Painting concrete can greatly improve the appearance and protect the surface from damage. However, applying paint directly to bare concrete rarely produces good results. That’s because the porous nature of concrete allows paint to soak in unevenly, which can leave a splotchy, uneven appearance. Priming concrete before painting helps prevent this problem.
What is concrete priming?
Concrete priming involves applying a special primer designed for concrete surfaces prior to painting. The primer seals the porous concrete surface so regular paint can’t penetrate into the small holes and spaces in the concrete. This allows the paint to glide onto the surface smoothly and evenly.
Some of the key benefits of priming concrete before painting include:
- Creates a uniform surface for paint to adhere to
- Seals pores in concrete so paint doesn’t soak in unevenly
- Allows for more even color and sheen
- Helps paint last longer by improving adhesion
- Reduces the amount of paint needed by preventing absorption
What happens if you don’t use a concrete primer?
Skipping the priming step and applying paint directly to raw concrete can lead to a variety of problems, such as:
- Uneven appearance – Paint will soak into porous areas but remain on the surface of denser areas, creating a blotchy, uneven look.
- Poor adhesion – Paint adheres poorly to the bare concrete surface, causing it to peel or chip off more easily.
- Efflorescence – Water trapped under the paint causes white, powdery deposits to form on the surface as it escapes through the paint film.
- Increased costs – More paint is required to compensate for absorption into untreated concrete.
- Shortened lifespan – The paint job doesn’t last as long and requires more frequent repainting.
How does concrete priming work?
Concrete primer contains sealers and binders that work together to fill pores, even out absorbency, and create a uniform surface:
- Sealers – Oils and resins penetrate into the concrete to seal pores and prevent absorption.
- Binders – Acrylic or latex polymers bind to the concrete surface to create a coating the paint can adhere to.
- Fillers – Mineral deposits and ground limestone fill small voids in the surface.
The primers chemically react with the concrete, forming a hard, sealed layer. The subsequent paint then adheres to the cured primer instead of directly to the raw concrete.
How Sealers Work in Concrete Primer
Penetrating sealers containing oils, silicones, and acrylic or urethane resins are designed to soak into the concrete pores and adhere to the rough texture inside. As the sealer cures, the pores become filled and sealed so water, paint, and other materials can’t penetrate the surface.
Common sealers used in concrete primers include:
- Silane
- Siloxane
- Silicate
- Acrylic
- Urethane
Silane and siloxane sealers chemically react with the concrete to provide durable, long-lasting protection against moisture absorption. Acrylics and urethanes form a protective film on the concrete surface.
How Binders Work
In addition to penetrative sealers, concrete primers also contain polymeric binders. These bind to the concrete surface to eliminate dusting and form a continuous, adhered coating.
Acrylic and styrene acrylic binders are the most common. They cure to a hard film and chemically bond with the concrete to seal the surface. This allows the subsequent coats of paint to adhere evenly and properly.
Without a binder film from the primer, the bare concrete surface is dusty and insufficient for paint adhesion. The paint soaks in and fails to bind effectively.
What is the proper process for priming concrete?
Follow these basic steps for best results when priming concrete before painting:
- Clean and etch – Use degreasers to remove oil and dirt, then etch with acid to rough up the surface for better adhesion.
- Rinse – Power wash off any residue and allow concrete to dry completely.
- Apply primer – Roll on a uniform coat following the manufacturer’s directions.
- Let dry – Allow the recommended drying time before painting.
- Paint – Apply at least 2 coats of exterior concrete paint.
Be sure to select the right concrete primer for your particular paint type. Manufacturers often make specific primers designed to work with particular coatings. Carefully follow all label instructions for best results.
Proper surface prep and application are also critical. The concrete must be clean and dry before priming. Use a pump-up sprayer or roller to apply primer uniformly. Allow thorough drying between coats.
What types of primer work best for concrete?
There are several major categories of primers designed for concrete:
1. Latex or Acrylic
– Made from acrylic resins mixed with water
– Creates a thin, penetrating film on concrete
– Affordable option ideal for many concrete painting projects
2. Epoxies
– Contain epoxy resins and a curing agent/hardener
– Offer very durable adhesion and penetration
– Best for garage floors and industrial surfaces
3. Polyurethanes
– Oil-based urethane resins with excellent sealing properties
– Provide superior protection against moisture and stains
– Ideal for demanding industrial and commercial applications
4. Alkyds
– Made from alkyd resins suspended in solvent
– Bind strongly to form a hard, protective film
– Fast drying but contain high VOCs
For most residential painting, acrylic or latex-based concrete primers offer the best combination of affordability and performance. Epoxies and polyurethanes provide heavier-duty protection.
What sheen should the primer be?
Concrete primer sheens are designated as follows:
- Flat – Provides a dull, matte finish with no gloss or sheen.
- Eggshell – Has a soft, low-luster finish.
- Satin – Appears smooth with a hint of sheen.
- Semi-gloss – Offers moderate gloss between satin and gloss.
- Gloss – Dries to a shiny, light-reflective finish.
Most experts recommend a flat or eggshell concrete primer. The low sheen helps seal the surface evenly without forming a glossy film. This allows the primer to soak in better. Glossier primers may puddle and prevent adequate penetration.
A flat primer also provides an ideal base for the subsequent paint coats. Paint adhesion and coverage improve over low-sheen primers. The paint can provide the desired gloss level rather than relying on a glossy primer.
Do you have to use a primer for concrete?
While priming concrete before painting is not an absolute must, it is highly recommended by manufacturers, contractors and painting professionals. Priming offers important benefits that improve paint application and performance on concrete:
- More uniform appearance from improved paint adhesion.
