Cement Mortar is one of the most common and cheapest binding materials used in construction industry. Cement mortar is basically a mixture of cement, sand & water. It is used in various aspects of civil engineering works such as masonry, brickwork, plastering, flooring etc. There are two types, dry mortar and wet mortar.
Dry Mortar primarily constitutes of only sand and cement. To calculate the quantity of sand and cement for a dry mortar, a standard mix proportion should be chosen from the various mix ratios available. (1:1, 1:2, 1:3, 1:4, 1:6, 1:8)
+ water (& admixtures) → cement paste
+ fine aggregate → mortar
+ coarse aggregate → concrete
Estimation of Water, Cement & Sand quantity for Cement Mortar
Let us assume a standard quantity of 1m3 Cement mortar and a mix proportion of CM 1:6 (1 part Cement & 6 parts Sand). The quantity can calculated in two ways, one is by weight and the other by volume. Let us consider the volume method for the calculation of cement & sand quantity.
Dry quantity of mortar is equivalent to 1.2 to 1.3 times the quantity of wet mortar. This is due to the fact that voids are present in aggregates and cement. Actual value depend on the void ratio of the ingredients which are being used.
Hence, let us assume the quantity of dry cement mortar mix as 1×1.3 = 1.3m3.
The basic formula to calculate the volume of an ingredient is as follows:
Volume of dry ingredient = Volume of dry mortar x (Parts by volume of ingredient / Total parts of ingredient)
= 1.3 x (Parts by volume of ingredient / Total parts of ingredient)
Quantity of cement in Cement Mortar
Here, for 1:6 mix, total number of ingredients in the mortar is 6+1 = 7.
Hence, volume of cement in mortar = Volume of dry mortar x (Parts of cement / Total parts of ingredient)
= (1.3×1)/7 = 0.185 m3
Since the cement is available in bags, volume of 1 cement bag (50kg) is 0.0347 m3.
0.185 m3 = (1.3×1)/(7×0.0347) = 5.35 bags
Quantity of sand
Volume of sand is = Volume of dry mortar x (Parts of sand / Total parts of ingredient)
= (1.3×6)/7=1.14 m3 of sand or fine aggregate
Quantity of Water
For wet mortar recommended water-cement ratio varies from 0.4 to 0.6. Further, water requirement depends on any admixture added to mortar to improve its workability. Admixtures must be added as per suppliers specifications. Hence, water required
= 5.35 bags x 0.0347 = 0.11 m3 water
= 0.11 x 1000 l = 111 liters of water
Apart from this, labour is also required for the purpose of batching and mixing of the cement mortar.
Mortar Material Cost Estimate:
Volume of wet mortar = 1m3
Volume of dry mortar = 1.3m3
Mix Ratio = 1:6
Quantity of cement = 5.35 bags
Quantity of sand = 1.14 m3
|1.||Cement||5.35||Bags||Rs. 350||Rs. 1,872.5|
|2.||Sand||1.14||m3||Rs. 1250||Rs. 1,425|
Estimation of labour cost for Cement Mortar
1 Mazdoor = 0.27 days
1 Bhishti = 0.07 days
|Sl. No.||Labour||No. of days||Wage per day||Amount|
|1.||Mazdoor||0.27||Rs. 400||Rs. 108|
|2.||Bhishti||0.07||Rs. 350||Rs. 24.5|
Total Estimation of Cement Mortar
Sum of material and labour cost = 3,297.5 + 132.5 = 3430/-
Assume 1.5% for water charges = (1.5/100) x 3430 = 51.45/-
Assume 10% for contractor’s profit = (10/100) x 3430 = 343/-
Total Cost = 3430 + 51.45 + 343 = 3,824.45/-
Types of Cement Mortar based on its applicability
Type N mortar
It is generally used for internal and external plastering of parapet walls, exterior walls and interior walls. It is also best suitable for flooring. The initial and final setting time ranges from 2 hours and 24 hours respectively. It has the lesser compressive strength in comparison with the other types of mortars. Its compressive strength ranges from 700-900 psi (5 to 7 Mpa).
Type S mortar
This type of mortar can only be used on load bearing exterior walls, interior walls and parapet walls. The time of setting ranges from 1.5-24 min/hour. The compressive strength ranges from 1800-2800 psi (13 to 20 Mpa). It is best suitable for substructures such as masonry foundations, retaining walls, sewers, manholes etc.
Type M mortar
It consists of highest amount of Portland cement with compressive strength ranging from 1800-3000 psi (13- 21 MPa). It can bear heavy loads and can be used for driveways, heavy foundation, retaining wall etc.
Admixtures used in Cement Mortar
The requirement of right workability is the main essence of good concrete. Addition of extra water increases the workability of concrete but results in concrete cancer and segregation. To overcome this, Plasticizers (also known as water reducers) are used. They impart plasticizing effect in wet concrete and increase the workability of concrete without using excess of water. The plasticized concrete improves the desirable quality of plastic concrete and naturally increases the strength of concrete. Plasticisers are generally used in the amount of 0.1% to 0.4% by weight of cement which results in 5% to 15% reduction in mixing water.
Super plasticizers are improved and more enhanced chemical admixtures with highly effective plasticizing effects on wet concrete. Super plasticizers are chemically different from normal plasticizers. It allows the reduction of water up to 30% without affecting the workability of mortar. It also has additional advantages such as self-levelling, self-compacting and produce high strength and high performance concrete.
Polyvinyl Acetate (PVA)
Bonding type admixtures are basically water emulsions of various organic materials which are mixed with cement or mortar grout and applied over the old surface prior to patching with mortar or concrete. The polymers used as admixtures as Polyvinyl chloride and Polyvinyl Acetate. The main function of this admixture is to increase the bond strength between old and new concrete surfaces. They are added in proportions of 5% to 20% by weight of cement. These admixtures are effective only on clean and sound surfaces.
Waterproofing Admixtures in Cement Mortar
Certain additives are added to the concrete to make the structure water resistance. This is generally achieved by either water repelling agent or pore filling agent. In water repelling type materials like Soda, Potash soaps, Calcium soaps, vegetable oils, fats, waxes and coal tar residues are used. They act as water repellents which makes the concrete impervious. In Pore filling type materials like Silicate of soda, Aluminium & Zinc sulphates, and Aluminium & Calcium chloride are used. These materials are chemically active pore fillers. Chemically Inactive pore fillers are also used in market such as earth fullers, chalk and talc. In addition, they also help accelerate the setting time of concrete.