How to Render

How to Render a Brick Wall or House or Ferro Cement Structure

Plastering is coating a surface with cement render or plaster finish on an internal or external wall. Plaster is for the decoration and protection of every building.

The role of external plaster is not only for decoration but to primarily protect the covering structures of the building against the impacts of the external environment (rain, wind, sunshine) in addition to thermal and sound protection of interior areas.

Render is also commonly used as a structural component of ferro cement construction.

Courtesy of Cockburn Cement you may Download a copy of their Basic Rendering Guide

Basic-Rendering-Instructions by CC

RENDERING BASICS

Cement-based renders improved fire rating and give an improved appearance through the use of coloured or textured renders.
To get the best results it is important that the mix is suited to the background surface, that it is properly applied to the correct thickness in the appropriate number of coats and that attention is paid to curing.

PREPARING THE SURFACE TO BE RENDERED

Before you start make sure that the surface you are rendering is free of dirt, dust, oil, grease, paint, silicone or friable material. Smooth dense surfaces with low absorption rates like concrete or metal window frames should be prepared with a “dash coat” prior to the application of the render.

A dash coat is simply a very strong mix of cement and water which is flicked over the wall or metal window frames creating a surface for the render to grip to. Leave the dash coat to dry for a minimum of 24 hours before you start to apply the render.

Highly absorbent surfaces like porous brick will normally require pre-soaking to prevent water loss from the freshly applied render.

MIXING THE RENDER

  • First, decide on the type of render finish you want. Determine the correct mix ratios and roughly how much material you will require.
  • When mixing renders by hand, measure the quantities carefully using the same measuring container for all ingredients.
  • Renders should be mixed on a hard flat surface or in a cement mixer or wheelbarrow.
  • Mix up enough render that can be used up in 30 – 40 minutes.
  • Ensure that all the materials are thoroughly mixed.
  • Add water only a little at a time. It can be very easy to add too much water and destroy the integrity of the render

APPLYING THE RENDER

As a guide for thickness, you can nail wooden battens of the correct desired thickness vertically on the walls to give you  flat surfaces to screed from

Rendering by Steel Float –  start forcing the first layer of render onto the wall. Keep applying the render until you have reached the desired thickness. Once the thickness has been reached, use a straight edge such as a metal leveller and screed off the render using a sawing motion. Gently trowel smooth with a steel float or a sponge depending on the finish desired.

Render can be applied to walls and ceilings significantly faster saving a lot of labour by using the right render spray equipment.

If you are applying more than one coat, you will need to let each coat dry for at least 3 – 7 days. You will then need to scratch each coat with a sharp object to provide a good surface for the second coat of render to bond to.

FINISHING THE RENDER

A number of decorative finishing effects can be achieved using different finishing techniques on the final coat.

Trowel Finish – Achieved by skimming the final coat using a wooden float to produce a smooth dense surface.

Bagged / Patterned Finish – Achieved by rubbing a ball of damp hessian into the surface which produces patterns depending on the style of rubbing.

Sponge Finish – Mopping or sponging the hardened surface with a damp sponge achieves a sponge-textured finish.

Care should be taken not to let the water run down the wall spoiling the finish by washing the cement out of the render.

Roughcast Finish – Throwing and flicking the final coat onto the surface achieves a rough cast finish,

Textured Finish – Textured finishes can be achieved by the addition of a coarser aggregate being added to the mix for the final coat.

One More Thing About Cement Rendering

On hot days where the temperature exceeds 27 degrees C, it is highly recommended that you either render early in the morning or late afternoon. If you need to do the job during the heat of the day or in direct sun, slightly dampen the brickwork with a fog spray before applying the render. This ensures that the bricks do not suck the water out of the render mix before it has time to adhere properly to the brickwork.

 

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