PLASTERING – THINGS EVERY ENGINEER SHOULD KNOW

PLASTERING

plastering

The following topics are covered in this post.

1. What is plastering?
2. What are the requirements of good plaster?
3. Different types of mortars for plastering
4. Number of coats of plastering
5. How to preparation of background before plastering?
6. What are the recommended mortars mixes for different situation?
7. What are the defects in plastering?

WHAT IS PLASTERING?

Plastering is the process of covering rough surfaces of walls, columns, ceilings and other building components with thin coat of mortars to form a smooth durable surface. The coating of mortar is termed as plaster.

Plastering is done to achieve the following objects:

• To protect the external surfaces against penetration of rainwater and other atmospheric agencies.
• To give smooth surface in which dust and dirt cannot lodge.
• To give decorative effect.
• To protect surfaces against vermin.
• To conceal inferior materials or defective workmanship.

REQUIREMENTS OF GOOD PLASTER

The plaster material should fulfill the following requirements:

• It should adhere to the background, and should remain adhered during all variations in seasons and other atmospheric conditions.
• It should be hard and durable.
• It should possess good workability.
• It should be possible to apply it during all weather conditions.
• It should be cost efficient.
• It should effectively check penetration of moisture.

TYPES OF MORTARS FOR PLASTERING

The selection of type of plaster depends upon the following factors:

• Availability of binding materials.
• Durability requirements.
• Finishing requirements.
• Atmospheric conditions and variations in weather.
• Location of surface (i.e. exposed surface or interior surfaces).

CEMENT MORTAR

Cement mortar is the best mortar for external plastering work since it is practically non-absorbent.

It is also preferred to lime plaster in both rooms etc., and in damp climates. Cement mortar is much stronger than lime mortar. The mix proportion (i.e. cement : sand) may vary from 1:4 to 1:6. Sand used for plastering should be clean, coarse and angular.

Cement plaster is applied either in two coats or in three coats, the former being more common.

For inferior work, single coat plaster is sometimes provided.

NUMBER OF COATS OF PLASTER

The background over which plastering is to be done depend upon the type of wall construction, such as random rubble (R.R.) masonry, coarsed rubble masonry, brick masonry

Background	No of Coats
Stone work	3 or 2
Brick work or hollow blocks	2 or 1
Concrete cast in situ	2 or 1

Note: If plastering is done in single coat only, its thickness should not exceed 12 mm nor should it be less than 6 mm.

TWO COAT PLASTER

The following procedure is adopted:

• The background is prepared by raking the joint to a depth of 20 mm, cleaning the surface and well-watering it.
• If the surface to be plastered is very uneven, a preliminary coat is applied to fill up the hollows, before the first coat.
• The first coat or rendering coat of plaster is applied, the thickness being equal to the specified thickness of plaster less 2 to 3 mm. In order to maintain uniform thickness of plaster, 15 cm x 15 cm size. Two dots are so formed in vertical line, at a distance of about 2 m, and are plumbed by means of a plumb. A number of such vertical screeds are formed at suitable spacing. Cement mortar is then applied on the surface between the successive screeds and the surface is properly finished.
• Before rendering hardens, it is suitably worked to provide mechanical key for the final or finishing coat. The rendering coat is trowelled hard forcing mortar into joints and over the surface. The rendering coat is kept wet for at least 2 days, and then allowed to dry completely.
• The thickness of final or finishing coat may vary between 2 and 3 mm. Before applying the final coat, the rendering coat is damped evenly. The final coat is applied with wooden floats to a true even surface and finished with steel trowels. As far as possible, the finishing coat should be applied starting from top towards bottom and completed in one operation to eliminate joining marks.

THREE COAT PLASTER

The procedure for applying three-coat plaster is similar to the two-coat plaster except that an intermediate coat, known as floating coat is applied. The purpose of this coat of plaster is to bring the plaster to an even surface. The thickness of rendering coat, floating coat and finishing are kept 9 to 10 mm, 6 to 9 mm and 2 to 3 mm respectively. The rendering coat is made rough.

The floating coat is applied about 4 to 7 days after applying the first coat. The finishing coat may be applied about 6 hours after the application of floating coat.

SINGLE COAT PLASTER

This is used only in inferior quality work. It is applied similarly as two-coat plaster except that the rendering coat, as applied for two-coat plaster, is finished off immediately after it has sufficiently hardened.

