Most of the houses in villages are built either with kachha (Sundried) bricks or blocks, or with lump mud. Mud walls are protected against damage from rain by applying mud plaster, consisting of local soil or mud collected from village pond mixed with bhusha (wheat straw) on outer walls, rendering with gobri (Cow dung slurry). This traditional method of application of mud plaster of course is cheap; however can not with-sand even a few hours of continuous rains, with the result that usually the mud plaster gets eroded and considerable damage is done to the house. Thus a water proof mud rendering on mud walls can save the walls from frequent damage and increase its durability and life for 30 to 35 years with normal annual maintenance.
The problem of durability of mud plaster is two fold. Firstly the plaster should be non-erodable and secondly it should be water proof against local rain fall. The reason for the first requirement is obvious. As regards water proofness the necessity arises from the mechanism of separation of a plaster from kachha wall. During the continuous rain, moisture penetrates through out the plaster and softeness the surface of the wall in contact with the plaster, thereby weakening the bond between the wall face and the plaster. Normally on drying out, the adhesion between the wall surface and the plaster should be fully restored, but due to the differential shrinkage between plaster and wall, local stresses develop, which are too high for the weakened bond between the plaster and the softened wall face to overcome. A partial separation thus occurs and by repeated wetting and. drying, due to alternating rainfall and sun shine, the plaster ultimately comes off in flakes.
If a bitumen cut back, prepared with, bitumen having 80/100 penetration & kerosene oil, is mixed to the ordinary mud mortar (having bhusa) is applied on the mud wall, it will provide a non-erodable and water proof plastered surface.
Normally soil, from the bottom of village pond, is collected and mixed with the local soil and bhusa in suitable proportions for the purpose of plastering.The soil shall have a clay contents between 20- 25% and sand between 40-45%, remaining being the silt, peat loam etc. The soil shall be free from any organic material, gravels, pebbles etc. The soil so selected shall be keptwet and kneaded every day for a period of 10 to 14 days. The soil having a plasticity index ranging from 6 to 10 is found to be suitable for plaster. If laboratory testing facility is available plastic limit, liquid limit, and plasticity index, may be ascertained. It may be noted and stressed here, that the performance of a good mud plaster will largely depend upon the selection of suitable soil mixed in correct proportion.
The strength of mud mortar increases considerably by addition of fibers from decayed Bhusa or Wheat Straw which acts as reinforcement to the soil and increases the cohesion. Where wheat is not grown, rice straw may be used in its place. The size of bhusa i.e. the aspect ratio plays an important role in the strength of mortar. Normally a length of 20 mm and width 2 mm or aspect ratio of 10 is suitable for mortar. The period for which bhusa is decomposes also plays important role in the quality of mud plaster. Bhusa at the rate of6% by weight of dry soil, i.e. 64 Kg for every cubic meter of soil, is added to the dry soil and thoroughly mixed. The mix is formed into a round/circular heap and water is flooded in between the space to keep it constantly wet for 10 to 15 days. The mortar is kneaded every day by man’s feet as well as overturned by showel two to three times for a period of 10 to 14 days, depending upon local climate. Within this period the Bhusa fibers are disintegrate (i,e. 14 days in winter and rainy season and 10 in summer) and become soft which can be easily felt and identified by taking a lump of mortar in hand. In case old stored bhusa is available it should be preferred since it will shorter the time needed for disintegration of bhusa and will allow early use of mortar This is the usual traditional practice of preparing conventional mud mortar, but for getting good result the above sequence may be followed. Suitability of mud mortar for plaster so prepared may also be tested by applying some plaster in small patches of say 1 m x 1 m on the wall and is observed till it is completely dried. If the plaster does not have any appreciable cracks, the plaster is suitable; otherwise more sand is added to make it in suitable proportion
Bitumen of 80/1 00 grade penetration and kerosene oil is mixed in the proportion of 5:1 preparing cut back i.e. 53.25 kg. of bitumen and 10.5 litre of kerosene oil for every cubic metre of dry soil. Bitumen is heated till it melts and this molten bitumen is slowly added to the kerosene oil kept in a separate container, keeping the whole mixture stirred until the whole of bitumen is added.
The bitumen cut back so prepared is added to the mud mortar prepared earlier in the traditional manner as described above. The required quantity of cut back is taken from the container and it is spread over the heap of mud mortar uniformly and worked up with spade immediately after, several times to ensure its thorough mixing. Any undesirable matter, lump of mud, or bitumen formed should be removed. When the plaster is ready for use it will show a good workability and plasticity.
