Rendering is a coating of cement + sand, which can be applied to both internal and external walls and performs a lot of functions, as well as for the waterproofing, inclement weather protection (UV depreciation), fire rating, appearance through colored or texture application, and a plenty of others positive features. To achieve a quality result it is very important that the ratio is adequated to the background surface, what needs to be properly applied in accordance with the thickness and materials.
Starting the rendering materials calculation by a briefly “step-by-step” guide, what will allow the concepts understanding. Let’s go in the following manner:”
For a sample calculation, let’s assume the quantity for 100 m² a 12mm thick plaster and a mix ratio of 1:6.
- Rendering thickness: 12mm = Converting to meter (12/1000) = 0,012m
- Cement mortar ratio for wall rendering: 1 : 6 ( Proportion Cement : Sand )
STEP 1: Calculate the volume of cement mortar required:
We are calculating it for 100 m² and 12 mm thickness (Assumption).
So, Volume of plaster = Area X Thickness = 100 X 0.012 = 1.2 m³
This is a wet volume that means we need this quantity of mortar after mixing, so we need to define the dry volume, what would be the material`s quantity to be dropped into the mixer.
STEP 2: Calculate the dry volume of mortar required.
For achieve the dry volume, we have to add 30-35% as bulkage of sand, let’s adopt 35%, and wastage as 20%.
Remember that wet volume is always less than the dry volume!
So, Dry volume = (Wet Volume) X (Natural Volume + Bulkage (%) + Waste (%))
1.2 m³ X ( 1 + 0.35 + 0.20 ) = 1,86 m³
STEP 3: Calculate the total volume of sand and cement.
Sand required (6 Parts) = 1.86 m³ X 6/7 = 1,59 m³
STEP 4: Calculate the commercial volume for sand and cement.
Once we got the total volume, we need to split into commercial sizes, what will define the total quantity of bags of sand and cement needs to be purchase:
- A 20kg (standard density) bag of general cement has around 0347 m³.
So, 0.265 m³ / 0.0347 = 7.66 bags (Approx. 8 Bags)
And Sand, as it can be ordered bulkage, keeps the same volume: 1,59 m³
Now you are able to calculate the cement and Sand requirement for other Thickness, just need to design mix in the similar fashion.
Furthermore, let´s remember some important point that must be considering to the execution:
- Before the start, ensure that the surface you will rendering is free from dirties.
- Cement rendering thickness should not exceed more than 12-15mm, if there is need, do not do that in one go, or consider acrylic mortar application;
- Be accurate over the measuring boxes you are using for mixing; a consistent ratio will grant the quality and avoid undesired issues;
- Ensure you are choosing a good quality of cement and pure sand, it is essential to achieve the desired result;
We hope that you learn how to Quantity of sand and cement for a job!
Now you are able to start, have a great and successful rendering job!
Super Render Team.