PREPARATION OF BACKGROUND

For plastering new surfaces, all masonry joints should be raked to a depth of 10 mm in brick masonry and 15 mm in stone masonry for providing key to the plaster. All mortar droppings and dust, and laitance (in case of freshly laid concrete) should be removed with the help of stiff wire brush. Any unevenness is levelled before rendering is applied. For finish applied in three coats, local projections should not be more than 10 mm proud of general surface and local depressions should not exceed 20 mm. For two-coat plaster, these limitations are 5 mm and 10 mm respectively. The surface should be washed with clean water and kept damp uniformly to produce optimum suction. In no case should the surface be kept so soaked that it causes the green mortar to slide off, or so dry that it causes strong suction which withdraws moisture from mortar and makes it weak, porous and friable. If plaster is to be applied on old surface, all dirt, oil, paint etc. should be cleaned off. Loose and crumbling plaster layer should be removed to its full thickness and the surface of the background should be exposed and joints properly raked. The surface should be washed and kept damp to obtain optimum suction.

RECOMMENDED MORTAR MIXES FOR DIFFERENT SITUATION

Sl No	Situation	Composition of Mortar	I.S. Grading of Lime
1	External Plaster in localities where rainfall is less than 500 Mm per year and where sub- Soil water is not within 2.5 m Below the ground surface:
	(a) Below D.P.C	1 cement 6 sand	–
		1 cement 2 lime 9 sand	B or C
		1 lime 2 sand	A
		1 lime 1 sand 1 surkhi	B or C
		1 lime 2 surkhi	B or C
	(b) Above D.P.C	1 cement 2 lime 9 sand	B or C
		1 lime 2 sand	A
		1 lime 1 surkhi sand	B or C
		1 lime 2 surkhi	B or C
2	External plaster in localities where rain fall is more than 1300 mm per year and where subsoil water is not within 2.5m below ground surface:
	(a) Below D.P.C	1 cement 4 sand	–
		1 cement 1 lime 6 sand	B or C
		1 lime 2 surkhi	B or C
	(b) Above D.P.C	1 cement 2 lime 9 sand	B or C
		1 lime 2 sand	A
		1 lime 1 sand 1 surkhi	B or C
		1 lime 2 surkhi	B or C
3	External plaster in localities where the subsoil water is within 2.5 m of the ground
	Below D.P.C	1 cement 3 sand
4	Internal plaster in all localities	1 lime 2 sand	A
		1 lime 1 surkhi 1 sand	B or C
		1 lime 2 surkhi	B or C
		1 cement 2 lime 9 sand	B or C

Note: the ratio of lime varies with % purity of lime and these ratios may be suitably adjusted depending upon local practice.

DEFECTS IN PLASTERING

The following defects may arise in plaster work:

1. Blistering of plastered surface

This is the formation of small patches of plaster swelling out beyond the plastered surface, arising out of late slaking of line particles in the plaster.

2. Cracking

Cracking consists of formation of cracks or fissures in the plaster work resulting from the following reasons:

• Imperfect preparation of background.
• Structural defects in building.
• Discontinuity of surface.
• Movements in the background due to its thermal expansion or rapid drying.
• Movements in the plaster surface itself, either due to expansion (in case of gypsum plaster) or shrinkage (in case of lime sand plaster).
• Excessive shrinkage due to application of thick coat.
• Faulty workmanship

3. Crazing

It is the formation of a series of hair cracks on plastered surface, due to same reasons which cause cracking.

4. Efflorescence

It is the whitish crystalline substance that appears on the surface due to presence of salts in plaster-making materials as well as building materials like bricks, sand, cement etc. and even water. This gives a very bad appearance. It affects the adhesion of paint with wall surface.

Efflorescence can be removed to some extent by dry brushing and washing the surface repeatedly.

5. Flaking

It is the formation of very loose mass of plastered surface, due to poor bond between successive coats.

6. Peeling

It is the complete dislocation of some portion of plastered surface, resulting in the formation of a patch. This also results from imperfect bond.

7. Popping

It is the formation of conical hole in the plastered surface due to presence of some particles, which expand on setting.

8. Rust stains

These are sometimes formed when plaster is applied on metal laths.

9. Uneven surface

This is obtained purely due to poor workmanship.

QUALITY ASSURANCE FOR CEMENT PLASTERING

Plastering is a process of applying one or more coats of mortar to a concrete surface, brickwork, stone masonry or lathing. It must be durable such that it resists the penetration of moisture and should be able to weather uniformly. It should also be pleasing in appearance. These properties depend upon materials used, composition of mix, and degree of mechanical bond between the plaster and the backing surface and workmanship.

