Skimming The Surface: A Guide To Concrete Wall Skim Coating

Skim coating is a great way to give your concrete walls a smooth, professional finish. It is a process of applying a thin layer of material, such as cement, over a wall to even out the surface and create a smooth finish. This technique is often used to cover up cracks and imperfections on interior walls and can also be applied to concrete surfaces like driveways, patios, and sidewalks. Before starting the skim coating process, it is important to properly prepare the area by removing any loose debris and filling in any cracks. The coating process itself involves using a trowel or squeegee to apply a thin layer of cement-based material, which will then dry and harden into an even coat.

Preparing the wall and work area

First, ensure you have the right tools and materials for the job. You will need safety gear, including gloves and eye protection, to shield yourself from dust and chemicals. It is also recommended to have a facemask to prevent inhalation of concrete dust. Basic supplies include an all-purpose joint compound or drywall mud, a trowel or putty knife, sandpaper or steel wool, primer, and paint.

Next, prepare the work area by laying plastic drop cloths on the floor to catch any falling debris or spills. Cover any furniture and items in the room that cannot be moved out. It is important to ensure good ventilation in the workspace to manage the strong odours of the compounds and prevent irritation.

Now, it's time to prepare the wall. Start by removing any loose debris, such as dirt or cement chunks, from the wall with a vacuum, broom, or a damp cloth. If there are any cracks or holes, fill them with an appropriate filler material. For a smooth finish, sand down rough patches on the wall until they are level and even. You can use a wire brush to thoroughly clean the wall and ensure the skim coat will adhere well.

Once the wall is clean and smooth, apply a primer to seal the surface. A fast-drying, stain-sealing drywall primer will help prepare the wall for the skim coat. Allow the primer to dry thoroughly before proceeding to the next step.

After priming, you may need to apply a base coat, especially if your wall has many imperfections or an uneven surface. You can use a joint compound or drywall mud for this step, applying it with a trowel or putty knife in thin, even layers. Ensure there are no gaps between applications. Allow this base coat to dry completely before proceeding.

With the wall prepared, you can now mix your skim coat material. Following the manufacturer's instructions, mix your chosen skim coat cement with water until it reaches the desired consistency, which should be similar to thick wallpaper paste. Ensure there are no lumps in the mixture.

Now you are ready to start the skim coating process. Working in small sections, spread the skim coat mixture onto the wall using a trowel or putty knife. Start at the top of the wall and work your way down and across, filling in any gaps or imperfections as you go. Use the flat side of the trowel to smooth out the mixture and create an even finish. Remove any excess cement with the edge of the trowel using a scraping motion. Ensure you apply a thick enough coat to achieve the desired coverage.

Allow the skim coat to dry for at least 24 hours before proceeding to the next steps, which may include sanding, priming, and painting, depending on your desired finish.

Choosing the right product

When skim coating a wall with concrete, it is important to select the appropriate products to ensure a successful and long-lasting finish. Here are some factors to consider when choosing the right materials:

• Type of Concrete: Select a cement-based skim-coat mix designed specifically for skim coating. This will ensure the right consistency and adhesion to the wall.
• Adhesion: Ensure the product you choose has good adhesion properties, especially if you are skim coating basement walls. Drylok is often recommended for its strong adhesion to concrete.
• Smooth Finish: If you desire a smooth finish, similar to plaster, consider using a product like Durabond, which can be easily sanded to create a smooth surface. Cement-based products may not provide as smooth of a finish.
• Moisture Resistance: For areas with potential moisture issues, such as basements, avoid using water-soluble products like joint compound or Durabond. Instead, opt for a product that is moisture-resistant or specifically designed for damp environments.
• Pre-mixed or Custom Mix: Decide whether you want to use a pre-mixed skim-coat product or create your own mix. Pre-mixed options, like the rapid set line from VOH, offer convenience and consistent quality. Custom mixes, on the other hand, allow you to tailor the mixture to your specific needs.
• Sealers: Consider using a sealer before applying the skim coat to improve adhesion and protect the wall. Water-based stain killers, such as Zinsser's Bulls Eye 1-2-3 primer, are effective and less odorous than solvent-based alternatives.
• Tools: Ensure you have the necessary tools for the job, including a trowel, putty knife, and a squeegee knife (e.g., Magic Trowel). The right tools will make the application process easier and help you achieve a professional finish.
• Safety: Always choose products that are safe to work with and ensure proper ventilation during application. Wear appropriate safety gear, such as gloves and eye protection, to safeguard your health.
• Experience: Consider your level of experience with skim coating. Some products, like Durabond, may be more suitable for those with more experience, while others, like joint compound, can be easier for beginners.
• Surface Preparation: Before applying any product, properly prepare the surface by removing dirt, dust, and debris. Fill any cracks or holes with an appropriate filler to create a smooth base for the skim coat.

