An Introduction To Sand & Cement Render
Modern cement renders are much harder and stronger than lime renders. A sealed or painted cement render can help a building in certain circumstances by helping prevent penetrating damp. Cement renders are generally mixed using ordinary Portland cement.
As these are so rigid, they are not suitable for older buildings as they crack and break in no time at all. Hydrated lime can be added to the cement mix to increase durability and flexibility of the render but it by no means cures all problems associated with cement render.
Cement render is generally a cheaper alternative to Lime Render. It is often applied as they are cheap for the builder to make and relatively easy to apply. Cement render also cures reasonably quickly when additives are used. Caution should be taken when specifying cement renders as they are incredibly rigid and will crack, spall or delaminate if there is any movement in the substrate or if the moisture content is too high.
Hairline cracks are a common issue with sand cement renders. When selecting a paint system, it ideal to select a paint with crack bridging properties. If the substrate cracks are any bigger then hair line it is advisable to fill these with a flexible filler that is paintable. The specified paint system should also be elastomeric. These elastomeric properties will resist any reflective cracks from the render substrate. As a crack or split in a paint film is a potential ingress point for moisture with could lead to damp issues.
Recommendations From Our Technical Team
Mapei Elastocolor Paint System
An excellent choice for painting sand cement renders is the Mapei Elastocolor painting system. The Elastocolor system is ideal for application on the both new and old sand and cement renders. Elastocolor protects a sand and cement render by forming a highly flexible film on the surface which is impermeable to moisture whilst remaining breathable. This product is also highly resistant to ageing and UV degradation.
KEIM Soldalit Paint System
Keim Soldalit is a superior paint product. You can apply it directly onto existing coatings or modern render without priming. This product will protect exterior surfaces in conditions exposed to weathering. It provides a long term protection system and will resist UV light damage, including some acids and chemicals. Soldalit also hinders the growth of algae and fungus. This is due to its excellent moisture resisting properties.
Bedec Extra Flex Masonry Paint
Bedec Extra Flex Elastomeric Microporous Masonry Paint with up to 400% elasticity for use over cracks. It is ideal for the protection of exterior masonry, roughcast, pebble-dash, brickwork, cement and concrete rendered surfaces. This paint provides surfaces with a smooth, long lasting finish. It even stretches up to 400%. This aids the prevention of further cracking after bridging the fine cracks.