Food Processing Plant Design & Layout 2(1+1)

Lesson16. Building construction

16.2 General requirement of plant floors

It is necessary to use different types of the flooring material depending upon the use of the flooring surface. One single type of floor in the entire plant is not possible if wear is to be kept to a minimum. Plant floor requires different types of flooring in order to cope with hazards and other problems of various sections. It is desirable that floors should impervious, durable and long lasting. The material of flooring should be such that it can be cleaned easily, if required, non-slippery and cost effective. The flooring is designed considering the effect of washing and cleaning as well as and the ability to withstand changes of temperature by provision of adequate expansion joints.

The provision of adequate fall and drains helps not only to avoid the possibility of water pools but also assists the rapid removal of milk spillage and cleaning solutions. This helps in reducing the corrosion effect to the flooring materials. Normally, the fall should not be less than 1 in 80 for effective removal of liquids. Drainage channels should be at least 15 cm from the wall and drainage channels should not be placed along side walls, as far as possible. Water seepage may cause corrosion of structural steel and weakens the flooring base or R.C.C. Fig. 16.1 shows a cross section of construction of floor.

16.3 Structural base

The structural base is usually of concrete or R.C.C. A concrete structural base may be cast as a slab directly on the ground/R.C.C. or it may be suspended slab pre-cast concrete units. It should be designed to resist all the static and dynamic stresses with provision of heavy foundation required for installation of equipments. The structural base should be made of good concrete and thoroughly compacted.

16.4 Waterproof membrane

One of the most important features at the time of planning and designing of the food plant floor is the use of water proof membrane in the floor to prevent liquids from penetrating to the base structure. The membrane should be impervious to water, resistant to corrosion, tough enough to resist damage during repairs of the floors and support loads. All joints should be thoroughly sealed to provide a continuous membrane surface. The membrane should be laid to have falls at the base structure and be extended to some distance up the walls. The material used for the membrane must be strong and yet flexible. Acid resistant asphalt laid at least 10-12 mm thick on a layer of bitumen felt is most commonly used. The best results are obtained when the asphalt is laid in two layers with all construction joints broken, i.e. two layers don’t have their joints coinciding. Good quality bituminous roofing filled with lap joints sealed with bituminous compounds is also used. Plastic films of polyethylene, polysorbetylene and polyvinyl chloride are also used for the purpose. Properties of water proof membrane are as under.

• Water proof membrane should be impermeable to water.
• It should be resistant to corrosive liquids and substances.
• It should be strong enough to support the required load.

16.4.1 Types of water proof membranes

· Plastic sheet

· Chemicals

· Asphalt or Bitumen layer in the form of a thicker layer which is applied on walls to prevent leakage of water.

16.5 Flooring materials

Portland cement concrete is mostly commonly used as flooring material. The floors are resistant to abrasion and alkali. However, it is vulnerable to weak acids and deteriorates under the influence of liquid waste i.e. milk.

High alumina cement concrete resists acid solution above a pH 5.0 and is favorable than plain Portland cement. However, it is attacked by weak solutions of alkali and it loses its strength and resistance to abrasion under hot moist conditions. Hence, it is not regarded as a suitable flooring material for dairy plant.

Portland cement concrete often gives good service even where milk spillage occurs provided that regular cleaning takes place to remove the dairy wastes. Concrete floor shrink for several months after lying, but subsequently it expands and contracts with variations of temperature and moisture content. Such expansion and contraction may be of the order of 0.05% which may give rise to cracking or curling. Where plain concrete floors are likely to wet, joining gaps of about 12-13 mm (0.5”) width should be left open down to the waterproof membrane, and after the concrete has set, they should be filled with asphalt or other suitable joining material. The floors which may be subjected to considerable attrition and abrasion, the structural base should be covered by a topping of more resistant granolithic concrete.

Granolithic concrete contains more cement than ordinary cement concrete and gives good results in dairies, although its surface can be corroded slowly by lactic acids, milk residues and acid detergents. There is no shrinkage after laying concrete tiles which is made of granolithic concrete and cured under controlled conditions. They are laid in cement mortar of ratio 1:3. The joints between 1/8 and ½ inches wide must be completely filled with the same mortar. Concrete tiles may be tinted and similarly tinted mortar should be used for the joints.

