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How To Paint Concrete Floors

If you have decided to start painting a concrete floor, proper application is crucial for the effectiveness and longevity of the concrete floor paint or sealer. Here is a guide with some tips, to help the process of a successful application.

Preparing Concrete Floors

Thoroughly clean the floor to remove any surface debris, dirt, dust, and especially oil and grease stains. This step is essential as any dirt or other debris left will prevent the paint or sealer from adhering to the solid concrete substrate below.

If necessary, etch the concrete to ensure proper adhesion of the sealer. Etching involves using an acid-based solution such as Polycote Etch IT to remove the weak laitance and dust.  The etching solution will also help create a keyed texture to a smooth surface which then helps the sealer to penetrate and bond effectively to the substrate.

If the floor is already painted with a concrete floor paint, even an epoxy paint, make absolutely sure the old paint has fully adhered to the concrete surface, before painting a fresh coat over the top. If it is flaking or not adhered well, make sure it is fully removed (a wire brush will make this an easy job and is ideal for this), otherwise you are headed for failure. If you do paint over the top of old paint that is loose, even with an epoxy concrete coating, the end result will be no different than painting over a sheet of paper! Frankly, an utter waste of time and money!

For larger industrial sized floor areas, the professional way to prepare a concrete surface is to use a vacuum assisted shot blaster or diamond grinder. We have approved installers able to complete this work for you. Alternatively, we are able to hire the machinery for you to complete the work using your own labour and elbow grease. Diamond grinders can also help smooth out worn or poorly laid concrete in order for you to achieve a smooth finish.

Oil and any other contaminants must also be cleaned from the surface of concrete floors. Polycote Degrease IT is an excellent product to help remove contamination or other concrete stain. Degrease It is designed to lift the oil from the surface which can then be washed away with clean water and/or can be removed using a suitable aqua vac machine.

It is best to allow the concrete surfaces to dry as much as possible before applying the chosen concrete paint or concrete sealer.

Repairing Holes And Cracks

Repair any cracks or imperfections in the surface of the substrate prior to the application of the concrete floor paint. Cracks can compromise the effectiveness of the sealer and allow moisture to seep through, leading to potential damage. Fill in the cracks with a suitable low viscosity resin such as Crackfiller EP100. Fine blemishes and small holes can be filled with products such as Easi-fil which is a tough and extremely durable product that can be trowelled super smooth and will dry in less than 30 minutes.  Finally for larger holes, where maybe you might have impact damage or where bolts have been removed from the floor, products such as Cretex EP require minimal experience and will prove to be quick and easy to use.

Should you need to fill holes that are contaminated with oil on a garage floor for example, our Cretex OT Mortar is a highly specialised epoxy resin floor repair that includes oil tolerant resins in order to adhere to oil contaminated floors.  This should be included in your ‘must have supplies’, especially in garages and engineering workshops.

Allow any crack fillers or patching compounds to dry completely before applying the sealer coat.

Ensure Substrate Is As Dry As Possible

First and foremost, if you are intending to use a solvent based paints such as Flortex PU, it is crucial to ensure that the concrete floor is completely dry.  Solvent based products will not adhere to damp surfaces.

Water based Paints such as WD Primer, Flortex SG or Flortex Clearseal will adhere to damp concrete surfaces. However, even though they are tough and durable, we still strongly advise to have the floor as dry as possible and the reason for this is very simple:  If the floor is wet, the pores or the concrete are ‘filled’ with water and thus, the chosen primer will achieve little to no penetration of the substrate. The concrete paint will achieve far better adhesion and be far longer lasting if it is allowed to penetrate and ‘lock’ well into the substrate. Apart from this, any moisture left on the surface prior to application of the sealer may well result in an uneven finish as well as a poor or even non-cure situation.

High build and pure epoxy paints such as Flortex Professional and Flortex EP, should all be applied to a dry floor. If any water or dampness has been in the area, it is always advised to allow the surface to air dry for at least 24 hours and ensure there if appropriate air circulation. Of course, the use of dehumidifiers or fans, or raising the ambient temperature with the use of heaters, can all help speed up the drying process prior to painting concrete.

Has Your Floor Got A Damp Proof Membrane (DPM)?

A damp proof membrane is normally a plastic sheet that has been laid under the concrete in order to prevent damp rising up for the ground below. In older houses, this might have been a layer of bitumen or pitch.

If you have any evidence of rising damp, it is vital that you apply a DPM Primer as the first coat to prevent the water from rising and bubbling up through the chosen top coat. If the surface is very porous, it may be advisable to apply two coats. Concentrate on the edges of the room to make certain you have achieved a good seal. Remember, just one pin hole is all it takes to empty a swimming pool! If you are unsure as to rising damp, a moisture test would be advisable that will show if there is an excess moisture present within the substrate.

Is Your Concrete Showing Any Signs Of Oil Contamination?

If you have any oil contamination within the concrete, particularly on garage floors, standard paints, including epoxies and polyurethanes, will NOT stick. You MUST clean the area of any oil contamination. If you need a degreaser to help accomplish this, especially stubborn oil, Polycote Degrease IT is an excellent product to lift the oil from the floor so that you can clean this away thoroughly.

