Plaster deduction rules as per is code 1200:1976 Part-12 with CPWD Specifications

 Introduction

Plaster work is a very common item in building constructions. I have explained very important interview questions for billing engineers, site engineers and quantity surveyors.
This article clearly explains plaster measurement and deduction rules for wall and ceiling plaster work.
These questions are most commonly asked in billing engineer and site engineer interviews.

What is cement plaster work ?

Plaster work means covering brick or concrete surfaces with cement mortar
Cement plaster shall be 12MM, 15MM, or 20MM thick as specified in the BOQ item.
Make the surface smooth
Protect the wall
Improve Appearance

Plaster work can be done on
Walls, Ceiling, Columns, Beams.

Plaster deduction Rules clause 3.8 ?

Plaster Deduction Rules
Clause 3.8.2  No deduction for Small opening like Exhaust fan, Duct opening, Ventilator Etc. having area upto 0.5 m²,  No Deduction is made and plaster is measured as full wall area. No addition and no deduction.
Deduction for opening area more than 0.5 m²  and upto 3 m², No addition shale made for jambs, sills, soffits etc.  When both faces of wall are plaster with same plaster. Deduction shall be made only one face. If one face of wall are plaster deduction shall be made 50% of opening area no addition for jambs, sills, soffits, etc.
In case opening area above   3 m²  each  Full area shall be deduction each side, but jambs, soffits, sills etc. measured.
Clause 3.8  deductions 1200:1976 part-12
Sr. no.	Opening area	Deduction Action	Jambs, Soffit, sills, etc.
1	Area upto 0.5 m²,	No deduction	No Addition
2	Area more than 0.5 m²   Less than 3 m²	50% area Deduction ( One face wall )	No Addition
3	Area Above  3 m²,	Full Area Deduction	Add Measured
4	When the window or door thickness is parallel to the wall thickness, the wall surface and door, window surface are on the same line. In this case, no extra plaster is done on jambs or sill, so no addition is allowed. Full opening deducted each face.
5	Dimensions shall be measured Nearest 0.01M
6	Area shall be measured Nearest 0.01 m²
7	300MM below measured in running metre and above 300MM measured in m².
8	Clause 3.5 Plastering height greater than 10M above Ground floor shall be measured separately in stage 5M each story for External plastering work
9	Clause 3.12 Measurement of wall plaster  ( Dimension taken before  plastering work )

Extra height For plaster work

If plastering is done at a height more than 10 meters from ground level, then it must be measured separately.  
Now understand carefully          

Simple Table for Easy Understanding
Sr. no.	Condition	How to Measure	Reference
1	Exterior plaster above 10M Height	Measure separately In stages of 5-M	CPWD specifications Clause 13.1.9.8
2	Example	If building height is 20 meters
3	Each 5 m height above 10 m is measured separately	0 to 10 m → normal measurement 10 to 15 m → separate measurement 15 to 20 m → separate measurement

Cement  Consumption  for plaster work

How many types of ratio follow below

Description of Item	Cement Mortar Ratio	Quantity Per Sqmr	CPWD - 2014	Remark & Description of work
CEMENT PLASTER (IN FINE SAND)
12 mm plaster	(1 : 4)	5.47	547	547 KG cement  in 100 SQMR plaster for 12MM plaster 1 SQMR in 5.47KG cement plastering work
12 mm plaster:	(1 : 6)	3.6	360	360 KG cement  in 100 SQMR plaster for 12MM plaster 1 SQMR in 3.6KG cement plastering work
15 mm plaster:	(1 : 4)	6.54	654	654 KG cement  in 100 SQMR plaster for 15MM plaster 1 SQMR in 6.54KG cement plastering work
15 mm plaster:	(1 : 6)	5.6	560	560 KG cement  in 100 SQMR plaster for 15MM plaster 1 SQMR in 5.6KG cement plastering work
CEMENT PLASTER WITH A FLOATING COAT OF NEAT CEMENT
12 mm plaster	(1 : 3)	9.54	954	954 KG cement  in 100 SQMR plaster for 12MM plaster 1 SQMR in 9.54KG cement plastering work
12 mm plaster:	(1 : 4)	7.67	767	767 KG cement  in 100 SQMR plaster for 12MM plaster 1 SQMR in 7.67KG cement plastering work
15 mm plaster:	(1 : 3)	10.97	1097	1097 KG cement  in 100 SQMR plaster for 15MM plaster 1 SQMR in 10.97KG cement plastering work
15 mm plaster:	(1 : 4)	8.74	874	874 KG cement  in 100 SQMR plaster for 15MM plaster 1 SQMR in 8.74KG cement plastering work
CEMENT PLASTER IN TWO COATS
18 mm cement plaster in two coats under layer 12 mm thick cement plaster 1:5 finished with a top layer 6mm thick cement plaster 1:6.		6.26	626	626 KG cement  in 100 SQMR plaster for 18MM plaster 1 SQMR in 6.26KG cement plastering work
6 MM CEMENT PLASTER
6 mm plaster	(1 : 3)	3.67	367	367 KG cement  in 100 SQMR plaster for 6MM plaster 1 SQMR in 3.67KG cement plastering work

