Choosing The Right Product for Your Foundation Parging
Last modified: 2019/01/09 | Approximate reading time 3 mins
In Canada, hot summers alternate between cold winters, with frost on the ground and melting snow. In addition to its decorative role, the foundation parging can create a barrier against the inclement weather of our northern climate, temperature shocks, and the sun. It is up to you to choose the right type of plaster!
The part of the foundation that protrudes from the ground, in other words: the base of the exterior wall of your home, is exposed to open air and the sun. This part of the foundation walls must be covered with an applied coating known as parging. Applied to mask the form lines and the imperfections of the surface, whether poured concrete or in concrete blocks joined together, parging plays a decorative role. Note that its application is not required by the Construction Code.
In the case of foundation walls that are insulated from the outside, the application of foundation parging that has been reinforced with a wire mesh or another rigid finishing material is mandatory to protect the insulation from temperature shocks and the sun.
What are the different types of parging?
Simple and affordable, cement plaster is applied to the trowel and smoothed over with a sponge to give a sleek finish or sprayed to get different textures. There are several mixtures of cement parging.
Retailers offer new products such as Ultra-bond parging mix that adheres to concrete foundations, brick and wire mesh. You can also find cement parging in a dry mix specifically designed to conceal irregularities such as joints, colour variations, and deformations, as well as conceal the slight cracks (microcracks). One bag roughly covers an area of 130 sq. ft. and all you need to add is water.
Photo: Johanne & Carole Brunet
Do not change the brand or manufacturer during your project, otherwise, you risk having your exterior foundation having colour variations. Unless you wish to use it for artistic expression, the decorative role of parging remains to mask the foundations in a uniform way.
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Colourful and with greater elasticity than cement parging, acrylic parging increases the adhesion, the flexibility and the tightness. Yellow, red or blue, this product offers a large palette of colours and textures while being ideal for places that are exposed to the weather and de-icing salt. On the other hand, these benefits do come at a cost. Acrylic parging is more expensive than cement parging.
Stratification is done in two layers. The base layer is a liquid mixture of acrylic polymer and Portland cement to which a fibreglass mesh is added so that this layer is shock-resistant to help avoid cracking. The topcoat is composed of polymers which contain colours. As soon as the coating is dry, it will retain its clean appearance for many years.
Photo: Bev Norton
Instead of the first layer, you can opt for lightweight concrete panels consisting of a concrete core, both sides of which are covered with a fibreglass mesh. These panels are highly resistant to moisture, they do not rot or disintegrate, and they do not swell when exposed to water. In addition, they are shock-resistant and extremely durable. The second layer remains indispensable.
Eco-friendly, colourful and textured, crushed stone parging combines the advantages of acrylic parging with the advantages of cement parging. Lightweight, supple, resistant and durable, this type of plastic can give the appearance of granite and it applies with a trowel like cement.
What are the best pargings for straw bale foundations?
Cement/lime render uses a raw material (lime, cement and mortar sand) that is readily available on the market and doesn’t require much handling. The application can be done in two layers, the first of which must be striated to apply the second. This type of render resists erosion and protects against rain, in addition to establishing a thermal mass.
On the other hand, cement/lime render is less permeable to water vapour, which can cause moisture accumulation within the wall. The cement has little flexibility, which is not ideal to cover a material like straw. It can peel off, blister, and crack. Repairs for this type of render are done with latex glue.
Clay render uses inexpensive raw materials, except for transport, which can be repaired easily. Unlike cement, the clay is not corrosive, adheres very well on the surface of a bale of straw and is very permeable to water vapour. The hydrophilic property of the clay provides this material with an ability to capture excess moisture. As for cement, this type of render can form a thermal mass.
On the other hand, clay render requires a lot of manipulation since it must be extracted about 1 year in advance for it to be dry when used, on top of needing to apply four layers. The clay must be protected from the weather, is not very resistant to erosion and must not be applied too close to the ground.
Photo: Doug Kerr
Translation by: David Ben-Zaken
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