SURFACE PREPARATION:

The joint shall be raked to a depth of 15 mm for brickwork and 20 mm for stonework. For new work, where subsequent plastering is to be done, the raking of joints shall be done during the progress of the work, when the mortar is still green. Dust or mortar powder (loose mortar) shall be washed out. The whole surface shall be thoroughly cleaned and brushing and scrapping shall remove efflorescence, if any. The surface thoroughly washed with water, cleaned and kept vet for the day previous and up to the time start the work is started, and shall be kept very damp during the progress of the plastering.

BONDING:

Cement mortar has two types of bonds with its backing one being mechanical in which the mortar squeezes into the irregularities and gets interlocked when hardened and other due to the adhesive property of Portland cement on hardening. The degree of bond will therefore depend on the roughness of surface to be treated and the quality of cement and sand used in preparation of mortar.

CONCRETE SURFACE:

All monolithic concrete walls should be roughened by hacking at close intervals with bush hammers or with a chisel and hammer and then washed thoroughly with water to remove all dirt and loose particles. Monolithic concrete can be roughened with a heavy wire brush or a special scouring tool if forms are removed early. Forms for concrete, that is to receive plaster, should not be given excessive mould oil coating. as it is likely to remain on the concrete, interfering with the bond. Special care must be taken to remove the mould oil coating before plaster is applied. Curing compound if used should also be removed completely before commencing the plasterwork.

BRICK AND STONE MASONRY:

There are excellent bases for direct application of cement plaster. The surface should be hard, rough and clean. The joints should be racked. It may be desirable to roughen with a pick or a similar sharp tool if the surface of stone is too smooth.

TOOLS FOR PLASTERING:

Following tools are used for plastering – Gauging trowel, floats, floating rule, plumb bob, straight edge, bushes, set square, sprit level, scratcher, plumb rules etc.

MATERIAL:

Materials conforming to the following requirements should be used.

MORTAR:

Cement mixed with fine aggregate should produce smooth, plastic, cohesive, strong and workable mortar. Cement plaster shall unless otherwise specified, to be the following proportion and thicknesses. The mortar of specified mix shall be used.

Situation	Mix Proportion	Thickness
Ordinary building	1:6	13 mm
Important building	1:4	13 mm
Drain, skirting, dados, etc	1:3	13 mm for drains, & 19 mm for skirting and dados
Septic tanks, reservoirs etc	1:2	19 mm

CEMENT:

At present 33 grade and high grade cement such as 43 grade and 53 grade are being used. These are essentially recommended for use in concrete. It is also used in masonry and plastering work.

FINE AGGREGATE:

Sand must be clean, sharp, suitably graded, and free from all deleterious and impure matter. Deleterious materials beyond a certain limit adversely affect the hardening, strength, durability or the appearance of the plaster or causes corrosion of metal lathing or other metal in contact with plaster.

GRADING OF SAND:

Most suitable particle size grading of sand plasterwork for internal and external walls and ceiling is given below:

IS Sieve Size	Passing (in %)
10.0 mm	100
4.75 mm	95 – 100
2.36 mm	95 – 100
1.18 mm	90 – 100
600 micron	80 – 100
300 micron	20 – 65
150 micron	0 – 50

WATER:

Water used in plasterwork should be of quality suitable for drinking purpose. It should be free from chlorides and organic impurities.

WATER PROOFING COMPOUND:

Generally, they are not required specially if correct type and quality of other materials of mortar are available. Where it is used, it should disperse uniformly and mixed properly in mortar.

WORKABILITY ADMIXTURES:

Plasticizers can be used in warm or hot weather condition as desired with field requirements.

SCAFFOLDING:

It is always advisable to provide double scaffolding for plastering work. It is easier to fix and remove at various heights without damaging the masonry or plaster.

MIXING OF INGREDIENTS OF PLASTER:

It is preferable to mix the ingredients in a mixer. Dry mortar is mixed initially and thereafter water is added to the dry mix to get the required consistency. It is observed that excess mortar is often prepared and not utilised in time. The workers even break for lunch leaving the wet mixed mortar to dry out. Water is again added resulting in lower strength and more shrinkage problem. The quantity of the mortar made at a time should be such that it can be consumed within 30 minutes. Any mortar that falls to the ground in the process of application, it is thrown away and on no account re used. If excess mortar is prepared it dries up either due to evaporation of water or due to water absorption by sand and / or due to water consumed by cement hydration. Addition of water should be carefully monitored and should be added in such a quantity that it gives the required workability

APPLICATION OF PLASTER:

The walls shall be prepared as above and rendered with a mortar of cement and fine sand in specified proportions. At suitable intervals, 15 cm x 15 cm mortar squares to full thickness of base coat shall be first laid to serve as a guide to ensure a plane, smooth layer of plaster over the entire surface of the wall.

