Skimming Over Cinder Blocks: Mastering The Exterior Wall's Smooth Finish

Skim coating an exterior cinder block wall is a process that can be done in a few different ways, depending on the desired finish and the condition of the wall. The process involves applying a thin layer of material over the cinder block to create a smooth and even surface. One method is to use a traditional 3-coat plaster finish, which requires attaching wire lath directly to the block and then applying the plaster. Another method is to use a product like rapid-set plaster, which requires advance training and certification to apply. For a more user-friendly option, a pre-mixed product from a home improvement store can be used. The choice of material also depends on the condition of the wall, with some methods being more suitable for walls with paint or gloss paint. It is important to prepare the wall properly, including cleaning, roughing up the surface, and ensuring it is free from dust and grease.

The process of skim coating a cinder block wall is called parging

To begin the parging process, you need to ensure the cinder blocks are damp. This can be done by spraying the wall with water. The next step is to mix the parging material. A common mixture is three parts masonry sand, two parts Portland cement, and one part lime. You can also add a concrete bonder to the mix to improve adhesion.

Once the mixture is ready, use a trowel to spread it evenly over the wall. It is important to work in sections, especially if the job is large. After applying the mixture, wait for it to set. You'll know it's ready when the mortar turns shiny.

Now, it's time to use a wet sponge float to smooth out the surface. Dip the sponge frequently in a bucket of water to keep it clean and wet. This step is crucial for achieving a consistent finish. Be careful not to make the surface too wet, as it can cause the skim coat to come off.

If you want a sand finish, mix the mortar with a little extra water to make it thinner. Apply it with a smooth plasterer's trowel, using a hawk to hold the mortar. Once the mortar sets, use a wet sponge float in a circular motion to bring the fines to the surface and create a consistent texture.

For a smooth finish, stick with the steel trowel. After applying the mixture, wait for it to set, and then trowel it smooth. This process is similar to creating a float finish or a slick finish on a slab.

Parging is a straightforward process, but it requires some skill and practice to master. It is important to pay attention to timing and maintain the right level of moisture for a successful skim coating of a cinder block wall.

A mixture of three parts masonry sand, two parts Portland cement and one part lime is effective

Skim coating a cinder block wall is a great way to repair and smoothen uneven surfaces. While there are different approaches to this, a mixture of three parts masonry sand, two parts Portland cement, and one part lime is considered effective. This mixture is commonly referred to as a parging mix.

The process of applying this mixture is called parging, and it is often used to repair and refinish concrete walls. Parging mixes are easy to work with and are suitable for vertical surfaces, making them ideal for skim coating cinder block walls.

When preparing the mixture, it is important to ensure that the ingredients are properly combined. The sand and cement should be mixed first, and then the lime can be added. It is also crucial to note that the ratio of ingredients can be adjusted slightly depending on the specific requirements of the project. For instance, adding more cement will increase the strength and stickiness of the mixture but will make it less workable. On the other hand, a ratio with more sand will be more workable but less strong.

Additionally, hydrated lime can be added to the mixture to enhance its properties. Lime helps to reduce shrinkage cracks and improve the mortar's waterproof qualities. By adding lime, the mixing ratio becomes approximately 1:6:15 of lime, cement, and sand.

When applying the skim coat, it is important to ensure that the wall is properly prepared. The surface should be cleaned and free of dust and grease. Any loose materials or deteriorating skim coats should be removed, and a pressure washer can be used to ensure the wall is thoroughly cleaned.

Once the wall is prepared, the mixture can be applied using a trowel or float. It is important to work in small sections, as the mixture will need to be allowed to set before moving on to the next area. The mixture should be applied in a thin, even layer, and a circular motion with a wet sponge float can help to create a consistent finish.

Add a concrete bonder to the mixture for better results

When skim coating an exterior cinder block wall, adding a concrete bonder to the mixture can significantly improve the adhesion of the skim coat to the wall. This is especially important for vertical surfaces, as the mixture needs to be able to stick to the wall without cracking or peeling.

Concrete bonder is a liquid additive that is mixed into the concrete or mortar mixture. It acts as a powerful adhesive, creating a strong bond between the skim coat and the cinder block wall. This helps to ensure that the skim coat will not only go on smoothly but also last longer without cracking, peeling, or chipping.