Remember to carefully read and follow the manufacturer's instructions for any product you choose to ensure optimal results and adhere to safety guidelines.

Mixing the skim-coat cement

Preparing the Workspace:

Before you begin mixing, it's important to lay plastic drop cloths on the floor to protect it from any spills or mess. Make sure to cover any furniture or items in the room that might get affected by the skim-coating process.

• Start by filling a 5-gallon bucket halfway with water.
• Add the skim-coat cement mix to the water.
• Use an electric drill with a stirring bit to mix the cement and water thoroughly.
• Continue mixing while gradually adding more powder until you achieve the desired consistency. The ideal consistency should be similar to thick wallpaper paste.

Applying the First Layer:

• Begin at one end of the wall, starting from the top and working your way down.
• Dip a cement trowel into the bucket of mixed cement and fill it halfway.
• Spread the cement onto the wall using the flat side of the trowel, ensuring a smooth and even application.
• Remove any excess cement using the edge of the trowel with a scraping motion.
• Apply the skim coat thickly enough to cover the surface evenly.
• Allow the skim coat to dry completely (approximately 24 hours) before proceeding to the next steps.

Additional Tips:

• Always wear proper safety gear, such as gloves and eye protection, when working with cement.
• Make sure the wall is clean and free of any loose debris or substances before applying the skim coat.
• If you're working in a humid environment, consider using a space heater and a box fan to expedite the drying process.
• Depending on the temperature, allow ample drying time between coats, typically around 24 hours.

Applying the skim-coat

Before you begin skim-coating, ensure the area is properly prepared. Remove any loose debris from the surface with a vacuum cleaner or broom, and wipe it down with a damp cloth if necessary. Fill any cracks with the appropriate filler material and sand down rough patches until they are completely smooth. It is crucial to remove any dirt, dust, or debris from the concrete to prevent an uneven finish and air pockets in the final product.

Now, lay plastic drop cloths on the floor to protect it from the skim-coating process. Cover any furniture or items that will remain in the room during this procedure.

Next, scrape the wall lightly with a 6-inch drywall knife to remove any loose cement or other substances. This step ensures that the skim coat will properly adhere to the wall.

For the skim-coating mixture, fill a 5-gallon bucket halfway with water and add a skim-coat cement mix. Use an electric drill with a stirring bit to mix the cement and water thoroughly. Keep adding the powder until the mixture reaches the consistency of thick wallpaper paste.

Starting at one end of the wall, at the top, begin applying the skim coat. Dip the cement trowel into the bucket of cement and fill it halfway. Spread the cement onto the wall, using the flat side of the trowel to smooth it out. Use the edge of the trowel to remove any excess cement with a scraping motion. Ensure you apply a thick enough coat to cover the surface with an even layer of cement.

Work your way down and across the wall's surface, section by section. Allow each section to dry for 24 hours before moving on to the next, and before painting. You can speed up the drying process by using a space heater and a box fan, especially in humid conditions.

You may need to apply multiple coats to achieve the desired smoothness. Two to three coats are common, and it's important to let each coat dry completely before applying the next. The desired thickness after all coats is typically 1/8 inch.

Once the final layer is dry, use sandpaper or steel wool to lightly sand down the entire area until it is smooth. Then, prime and paint the wall to finish the process.

Aftercare and maintenance

Once you've skim-coated your concrete wall, there are several important aftercare steps to ensure the coating's longevity and maintain its appearance.

Firstly, it's crucial to clean the wall with a mild detergent or degreaser and warm water. Use a soft brush or mop to remove any dirt or debris accumulated during the coating process. This step ensures the wall is ready for the next step, sealing.

Sealing the skim-coated wall is essential to protect it from staining, fading, and damage caused by moisture and weather elements. Choose a quality sealant and follow the manufacturer's instructions for application.

Regular maintenance is key to keeping your concrete wall in good condition. Sweep away dirt and debris to prevent discolouration and apply additional coats of sealant every few years to maintain its protective qualities.

If you notice any chips or cracks in the concrete, address them promptly to prevent them from worsening. Similarly, if you notice any bubbling, use a putty knife to gently scrape off the excess material, smooth the area, and apply a new thin layer of skim coating.

Another issue to look out for is cracking, which can occur due to improper mixing. Always ensure the components are thoroughly mixed before use. Finally, discolouration soon after application usually indicates insufficient drying time, so be sure to follow the manufacturer's instructions for curing times.

Frequently asked questions