and will reduce its subsequent adhesion.


Prior to the later application of Aquepoxy® Concrete Floor Finish, any surface defects such as projections from the concrete which are greater than say 1-2 mm in height, and which have not been remedied through mechanical grinding, should be corrected appropriately. At the same time any holes or cracks which are present may be repaired (e.g. by using a paste of Aquepoxy® Concrete Floor Finish together with Ordinary Portland Cement), and any such repair patch to be permitted to cure before subsequent application of Aquepoxy® Concrete Floor Finish. Surface defects which have not been appropriately addressed may still remain visible even after coating with Aquepoxy® Concrete Floor Finish.


Once the surface preparation has been carried out to achieve a surface which is acceptable, then application of Aquepoxy® Concrete Floor Finish may proceed. Further details on application of Aquepoxy® Concrete Floor Finish are contained in our separate Application Guide.

We point out that information is subject to change without notice. These suggestions and data are based on information we believe to be reliable. They are offered in good faith, but without guarantee, as substrate, methods of use of our products and actual site conditions are beyond our control. We recommend that the prospective user determine the suitability of our materials and suggestions before adopting them on a commercial scale.

Aquepoxy® is a registered trademark of Sandmar Products Australia Pty. Ltd. 


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