Cement render

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Rendered house in Greece A Greek house and walls rendered and white washed.jpg
Rendered house in Greece
Rendered house in France A rendered and painted French house.jpg
Rendered house in France

Cement render or cement plaster is the application of a mortar mix of sand and cement, (optionally lime) and water to brick, concrete, stone, or mud brick. It is often textured, colored, or painted after application. It is generally used on exterior walls but can be used to feature an interior wall. [1] Depending on the 'look' required, rendering can be fine or coarse, textured or smooth, natural or colored, pigmented or painted.

Contents

The cement rendering of brick, concrete and mud houses has been used for centuries to improve the appearance (and sometimes weather resistance) of exterior walls. It can be seen in different forms all over southern Europe. Different countries have their own styles and traditional colors. In the United Kingdom, cement is optional. [2] In other countries, lime is optional. [3] The cement in render hydrates the same way it does in concrete. [4]

Render finishes

Different finishes can be created by using different tools such as trowels, sponges, or brushes. [5] The art in traditional rendering is (apart from getting the mix right) the appearance of the top coat. Different tradesmen have different finishing styles and are able to produce different textures and decorative effects. Some of these special finishing effects may need to be created with a thin finishing top coat or a finishing wash. [6]

Traditional rendering

Cement render consists of 6 parts clean sharp fine sand, 1 part cement, and 1 part lime in some parts of the world. [7] The lime makes the render more workable and reduces cracking when the render dries. Any general purpose cement can be used. Various additives can be added to the mix to increase adhesion. Coarser sand is used in the base layer and slightly finer sand in the top layer.

The application process resembles the process of applying paint. To ensure adhesion, the surface to be rendered is initially hosed off to ensure it is free of any dirt and loose particles. Old paint or old render is scraped away. The surface is roughened to improve adhesion. For large areas, vertical battens are fixed to the wall every 1 to 1.5 meters, to keep the render flat and even. [8]

Acrylic rendering

There is also a wide variety of premixed renders commercially available for different situations. Some have a polymer additive added to the traditional cement, lime and sand mix for enhanced water resistance, flexibility and adhesion. [9] [10]

Acrylic premixed renders have superior water resistance and strength. [11] They can be used on a wider variety of surfaces than cement render, including concrete, cement blocks, and AAC concrete paneling. These acrylic modified renders may still be too brittle and cannot be applied over substrates like fiber cement sheeting, as they will crack on the joints and can allow water to enter the sheet and cause delamination of the coatings. The newer technology polymer exterior cladding such as expanded polystyrene (EPS) can have these acrylic modified renders applied to them with the inclusion of an alkali resistant mesh encapsulated between the render coats. Some premixed acrylic renders have a smoother complexion than traditional renders. There are also many various acrylic-bound pigmented 'designer' finishing coats that can be applied over acrylic render. Various finishes, patterns and textures are possible such as sand, sandstone, marble, stone, stone chip, lime wash or clay like finishes. There are stipple, glistening finishes, and those with enhanced water resistance and antifungal properties. Depending upon the product, they can be rolled, troweled or sponged [12] on. A limited number can also be sprayed on. [13] Acrylic renders usually take only 2 days to dry and thus much faster than the usual 28 days for traditional render.

A disadvantage of acrylic render vs. traditional rendering is that acrylic render lacks the sustainability and environmental compatibility of traditional cement-and-mineral render. All buildings have a finite lifetime, and their materials will eventually be either recycled or absorbed into the environment. As acrylics are synthetic polymers, they do not break down by natural weathering the same way that a cement, sand, and lime mixture will, and so will persist in the natural environment for much longer as synthetic chemical compounds that have unknown long-term effects on ecosystems. Also, the application and drying process of solvent based acrylic resin render involves the atmospheric evaporation of pollutant solvents—necessary for the application of the resin—which are hazardous to the health of humans and of many organisms on which humans depend. Synthetic polymers such as acrylic are manufactured from chemical feedstocks such as acetone, hydrogen cyanide, ethylene, isobutylene, and other petroleum derivatives. The polymer products cannot be fully recycled (using present technology or any that can be confidently expected to be developed), so new raw materials, taken from the finite and diminishing supply of raw natural resources, must always be put into their manufacture, making the process unsustainable. Traditional cement-based render does not have these problems, making it an arguably better choice in many cases, despite its working limitations. Using Waterborne resins will not have these disadvantages. [14] [15] [16]

See also

Related Research Articles

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<span class="mw-page-title-main">Paint</span> Pigment applied over a surface that dries as a solid film

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<span class="mw-page-title-main">Varnish</span> Transparent hard protective finish or film

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<span class="mw-page-title-main">Terrazzo</span> Cementitious composite material, usually used in flooring

Terrazzo is a composite material, poured in place or precast, which is used for floor and wall treatments. It consists of chips of marble, quartz, granite, glass, or other suitable material, poured with a cementitious binder, polymeric, or a combination of both. Metal strips often divide sections, or changes in color or material in a pattern. Additional chips may be sprinkled atop the mix before it sets. After it is cured it is ground and polished smooth or otherwise finished to produce a uniformly textured surface. "Terrazzo" is also often used to describe any pattern similar to the original terrazzo floors. Modern forms of terrazzo include polished concrete.