We then strongly advise the use of Polycote OT Primer, which is an oil tolerant primer which has been professionally formulated to adhere strongly to oil contaminated concrete. You must remember that the oil has sunk down into the pores of the substrate and even after cleaning the floor, the underlying oil will rise by capillary attraction and simply lift the paint you hope to apply. This is very reason why thousands of companies cannot get the paint to stick!

Rest assured, Polycote OT Primer will solve this issue. However, if the surface is very porous, it may be advisable to apply two coats in order to completely seal the surface.

Applying The First Coat Or Primer Coat

First and foremost, it is essential to read and understand the application instructions as stated on the product data sheet BEFORE proceeding. Different floor paint and sealers can be applied similarly by paint roller, brush, squeegee, or sprayer. Each paint type will have different application methods, coverages and drying times. Again, the product data sheets will have all of the information you need prior to painting.

It is important to apply enough primer to be able to penetrate the surface to not only seal the concrete but to allow a good bond. It is always advisable to apply an even coat as much as possible. However, you will almost always find that some parts of the floor are more porous than others. This will be why the first coat might appear patchy. The paint will soak into some areas due to the concrete being more porous, whereas in other areas where the concrete is denser, the paint starts to build on the surface and has begun to show a nice even sheen. This is all perfectly normal, and the second coat should then achieve a nice even finish.

Apply the paint evenly, working in small sections. Start from one corner of the room and work your way towards the exit to avoid stepping on the freshly applied sealer. Ensure that the sealer is applied evenly and without leaving puddles or streaks.

Applying The Top Coat

It is important to wait for the first coat to dry completely BEFORE applying the second coat.  If the substrate is really porous, then it may be advisable to apply a second coat. This is particularly relevant when using Polycote DPM Primer or Polycote OT Primer. Indeed, should any further coats be required, allow the existing coat to cure before continuing with any further applications.

If you have high traffic areas, a high build epoxy top coat such as Flortex Professional would be highly recommended.

Avoid over-application and brush out any puddling, as this may lead to a uneven paint finish.

How To Achieve A Non Slip Finish

Almost all of our top coats have an anti slip option available. This is where the ‘standard’ coating is supplied with a non slip aggregate that is either mixed in with the paint prior to application, or can be sprinkled onto the first coat whilst it is wet and then the second (top) coat is applied over to completely seal in the aggregate.

You may well have been frustrated in the past due to the so called non slip paint becoming smooth after only a short period of time and this is simply due to the poor strength of the aggregate used to achieve a slip resistant finish.  The calcined bauxite aggregate we supply, has one of the highest levels of shore hardness with a Mohs level of 8.5. and can withstand both constant and heavy traffic, and still maintain good slip resistance for many years. For more information on the Mohs levels, see https://www.nps.gov/articles/mohs-hardness-scale.htm

Curing And Drying Times

After applying the sealer, allow it to cure and dry according to the manufacturer’s instructions, before allowing use of the area. Remember that the curing and drying time can vary greatly depending on the environmental conditions as well as the type of sealer used.

To allow for the correct and sufficient curing times will ensure the sealer not only bonds effectively with the concrete but will also withstand the wear and tear of daily life and thus, provide long-lasting protection. It is crucial to follow the recommended curing time before subjecting the floor to regular use.

Hazards To Avoid When Painting Concrete Floors

Applying sealer too thin

When applying too thinly, often when persons are trying to cover an area as cheaply as possible, remember that you will have next to no penetration and the final coating will be very weak.  The longevity of even an expensive paint when applied to thinly will be hugely reduced!

Applying sealer too thick

The top two reasons why you should not apply too thickly:

1) If it is a water or solvent based product, and it is applied in a very thick coat, the top surface of the coating will begin to ‘skin’ over and thus the curing begins.  However, the water (or solvent) this is within the coating itself then has to percolate through the surface skin in order for it too, to cure. This the overall curing time of the paint will be exponentially longer.

2) Applying any top coat too thickly may well result in the floor looking patchy rather than leaving a nice even finish.

Use of chemicals

No matter whether you use basic cleaning chemicals or the possibility of more harsh chemicals spilling onto the floor, make sure the coating has the fully cured before being exposed to chemicals.

Water, Condensation, Dew Point.

It is best to allow the coating to cure for at least 24 hours before being subjected to water allow.

High humidity levels and/or condensation dripping down onto the concrete floor can cause an uncured sealer to ‘bloom’ thus causing an unsightly whiteness to the surface.  This discolouration does not normally have too much of an ill-effect and will, in many cases, actually ‘wear off’ over a period of time.  However, if the coating is subjected to too much surface water, and in the worst case scenario, this can result in a poor or even non-cure situation.

Mixing and Pot-Life

If you have decided to use a twin pack resin sealer to paint your concrete floors, make certain that the product is mixed in the correct proportions. as stated on the data sheet.

Mixed materials will then have a pot life that can be anywhere from 5 minutes to 2 hours.  The pot life is the period of time you have to apply before the coating goes too hard and is mostly dictated by the curing time of the said product.  The faster the curing time, the shorter the pot life. Please consult with the manufacturer’s product data sheets BEFORE mixing.

Finally, and for obvious reasons, don’t mix more material than what you can apply within the given (pot-life) time.

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