Ceramic floor tiles can be used for flooring where moderate resistance to wearing is expected. These tiles are resistant to attacks by acids and alkalis. These tiles are available in different sizes such as 6” x 6”, 9” x 4.5”, 9” x 6”, 9” x 9”, 12” x 12” etc. These tiles should be thick so as to resist impact damage. Coved tiles should be used at joints between floors and walls. The tiles should be properly laid using appropriate bedding mortar and high grade filling material.

16.5.1 Requirements of a food plant floor or characteristics of a food plant floor

• They should be impervious, smooth and easy to clean.

• It should be able to withstand the effect of lactic acid.

• It should be able to resist the effect of the cleaning solution, steam or hot water.

• It should be strong enough to withstand the effect of falling objects, cans, boxes (impact resistance)

• It should have high resistance to abrasion (wear and tear).

• It should have desired slope towards drains

• In processing section, the slope should be 1:80.

• In bottling section and RMRD, the slope should be 1:40.

16.5.2 Different types of floor:

• Cement concrete floor

• Terrazzo floor used in offices

• Tile floor having either natural stones or synthetic tiles

• Metal floor

• Grill floor

16.6 Bedding and jointing for tile floors

The optimum result can be achieved by adopting most appropriate way of laying and filling the joints. The materials used for the purpose mainly depend on the type of flooring material used in different sections of a plant. Some of the ways of bedding and joining the floor tiles are given below.

16.6.1 Portland cement

Portland cement mortar is most commonly used for bedding material for fixing floor tiles/stones. Portland cement mortar is resistant to alkalis, but it is attacked by acids and dairy wastes. It is necessary to take adequate care to make water tight joint.

16.6.2 Super sulfated cement

Super sulfated cement is a mixture of ground blast furnace slag, calcium sulfate and Portland cement. It requires special care during hardening after laying. It is resistant to acidic and alkalis.

16.6.3 Rubber latex cements

Rubber latex cements are available for in situ floorings and are based on polyester and epoxy resins. Unsaturated polyesters which in the presence of a catalyst, react with another resin such as styrene, are usually employed for polyester flooring. It is susceptible to attack by alkalis and therefore cannot be used in dairy plants.

16.7 Metal tiles, plates and grids

Metal tiles of two main types.

1) anchor steel plates

2) cost iron metal tiles

Both types are very suitable to resist impact and abrasion in dairies. They also resist the action of alkalis but they are subject to attack by weak acids.

The anchor plate is usually 12” x 12”size made of 10 gauge steel in the form of a shallow tray of about 7/8” thickness and the wearing surface is punched to give downwardly projected twisted anchors which anchor the plate to the bedding material. For laying the anchor plates, upturned tray is filled with concrete and after inversion it is tamped into position until it is firmly embedded in the concrete.

The cast iron metal steel is made of a square or a right angled triangle, apart from the hypotenuse, the sides of each type are 12” long and the tile is about 1” thick and has a projecting foot at each corner. These tiles are bedded in cement mortar and tamped down until the feet rest firmly on the structural base, so that the stresses on the tile are transferred evenly to the structure.

Metal plates are used frequently on dispatch docks and in cold stores to provide very durable wearing surfaces over concrete flooring. Metal grids are sometimes incorporated in floor surfaces as reinforcement against abrasion and are embedded in the topping so that the upper side of the grid is flush with the floor surface.

16.7.1 Cast iron grill floor

Cast iron tiles have a hollow honey comb-like structure which gives a strong surface and has no slipperiness. This type of tiles has no problem of looseness from concrete surface. It gives less noise than metal tiles when cans are moved over it. This floor has high impact and abrasion resistance. Some time, concrete part of cast iron grill floor may be eaten away due the action of h milk or acid. .

16.7.2 Cement Concrete Floor

The general construction includes a structural base of RCC or concrete, a screed laid to fall, a water proof membrane, a bedding mortar and a top finishing surface or layer or a wearing surface.

16.7.3 Curing of concrete:

Curing of concrete is necessary to increase the strength and water tightness as cement reacts with water at a slow rate and it then becomes hard. The aggregate then formed has no reaction but it forms a strong bond and fills in the pores. Normally the structural base is 10-15 cm thick. Concrete food plant generally comprises cement to sand to aggregate in the ratio 1:3:5.

