Exposed brick walls have a rustic charm, but sometimes a smooth, modern finish is what a room truly needs. Transforming a brick surface with plaster can completely update a space, making it feel brighter and more contemporary. Many homeowners are intimidated by the thought of plastering, picturing it as a messy, difficult job best left to professionals. However, with the right preparation and technique, it’s a project that a determined DIYer can successfully tackle.
Learning how to plaster over brick is a skill that can save you a significant amount of money while giving you complete control over the final look of your walls. This guide is designed for beginners, breaking down the process into clear, manageable steps. From preparing the brick surface to applying the final smooth coat, we will walk you through everything you need to know to achieve a professional-quality finish and give your room a stunning new look.
Why Plastering Over Brick Is a Great Home Upgrade
Plastering over an existing brick wall is a fantastic way to modernize an interior space without the need for major demolition. It provides a clean, seamless surface that is perfect for painting or wallpapering, opening up a world of design possibilities.
Beyond aesthetics, a layer of plaster can improve a room’s insulation, helping to regulate temperature and even providing a small amount of soundproofing. It’s a cost-effective renovation project that adds significant value and visual appeal to your home, transforming an old-fashioned or dated look into a fresh, contemporary style.
8 Step-by-Step Guide: How to Plaster Over Brick
Step 1: Prepare the Brick Surface Thoroughly
Proper surface preparation is the most critical step for ensuring your plaster will have strong adhesion and a lasting finish. Begin by cleaning the brick wall thoroughly with a stiff-bristled brush and a solution of sugar soap or a similar degreasing cleaner to remove any dust, soot, grease, and loose debris. If you encounter any mold or mildew, treat it with a specialized fungicide.
After cleaning, rinse the wall with clean water and allow it to dry completely. Any paint or old sealant must be removed, either by sandblasting, chemical strippers, or a wire brush, as these coatings will prevent the plaster from bonding correctly.
Step 2: Repair Any Damaged Brick and Mortar
Once the wall is clean and dry, carefully inspect the brickwork for any damage. Look for crumbling bricks or loose, cracked mortar joints.
Any unstable areas will compromise the integrity of your new plaster finish. Use a hammer and chisel to carefully chip away any deteriorated mortar. Replace any severely damaged bricks. Repoint the mortar joints using a fresh mortar mix, pressing it firmly into the gaps with a pointing trowel. Ensure the new mortar is flush with the existing brickwork. Allow any repairs to cure completely, which can take several days, before proceeding to the next step.
Step 3: Apply a Bonding Agent or PVA Glue
Brick is a highly porous material, which means it can suck the moisture out of the plaster mix too quickly, causing it to dry improperly and crack. To prevent this and ensure excellent adhesion, you must prime the wall. Apply a generous coat of a specialized plaster bonding agent or a diluted solution of PVA glue (typically one part glue to four parts water) to the entire brick surface. Use a large brush or a roller for even application. This sealer creates a barrier that controls the suction of the brick, allowing the plaster to cure at the correct rate.
Step 4: Mix the First Coat of Plaster (Scratch Coat)
The first layer of plaster, known as the scratch coat or render coat, provides a solid, level base for the final finish. You will typically use a cement-based render or a browning plaster for this layer. Mix the plaster according to the manufacturer’s instructions, adding the powder to clean water in a large bucket. Mix thoroughly with a paddle mixer attached to a drill until you achieve a smooth, consistent, thick paste-like texture that holds its shape on a trowel without sliding off. Getting the plaster mix right is essential for learning how to plaster over brick successfully.
Step 5: Apply the Scratch Coat to the Wall
Load some of the plaster mix onto a hawk or a plastering float. Using a steel trowel, apply the plaster to the wall in a firm, upward sweeping motion. Start at the bottom corner and work your way across and up the wall. Aim for a consistent thickness of about 1/4 to 3/8 of an inch (6-10mm). The goal of this coat is not to be perfectly smooth but to cover the brick and fill the mortar joints completely. Keep your trowel at a slight angle to the wall to spread the material evenly.
