3.0. ESTIMATING MASONRY

The most commonly used material in masonry works is the concrete hollow blocks. Estimation of masonry works involving CHB includes the following items:

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1. Concrete hollow blocks
2. Cement for mortar and plaster
3. Sand for mortar

Different procedures in calculating the number of CHB are available. Most of which utilize the area of spans using CHB.

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3.1. CONCRETE HOLLOW BLOCKS (CHB)

Dimensions of concrete hollow blocks are standardized at 16 inches length by 8 inches height (0.40m x 0.20m). The only dimension which varies is the thickness. CHB thicknesses range from 4 inches to 8 inches. 

• 4 inches (0.10m) thick CHB is typically used for CHB partitions.
• 6 inches (0.15m) thick CHB is used for exterior walls.
• 8 inches (0.20m) thick CHB is used for special walls.

3.1.1. THE FUNDAMENTAL METHOD

This method uses the dimensions of block - 8inches height by 16 inches length (0.2x0.40m). Vertical and horizontal layers of the wall will be computed by dividing the wall's height (length) by a unit CHB. The total number of CHB will be the product of the vertical layers by the horizontal layers.

3.1.2. THE AREA METHOD

The area method is based on the number of CHB that will fit a square meter then having this compared with the area of wall to be estimated.

Example 3.1.1 Estimating CHB using the two methods 
Example 3.1.2. Estimating CHB in a concrete structure (Two methods)
Example 3.1.3. Estimating CHB of an irregular wall

3.2. MORTAR

Mortar can be mixed with sand-cement or sand-cement-gravel mixture. Although the mixture with gravel will yield higher strength, most construction procedures apply sand-cement mixture for workability. 

There are two uses of mortar in block laying:

• Cell filler - mortar placed inside CHB cells to keep the masonry into one solid structure. The CHB thickness affects the volume of the hollow cells in a CHB. Regardless of the thickness of the CHB, CHB is made with standard size of 8"x16" using 1" thick concrete sides. The cell length also remains the same at 3".

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• CHB laying - mortar used to stick the various layers of CHB. The standard thickness used for laying CHB is half an inch (12mm) or 0.012m.

3.2.1. THE VOLUME METHOD

Cell filler considers 4 cells in each CHB - 3 internal cells and 2 of half end cells- with the varying volume of each cell. Estimation of the materials for mortar will be through a table with different mixture classes as well.

CLASS	PROPORTION	CEMENT	CEMENT	SAND
		40kg	50kg
A	1:2	18.0	14.5	1.0
B	1:3	12.0	9.5	1.0
C	1:4	9.0	7.0	1.0
D	1:5	7.5	6.0	1.0

3.2.2. THE AREA METHOD

This method is much simpler as it uses a table with the standard volume of mortar needed in each square meter area.

CHB SIZE	CHB NUMBER	A	B	C	D	SAND
		(40kg)	(40kg)	(40kg)	(40kg)
cm	per sqm	bags	bags	bags	bags	cu.m.
10 x 20 x 40	12.5	0.792	0.522	0.394	0.328	0.0435
15 x 20 x 40	12.5	1.526	1.018	0.763	0.633	0.0844
20 x 20 x 40	12.5	2.260	1.500	1.125	0.938	0.1250

3.2.3. THE HUNDRED BLOCK METHOD

This method is similar with the are method but using a table per 100pcs of CHB instead of per square meter of CHB.

CHB SIZE	A	B	C	D	SAND
	(40kg)	(40kg)	(40kg)	(40kg)
cm	bags	bags	bags	bags	cu.m.
10 x 20 x 40	6.336	4.176	3.152	2.624	0.3480
15 x 20 x 40	12.150	8.104	6.072	5.064	0.6750
20 x 20 x 40	18.072	12.000	9.000	7.504	1.0000

Example 3.2.1. Estimating mortar materials in a wall

Example 3.2.2. Estimating mortar materials in a concrete structure

3.3. PLASTER

Plaster is only made of cement and fine sand. It is applied typically at half an inch (0.0125m) thickness.

Again, the estimation of plaster comes in two methods:

• Volume method. This method implores using the area of the wall to be plastered multiplied by the design thickness of the plaster. The total volume will then be multiplied by the factors of concrete mixture from the same table used for mortar-volume method.