The mortar shall be dashed against the surface to be plastered with considerable forced, and shall be thoroughly worked into all joints and other surface depressions, to ensure a permanent bond. The plaster surface will be roughened and not beaten.

Ceiling plaster shall be completed before commencement of the wall plastering. Plastering shall be started from the top and worked down, filling all putlog holes in advance of the plastering as the scaffolding is being taken down.

All corners arise, angles and junctions shall be truly vertical or horizontal as the case may be, and shall be carefully finished. Rounding or chamfering corners, arises, junctions, etc., where required, shall be carried out with proper templates to the required sizes.

At the end of the day suspending plastering work shall be left cut clean to line both horizontally and vertically. Horizontal joints in plasterwork shall not occur on parapet tops and copings.

COATS FOR PLASTERING:

SCRATCH COAT:

The thickness of this coat should approximately 10 mm to 12.5 mm and must be laid over the full length of the wall or the natural breaking points like doors and windows.

BASE COAT (IN CASE OF THICK PLASTER):

The surface of scratch coat should be dampened evenly before base coat is applied. This coat is about 10 mm thick depending upon the overall thickness and then roughened with a wooden float to provide bond for the finishing coat. The second coat must be damp cured for at least seven days and then allowed to become dry.

FINISHING COAT:

Before this coat is applied, the base cat is dampened evenly. Joints should be avoided and the finishing coat should be applied in one operation with thickness not exceeding 6 mm.

EXTERNAL PLASTER:

The external plaster is made in richer cement mortar proportion than the internal plaster. It is usually done in two layers. First layer is of 10 to 12.5 mm and final layer is of 6mm thickness. Waterproofing compound may be added in case the plaster is exposed to severe wet conditions. The finish can be of the type specified.

INTERNAL PLASTER:

The internal plaster is usually done in single layers of 12.5 mm.

FINISH:

The plaster shall be finished to a true and plumb surface and to the required degree of smoothness. The work shall be tested frequently as it precedes with a true straight edge not less than 2.5 m long and with plumb bobs. All horizontal surfaces shall be tested with a level and all jambs and corners with plumb bob as the work proceeds.

PLASTER FINISHES:

There are four different types of finishes that can be obtained with cement plaster.

SMOOTH FINISH:

When a smooth finish is desired, the minimum amount of working should be applied to the wetted surface and the wooden float, rather than a steel trowel is to be used.

ROUGHCAST FINISH:

This finish suitable for rural or coastal areas and the sever conditions of exposure. This is a finish, which is splashed on to the surface as a wet mix and left rough. The maximum sizes of sand, crushed stone or gravel vary from 12.5 mm to 6.3 mm.

PEBBLE DASH FINISH:

This is most durable of all finishes and is generally free from defects. This gives a rough texture and is obtained by means of small pebbles or crushed stone, graded from 12.5 mm to 6.3 mm being splashed on to a fresh coat of mortar and left exposed. This pebbles or stones are sometimes lightly pressed or tapped in to the mortar.

TEXTURED FINISHES:

Textured finishes are now becoming very popular and may be obtained in a variety of ways in many different designs. Special effects can be obtained by scraping the surface of the rendering with a straight edge hacksaw blade or with the edge of a steel trowel.

CURING:

Curing shall be started 24 hours after finishing the plaster. The plaster shall be kept wet for 7 days during which period it shall be suitably protected from all damages at the contractor’s expenses by such means as the Engineer may approve. The dates of plaster shall be legibly marked on the various sections of the wall so that curing for the specified period thereafter can be watched.

MINIMISING DEFECTS IN PLASTERING WORK

Defects in plastering work can be minimised by following the below mentioned techniques.

