Parging: The Ultimate Protective Coat

A parge coat is a thin coat of cement or polymeric mortar applied to concrete or masonry walls to refine the surface. The process, known as parging, is usually carried out by a mason using a trowel, and can be done by hand or with a spray. The purpose of parging is to fill in imperfections, level the surface, and protect the wall from the elements. It can also be used to create airtightness and improve energy efficiency. Parging is a low-cost alternative to repointing and can be used to prepare a surface for a top coat.

The mixture

Parging is made from a blend of lime, water, and cement. The mixture is challenging to get right, as the ratios and balance must be precise. If the mixture is not prepared correctly, it can cause the parging to crack and not stick to the wall, leading to structural problems when exposed to harsh weather conditions. Therefore, it is recommended to leave the mixing to an experienced professional.

The correct mixture will depend on the specific structural and climatic needs of the building. For example, the parging mixture for a wall that needs to withstand heavy rain and snow will differ from a wall in a dry climate. A professional will be able to assess these needs and make the appropriate mixture.

Once the mixture is ready, it is applied to a wet wall with a masonry trowel. The thickness of the coating should be at least 6mm. The application technique will vary depending on the desired surface texture. For a smooth wall, the mortar is trowelled onto the wall. To create a textured wall, gravel, pebbles, or other materials can be mixed into the parging before application.

The parging can then be painted to match the desired décor. Additionally, stucco can be applied over unpainted parging to add a decorative finish. However, it is important to ensure that the parging has cured properly, which requires a temperature of at least 5°C for several days.

Application

A parge coat is a thin coat of cementitious or polymeric mortar applied to concrete or masonry walls. It is typically applied with a trowel and pressed into the existing surface to create a contiguous surface. The process of parging involves applying a layer of smooth cement to walls built with blocks, providing a smooth surface on which different coatings can be applied, such as waterproofing and paints.

Parging is usually done by a mason and is a standard treatment for a structure's foundation and exterior walls, especially if these walls are made of masonry. It is important to work with an experienced professional when applying a parge coat, as adding the proper types and amounts of each component can be challenging. If not done correctly, bad blends can cause cracked parging and issues with the parging sticking to the wall, leading to potential structural problems.

The parging mixture is made from a blend of lime, water, and cement. Once the mixture is ready, it is applied to a wet wall with a masonry trowel. The mortar can be applied to create a smooth wall or a more textured wall, depending on the desired aesthetic. Texturing can be achieved by mixing in gravel, pebbles, and other materials into the mix before application. The coating should be at least 6mm thick and can be applied by hand or by spray.

Parging has several purposes, including improving or creating airtightness, filling air voids, and preparing the wall for a top coating. It can also be used to level the surface for aesthetic reasons and to add structural insulation. Parging is a low-cost alternative to repointing, providing structural cohesiveness to masonry walls whose mortar has begun to fail. It can also be applied to walls with signs of brick deterioration, in combination with a steel mesh to add strength and support.

Benefits

A parge coat is a thin coat of cement or polymeric mortar applied to concrete or masonry to refine the surface. The process, known as parging, is usually carried out by a skilled mason and has many benefits.

Surface Refinement

A parge coat can be applied to fill in imperfections such as air voids, to level a surface for aesthetic reasons, or to prepare a surface for top coating. This creates a contiguous, smooth surface that can be painted to match the décor of a home.

Protection

Parging acts as a protective barrier, shielding vulnerable areas of a structure from inclement weather, such as rain, snow, and ice. This helps to protect the concrete blocks and masonry work from external forces, including wind, and removes the risk of moisture seeping into a masonry wall, which can cause cracking when frozen.

Energy Efficiency

The coat improves a home's energy efficiency by reducing air leakage through cracks, joints, and porous wall constructions. This, in turn, reduces energy consumption and improves comfort. It also acts as an extra layer of insulation, ensuring the home is as energy-efficient as possible.

Acoustic Performance

A parge coat improves acoustic performance by reducing the number of soundwaves that travel through walls, leading to less noise.

Cost-Effective

Parging is a low-cost alternative to repointing, providing structural cohesiveness to masonry walls whose mortar has begun to fail. It is also an affordable way to improve a home's protection against bad weather.

Airtightness

Parging can be used to create airtightness for apartments and improve overall insulation.

Comparison to stucco

Parging and stucco are similar in many ways. Both are applied manually using a trowel, allowing for a range of textures and finishes depending on the technique used. They are also both applied to block or brick surfaces. However, parging is used as a base coat to cover and refine the surface of exterior walls, particularly those made of concrete, concrete blocks, or bricks. It serves to protect the wall from moisture intrusion and weather-related damage, improve thermal insulation, and enhance the overall aesthetic appeal of the building. On the other hand, stucco is applied in several layers over a lath base, giving it a solid, durable surface that can withstand harsh weather conditions and resist cracks. Stucco is primarily used for its aesthetic and insulative properties, providing a decorative finish to the upper walls and facades of buildings.

The materials used for parging and stucco also differ slightly. Parging is typically made from a mix of Portland cement, sand, lime, and water, while stucco is made from a mixture of cement, lime, sand, and water, and sometimes includes additives for enhanced strength and flexibility. The application process for stucco is more labour-intensive and requires skilled craftsmen to ensure a uniform and attractive finish. Stucco dries to a hard, rock-like consistency, creating a protective shell around the building, whereas parging may require more frequent maintenance due to its susceptibility to cracking.

Parging is often used as a cost-effective way to improve the durability and appearance of a building's exterior without the need for extensive masonry work. It can be applied in very thin coats, with multiple coats creating a thicker finish as needed. Stucco, on the other hand, is known for its durability, versatility, and aesthetic appeal, making it a favoured choice for exterior wall finishes. Stucco's adaptability allows it to complement a wide range of architectural styles, from Mediterranean villas to contemporary homes.

When to use

A parge coat is a thin coat of cementitious or polymeric mortar applied to a masonry background. It is used to seal the surface and improve the aesthetic of the wall.

A parge coat is a simple and affordable way to improve your home's protection against inclement weather. It acts as a barrier that shields vulnerable areas of your structure from rain, snow, and ice.

Parging is often used when there is severe and widespread brick deterioration on building walls. The cement coating essentially covers over the brick surface. It is considered a best practice to apply a galvanized steel mesh over the wall surface before the first application of cement parging, referred to as the "scratch coat". The scratch coat may include a grooved appearance, achieved using a notched trowel.

A parge coat is also used to fill "bug holes or pinholes" in concrete surfaces. These holes can result in outgassing, the expulsion of trapped air within a cement mixture.

Parging is a low-cost alternative to repointing, providing structural cohesiveness to masonry walls whose mortar has begun to fail. It can also be used to create airtightness for apartments.

A parge coat will need to be applied to the internal brickwork when drylining in a new house. This is to reduce air leakage through cracks, joints, and porous wall constructions, thereby reducing energy consumption and improving comfort and acoustic performance.

Parging can also be applied to inner basement walls to add to structural insulation.

Frequently asked questions