CLASS	PROPORTION	CEMENT	CEMENT	SAND
		40kg	50kg
A	1:2	18.0	14.5	1.0
B	1:3	12.0	9.5	1.0
C	1:4	9.0	7.0	1.0
D	1:5	7.5	6.0	1.0

• Area method. Another table is provided for this method. The only parameter needed is the area of the wall to be plastered.

MIXTURE	8mm	12mm	16mm	20mm	25mm
CLASS	THK	THK	THK	THK	THK
A	0.144	0.216	0.288	0.360	0.450
B	0.096	0.144	0.192	0.240	0.300
C	0.072	0.108	0.144	0.180	0.225
D	0.060	0.090	0.120	0.150	0.188
SAND	0.008	0.012	0.016	0.020	0.025

Example 3.3.1. Estimating plaster materials for a wall

Example 3.3.2. Estimating plaster materials for a small structure

3.4. WALL FOOTING

Masonry walls require wall footing in cases where there is no grade beam to hold the wall or partition. Unless specified in the plans, wall footings can be configured as shown:

Two methods of estimating wall footing are listed below:

• Volume method. Measure the volume of the concrete from plans and determine the proportions from concrete volume method.

CLASS	PROPORTION	CEMENT	CEMENT	SAND	GRAVEL
MIXTURE		40kg	50kg
		bags	bags	cu.m.	cu.m.
AA	1:1.5:3	12.0	9.5	0.5	1.0
A	1:2:4	9.0	7.0	0.5	1.0
B	1:2.5:5	7.5	6.0	0.5	1.0
C	1:3:6	6.0	5.0	0.5	1.0

• Meter length method. With a table, the Meter Length method estimates concrete materials easily. The length of wall footing is an important factor in using the table.

DIMENSION	A	B	A	B	SAND	GRAVEL
	40kg	40kg	50kg	50kg
cm	bags	bags	bags	bags	cu.m.	cu.m.
10 x 30	0.270	0.225	0.210	0.180	0.015	0.030
10 x 35	0.315	0.263	0.245	0.210	0.018	0.035
10 x 40	0.360	0.300	0.280	0.240	0.020	0.040
10 x 50	0.450	0.375	0.350	0.300	0.025	0.050
15 x 40	0.540	0.450	0.420	0.360	0.030	0.060
15 x 45	0.612	0.510	0.473	0.405	0.034	0.068
15 x 50	0.675	0.563	0.525	0.450	0.038	0.075
15 x 60	0.810	0.675	0.630	0.540	0.045	0.090
20 x 40	0.720	0.600	0.560	0.480	0.040	0.080
20 x 50	0.900	0.750	0.700	0.600	0.050	0.100
20 x 60	1.080	0.900	0.840	0.720	0.060	0.120

Example 3.4.1. Estimating wall footing for a wall

Example 3.4.2. Estimating wall footing for a structure

Example 3.4.3. Estimating wall footing for a structure
Example 3.4.4. Estimating masonry for a wall

3.5. RETAINING WALLS

Retaining walls are constructed for slope protection. The effect of the soil pressure, which is usually triangular, affects the height of the retaining wall.

These walls are made of:

1. Rip-rap
2. Concrete

3.5.1. RIP-RAP

Rip-rap can be constructed with or without grout. Stones used for rip-rap are also in different classes:

Class A. 15 to 25kg rocks [50% weigh more than 20kg]

Class B. 30 to 70kg rocks [50% weigh more than 50kg]

Class C. 60 to 100kg rocks [50% weigh more than 80kg]

Class D. 100 to 200kg rocks [50% weigh more than 1500kg]

The grout proportions for rip rap as volume method is as follows:

STONE CLASS	A	B	C	SAND
	40kg	40kg	40kg
Class A	2.574	1.716	1.287	0.143
Class B	2.448	1.620	1.214	0.135
Class C	2.232	1.488	1.116	0.124
Class D	1.944	1.296	0.972	0.108

Example 3.5.1. Estimating A Grouted Rip-rap

3.5.2. CONCRETE RETAINING WALL

Estimation of concrete retaining wall is similar to slab estimation. The volume of the retaining wall will be determined after which multiplied with the factors presented on concrete volume method.

MIXTURE	PROPORTION	40kg	50kg	SAND	GRAVEL
		CEMENT	CEMENT
AA	1:1.5:3	12.0	9.5	0.50	1.0
A	1:2:4	9.0	7.0	0.50	1.0
B	1:2.5:5	7.5	6.0	0.50	1.0
C	1:3:6	6.0	5.0	0.50	1.0

Example 3.5.2. Estimating A Concrete Retaining Wall