16.8 Bedding mortar:

The layer of the bedding mortar is generally kept around 2-3 cm thick. It has a ratio of cement to sand as1:3. Its function is to give attachment to the top surface.

16.9 Terrazzo floor

It is similar to concrete floor, and is generally used in offices, labs and such other places where decorative effect is required. Before hardening the top surface, marble chips of irregular shape are fixed on the upper surface and pressure is applied so that the marble chips get embedded on the wet top surface of the cement floor. After hardening, the surface is finished smooth so that the marble chips fixed on the top give a good appearance. Colored cement may be used to impart better look. Its main limitation is that it cracks when it comes in contact with hot and cold water due to thermal expansion and contraction.

16.10 Tile floor

Two types of tiles can be used viz. natural stone or synthetic (artificial) tiles.

16.10.1 Natural Stone or Kota Stone:

It is obtained from quarries and is then cut to the required size. They are available in different colors like red, buff, light green, brown and yellow. Acid resistant Kota stone (popularly known as Mandana stone) is also available, which can be used in the food industry. In order to be used in the food plants, the stone should have a minimum thickness of about 3 - 4 cm. They may be square or rectangular and should have a 90⁰ angle edges. The top surface should be polished and the bottom is kept unpolished to get better gripe with bedding mortar.

16.10.2 Concrete or Cement Tiles/ Artificial Tiles

These tiles can be made by making the desirable size mould using mortar and then hydraulic pressure is applied to make it non-porous and stronger. Marble chips of different colors may also be included in this type of tiles. Cement may be high alumina cement or colored cement. The size of the tiles may be 12” x 12”, 18” x 18” etc. These tiles are cured in water for 5-7 days and subsequently laid on bedding mortar. Various types of grinders are employed for surface finish of the floor. These types of tiles are rarely used as many other verities of tiles are available.

16.11 Maintenance of floors

The following points should be considered for the maintenance of the floor of different sections of food plant.

1. Regular cleaning floors is essential for hygiene, safety and long life of floor.

2. All the joints should be carefully observed for any water/milk/chemical penetration through the joints. Seal the joints using cementing material, if any defect is noticed.

3. Remove waste water etc. from the floor in order to cause insanitary or slippery conditions.

4. Floors soiled with oil should be cleaned by scrubbing with detergent and water.

5. In milk handling plant Lactic acid are formed as milk sours, therefore, early removal of spilled milk is desirable.

6. Use appropriate chemicals or combination of chemicals for floor cleaning. Don’t sprinkle chemicals on the floor as it may damage the floor surface. Use mild detergent solution with low free sulphate is recommended for floor cleaning.

7. Hand scrubbing with brushes or electric scrubbing followed by rinsing with clean water is recommended.

16.12 Structural aspects of foundations, roofs, ceilings, walls, doors and windows

Structural aspects of plant building are very important as it is necessary to design the plant considering strength and vibrations of machines. The design aspects of roofs, ceilings, walls etc. are carefully designed to maintain required hygienic conditions in the plant. The basic principles of design of dairy building are the same as that of normal factory building. Adequate care is necessary to consider sanitary aspects while designing and selecting building materials.

16.12.1 Foundation

Foundation of building should be strong enough to support super structure and to resist vibrations and impact load of heavy machineries. The design of foundation depends upon the nature of structure which they have to carry and the properties of soil the soil. The structure may consist mainly of load bearing columns/walls which are required to support the structure. It is necessary to work out the total load to be supported. The actual design of foundation is based on these aspects as well as the quality of sub-soil.

16.12.1.1 Traditional strip foundation

This is the most usual variety and consists of concrete say 9 inches thick laid at the bottom of the trench 3 feet deep. The width that the concrete extends beyond the faces of the wall depends upon the bearing capacity of the soil. It is necessary to follow standard guidelines to decide the width of the concrete. These aspects depend on the local soil conditions as well as factor of safety to consider in the design of the building. It is not possible to generalize the design aspects of foundation. There are regions where the traditional foundation with load bearing wall is not recommended owning to soil conditions reveling in that area. Column and beam type of structure may be required to support the load and other stresses.

