Deep-Jointed Block Painting: A Step-By-Step Guide

Painting a concrete block with deep joints requires a few extra steps compared to painting a regular wall. The first step is to clean the concrete block and ensure it is completely dry. Then, seal any cracks or joints with a foam backer-rod and polyurethane caulk. Next, apply a coat of primer to the concrete block, ensuring that all pores are filled. Finally, apply a coat of paint. For highly moist surfaces, it is recommended to use elastomeric paint.

Prepare the surface by cleaning and repairing

Preparing the surface by cleaning and repairing is essential for achieving a successful paint job. The quality and longevity of a paint job depend heavily on how well the surface is prepared before painting. Proper preparation enhances paint adhesion, improves appearance, and increases resistance to wear, moisture, and corrosion.

First, inspect the surface to evaluate its current condition. Identify old coatings, rust, dust, oil, grease, or other contaminants. Detect surface defects like cracks, dents, or corrosion. The material type—metal, wood, concrete, or plastic—will determine the method and intensity of preparation. For instance, metal surfaces often require sandblasting to remove rust, while concrete may undergo acid etching to open its pores.

Next, thoroughly clean the surface to remove any contaminants that could affect paint adhesion. The method of cleaning depends on whether you are painting interior or exterior walls. For interior walls, begin by using a duster or dry cloth to wipe down the wall, paying special attention to corners and where the wall meets the ceiling and floor. Then, use a damp cloth or soft sponge soaked in warm water and a mild detergent to wipe down the walls. Kitchen walls, which are often exposed to more smoke, oil, and splatters, may require a grease-cutting detergent. For exterior walls, cleaning is even more critical as they are exposed to environmental debris. If there is mould or mildew on exterior walls, use a store-bought mildew remover or a mixture of one part bleach to three parts water.

After cleaning, roughen or remove surface layers through sanding, grinding, wire brushing, or abrasive blasting. This allows for better bonding of the paint. Sanding is commonly used for wood, while metal surfaces may require welding or epoxy putty. Once abrasion is complete, repair any visible damage or imperfections. Fill cracks, holes, dents, and uneven areas with suitable fillers or patching materials.

Finally, apply a primer to the surface. Primer improves paint adhesion, seals porous surfaces, blocks stains, and provides corrosion resistance. There are primers available for every project and substrate. For example, metal primers contain anti-rust agents, while concrete primers prevent moisture penetration.

Choose the right primer

Painting a room may seem simple, but getting a smooth paint job can be difficult. Primer is a preparatory coat that readies the surface for paint application, acting as a base coat for the top coat of paint. It is not always necessary, but it can be essential for a long-lasting paint job.

The first step in choosing the right primer is to determine whether you need one at all. If you are working with a previously painted surface that is in good condition, you likely do not need to prime. However, if you are working with bare substrates that have not been previously painted or coated, primer is highly recommended.

The next step is to identify the type of coating used on the surface, if there is one. To do this, rub a cotton ball dipped in 70% isopropyl alcohol on the surface. If the paint comes off, it is an acrylic-based paint; if it does not, it is an alkyd-based paint.

Once you have determined that you need primer, you can choose between an acrylic primer or an alkyd (oil-based) primer. Acrylic primers offer easier application, water clean-up, and fewer environmental considerations. They can be used for almost any surface, including wood, laminate, and metal, unless there is rust. Alkyd primers offer superior stain blocking and are a good choice for interior and exterior bare wood substrates. They are also a good option if you have removed wallpaper, as they seal the residual adhesive. Most acrylic and oil-based primers will accept both acrylic and oil-based top coats.

If you are dealing with stains, severe odors, or moisture damage, you may want to use a stain-blocking primer, which is available in both oil-based and water-based versions. Oil-based primers give off a strong smell and require paint thinner for cleanup, but they are more reliable for blocking water-based odors and stains like rust, nicotine, smoke, and water. Water-based stain-blocking primers offer easy cleanup and less odor and come in low- and no-VOC formulations.

Finally, if you are painting outside, you should never use shellac primer. Latex or oil-based primers will specify if they are meant for interior or exterior surfaces.

Apply primer

Applying primer is an important step in the painting process as it helps the paint adhere to the surface better and produces a good finish. It also helps cover existing paint colours and blemishes. Before applying the primer, ensure you have enough to cover your entire surface. A gallon of primer covers between 250 to 400 square feet of the surface. You may need two coats of primer over heavy stains or tannin-rich wood. Most primers can be tinted to help with coverage, especially when using bright or deep colours.

To apply the primer, start by cutting in a 3-foot by 3-foot section. Using a 9-inch roller, cover the roller entirely with primer and roll off any excess on a ridged paint tray. Then, paint a vertical strip at the cut-in corner and work around the room, applying primer from top to bottom. Reload the roller when necessary and always overlap areas of wet primer.

If you are priming around corners or places where walls, moulding, and ceilings meet, use a 2-inch nylon-polyester paintbrush or corner pad. Brush primer on areas that need special attention, such as joint compound, patches in drywall and plaster, areas of bare wood, and any places treated with a stain blocker.

If a second coat of primer is required, allow the first coat to dry completely before applying the second coat. Once the primer is applied, lightly sand your primed wall with fine-grit sandpaper to smooth the surface for painting.

Choose the right paint

To paint nine square blocks with deep joints, it is important to choose the right paint for the job. The type of paint you will need depends on the material of the blocks you are painting. If you are painting concrete blocks, you should use a concrete and masonry primer. For basements and outdoor walls, a waterproof primer is necessary. The primer helps the paint adhere to the wall by filling the pores of the concrete and neutralising the pH.

Once the primer is dry, you can begin to paint. For concrete blocks, the best types of paint are acrylic latex paint, elastomeric paint, and milk paint. Elastomeric paint is ideal for areas with high moisture, such as basements. If you are painting indoors, be sure to use interior concrete paint, and for outdoors, use exterior concrete paint.

If you are painting cinder blocks, you should also use a masonry bonding and filling primer. After the primer has dried, you can apply the paint with a roller and follow up with a small brush to get into the small spots and crevices. You can also use a paint sprayer, but you will still need to use a hand brush for the edges and corners.

For a long-lasting paint job on a block wall, one source recommends mixing white emulsion paint with cement to create a nice grey colour. This combination is said to last about 35 years.

Additionally, if you are painting concrete blocks that are prone to moisture, Drylok is recommended to prevent darkening and seepage.

Apply paint

To paint a 9-square block with deep joints, you will need to first prepare the surface by cleaning and priming the blocks. Use a putty knife or paint scraper to remove any current paint. If the blocks are exposed to water, you may notice a white powder coating on the outside, which can be removed by scrubbing with a masonry cleaner and a scrub brush. Allow the cleaned areas to dry completely for 24 to 48 hours before proceeding.

Next, seal any cracks or joints with polyurethane caulk. Insert a backer rod into the joint first, ensuring it is slightly thicker than the joint itself. Then, apply the caulk liberally with a caulking gun, covering the joint completely. Smooth the sealant with a plastic spoon and mineral spirits for a neat finish.

Now, you are ready to prime the blocks. Choose a bonding and filling primer that is latex acrylic-based and apply it with a nap roller. Allow the primer to dry for at least 4 hours or as recommended by the manufacturer.

Finally, it is time to apply the paint. Use a high-quality acrylic latex paint in your desired colour. For large areas, use a paint roller, and for smaller areas, you can hand-paint. Ensure the paint is applied evenly and smoothly. Allow the first coat to dry for 12 hours before adding a second coat if needed.

Remember to work in a well-ventilated area and wear protective gear when working with paint and chemicals.

Frequently asked questions