Mud plaster is normally applied on the walls constructed by lump mud, sundried blocks or bricks. The mud wall surface usually is not uniform or in plumb. Hence the following steps should be followed before applying the mud plaster:.
-Scrap the undulation, irregularities and loose particles, if any with the trowel so as to make the surface uniform.
-Any appreciable crack may be filled with ordinary mud mortar and allow to dry.
-The plaster is commenced from the upper portion coming towards the bottom.
-Apply the plaster in uniform thickness of 12 mm with a trowel and finish it smooth. However if any appreciable crack, it should be filled with the same nonerodable mud mortar and finished properly.
The mud plaster is completely dry a gobri rendering is applied on the plastered surface by hand in two coats. Second coat is applied in vertical direction after drying the first coat. The gobri (cow dung slurry coat) is effective in filling the hair cracks and voids in the plaster and helps in stopping further cracks of plaster. To prepare the slurry, 1 part of cow dung, and 1 part of soil, is mixed and water is added to form a thick paste. To this paste, bitumen cut back, is added.
The extra labour requirement is nominal and the villager may contribute it is as self-help. A rate analysis for 12 mm thick ordinary mud plaster as well as non-erodable mud plaster based on the cost of material and labour.
Soak the soil for at least 12 to 15 days and Add bitumen to kerosene oil and not the otherway, otherwise kerosene remains on top & mixing will be difficult. Do not heat Kerosene Oil. Pour the cut back into the prepared soil and knead it with feet and spades. Remember bitumen or Kerosene Oil does not harm the skin. Fill irregularities ill mud walls with ordinary mud plaster & then apply NEM plaster in uniform thickness. Thickness of plaster should not be less than 12 mm and not more than 15 mm.
Advantage–
-This plaster is water repellents & erosion resistant, more durable and provides safety against collapse of wall in rainy season.
-The life of the plaster is more than 30 years with annual maintenance by applying bituminized gobri only.
-On the basis of several trials conducted in the laboratory as well as on the walls of several houses in villages around Roorkee it has been established that NEM plaster is durable & its life is more than 30 years.
-It gives a uniform finish and it can be finished with white/colour wash if desired. It improves the aesthetics of the village houses
How to do Waterproof Mud Plaster?
Problems with Ordinary Mud Plaster
The problem of durability of mud plaster is two fold. Firstly the plaster should be non-erodable and secondly it should be water proof against local rain fall. The reason for the first requirement is obvious. As regards water proofness the necessity arises from the mechanism of separation of a plaster from kachha wall. During the continuous rain, moisture penetrates through out the plaster and softeness the surface of the wall in contact with the plaster, thereby weakening the bond between the wall face and the plaster. Normally on drying out, the adhesion between the wall surface and the plaster should be fully restored, but due to the differential shrinkage between plaster and wall, local stresses develop, which are too high for the weakened bond between the plaster and the softened wall face to overcome. A partial separation thus occurs and by repeated wetting and. drying, due to alternating rainfall and sun shine, the plaster ultimately comes off in flakes.
Solution with Improved Technique
If a bitumen cut back, prepared with, bitumen having 80/100 penetration & kerosene oil, is mixed to the ordinary mud mortar (having bhusa) is applied on the mud wall, it will provide a non-erodable and water proof plastered surface.
Preparation of Mud Mortar
Normally soil, from the bottom of village pond, is collected and mixed with the local soil and bhusa in suitable proportions for the purpose of plastering.The soil shall have a clay contents between 20- 25% and sand between 40-45%, remaining being the silt, peat loam etc. The soil shall be free from any organic material, gravels, pebbles etc. The soil so selected shall be keptwet and kneaded every day for a period of 10 to 14 days. The soil having a plasticity index ranging from 6 to 10 is found to be suitable for plaster. If laboratory testing facility is available plastic limit, liquid limit, and plasticity index, may be ascertained. It may be noted and stressed here, that the performance of a good mud plaster will largely depend upon the selection of suitable soil mixed in correct proportion.