16.12.1.2 Stepped foundation

The foundation of building should be strong enough to support the superstructure. The size of foundation is governed by its depth and width which are determined by the soil type and load acting on it. The size of the foundation should be determined on the basis of bearing pressure of the soil in which it is built.  

A typical section of stepped foundation for 13.5 inch thick wall is shown in Figure 16.1

16.12.2 Walls

Walls for plant buildings are made of brick, concrete, concrete block, aluminum and glass. Bricks are widely used for the construction of walls. It is relatively cheaper and proper plastering and painting makes the walls quite water proof. In many sections, glazed tiles are laid up-o the height of 7 feet or more for ease of cleaning. With adequate care, repairs can be made without spoiling the appearance of the building.

Concrete walls are relatively costly and repairing is difficult. Provision is necessary to tackle the need of unsightly repairs. Aluminum partition walls can be made using flat panel construction or corrugated sheets. Glass panels used in building give good lighting but it is essential to keep the glass surfaces clean.

Walls which are made up of brick or stone are mainly two types.

• Partition wall: To divide an area into two or more compartments or cabinets, etc. The width of partition wall using standard brick is about 4”.

• Load bearing wall: Walls which can take loads of structure of ceiling or of superstructure. The width of the load bearing wall using standard brick is 14” or 9”.

16.12.2.1 Construction of brick walls

The dairy buildings are of two types namely single or two storey building having load bearing walls. Another type of building is having column and beams which supports the entire load of the building. The load of the building is transferred to the soil by beam and columns. It may be multi-storied building or even single storied building. In this case, walls are simply dividing the area in to different portions/sections. The strength of wall is not much important as the entire load is taken by beams and columns. If the size of room is small in case of load bearing structure, beam is not required. The external walls take the load and transfer it to the soil. In construction of walls using bricks, it is desirable to staggered the joints. Mortar of suitable proportion of cement to sand ratio is recommended for different types of walls. Optimum quantity of water is necessary in the mortar for proper spreading and setting of plaster.

16.12.2.2 Surface finishing for walls

Plastering using cement to sand ratio of 1:2 or 1:3 is used for surface finish of walls. The plaster is generally applied in two coats (1) floating coat and (2) finished coat. The floating coat of the plaster is 1.5 to 2.0 cm thick. The main purposes of plastering are as follows.

• To hide irregularity of walls (grooves)

• To avoid unevenness of wall during construction

• To improve the appearance of the wall

• It provides or facilitates the application of suitable paint

• It also prevents deterioration and protects the wall from external atmospheric effect.  

Ceramic glazed tiles/vitrified tiles are also used for the purpose of wall finish.

16.12.3 Ceramic/Glazed Tiles

Glazed tiles are laid up to the height of 2 m in the processing room and other sections of dairy plant. The use of glazed tiles provides a surface which can be easily cleaned and hygienic conditions can be maintained. These tiles also make the wall waterproof.

16.12.3.1 Classification of Tiles

• Non – vitreous: Non-vitreous tiles has a high degree of moisture absorption greater than 7% of the weight of the tiles. Even though, it does not prevent the tiles from having high degree of strength and it also facilitates installation because of their adherence to the mortar.

• Semi-vitreous: These tiles have a high density that limits the moisture adsorption to 3-7% of the weight of the tiles.

• Vitreous: These tiles have a moisture absorption of 0.5 to 3.0%.

• Impervious: These tiles are the hard and their moisture absorption is less than 0.5% and they are readily cleaned off stains and dirt.

In lower portion of the wall of RMRD and cold store, damage may occur. Skirting is provided in the processing room to make lower portion of the wall hard. Bumper rails in cold store and railing on the walls are provided to prevent the damage due to crates/cans. Wherever walls are not covered with tiles, they are plastered and painted. Use of good quality paint is recommended for painting of walls.

16.12.4 Doors and windows

Doors and windows are subject to gruelling condition existing in food plant. The door of stainless steel is the best choice in many food plants. Hard wood or water proof plywood may be used for making doors and windows. Aluminum or aluminum alloys can be used but the alkaline cleaning materials which are used in milk plants may spoil the surface. Doors of ordinary steel sheet on a steel base are sometimes used, but in such cases, the whole door must be galvanized or protected against corrosion.

