One of the many important technicalities, knowledge of which one must have before commencing construction works on site is regarding mortar concrete ratios. Various ratios required for respective jobs have already been predefined by engineers however some are mentioned on construction drawings that must be followed to ensure quality. Brickwork, plaster, concrete etc have its own different ratios that vary in strength. Though it might be a very minor technicality throughout the construction process that needs to be taken care of, but it is very much critical and can have a significant impact on overall construction, quality and most importantly the cost. Many contractors and builders intentionally or unintentionally tend to ignore and do not keep an eye and check on labor during manual mixing process that results in deficient ratios, hence compromising the quality. Hence to ensure a good workmanship it is necessary to take care of this very minor yet an important technical procedure at all stages of house construction.
What is the method of writing or defining mortar or concrete ratios?
Ratios are always defined in following formats:
Where A mostly indicates quantity of cement, B indicates quantity of sand or fine aggregate and C indicates quantity of crush or course aggregate.
What are the most common mortar ratios?
Mortar is used for bonding of brick layers in brickworks as well as for final rendering of brick walls known as plastering. Ratios used for these tasks are:
Ratios such as 1:3 and 1:4 are mostly used for plastering and for thinner layers of brickwork where more strength is required whereas 1:5 and 1:6 are most commonly used for normal brickwork. More the ratio of sand means weaker the mortar and lesser the ratio of sand means stronger mortar.
What are the most common concrete ratios?
Concrete is used in slabs, columns, rafts, foundations and beams to hold a structure together. If used with reinforcement then it is referred to as reinforced cement concrete whereas if used without concrete then it is called plain concrete or lean concrete required mostly for general floorings. Most common ratios used for concrete are:
1:4:8 or M7.5
1:3:6 or M10
1:2:4 or M15
Ratio used for slabs, columns, foundations, rafts and beams in residential construction is mostly M15 or 1:2:4 whereas ratios such as 1:4:8 and 1:3:6 are used for PCC (plain cement concrete) pads and flooring.
How to check mortar mixing ratios on site as a layman?
In small and medium scale residential or commercial projects, metal dishes and wheel barrows are used to carry and mix material as shown in picture below(medium and large sized metal dishes). Metal dishes are available in two sizes whereas wheel barrow is of standard size.
Cement bags available in market have a net weight of 50 kg which consists of 1.25 cft of cement. One medium sized metal dish accommodates approximately 20 kgs of cement, hence one cement bag = 2.5 medium sized dishes. Now let us suppose that proposed ratio to be mixed is 1:4, it means that 4 parts of sand are to be mixed with 1 equal part of cement. If mixing is being done in proportion to 1 cement bag, then 10 medium sized dishes of sand would be required to make a mixture of 1:4. (2.5 x 4 = 10). Similarly if ratio to be mixed is 1:6, then 15(2.5 x 6 = 15) medium sized dishes of sand would be required in proportion to 1 bag of cement.
If metal dishes being used are of relatively larger size, then 2 dishes would be required to accommodate 1 complete bag of cement. In this case for a mixture of 1:4, 8 dishes of sand would be required for 1 bag of cement to obtain required ratio (2 x 4 = 8) whereas 12 dishes of sand would be required to make a mixture of 1:6.
Another scenario for mixing can be by using wheel barrows. 1 wheel barrow can accommodate 5 medium sized metal dishes. Hence to make a mortar mixture of 1:4 ratio using wheel barrows, 1 bag of cement would require 2 full wheel barrows of sand. And 3 full wheel barrows of sand would be require in proportion to 1 bag of cement for making a 1:6 mortar mixture.
How to check concrete mixing ratios on site as a layman?
Concrete is required in foundations or basement rafts, retaining walls, beams, columns,PCC and slabs. Most of the time concrete is required in bulk quantity, hence mixing is done using mixer machines. Material content in concrete that includes cement, sand (fine aggregate) and crush (course aggregate) is dumped in material collector of a mixing machine by using wheel barrows. Most important ratio of concrete that is required in most of the cases is 1:2:4, this means that for each single bag of cement (5o kg) 2 parts of sand and 4 parts of crush are required to make the said ratio. As described earlier, 1 wheel barrow accommodates 5 medium sized dishes, and 2.5 same sized metal dishes can be filled with 1 cement bag (50 kg). This means that for each bag of cement, 1 full wheel barrow of sand (2.5 x 2 = 5) and 2 full wheel barrows of crush (2.5 x 4 = 10) would be required to make a ratio of 1:2:4. Very important ingredient in concrete mixture is the quantity of water. For a perfect mixture and for understanding as a layman, water should be kept in range of 25 to 30 litres for 1 bag of cement while making a ratio of 1:2:4. Similarly for making a ratio of 1:3:6 that is required in PCC, instead of increasing quantity of sand and crush, quantity of cement is decreased to around 30-35 kgs.