Awareness to layman in building construction

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Awareness to common people or layman for  better construction of residential building-

Introduction

Life of a residential building is depended on numerous factors. If these factors. are well managed, life of the constructed house may extend to 80 years or even more with little periodic future expenditure only.  Any fear of major cracks, unwanted deflections, roof leakage, major dampness, growth of tree roots etc to the house that makes the residents unhappy, keeps them in  anxiety, discomfort should be treated that the normal life of the building has been affected badly and not worthy for living, even if the building has not collapsed. Some of the essential features  necessary to be fulfilled for a multi storied construction  are preparation of drawing/design, estimate, specification of items and materials, quality controlling including testing of materials, soil investigation, codal guidelines and many other factors. Among them a very large number of factors are not considered for a residential house up to G+1 or G+2 nor these technical issues are easy to grasp by the common men. Therefore guidelines presented here is restricted to a very small periphery of Civil Engineering which, however small, will benefit a large population world-wide.

In the rural area of India and its sub continent a large population make their residential house without consulting with professional persons possibly due to non availability of such reliable persons or to save money for a short term gain which in the long term may prove to be much costlier. They largely depend on the mason/head mason. In fact,  the mason by dint of his long experience in this field has hold of the required technical issues to take care but the owner lacks these issues badly because he makes his house possibly once in his lifetime, thereby  net result mostly  goes against the owner in the form of inconvenience, lack of comfort and some adverse occurrences.

The basic purpose of this presentation is  to impart awareness to a large section of the people who knows very little about the key features, however in keen interest, of making a long lasting and durable house,  lot of images & sketches  have been pasted which should be given more importance to get a quality construction.


Assumptions:

This article is formulated for a large section of the people who does not know the basics of Civil Engineering, .  A popular section of society, particularly in village area, purchase materials of their own and engage a head mason, carpenter, plumber, electrician etc for construction of their house on contract basis or on daily wage basis. This article is restricted to masonry construction work only. Peoples are mostly depended on the mason while interest of the mason and owner is quiet different. Head Mason is more intended to save the labour cost by engaging unskilled labour thus infringing the quality of workmanship and building as well. Effect of all bad workmanship in civil engineering construction  does not come into reality in the short duration but in the long duration it might be a fatal to the users of the building. Thus Life of such residential building and its standard of service is largely depended on the knowledge of the Head Mason, his intention, time spent by head mason (mostly he takes more contract in hand at a time) during the construction, his dependence on the skilled/unskilled labours, basic knowledge of the owner, time spent by the owner during construction stage etc. At the same time, owner is intended to get good works at reasonable or cheap price which may infringe the selection of proper labour contractor. There may remain  a hide and seek game between the owner and labour contractor. To get a comparatively better quality performance the owner has to seek a reputed labour contractor with little higher cost and to have some technical knowledge  as well to ensure them during construction. In addition to above it is also assumed that  

1. There is no facilities available nor such custom for testing material like cement, steel, concrete etc. in the rural area

2. the owner has not engaged any qualified supervisor for periodic inspection in the construction phase. 

3. It is understood that there is no custom of soil testing for such small building.

4. It is considered that aggregates-stone, sand etc shall be procured from a reliable source, best available in the locality and there is no scope of testing of the materials.

Essential features of a sound Building:

1- Cement:             
 

a. Shall be of any branded company available as used by many others in the area. It is important that the cement is of a reputable brand.

b. Date of manufacture shall be checked. As older the manufacturing date, lesser  is the strength of cement

c. Better not to store cement in advance. If unavoidable may be stacked in a water-tight and closed shed on wooden floor or platforms raised at least 3 inch and to use it within 03 months from the date of manufacture. A physical check to do that lump (Fig-1) has not formed before use of cement, however soft lump, making dust with little pressure, is not harmful.

d. Cement available in the market are OPC-33, 43 & OPC-53 grade (OPC= Ordinary Portland Cement) may be used any one, ultimate strength for all are same, initial strength is different. Grade of cement is recorded on the bag itself to be checked. Nowadays OPC- 33 is not being produced. For the typical residential building  OPC-43 is the best choice, slightly cheaper than OPC-53 also. 