Addition of Bhusa
The strength of mud mortar increases considerably by addition of fibers from decayed Bhusa or Wheat Straw which acts as reinforcement to the soil and increases the cohesion. Where wheat is not grown, rice straw may be used in its place. The size of bhusa i.e. the aspect ratio plays an important role in the strength of mortar. Normally a length of 20 mm and width 2 mm or aspect ratio of 10 is suitable for mortar. The period for which bhusa is decomposes also plays important role in the quality of mud plaster. Bhusa at the rate of6% by weight of dry soil, i.e. 64 Kg for every cubic meter of soil, is added to the dry soil and thoroughly mixed. The mix is formed into a round/circular heap and water is flooded in between the space to keep it constantly wet for 10 to 15 days. The mortar is kneaded every day by man’s feet as well as overturned by showel two to three times for a period of 10 to 14 days, depending upon local climate. Within this period the Bhusa fibers are disintegrate (i,e. 14 days in winter and rainy season and 10 in summer) and become soft which can be easily felt and identified by taking a lump of mortar in hand. In case old stored bhusa is available it should be preferred since it will shorter the time needed for disintegration of bhusa and will allow early use of mortar This is the usual traditional practice of preparing conventional mud mortar, but for getting good result the above sequence may be followed. Suitability of mud mortar for plaster so prepared may also be tested by applying some plaster in small patches of say 1 m x 1 m on the wall and is observed till it is completely dried. If the plaster does not have any appreciable cracks, the plaster is suitable; otherwise more sand is added to make it in suitable proportion
Preparation of Bitumen Cut Back
Bitumen of 80/1 00 grade penetration and kerosene oil is mixed in the proportion of 5:1 preparing cut back i.e. 53.25 kg. of bitumen and 10.5 litre of kerosene oil for every cubic metre of dry soil. Bitumen is heated till it melts and this molten bitumen is slowly added to the kerosene oil kept in a separate container, keeping the whole mixture stirred until the whole of bitumen is added.
Preparation of non-erodable and Water Proof Mud Plaster
The bitumen cut back so prepared is added to the mud mortar prepared earlier in the traditional manner as described above. The required quantity of cut back is taken from the container and it is spread over the heap of mud mortar uniformly and worked up with spade immediately after, several times to ensure its thorough mixing. Any undesirable matter, lump of mud, or bitumen formed should be removed. When the plaster is ready for use it will show a good workability and plasticity.
Application of Plaster
Mud plaster is normally applied on the walls constructed by lump mud, sundried blocks or bricks. The mud wall surface usually is not uniform or in plumb. Hence the following steps should be followed before applying the mud plaster:.
-Scrap the undulation, irregularities and loose particles, if any with the trowel so as to make the surface uniform.
-Any appreciable crack may be filled with ordinary mud mortar and allow to dry.
-The plaster is commenced from the upper portion coming towards the bottom.
-Apply the plaster in uniform thickness of 12 mm with a trowel and finish it smooth. However if any appreciable crack, it should be filled with the same nonerodable mud mortar and finished properly.
Application of Gobri (Cow Dung Slurry)
The mud plaster is completely dry a gobri rendering is applied on the plastered surface by hand in two coats. Second coat is applied in vertical direction after drying the first coat. The gobri (cow dung slurry coat) is effective in filling the hair cracks and voids in the plaster and helps in stopping further cracks of plaster. To prepare the slurry, 1 part of cow dung, and 1 part of soil, is mixed and water is added to form a thick paste. To this paste, bitumen cut back, is added.
Cost Economics
The extra labour requirement is nominal and the villager may contribute it is as self-help. A rate analysis for 12 mm thick ordinary mud plaster as well as non-erodable mud plaster based on the cost of material and labour.
Precautions
Soak the soil for at least 12 to 15 days and Add bitumen to kerosene oil and not the otherway, otherwise kerosene remains on top & mixing will be difficult. Do not heat Kerosene Oil. Pour the cut back into the prepared soil and knead it with feet and spades. Remember bitumen or Kerosene Oil does not harm the skin. Fill irregularities ill mud walls with ordinary mud plaster & then apply NEM plaster in uniform thickness. Thickness of plaster should not be less than 12 mm and not more than 15 mm.
Advantage–
-This plaster is water repellents & erosion resistant, more durable and provides safety against collapse of wall in rainy season.
-The life of the plaster is more than 30 years with annual maintenance by applying bituminized gobri only.
-On the basis of several trials conducted in the laboratory as well as on the walls of several houses in villages around Roorkee it has been established that NEM plaster is durable & its life is more than 30 years.
-It gives a uniform finish and it can be finished with white/colour wash if desired. It improves the aesthetics of the village houses
How to do Waterproof Mud Plaster?
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