To use a concrete bonder, simply add the recommended amount to your mixture and mix thoroughly. It's important to follow the manufacturer's instructions for the specific concrete bonder you are using, as different brands may have slightly different mixing ratios.

Once your mixture is ready, you can apply it to the cinder block wall. First, thoroughly wet the entire wall, then re-wet a small section at a time, applying the mixture to each section as you go. This will ensure that the mixture adheres properly to the wall. Use a trowel or paintbrush to apply an even layer of the mixture, working in small sections until the entire wall is covered.

Adding a concrete bonder to your mixture will result in a stronger, more durable skim coat that is less likely to crack or peel over time. It is an important step in the process of skim coating an exterior cinder block wall, helping to ensure a high-quality, long-lasting finish.

Clean the wall with a pressure washer to remove loose material

To skim coat an exterior cinder block wall, it is important to start by cleaning the wall with a pressure washer to remove loose material. This will ensure that the skim coat adheres properly to the wall and create a smooth, even surface for the coating to be applied.

Gather the Right Tools and Safety Equipment:

Obtain a pressure washer with a pressure rating of at least 2000 PSI. Choose a nozzle tip with a 25-40 degree angle to prevent damage to the cinder block wall. Wear protective gear, including eye protection, gloves, and non-slip shoes.

Protect the Surroundings:

Cover any nearby plants or bushes with plastic sheeting or tarps to shield them from the cleaning solution and water pressure. Move or cover outdoor furniture to avoid accidental contact with the pressure washer.

Inspect and Prepare the Wall:

Before starting, inspect the wall for any damage or loose mortar. Use a wire brush to remove loose mortar from cracks, and fill any gaps with fresh mortar to prevent water seepage.

Set Up the Pressure Washer:

Carefully read and follow the manufacturer's instructions for setting up the pressure washer. Fill the detergent tank with a cleaning solution suitable for brick or concrete walls.

Select the Appropriate Pressure and Nozzle:

Choose a pressure setting between 2000-3000 PSI to effectively clean the wall without causing damage. Use the recommended 25-40 degree nozzle tip to avoid harming the cinder blocks or mortar.

Start Cleaning from the Top:

Begin cleaning the wall from the top, working your way down in sections. This will prevent the cleaning solution from dripping onto already cleaned areas.

Move the Pressure Washer Slowly and Evenly:

Move the pressure washer back and forth over the wall in a slow, steady motion, overlapping each pass by about one-third to ensure even coverage.

Avoid Direct Spraying of Mortar and Brick Edges:

Do not spray directly at the mortar or edges of the cinder blocks. Instead, hold the nozzle at an angle to allow the water to spray onto these areas from different directions.

Rinse and Dry the Wall:

Once the cleaning is complete, thoroughly rinse the wall with clean water to remove any remaining cleaning solution or debris. Allow the wall to air dry naturally before proceeding with the skim coating process.

By following these steps, you will effectively clean and prepare the exterior cinder block wall for skim coating, ensuring a smooth and durable finish.

Use a concrete adhesive for decorative walls

If you are looking to skim coat an exterior cinder block wall for decorative purposes, you may want to consider using a concrete adhesive.

Concrete adhesive is a bonding agent used to join or bond concrete surfaces together. It works by creating a strong chemical bond between the adhesive and the concrete, providing enhanced strength and durability. This can be a great option for bonding two concrete surfaces together, such as when you are skim coating a cinder block wall.

When choosing a concrete adhesive, look for a product that is strong, flexible, and waterproof. Adiseal, for example, is a high-performance construction adhesive that provides a strong and flexible bond on concrete, both outdoors and indoors. It is also waterproof, making it suitable for use in various weather conditions.

To ensure a high-quality bond, it is essential to clean the concrete surface thoroughly before applying the adhesive. Remove any dust, grease, paint, or other dirt from the surface. You can use a mixture of water and detergent with a stiff brush, or for a more thorough cleaning, consider jet washing or sandblasting. Once the surface is clean, apply the adhesive evenly to the cinder block wall, following the manufacturer's instructions for the specific product you are using.

Keep in mind that concrete adhesive may not be suitable if you are looking to fill in large gaps or pits in your cinder block wall. In that case, you may need to consider a different product or a combination of products to achieve the desired results.

By following these steps and choosing a high-quality concrete adhesive, you can successfully skim coat your exterior cinder block wall for a decorative finish.

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