What is a Parge Coat?

When it comes to home improvement and masonry, you might have encountered the term “parge coat.” Despite its somewhat obscure name, a parge coat plays a vital role in protecting and enhancing the aesthetic appeal of various structures.

What is a parge coat?

A parge coat is a thin layer of mortar applied over a masonry surface. This coating is typically used on block or concrete walls to provide a smooth, uniform finish. The term “parging” refers to applying this mortar coat. Parging serves several purposes, including improving the wall’s appearance, providing additional protection against weather elements, and covering imperfections in the masonry work.

A typical parge coat is made from cement, sand, and water. Sometimes, additives are included to enhance the properties of the mortar, such as increasing its water resistance or improving its adhesion to the surface. The consistency of the mix is crucial; it should be thick enough to adhere to vertical surfaces without sagging but pliable enough to spread easily.

Applications

Parge coats are commonly used in various scenarios, including:

1. Basement walls: One of the most common applications is on basement walls. Parging can help seal the porous concrete blocks, reducing moisture penetration and preventing minor leaks. This can be especially important in older homes where the basement walls might be more prone to moisture issues.
2. Exterior walls: A parge coat can enhance the appearance of exterior walls, especially those made of concrete blocks, by providing a smooth, finished look. It can also serve as a base for painting or other decorative finishes, allowing for greater versatility in home design.
3. Foundation walls: Parging is often used on the above-ground portion of foundation walls to protect against weather damage and improve aesthetics. It can help shield the foundation from rain, snow, and ice, which can cause wear and deterioration over time.
4. Repair work: Parging can effectively repair minor cracks and surface damage on masonry walls, restoring both structural integrity and appearance. It’s a practical solution for rejuvenating older buildings without requiring extensive renovation.

Benefits of parge coats

Using a parge coat offers several benefits:

• Enhanced appearance: A smooth, uniform finish improves the visual appeal of otherwise rough or unattractive masonry surfaces, significantly boosting a property’s curb appeal.
• Protection against elements: Parging provides an extra layer of protection against moisture, reducing the risk of water damage and improving the wall’s longevity. It also helps prevent the freeze-thaw cycle that can cause masonry to crack and deteriorate.
• Improved insulation: By sealing gaps and cracks, a parge coat can contribute to better insulation, helping to keep your home warmer in the winter and cooler in the summer. This can lead to energy savings and increased comfort. Whilst any improvement in the thermal mass and insulating capabilities of walls is crucial, a parge coat cannot match the performance of external wall insulation.
• Cost-effective: Parging is relatively inexpensive and straightforward compared to other methods of finishing or repairing masonry surfaces. It’s a cost-effective way to maintain and improve the value of your property.
• Acoustic performance: Fewer sound waves travel through the walls directly, leading to less noise.

How to apply a parge coat

Applying a parge coat involves several steps, and while it can be a DIY project, it’s often best handled by professionals to ensure a durable and even finish. Here’s a detailed overview of the process:

1. Surface preparation: The masonry surface must be clean and free of loose debris, dust, and grease. Any significant cracks or holes should be filled beforehand. A thorough cleaning ensures that the mortar adheres properly to the surface.
2. Mixing the mortar: A suitable sand, cement, and water mix is prepared. The consistency should be thick but workable. Additives can be included to improve the mortar’s properties, such as bonding agents for better adhesion or waterproofing agents for increased resistance to moisture. Depending on the type of material chosen, it may be sprayed onto the wall. Many spray machines have hopper attachments which mix your dry material with water to produce a homogeneous mixture.
3. Application: The mortar is applied to the wall in a thin, even layer, typically about 1/4 inch thick, using a trowel. Working the mortar into the surface is important to ensure good adhesion. Sometimes, a metal lath may be installed over the surface to provide additional grip for the mortar.
4. Smoothing: The surface is then smoothed out using a float or a trowel to achieve the desired finish. Different techniques can create various textures, from a smooth finish to a more rustic, textured look.
5. Curing: After application, the parge coat needs to cure properly. This involves keeping it moist for several days to prevent cracking and ensure it sets correctly. Proper curing is essential to achieve a strong, durable finish.

Common questions

1. How long does a parge coat last? A well-applied parge coat can last many years, often up to 30 years or more, especially if maintained properly. Regular inspections and prompt repairs can extend its lifespan.

2. Can I paint over a parge coat? Yes, once it has fully cured, you can paint over it. Painting can provide additional protection and allow customisation to match your home’s aesthetic. As a parge coat is often painted, the initial application does not need to be perfectly smooth. However, it is crucial to apply a breathable topcoat like a Silicone Render or Silicone Paint. As the parge coat is applied to porous surfaces like bricks and is designed to breathe, the topcoat cannot trap moisture behind it.

3. What is the difference between parging and stucco? While both are mortar-based coatings, stucco typically involves multiple layers and is often used as a decorative finish. Parging is usually a thin coat applied primarily for protection and aesthetic improvement.

4. Can parging fix structural issues? Parging is not a solution for significant structural problems. It can cover minor cracks and surface damage, but major structural issues require professional assessment and appropriate repairs. The decision to apply a parge coat or seek further help depends on the depth. For example, EWI-260 Levelling Mortar can smooth surfaces up to a maximum thickness of 50mm.