1.      Measurement book with Example

	PROJECT NAME		Sun Tower Greater Noida
	CLIENT NAME		Onsite XL
	CONTRACTOR NAME		SANGEETA DEVI
	RUNNING BILL No.		RA-01
MEASUREMENT  BOOK
S.No.	Description	Unit	No.	No.	L	B	H	Qty.	Remarks
	EXAMPLE -1
	Plain Wall
	Wall	M²	1	1	5		3	15
	Final quantity								15M²
	EXAMPLE -2
	Wall with small opening upto 0.5M²
	Wall	M²	1	1	4		3	12
	Ventilator	M²	1	1	0.6		0.6
	No Deduction                  No Addition
	Final quantity								12M²
	EXAMPLE -3
	Wall with medium opening  0.5M²  to  3M²
	Wall	M²	1	1	6		3	18
	Window	M²	-0.5	1	1.5		1.2	-0.9
	Deduct 50% opening area one side wall
	No jamb, soffit, Sill addition
	Final quantity								17.1M²
	EXAMPLE -4
	Wall with large opening  above 3 M²
	Wall	M²	1	1	5		5	25
	Door	M²	-1	1	1.5		2.5	-3.8
	Deduct the Full opening area each side
	add jamb,	M²	2	1	0.23		2.5	1.15
	add soffit,	M²	1	1	0.23		1.5	0.35
	Final quantity								22.745M²
					Total quantity			66.85
					Previous			0.00
					This Bill			66.85

1.      Follow the CPWD Specifications Cement plaster work

Clause 13.1 Plaster Thickness

Plaster  thickness can be 12MM, 15MM, or 20MM as specified in BOQ item.

Clause 13.1.1 Scaffolding

For all exposed brick work or tile work double scaffolding independent of the work having two sets of vertical supports shall be provided. The supports shall be sound and strong, tied together with horizontal pieces over which scaffolding planks shall be fixed.

Clause 13.1.2 Surface Preparation

Rake joints Properly
Remove Dust, Loose mortar
Wash surface and keep it wet before plaster.
Before start must scaffolding arrangement.
Surface must clean, rough  and wet before start plaster work

Clause 13.1.3 Cement plaster mortar

Ratio Mix as specified in BOQ item.
External plaster under coat Fine aggregate Zone IV
Final Finish coat Fine aggregate Zone V
Most Commonly use Ratio
1:4 (1 cement : 4 fine sand)
1:6 (1 cement : 6 fine sand)
Sand quality changes depending  on coat types.

Clause 13.1.4 application of cement plaster

Ceiling plaster complete before wall plaster
Plaster start from the top move to downward

Clause 13.1.5 Curing

Curing should start after the plaster becomes hard enough so that sprinkling water does not damage or wash it.
The plaster shall be kept wet for a period of at least 7 days.
Mark the executed date on plaster for curing record.

Clause 13.1.8 Precaution for plaster

Before start plaster check all opening, electric point, wall line , ceiling level etc.
Fixing 150MM  wide Chicken wire with U nail 150 C/C before plastering work on vertical.
Keep wall plaster separate from Ms door frame  plaster by making a small groove (max 6 mm) while plaster is fresh.
If plaster has cracks, hollow sound, or soft/defective areas, cut that portion in rectangle shape and redo it.

Clause 13.1.9 Measurement of cement plaster

Plaster work measured in Square mater 2 Decimal.
Dimensions shall be measured Nearest 0.01M
Area shall be measured Nearest 0.01 m²
300MM below measured in running metre and above 300MM measured in m².
Circular work not exceeding 6 m in radius.
Exterior plastering at a height greater than 10 m from average ground level shall be measured separately in each Story height in stages of 5M height.
Plaster Deduction follow the deduction table.

Conclusion

Plaster deduction rules are clearly defined as per CPWD specifications.
Small openings are ignored, medium openings get partial deduction, and large openings get full deduction with separate measurement of jambs and soffits.
Understanding these rules is essential for accurate billing and quantity calculation