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Plaster is a building material used for the protective or decorative coating of walls and ceilings and for moulding and casting decorative elements. In English, "plaster" usually means a material used for the interiors of buildings, while "render" commonly refers to external applications. The term stucco refers to plasterwork that is worked in some way to produce relief decoration, rather than flat surfaces.

<span class="mw-page-title-main">Stucco</span> Construction material made of aggregates, a binder, and water

Stucco or render is a construction material made of aggregates, a binder, and water. Stucco is applied wet and hardens to a very dense solid. It is used as a decorative coating for walls and ceilings, exterior walls, and as a sculptural and artistic material in architecture. Stucco can be applied on construction materials such as metal, expanded metal lath, concrete, cinder block, or clay brick and adobe for decorative and structural purposes.

<span class="mw-page-title-main">Siding (construction)</span> Exterior cladding on building walls

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<span class="mw-page-title-main">Plasterwork</span> Construction or ornamentation done in plaster or a similar material

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<span class="mw-page-title-main">Sealant</span> Substance used to block the passage of fluids through openings

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<span class="mw-page-title-main">External wall insulation</span>

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An external render is, in its most basic form, a coating applied to the walls of a building, to provide a protective coating which would prevent rain penetration. It also acts as a decorative finish to enhance the appearance of a building.

Waterborne resins are sometimes called water-based resins. They are resins or polymeric resins that use water as the carrying medium as opposed to solvent or solvent-less. Resins are used in the production of coatings, adhesives, sealants, elastomers and composite materials. When the phrase waterborne resin is used, it usually describes all resins which have water as the main carrying solvent. The resin could be water-soluble, water reducible or water dispersed.

<span class="mw-page-title-main">Chalk paint</span> Water-based paint made with chalk

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References

  1. Pros, Sydney Rendering (27 March 2021). "Applications of Cement Render for Your House" . Retrieved 9 March 2023.
  2. "Basics of Rendering A Wall with Sand & Cement". Lee Jones Building And Roofing. Retrieved 13 January 2022.
  3. "Is sand and cement render outdated? | External Rendering". 27 January 2014. Retrieved 13 January 2022.
  4. "Cement hydration". Understanding Cement. Archived from the original on 17 October 2012. Retrieved 1 October 2012.
  5. "Rendering". designingbuildings.co.uk. Retrieved 6 February 2022.
  6. "Rendering Exterior Walls and Outside Wall Rendering including Rendering a House". DIY Doctor. Retrieved 6 February 2022.
  7. "How much cement sand and lime do I need for rendering". Civil Sir. 17 May 2021. Retrieved 13 January 2022.
  8. "Wall Rendering Techniques". Home Guides | SF Gate. 20 September 2010. Retrieved 13 January 2022.
  9. Polymer modified cements and repair mortars. Daniels LJ, PhD thesis Lancaster University 1992
  10. Melander, John M.; Farny, James A.; Isberner, Albert W. Jr. (2003). "Portland Cement Plaster/Stucco Manual" (PDF). Portland Cement Association. Archived (PDF) from the original on 12 April 2021. Retrieved 13 July 2021.
  11. "Acrylic Rendering vs Cement Rendering | Rok Rendering". rokrendering.com.au. Retrieved 13 January 2022.
  12. "Guide to basic rendering". Swan Cement. Retrieved 6 February 2022.
  13. "Sprayplaster System and Polymer Modified Renders". monocote.com. Retrieved 6 February 2022.
  14. Howarth, GA (2003). "Polyurethanes, polyurethane dispersions and polyureas: Past, present and future". Surface Coatings International Part B: Coatings Transactions. 86 (2): 111–118. doi:10.1007/BF02699621. S2CID   93574741.
  15. Howarth, G.A. and Hayward, G.R., "Waterborne Resins", OCCA Student Monograph No. 3, Oil and Colour Chemists' Association, UK, 1996.
  16. Howarth, G.A (1995). "5". In Karsa, D.R; Davies, W.D (eds.). Waterborne Maintenance Systems for Concrete and Metal Structures. Vol. 165. Cambridge, U.K: The Royal Society of Chemistry. ISBN   0-85404-740-9.

Further reading