Plastic sheet can be used with a wooden or metal frame. There are many options available for the selection of doors and windows. It depends on the requirement, cost, maintenance etc.

Doors for cold rooms must be thermally constructed from timber/PUF panels and cladding of S.S. may be used for protection of insulation. All door fittings should be of rust proof material and of robust construction, particularly in case of swing doors. The locking mechanism for cold store room doors must always be such that it can be operated from inside the cold room.

16.12.4.1 Doors

The provision of doors in a building should be carefully made considering the movement of materials, persons, location of door, size requirement, type of door etc. The height of the door should be more than 2m inside the frame. Regarding the width of the door, it should be designed for the particular requirements. Usually, it varies from 0.75 m to 1.5 m depending on the type of the room. When the width is more than 1 m, double shutters may be used. The normal height of door is 2 m but it may be more in case of workshop, boiler room and garages. A rolling shutter may be used for large size doors especially in boilers, garages and workshop. The number of doors depends on the type of room and size of the room. Hardwood or laminated plywood may be used for preparation of doors. Wood or plywood doors should be protected from moisture and water by painting.

Types of doors:

• Ledged door

• Ledged and braced door

• Frame and ledge door

• Frame and panelled door

• Louvered door

• Flush door

• Door without hinges

• Sliding door

• Rolling steel door

• Collapsible door

• Revolving door

Flush doors are manufactured in standard sizes to facilitate mass production. It consists of a skeleton or hollow frame of rails and stiles covered with plywood or any other type of reconstructed wood. Louvered doors maintain free flow of air and also maintain privacy. The door without hinges such as sliding door, rolling door etc. are used in large size doors.

16.12.4.2 Windows

The purpose of providing windows in building is to get ventilation and natural light. Openable windows provide both air and light, while non-openable windows provide only light. The size of window and its location are very important to achieve optimum advantage. In deciding the location of windows cross ventilation is kept in mind for office building. Fixed glass windows are also provided in plant building to get natural illumination. It is recommended that

1/10^th of the floor space is allowed for the window, of which one half should be capable of opening, when required. Another thumb rule adopted is that window area is equal to the square root of the cubic contents of the room.

The exact location of the windows depends also on the purpose for which the room is used. For example, in an ordinary living room, the sill of the window should be kept at about 2.5 feet over the floor level while in bathrooms or a lavatory. The window will be kept at a higher level, so that even when the shutter is open, there should be privacy to the occupant. The window sill should be at a height of about 0.8m height from the floor. The height and width of the window depends on the type of window and number of windows. Entry to dust and insects should be prevented in the product processing room by providing a wire mesh. Total window area may be 20-25% of floor area.

16.12.5 Roofs and ceilings

The use of R.C.C.is widely used for roofs and ceilings. The R.C.C. is designed and executed properly to prevent leakage of water. Water proofing work is necessary to eliminate the chances of water penetration in the R.C.C. Use of good quality materials and proper workmanship during R.C.C. work is necessary to get better result. It is necessary to carry out curing of R.C.C. immediately after setting of the R.C.C. White ceramic/glazed tiles may be laid on the terrace to reduce the heating effect and to make the R. C. C. water proof. It depends on the local weather conditions to decide the need of water proofing requirements.

Slope is provided on the top to facilitate drainage of water. The thickness of the slab varies from10 cm to 15 cm depending on the size of the room and other structural considerations. Height of processing section is more in order to facilitate the service pipelines.

Roofs are classified as flat, semi-steep and steep depending on the slope provided. Flat roofs have rise from zero (level) to 8 inches per horizontal foot. The rise in semi-steep roofs varies from 3.25 to 12 inch rise per horizontal foot. The rise of steep roofs varies from 13 to 24 inch rise per horizontal foot. In many factories and food plants roofs are generally flat or semi-steep type.

The roof sheet of different materials such as PVC, fibre glass (FRP), polycarbonate etc. in various design are available for making roof of factory. These materials have advantage of light in weight and colour choice based on the requirement of the plant. Construction of a satisfactory roof is possible only when high standards are maintained during all phases of its construction. The selection of material for roof mainly depends on the weather conditions of the place. There are options available to select the best possible roof for the plant. Ceilings of the food plant must be smooth and impervious so that it can be easily cleaned and maintained. In the plants where air ducting is necessary, it is carefully planned with false ceiling of appropriate material.