Note- In 03 months storage, cement may loose its strength by 20% or more depending on the standard of storage. Cement in stock  absorbs moisture from the atmosphere undergoing chemical reaction forms lump and looses its strength. Expert opinion should be taken for use of old stock (not permitted beyond 06 months),may be tested if required.

2-Sand:

Coarse sand  for concrete
Fig-3

Medium Sand for brick work
and plaster
Fig-2

a. Sand shall be used as per best availability in the nearby area, however shall be free from mud, gravels, coal pieces, dusty particles, tree leaves. Mud/clay mixed sand not to be used (all these unwanted particles can be easily identified by naked eyes)

b. Dust shall not be more than 3% by weight, should not be visible in open eyes.

c. Coarse sand- Shall be used for Concrete work (Fig-3)

d. Medium Sand-Shall be used for brick work, plaster work and sand shall be screened for better finishing in plaster.(Fig-2)

3-Steel rod or reinforcement: 

a. It is important that the steel is procured from a reputable brand. Manufacturer's name is embossed in the Steel surface to be checked. Steel from Local manufacturer are rust sensitive and shall not be used. 

b. Steel shall not be coated with paints,oils and rust steel not to use.

4-Water: 

As far as possible drinking water to use for concrete work. Water containing some element in excess has long term detrimental effects on the building. Sea water contains harmful salts, hence can not be used.

 5- Stone material:

a. Shall be used as per best availability in the nearby area.                             

b. Shall be of varying sizes 5mm to 20mm, angular in shape as in Fig-5. 

c. shall be hard and heavier, free from mud,dust, wooden pieces, leaves etc.
d. Flat or elongated particles as in Fig-4 shall be avoided.

Flaky and Elongated stone
 material
not suitable for concrete
Fig-4

Angular stone for construction use
Fig-5

6-Minimum Grade of Concrete:
a. Where steel is provided (RCC-Reinforced Cement Concrete) Mix of concrete  shall be minimum M20 (1 cement : 1.5 sand :3 stone chips 5mm to 20mm size). This proportion should  be followed for concrete in floor, roof, sun shade, stair case, railing, lintel etc.

b. Where steel is not required i.e. for Plain concrete minimum grade shall be: M15 (1 part cement, 2 parts sand and 4 parts stone chips 5mm to 20mm size). 
M10 (1 part cement, 2 parts sand and 4 parts stone chips ) may be used as base layer in flooring, under footing etc.

7-Bricks:

Good quality bricks for

 construction work

Fig-6

a. Good quality bricks as best available in the local market from a reputed supplier.  
b. Bricks shall be uniform deep red colour, regular in shape, free from cracks. 
c. The size of bricks shall be 9¾ x 4¾ x 2¾ inch  (conventional). 190 x 90 x 90 mm (modular) or any other size as available in the locality.

d. Brick  must be soaked in water for 6 to 12 hours before work. Basic purpose of soaking  is that water present in the cement mortar does not get dried. Water is required to attain strength in cement mortar.

                                                                                                                  

8-Selection of Head Mason:

a. Selection of a Head Mason is an important issue for better workmanship. 
b. He should have a reputation in the area. 
c. His earlier construction work in the locality may be inspected to know his performance, particularly about line, level of the finished work e.g edges of  slab, column, sunshade and projections etc.

9-Mixing of Concrete:

Mixer machine should be 

preferred

Fig-7

a. It is the best to mix the concrete by a mixer machine to get dense and strong concrete. Mixing shall be continued until, the concrete mass will have a uniform colour. 

b. Where manual mixing is permitted  constant supervision is required to see that traces of sand and cement are not visible in the concrete mass. Improper mixing will loose the strength.

c. 5% extra cement should be added in case of hand mixing.

d. In general, masons allow long gap (sometimes even more than 01 hour) between pouring water and placing concrete during manual mixing which is detrimental to the strength of concrete. The same is applicable for cement mortar also. 