- Longer lasting paint job since the paint bonds better.
- Better protection against moisture damage.
- Less paint needed because the primer prevents absorption.
You can paint bare concrete without priming, but this is riskier and can produce disappointing results. The concrete surface may end up appearing splotchy or uneven. The paint may also peel or wear away more quickly unprotected by a primer layer.
For longevity and aesthetics, a primer designed for concrete provides crucial protection. The small upfront cost of a primer saves money in the long run by extending the life of the paint job and preventing the need for frequent repainting.
What are the alternatives to using concrete primer?
While priming is the best preparation method, here are a few alternatives to using a traditional concrete primer:
- Acid etching – Etching removes fine particles to profile the concrete. Acid solutions need extensive safety precautions.
- Mechanical abrading – Grinding or sandblasting roughens concrete for paint. Generates messy debris requiring clean up.
- Clear concrete sealers – Provide minimal sealing without improving paint adhesion.
- Latex bonding agents – Acrylic emulsions help paint bind but don’t seal pores.
These options do little to actually seal porous concrete and prevent uneven paint absorption. Most also require high labor costs.
Using a dedicated concrete primer offers a more effective DIY solution. The penetrating sealers fill pores while binders coat the surface, creating the ideal foundation for painted concrete.
Can you use drywall primer on concrete?
It’s best to avoid using regular drywall primer designed for wallboard on exterior concrete surfaces. While less expensive, drywall primer lacks the penetrating and adhesive properties needed for bare concrete.
There are a few issues that arise when using drywall primer on concrete:
- Does not seal porous concrete – Allows uneven paint absorption.
- Lacks binders to adhere paint firmly.
- Not formulated for alkalinity of concrete.
- Vulnerable to moisture damage.
- Indoor formula lacks durability outdoors.
Drywall primer brushes on easily but essentially just sits on top of concrete. Moisture and alkali in concrete can break down vinyl and cause the primer to fail.
Concrete-specific primers contain alcohol, acrylics, latex, and other materials selected specifically to primes bare concrete for paint. Their penetrating and adhesive properties provide long-lasting performance that drywall primers can’t match.
Does concrete primer expire?
Like all paint products, the ingredients in concrete primer can deteriorate over time, causing expired primers to perform poorly. Primers contain chemicals and resins that may become ineffective once past their usable lifespan.
Here are some signs that a container of old primer should be discarded:
- Separation – Liquid separates leaving residue behind.
- Odor – Smell becomes rancid or rotten.
- Color change – Grays or darkens.
- Thickness – Becomes a gelatinous or solid.
- Settling – Pigments sink leaving clear liquid.
These changes indicate the primer is no longer chemically stable and should not be used. Most have a shelf life of 2-5 years if stored sealed in ideal conditions. Check the manufacturer’s recommendations and discard once past the expiration date.
Using expired primer that has separated or spoiled won’t properly seal concrete and leads to failed paint jobs. The small savings isn’t worth poor results and added costs of repainting peeled paint. Purchase fresh primer just prior to starting a painting project.
Does temperature affect concrete primer?
Ambient air and surface temperature affect how concrete primer cures and performs. Most primers specify an ideal temperature range for application:
| Temperature | Effect on Primer |
|---|---|
| Below 50°F (10°C) | Curing slows significantly or stops. Not recommended. |
| 50-85°F (10-29°C) | Ideal range for curing and performance. |
| Above 85°F (29°C) | Primer dries too fast, reducing penetration. |
At low temperatures, the resins and polymers can’t form their bonding networks properly. High heat causes premature drying, preventing the primer from soaking in sufficiently before the surface film hardens.
Ideally, prime concrete when the temperature is predicted to remain between 50-85°F during application and drying. Avoid extreme heat, cold, or freezing conditions.
The surface itself should also be between 40-90°F to allow the primer to form a proper bond. Cooler surfaces inhibit adhesion.
Can you apply primer over damp concrete?
Concrete primer should never be applied to damp, wet, or freshly poured concrete. Primers require a dry, cured surface in order to bond and seal properly:
- Standing water blocks penetration into pores.
- Trapped moisture under primer causes paint failure.
- Concrete must be fully cured for primer to adhere.
- Wet surfaces prevent adequate bonding.
Ideally, allow new concrete to cure for at least 28 days before application. Use a moisture meter to verify old concrete is dry to sufficient depth.
Any standing water, rain, or condensation should be allowed to fully evaporate before priming. The manufacturer’s instructions will indicate the maximum allowable moisture content.
If concrete feels cool, appears dark, or leaves moisture residue on your hand, it’s too damp for effective priming. Allow additional drying time before priming.
Can you put primer over painted concrete?
For repainting previously painted concrete, priming is still a good idea before applying new paint:
- Seals porous areas if old paint is failing.
- Adheres layers for better inter-coat adhesion.
- Prevents lifting or delamination of new paint.
- Allows use of a different paint color or sheen.
However, the process differs from priming bare concrete:
– Lightly sand or etch painted concrete to roughen the surface.
– Spot prime bare areas where old paint has peeled.
– Apply a thinner, soaking coat of primer over the full painted surface.
Without proper prep, new paint may fail to bond to slick or aged paint layers. Effective use of primer provides a fresh foundation for improved paint adhesion over existing coatings.
Conclusion
Applying paint to raw, porous concrete almost always leads to an uneven, blotchy appearance and poor paint adhesion. Dedicated concrete primers contain essential sealers, binders and fillers that prevent these problems.
Primers even out absorbency variations, create a uniform surface for paint adhesion, and provide a protective barrier against moisture damage. Taking the time to properly prime concrete before painting results in a more attractive finish and longer lasting paint job.