16.13 Drain and drain layout for food plant especially dairies

The ratio of milk to water used in various dairy plants varies from 1:1 to 1:3 depending on the type of plant. The old figure of water use was quite large but now water conservation measures resulted in to considerable low level of water consumption. Water is mainly used for washing of equipments, floors, milk crates/cans, hot water, chilled water etc. When water is used in dairy plants, it is necessary to provide drains and piping arrangement to transfer the waste water to effluent treatment plant (ETP) of the dairy. The drains and pipeline layout should be such that it maintains hygienic conditions in the processing area and waste water containing milk resides is efficiently collected from all the sections and finally supplied to the ETP plant.

16.13.1 Drainage system for plants

Drainage system is very important in any dairy and food plant. Therefore, it is one of the essential considerations at the stage of planning and design of processing building. It is important to provide adequate numbers of sanitary drains coupled with waste water conveying system to transfer the effluent to the treatment plant. Any shortcomings may lead to choking of drainage pipelines and unhygienic conditions in the plant. Cast iron or PVC pipelines are commonly used for conveying of effluent in dairy plants. The planning and lay out of the drainage system is done in such a way that it is possible to separate high BOD and low BOD effluent. This is necessary to adopt different methods for the treatment of effluent. Anaerobic method of treatment of high BOD effluent is getting considerable importance in dairy industry as its operating cost is low and it generates methane gas which can be used for boilers. The following points should be considered while planning and laying of drainage system.

1. Select the most appropriate type of drains and entire system considering hygienic conditions.

2. Use the drains which can be cleaned easily.

3. Provide adequate number of drains considering the maximum flow of water.

4. Use of 4”-5” (100 mm to 125 mm) diameter pipe for drainage lines for handling milk plant wastes.

5. Regular cleaning of sanitary drains is recommended to avoid chocking of drainage system.

16.13.2 Floor traps for plant floors

A trap is a device which is used to prevent sewer gases from entering the processing area of the building. The traps are located below or within a plumbing fixture and retains small amount of water. The retaining water creates a water seal which stops foul gases going back to the processing area of the building from drain pipes. A good trap should maintain an efficient water seal under all conditions of flow. In Gujarat, sanitary trap used in large capacity dairy plant are popularly known as Amul trap (drain) which is fabricated using 2 mm thick stainless steel and is available with the sanitary design for dairy and food industry. These are available in various specifications and finish based on the need of industry.

Drains for plant floor may be square type or round type. A trap is placed beyond or underneath the drain. A typical floor trap is given in Fig. 16.3 which has two cast iron cover plates, the lower one perforated and the upper one slotted. The top plate retains big size materials such as bottle caps, threads, glass pieces etc. while lower perforated plate retains relatively smaller size materials. The debris retained on these plates can be removed.

16.13.3 Design consideration for drainage system of food plant

The efficient collection and conveying plant effluents are two important considerations for the drainage system. There are two categories of drainage system.

1. Drainage system for different sections of plant and laboratories,

2. Storm water drainage system for collection of rain water from roof, surface water from paved areas. This water is quite clean and can be handled for useful applications such as water re-charging of wells/tube wells. The system consists of big size cannels and cement pipelines of big diameter, pumping etc. This system of rain water management is also very important in order to eliminate water accumulation in the plant premises.

Since drainage system for different sections of food plant is continuously in use throughout the year and hence adequate attention is required to design and laying of the system. Some of the important points to be considered are indicated below.

Floor in the processing section should be laid with adequate fall so that water runs quickly to drain. This is also important to extend the life of the floor. The minimum slope should be 1:80 and slope up to 1:40 is considered better from point of view of drainage. The recommended slopes in floor towards drain for processing room is 0.25 inch per foot and 1/8^th inch per foot for cold store. The probable places where spillage may occur, the slope should be arranged in such a manner that liquids will flow to the drain by the shortest route.