Step 6: Score the Scratch Coat for Adhesion
While the scratch coat is still wet but beginning to firm up, you need to score its surface. This process, known as “scratching,” creates a rough texture that will provide a strong mechanical key for the second coat of plaster to grip onto. Use a plasterer’s scratch comb or a simple tool like a notched trowel or even an old fork. Make horizontal, wavy lines across the entire surface of the plaster. The scratches should be deep enough to create grooves but not so deep that they go all the way through to the brick.
Step 7: Apply the Second and Final Coat (Skim Coat)
After the scratch coat has fully cured (this can take 24-72 hours, depending on the product and conditions), you can apply the finish coat. For this layer, you will use a multi-finish or finishing plaster, which has a finer consistency. Mix it to a smooth, creamy texture, similar to thick custard. Apply this skim coat over the scratched base coat using your trowel. This time, the goal is to achieve a flat, smooth finish. Apply a thin, even layer, working in smooth, arching strokes to cover the entire wall. This is a key technique in knowing how to plaster over brick.
Step 8: Trowel the Wall for a Smooth Finish
Achieving a perfectly smooth finish requires several passes with the trowel as the plaster begins to set. After applying the skim coat, wait about 15-20 minutes for it to firm up slightly. Then, go over the entire surface again with a clean, damp trowel held at a very low angle to the wall. This will smooth out any lines and imperfections. Repeat this process two or three more times, adding a tiny amount of water to your trowel for lubrication on the final passes. This progressive smoothing is what creates the coveted glass-like surface.
Frequently Asked Questions
Do I Have to Use a Scratch Coat, or Can I Plaster Directly onto Brick?
It is highly recommended to use a base or scratch coat. Brick walls are often uneven, and the scratch coat provides a crucial leveling layer. More importantly, it creates a strong, uniform base with a mechanical key (from scoring) for the final skim coat to adhere to. Plastering directly onto the brick without this intermediate layer can lead to poor adhesion, cracking, and a finish that mirrors the unevenness of the brickwork below.
What Is the Difference Between Plaster and Render?
The terms are often used interchangeably, but there are differences. “Render” typically refers to the cement-based coatings used for the initial, rougher coats applied to masonry, especially for exterior work. “Plaster” usually refers to the gypsum-based, finer materials used for the final, smooth interior finish coats. In this project, you use a render or browning plaster for the scratch coat and a finishing plaster for the skim coat.
How Long Does It Take for Plaster to Dry Completely?
The drying time for plaster varies significantly based on the thickness, the type of plaster used, humidity, and ventilation.
- The initial scratch coat needs at least 24-72 hours to cure before applying the skim coat.
- The final skim coat will feel dry to the touch in a few hours, but it is not fully cured. It can take anywhere from a few days to several weeks to dry completely before it can be painted. A light pinkish-brown color turning to a uniform light pink indicates it’s drying.
Can I Plaster Over a Painted Brick Wall?
No, you should not plaster directly over a painted brick wall. The paint creates a barrier that will prevent the plaster from bonding to the brick surface, leading to delamination and failure. The paint must be completely removed before you begin. You can use methods like sandblasting (for exterior walls), chemical paint strippers, or vigorous scrubbing with a wire brush to remove all traces of paint.
What Is the Best Way to Clean My Tools After Plastering?
Clean your tools immediately after use, as dried plaster is extremely difficult to remove. Scrape off as much excess plaster as possible back into your bucket or into a trash bag. Then, wash the tools thoroughly with warm water and a stiff brush. Do not wash large amounts of plaster down the drain, as it can set in your pipes and cause severe blockages. Use a separate bucket for washing and dispose of the plaster-filled water responsibly.
Conclusion
Mastering how to plaster over brick is a transformative DIY skill that allows you to completely change the character of a room, creating a sleek, modern canvas from a dated or overly rustic surface. While it requires patience and attention to detail, the process is straightforward when broken down into manageable steps. By following the proper procedures for preparation, application, and finishing, you can achieve a professional-looking result you’ll be proud of.
Don’t be daunted by the idea of working with plaster. With the right tools and the knowledge from this guide, you are well-equipped to take on this project. Embrace the process, and enjoy the deep satisfaction of turning that old brick wall into a flawless, new surface.