Cement Rendering is widely used in Chester in plastering applications to new buildings , homes , industrial projects and to enhance old existing ones to repair and protect fretting mortar between decomposed brick joints. Cement rendering has become very popular due to its strength , low cost, durability against exterior exposure and moisture resistance on interior applications .
There are two types of cement render ; EXTERNAL AND INTERNAL . In external rendering The purpose is to achieve a consistent durable crack free wall finish that is called (sand finish ) or applied as a first coat before an acrylic texture coat system . All exterior cement applications must have a water repellent ad – mixture which aids in water ingress protection. Internal cement rendering is predominently used as a first coat render system to achieve a durable levelling coat over bricks then followed by a plaster set –coat.
Render is generally mixed on site by a cement mixer .Combining plasterers sand , GP cement, marvelime and water results in a consistent grey in appearance product that is applied by either hand tools or machine . The applied render when semi – hardened is levelled and smothened by drawing a Plasterers screeding rule across the surface .
Coloured cement render finishes are recommended to be applied in a two coat system . The first coat must be a stronger mix and when hardened this surface is scratched or raked with a suitable raking trowel . This initial process will provide an excellent bond for the final coloured coat . Before the final coat is applied it is essential that the first coat is brushed and lightly sprayed with water to improve adhesion to the substrate. Two coat systems work well when smooth brick surfaces are present . and weak bond strength is evident .Initial first coat with a bonding agent admix is highly recommended .
The function of cement is to provide strength and durability. A mix of 1: 1: 6 ( cement , lime and sand ) for general rendering applications is necessary . Using a weaker mix can lead to cracking / using a stronger mix can lead to rapid setting which in turn also leads to cracking . The grading of the sand plays an important role in rendering . When cement rendering as a base coat or first coat the coarser sand particles are more advantageous over fine particles, finer sand particles are more suitable for smother one coat systems ( sand finish) .
It is essential that the mixing is carried out in a methodically controlled manner,careful attention In accurately batching cement products and sparingly adding the required amount of water to the mix to achieve a soft smooth mix , suitable to be applied by trowel onto a brick substrate is significantly related to the quality and durability of the finished render .
Factors that can affect strength in render are ; exposure to wind and sun ( heat ) it is essential that adequate protection and cement curing is observed and if required the render must be kept damp to ensure correct cement hydration.
the use of admixtures such as air entraining agents , to improve the workability of the render mix are known to affect the strength in renders , marvelime is recommended over (calair) .
Methods to avoid defects in render are ; use all materials in accordance to the plastering standards and manufacturers instructions.
all backgrounds must be fully inspected and prepared
accordingly ( free of all dust and dirt )
in order to reduce excessive suction over the area
to be rendered , it may be necessary to dampen the
the thickness of the render should be between a
nominal (15 - 20 ) m/m for one coat applications .
understand different mix proportions for different
backgrounds and their correct application to substrates.
Chester Plaster & Render adhere to current rendering practices and understand the importance of ''quality '' , not only in workmanship but also ''quality ''in applying plaster products correctly.