The arrangement of drains in a large processing room is shown in Fig 16.4. In this layout, the entire floor of the large milk processing unit is divided into 8 segments and 8 floor traps have been placed to catch liquid flow from the floor segments. Liquid falling on any of the segments will quickly move towards nearest trap. Drains underneath the traps run in straight lines as shown in Fig 16.4 and meet the main drain line which later joins the main sever line. This type of layout is highly recommended for large milk processing rooms. For small processing rooms, this type of arrangement may be provided on the side of the wall keeping about 30-40 cm distance from the wall.

Vitrified salt glazed clay/concrete/PVC sever pipeline may be used to transfer the effluent to treatment plant.

16.14 Paints, coatings and mold prevention

The purpose of painting is to protect the building and engineering materials from corrosion and rusting. This will greatly enhances the useful life of the building and equipments. Painting and coatings also decorative look to the building. The selection of appropriate paint and coating material is very important to get optimum result. The control of mold growth over the building and other parts of walls, ceilings, cold storages etc. is one of the essential requirements in dairy and food plants.

16.14.1 Paintings

The objectives of painting are as under.

• It protects the surface from weathering effects and effect of other gases and fumes.

• It prevents decay of wood and wood based products.

• It prevents corrosion in metals used in dairy plants.

• It gives good appearance to the surface.

• Painting makes the surface smooth for easy cleaning.

• It makes the surface hygienically good, clean and attractive.

Paint is made of two broad components pigments or solid powders and vehicles (carriers), which transfer the pigment onto surface. Paint consists of base material, carrier, drier, colouring pigments and solvent. A base is a solid substance in a fine state which forms the bulk of paint. It forms opaque layer over the surface of the material to be painted. Vehicles are the liguid substances which hold the ingredients of paint in liquid suspension. Paints and other protective coatings deteriorate rapidly in dairy plants because of constant exposure to moisture, acid, alkali and high humidity. Painted surfaces showing evidence of deterioration must be attended immediately to maintain coating of the paint on the surfaces. It is noticed that break in colour film may cause similar failure surrounding the area. If timely maintenance is not carried out, then hygienic conditions will be adversely affected. It is possible to extend the life of painted surface inside the plant by minimizing condensation of steam/water vapour by installing mechanical ventilators.

Adjoining rooms at different temperatures differ in vapour pressure which causes moisture migration from one room to another. Under such conditions, moisture may penetrate the paint film on the colder surface. In order to minimize this effect, the wall of the warmer room must have an impervious paint film to provide a vapour barrier.

The surfaces to be painted should be cleaned and dried before applying paint coating. Apply rust inhibiting primer on bare unpainted steel before applying colour coating. If previously painted surface is to be repaired, clean the metal surface by using wire brush and then apply the colour. Concrete and plastered surfaces should be thoroughly cleaned by means of wire brush to remove loose paint before applying new paint.

Dairy products readily pick up solvent fumes from paint and therefore, it is necessary to avoid brushing or spray painting in room containing milk or milk products. During painting, every effort should be made to provide the best possible ventilation both to minimize product contamination and to reduce the nauseating effect of the paint fumes on the painters. Ventilation should be continued until the paint is dry and the room is free of solvent fumes.

16.14.2 Characteristics of ideal paint

The following are the ideal properties of paint.

• Good spreading power

• Low cost

• Ease of application

• Drying in reasonable time

• Form hard and durable surface

• No effect on the health of painters/workers

• No effect of weather

• Attractive and pleasing appearance

• No cracks on drying

• Produce uniform film

16.14.3 Types of paints

16.14.3.1 Oil paint

It is oil based ordinary paint which is applied on wood, plywood, metal surfaces walls etc. It is necessary to apply oil primer before the application of two coats of oil paint. The surface to be painted should be free from moisture before the application of primer coat. These pains are available in glossy and mat finish variety to select as per the requirement. It can be applied with brush/spray painting or roller painting.

16.14.3.2 Plastic paint

It is water base colour which is commonly used for painting walls, ceilings, etc. It can be diluted with water. It is commonly applied with brush or roller. It is necessary to prepare the surface form the application of plastic paint. A primer coat of cement paint is applied on the surface and then wall putty is filled to make the surface smooth. The surface to be painted should be clean and rubbed with sandpaper/water paper to get very smooth surface. Subsequently, two coats of plastic paints are applied on the surfaces to be painted. Thousands of colour sheds can be prepared by addition of coloring agents in these paints. Colour suppliers have computerized system to add metered amount of coloring agents in the base of the colour. Hence, there is a wide range of colour sheds to select for the requirement. When the paint dries, film of binders, pigments and other solid is left on the surface. These paints are generally available in thick consistency and water is required to be added for uniform application on the surfaces. After drying of paint, surface can be washed.