10. Pouring and compaction:
a. It has to be ensured that concrete is not thrown on the mold/shuttering which may disintegrate the stone material from the concrete mass thus loosing its strength.
b. During pouring It has to be ensured that concrete has reached all corners of the mold e.g. column, deep and narrow beam otherwise it will have porous and weak concrete. 

Vibrator is essential
Fig-8

c. During pouring vibration has to be used. vibration removes the entrapped  air bubble inside the concrete and concrete fills the void easily  to get a dense and strong concrete after curing.
d. At the end of vibration/compaction, the air bubble rises up and the surface becomes smooth.
e. During pouring taping of mold should be continued reaching concrete to the narrow  space, every corner and  entrapped air bubble releases.
f. Staging/props has to be checked during pouring and compaction to tighten the wedges or any loose connection.
g. Concrete shall be Compacted within 30 minutes after adding water to get the best result. In this regard head mason/mason is not careful at all.
h. It has to be ensured that qty of water is proper and to be advised for adjustment. 

  

11-Quantity of water Vs Strength of concrete:

a. It is the tendency of the laborers to add more water so that it is easier to mix, to pour and easier to work with the concrete during compaction. 

b. In fact, more the water in the Mix  less is the strength of concrete and greater is the shrinkage cracks.

c. Water shall be added such that concrete paste  is not too soft like a fluid nor too stiff so as it is difficult for compaction. Too stiff concrete also looses strength due to improper compaction, however using vibrator little stiff concrete will give higher strength.

d. A  trial method should be applied to decide water quantity to make the concrete mix just workable so that it can be mixed, poured and well compacted. 

e. When vibrator is used, quantity of water will be  reduced, it actually gives more denser and stronger concrete. 

f. If sand, stone material contains moisture particularly in rainy season water addition during mixing  need to be adjusted considering the basis that concrete paste  is not too soft like a fluid nor too stiff that is difficult to work with it.

  

g. Mixing shall be checked by taking a handful of concrete and giving a round shape so that one should feel that   concrete is cohesive enough and stone material is not separated during light tossing.

12-Minimum Thickness of Roof Slab/Floor Slab: shall be 125mm.

corrosion due to less cover
Fig-9

13-Inadequate Cover:
        (Cover is very Important)

a. Adequate cover for steel is very important for long lasting construction work. 

Cover block between shuttering
and steel rod- Fig-10

b. Steel used in the Beam, slab, column etc. must be embedded inside the concrete as shown in Fig-11 to avoid  corrosion in the reinforcement/rod. 
c. In the Fig-9 Steel has exposed and corroded due to insufficient cover resulting concrete has cracked and fallen off.
d. Cover block must be provided and checked Fig-10.

Clear cover for steel/rod  shall be as per following:

                            
            Fig-11

Member                             Minm. Clear Cover
Slab--------------------------------15 to 20mm

Beam------------------------------ 25-30mm

column-----------------------------40mm

Footings----------------------------50mm

Stair case waist slab--------------15-20mm

14-Filled Up Land: 

When the house is to be constructed on low land and  the land needs filling to avoid excessive foundation cost, shall be developed at least with good quality sandy soil and immediate construction should not be done. May be required 2 years or more for consolidation unless special methodology adopted for filling and compaction. Clay soil for filling should be avoided, requires longer period for consolidation. Settlement continues even during and after construction. Expert advice must be taken if to carry out the construction on filled up soil.

15-Foundation on soft soil: 

a. Foundation of footing, wall shall not laid on visibly soft soil/ muddy soil, deeper level foundation is required.

b. Foundation near sloping ground shall be avoided. Soil condition is an important factor. Expert opinion must be taken when the soil is appearing soft.

16-Filling up the trench: 

The excavated area around the foundation of the building are to be filled up properly  well rammed and consolidated with water in various layers of 200 mm each and finally with an outward slope i.e away from the building wall so that rain water may not ingress into the foundation and weaken the soil below foundation .

