When it comes to wall rendering, you need the right type of sand to create a perfect render. The builders usually mix a certain amount of plastering sand, cement and hydrated lime for exterior walls rendering. The exterior walls with sand finish plaster then coated with paint or other texture coatings as desired. For internal walls rendering, you need to apply the float coat first as an undercoat before applying the finishing coat.
Unfortunately, the plaster of the wall can’t stay last forever. You will need walls re-rendering, especially for the exterior walls, as the weather exposure will damage them over time. A new layer of plaster will be needed to shield your home from the natural elements that fasten up the wall deterioration.
The process goes the same with interior plastering. However, to get an easily repaired wall, you need a soft finishing. The white set finishing coat is a suitable coat for interior plastering. You can easily repair or refurbish it using paint.
Step by Step: Wall Rendering Using Plastering Sand
1. Preparing the Surface
Before rendering, make sure the wall surface is free of dirt, oil, paint or anything that will prevent the render stick to the wall. The smooth, dense, pore less surfaces such as concrete or metal window frames are low absorption rate surfaces. You need to apply a “dash coat” first before rendering.
A dash coat is a strong mixture of cement and water applying to the metal window frames or wall to ensure the render will grip well to the surface. After applying the dash coat, let it sit for 24 hours or more before rendering. For the high absorbent surfaces such as sandstone, you need to soak it down to prevent water loss after applying the render.
2. Mixing Plastering Sand with Other Materials
The render requires plastering sand, water and lime as the mixture materials. The standard ratio for the render is 6 parts sand: 1 part cement: 1 part lime. You can use any type of cement for the render.
But, you need a particular type of sand with a fine texture and impurities-free. Plastering sand is the best sand you can use for the rendering mixture. Make sure you get the best sand price or competitive price from a trustable sand supplier. As the material used to increase the render elasticity and prevent it from cracking, you need to use hydrated lime. It is the most appropriate type of lime used for the render.
When mixing the render, measure all materials using the same gauge vessel. Mix the render on a hard and flat surface such as a concrete slab or board. You can use a cement mixer or mix it on a wheelbarrow as well. Mix an amount of render you can apply for the next 30 to 40 minutes.
Gather all dry materials and mix them until you get uniformed colour. Add the water gradually while you are mixing the dry materials. Mix it until you get a soft sticky texture. It should not fall easily from the steel float when you turn it upside-down. You can’t use the render if the texture is too wet. Discard it and start over again.
3. Applying the Render
For the renders thickness guide, use wooden battens and nail them vertically to the wall. The correct thickness wooden batten will give you clean edges to get a balanced thickness.
Use steel float to apply the mortar to the wall. Start applying the render from the bottom to the top until you get the desired thickness. When you reach the desired thickness, used a metal leveller (or a metal board with serrated teeth texture) to screed the mortar, fill the holes and make it balanced.
Apply the steps above for every render coat and let it dry for at least 3 to 7 days before applying the next coat.
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We recommend you do rendering at a time when the temperature below 27 Celsius. If it is impossible, dampen the brick wall using fog spray before applying the render to assure the brick wall won’t suck the render mix’s water before it has time to adhere to the wall.