16.14.3.3 Aluminum Paint

It consists of very finely ground aluminum suspended in a medium composed of a quick drying spirit varnish or slow drying oil varnish, according to the requirement. It protects iron and steel from corrosion far better than any other paint. It is widely used for painting marine pillars (supports), oil storage tanks, gas tanks, etc. It also resists heat to a certain extent, so it is applied to radiators, hot water pipes. It is also good for decorative purpose.

16.14.3.4 Anticorrosive paint

This paint consists of oil and strong drier with chromium oxide or lead or zinc chrome as pigment.

16.14.3.5 Emulsion paint

It contains binding material such as polyvinyl, synthetic resins etc. This paint is easy to apply and it dries within 2 hours. The surface of the paint is tough and it can be cleaned by washing with water. It is advisable to make the surface smooth before application of paint. A primary coat of cement paint is applied followed by two coats of emulsion paint.

16.14.3.6 Enamel paint

This paint is available in different colours. It contains white lead or zinc white, oil, spirit and resins. It dries slowly and forms hard durable surface which is not affected by acids, alkalis, fumes, etc.

16.14.4 Varnishes

It consists of resins dissolved in volatiles. It is made by dissolving the heated resins in hot oils and adding turpentine. Varnishes are available as transparent or translucent. The oil oxidizes to form a tough protective film. Depending on the solvent used, varnishes are classified as under.

• Oil varnishes

• Spirit varnishes

• Turpentine varnishes

• water varnishes

Linseed oil is used as solvent in oil varnishes while methylated spirit is used as solvent in spirit varnishes. Spirit varnishes dry quickly but it is not durable. It is used for furniture. In water varnishes, shellac is dissolved in hot water and required quantity of either ammonia or borax or potash or sods is added so that shellac is dissolved. Varnishes are applied by using smooth fine brush.

16.14.5 Painting for mold prevention

It is necessary to carry out painting on building and equipment by adopting recommended procedure in order to make the surface which is not suitable for mold growth. It is desirable to use paint containing a fungicide. The fungicide should be such that it is effective, non toxic, impart no odour or flavour to food products and be economical. Solubilized copper quinolinolate has been found to be an effective fungicide for paints, especially when combined with the paint during the manufacturing process. The surfaces containing mold growth may be treated with a hypochlorite solution containing 0.5 to 1.0% chlorine to prevent a general contamination of the area during the cleaning process. Many patented mold inhibitors are available to use as per the recommendation.

16.15 Painting Problems/ Failures:

The basic reasons for the defects in painting are due to (i) atmospheric conditions (ii) defective surfaces and (iii) Incorrect painting methods.

1. Alligatoring: It occurs due to application of relatively fast drying coat over one which is too soft. The reasons for soft under coat could be use of too much oil, use of unsuitable oil which dries to a soft film or due to insufficient drying time before another coat is applied.
2. Blistering and peeling: Blistering and peeling is caused by moisture penetration behind the film of paint on the wooden surface and plaster. The change in temperature causes vaporization of moisture which increases the volume. This causes a blister. This may also happen if the seasoning of wood is not done properly.
3. Cracking and scaling: This happens when paint becomes too brittle as it ages and then it begins to break. The wood expands and contracts due to moisture absorption which may break the film of colour. However, in the long run, the elasticity of the paint decreases. In order to overcome this, more elastic paints of higher grade should be used. In order to repaint the surface, first the old paint should be removed. This can be done by scrapping, using a sand paper or a wire brush, blow torch and scrapper or by using chemical solvents. (liquid paint removal).
4. Running and sagging: Use of too much oil results in sagging down and applying too much thick coat also results in sagging. Application of paint to very glossy a surface would also result in sagging. It is necessary to maintain proper viscosity and surface finish of the surface to be painted.
5. Wrinkling: Formation of wrinkles is due to improper drying of paints applied on the surface. This happens when surface dries quickly leaving undried paint below.