1. The brick and plastering work should be carried out by skilled masons in the best workmanship manner.
2. Bond of brick work should be properly maintained.
3. Efflorescence is removed by rubbing brushes on the damaged surface. A solution of one part of hydrochloric acid or sulphuric acid and five parts of clean water is prepared and it is applied with the help of brushes on the affected area. The surface is then washed with clean water. It should, however be remembered that it is desirable to prevent efflorescence than to cure it. Building material should be selected of superior quality and suitable methods of construction should be employed.
4. Water should not be used to wash the surface so as to remove efflorescence. In that case, soluble salts will be partly carried inside the surface and efflorescence will appear again. For this purpose, the deposit is brushed off from the surface as it appears and the surface is kept under observation for a further period of few days. After curing, if efflorescence appears again it is removed with a dry brush and the process is repeated till all the soluble salts are removed under the conditions of normal drying. It is advisable to postpone painting till efflorescence ceases.
5. Bricks of superior nature should only be used for brick work.
6. Water free from salts should be used for brick work and plastering work.
7. The surface to be plastered should be well watered so that it may not absorb water from the plaster.
8. Excessive trowelling should be avoided.
9. Damp-proof courses should be provided at convenient places in the building.
10. The overall construction should be such that penetration of moisture is prevented.
11. Fresh plastered surfaces should be protected from the superfluous quantity of water such as rain and excessive heat such as sun.
12. The concrete surface which is generally plain and smooth should be hacked to form kay when the concrete is green i.e. the moment the shutters are removed. However, this point is generally neglected and the work of plastering is taken up in a hurry on the surfaces a it is or with slight hacking. This will lead to peeling at later stage.
13. If the surface is not properly hacked, there are two alternatives to make the surface rough:
    • Clean the surface by water so as to keep surface wet & an acid treatment with 1 part of muriatic acid diluted in 10 to 20 parts of water applied on the surface. More than one coat may be necessary. After this treatment the wall should be washed through with water to remove all traces of acid.
    • Sometimes, some surfaces cannot be roughened by acid also and the better method would be a spatter dash key.

WHAT IS SPATTER DASH?

Spatter dash

It simply means a rich mixture of Portland cement and coarse sand thrown onto a background by a trowel, scoop, or other appliance so as to form a thin, coarse-textured of continuous coating. As a preliminary treatment, before rendering, it assists bonding of the undercoat to the background, improves resistance to rain penetration, and evens out the suction of variable backgrounds.

In this method a mixture of coarse sand (8mm and below) mixed to cement in the ratio of 1:1.5 and water equal to 0.5 part by total volume is dashed on the walling in an un-even manner. Where sharp sand is difficult to obtain, crushed hard stone (with fine particles eliminated) can also be used.

The water content will vary with the type of aggregate. The dry materials must be mixed thoroughly & then water gradually added. The mixture must be continually stirred during use.

The spatter dash need not cover every piece of surfaces and it is an advantage if parts of surface are not covered. The main object is to form a large number of small humps of mortar so as to make surface as irregular as possible. The thickness of spatter dash may be limited to 10 mm. On allowing 2 to 3 days with good curing; further work can be taken up. Of all the methods to provide a key, the spatter dash method is to be preferred in practically all cases.

14. In brickwork, raking of joints on the finished side should be done as soon as the day’s brickwork is over to provide effective keys for holding the plaster.

TECHNICAL PROPERTIES OF MORTAR

For the sake of projects, the newly mixed mortar should have good workability, and the hardened mortar should have the required strength, the bending power to the bottom face, little deformation and durability.

1. WORKABILITY OF FRESH MORTAR

The workability of fresh mortar refers to the comprehensive properties of mortar easy for construction and good for quality, including mobility and water retention. The mortar with good mobility is easy to be paved thinly and evenly on bricks and bonded with floors well.

A. MOBILITY (CONSISTENCY)

The mobility of mortar is the property that mortar can flow under the role of dead weight and exterior force. Fluidity is expressed by “sinking degree”, usually determined by the consistency of mortar. The bigger the sinking degree is, the better the mobility will be.

The selection of mortar mobility should be determined by masonry types, construction conditions, and weather. The consistency of masonry mortar should be selected according to project requirement.

B. WATER RETENTION

The water retention of mortar refers to the property of mortar to maintain moisture. When the mortar with good water retention is used in transportation, standing and pavement, water will not escape from mortar soon and the necessary consistency can be maintained. To keep a certain amount of water in mortar is easy to manipulate and also guarantees the normal hydration of cement to maintain the strength of masonry.

The water retention of mortar is expressed by layering degree, measured by mortar layering degree instrument. The mortar with good water retention has the layering degree of 10-30mm, and if it is more than 30mm, the water retention will be bad and easy to segregate; the mortar whose layering degree is less than 10 mm is not good for construction. Based on many experiments, the layering degree of cement mortar should be no more than 30mm, and the layering degree of cement mix mortar should be no more than 20mm.