17-Concreting thin section: 

Concreting in thin section like sunshade, coping or similar projection are the most neglected part of village/rural house even in towns and cities and lacks proper attention in these respect:

a. weak shuttering, improper compaction during concreting, irregular cover to the reinforcement leading to porous concrete, corrosion to reinforcement and cracks. In most of the building sunshades are found cracked much earlier.
b. Line and level is not maintained in sunshade, coping, fascia or similar projection which should be made in proper line and level during shuttering and casting not by plastering afterwards. 

c. Head mason has to be insisted, controlled and monitored of the above frequently. Certainly there will have better look.

18-Staging and shuttering: 

a. Shuttering may be of dressed timber true to line. 
b. Surface in contact with concrete shall be smooth. 
c. All joint gap of the shuttering should be closed to prevent the loss of water cement slurry from concrete.
d. Staging, propping and shuttering must be strong enough to sustain the weight of green concrete , weight of men, impact of vibration without  yielding.
e. Ensure that shuttering surface has been coated with suitable mould oil so as concrete does not stick when set.  
f. Ballhi propping is always better, if bamboo  is allowed that must be free from crack and as far as possible solid bamboo should be used.  

19-Shrinkage crack in concrete and protection: 

a. At the initial stage of laying, fresh concrete shrinks rapidly  and cracks,if allowed to drying by sunshine, blowing wind etc. 
b. To avoid such shrinkage and cracks,  fresh concrete surface shall be protected by covering with a plastic cloth around 2 hours after laying of fresh concrete so that it does not dry rapidly. Hence fresh concrete shall be protected  from sun, rain , wind , any kind of shocks, working people should not be allowed to walk on it. Materials for protection shall be arranged in advance.

20-Curing:

About 24 hours after laying of concrete, the surface shall be cured by flooding with water  or by covering with wet gunny bags. The  minimum curing shall be done for 
1. Cement concrete/RCC: 14 days. 
2. For Brick work/Stone work: 10 days
3. Any other cement works not less than 10 days 

21-Damp Proof Course (DPC): Dampness in a building  may result in unhygienic and unhealthy environment , even to mosquito breeding. Dampness  is also  harmful to the building in many  ways like damaging plaster, reinforcement corrosion, damage to wooden doors/windows, furniture etc. Therefore  it is  essential that  building should be free from dampness. A concrete layer or a layer of membrane has to be provided at plinth level to the full width of super structure wall to arrest ground water rising up through brick work by capillary action. In the old days (before 50 years or so), D.P.C was not generally  provided in construction works. Nowadays buildings are provided with DPC.  Workmanship shall be improved as suggested. a. Plain Cement Concrete  added with water proofing material may be adopted as damp proof course. Water proofing materials of branded manufacturer shall be used with quantity as per the manufacturer‘s specifications in the concrete mixture .  b. The thickness may be 40 to 50mm. Proportion-1 part cement:1.5 part sand:3  parts stone chips (10mm down).

c. Side shuttering  shall be strong enough so that it does not get disturbed during compaction and the mortar does not leak through. The concrete mix shall be tamped thoroughly to make a dense mass. (Generally, mason makes side shuttering in most casual manner being a small thickness & fresh concrete is simply laid and leveled without adequate tamping, leading to porous D.P.C or honey combing at the edges)  d. The damp proof course shall be laid continuously and the surface shall be double chequered for adequate bond with brick above.  e. Damp proof course shall be cured for at least seven days, after which it shall be allowed to dry. f. All  plaster work to toilet wall and toilet floor, during construction must be added with water proofing material, Quantity as per manufacturer's guidelines.   22-Soil Condition:  Soil investigation is hardly done in  rural residential construction up to G+1 or G+2. Foundation is adopted based on experience of head mason in earlier construction work in the nearby area without verifying the condition of old existing building. No specific thought is applied what the foundation should be. Following points to consider.  1. Soft clay-soil which is useful for paddy field,  is generally bad for a durable house. deeper and wider foundation may be required with at least 1 foot depth fine sand filling duly compacted in the trench.  2. If there is a history of cracks in the old buildings, houses, school buildings or  similar structures in the village or in the locality, foundation for new construction shall be decided in consultation with an experienced civil engineer and some easy empirical test may be carried as suggested to ascertain the foundation detail to be adopted. Note: Any suggestion, comments for further addition, improvement is welcome.