2. STRENGTH OF HARDENED MORTAR

The hardened mortar should have big strength which is expressed by strength grade. Compressive strength is the main basis for mortar strength. The strength grade of mortar, expressed by fm, is determined by compressive strength average (MPa) measured through curing a group of six cube specimens with side length of 70.7mm for 28d, the standard test method.

The strength grades of mortar include: M20, M15, M10, M7.5, M5 and M2.5, the six grades.

The strength of mortar is connected with its surface material. For the ordinary cement mortar, the following equation can be used to calculate its compressive strength.

3. ADHESION STRESS OF MORTAR

Brick and stone masonry is a solid entity composed of many blocks that are bonded by mortar as a whole. Thus, it is required that mortar must have a certain adhesion stress over bricks and stones. Generally, the more the compressive strength of mortar is, the bigger its adhesion stress will be. In addition, its adhesion stress is related to the surface, cleanness, and humidity of bricks and stones, as well as the construction and curing conditions. For example, bricklaying needs watering, and the surface without clay will improve the adhesion stress and ensure the quality of masonry.

4. DEFORMABILITY OF MORTAR

It is easy for mortar to get deformed when it bears loads or the temperature changes. If it deforms greatly or unevenly, the quality of masonry and surface will decrease and cause shrinkage and crack. When fine aggregates are used to mix the mortar, its deformation is bigger than the ordinary mortar. In order to prevent the cracks caused by uneven shrinkage deformation, hemp cut, paper strip and others fabric materials can be mixed in the surface mortar.

5. DURABILITY OF HARDENED MORTAR

The durability of mortar refers to the property to withstand wear and tear in the long-term use. The hydraulic masonry that usually contacts with water should be impermeable and frost-resistant, so the impermeability and frost resistance of hydraulic masonry should be considered.

A. FROST RESISTANCE

The frost resistance of mortar refers to the property to resist freeze-thaw cycle. Mortar is frozen and damaged because the water in its pores expands due to freeze and breaks the pores. Thus, dense mortar and the mortar with closed pores have good frost resistance. In addition, the factors influencing the frost resistance of mortar also include cement types, strength grades, and water-cement ratio.

B. IMPERMEABILITY

The frost resistance of mortar is the property to resist the infiltration of pressure water. It is mainly related to density and size and structure of the inner pores. The connecting pores inside mortar and the cellular structures and, pores formed when it is moulded, all of which can lead to water seepage of mortar.

DETERMINATION OF ORGANIC MATTER IN SOIL

PURPOSE:

This test is performed to determine the organic content of soils. The organic content is the ratio, expressed as a percentage, of the mass of organic matter in a given mass of soil to the mass of the dry soil solids.

STANDARD REFERENCE:

ASTM D 2974 – Standard Test Methods for Moisture, Ash, and Organic Matter of Peat and Organic Soils

SIGNIFICANCE:

Organic matter influences many of the physical, chemical and biological properties of soils. Some of the properties influenced by organic matter include soil structure, soil compressibility and shear strength. In addition, it also affects the water holding capacity, nutrient contributions, biological activity, and water and air infiltration rates.

EQUIPMENT:

• Muffle furnace,
• Balance,
• Porcelain dish,
• Spatula,
• Tongs

determination of organic matter in soil

TEST PROCEDURE:

(1) Determine and record the mass of an empty, clean, and dry porcelain dish (MP).

(2) Place a part of or the entire oven-dried test specimen from the moisture content experiment in the porcelain dish and determine and record the mass of the dish and soil specimen (MPDS).

(3) Place the dish in a muffle furnace. Gradually increase the temperature in the furnace to 4400C. Leave the specimen in the furnace overnight.

(4) Remove carefully the porcelain dish using the tongs (the dish is very hot), and allow it to cool to room temperature. Determine and record the mass of the dish containing the ash (burned soil) (MPA).

(5) Empty the dish and clean it.

DATA ANALYSIS:

(1) Determine the mass of the dry soil.

MD=MPDS-MP

(2) Determine the mass of the ashed (burned) soil.

MA=MPA-MP

(3) Determine the mass of organic matter

MO = MD – MA

(4) Determine the organic matter (content).

OM = (MO/MD)*100

ARTICLE WRITTEN BY

Prof. Krishna Reddy, UIC

Source:- www.civilblog.org