Review of waterproof painting techniques by using suitable Technology
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| Sunil Khairnar | Ashis Kumar Khan | Rajeev Kumar Goel |
* Sunil Khairnar, Ashis Kumar Khan & Rajeev Kumar Goel *Asian Paints Ltd. Mumbai
Aesthetics of the building is a major reason behind the painting of interior and exterior surface of the building; Painting provides beauty to the building and covers little defects present on the substrate (masonry, wood or metal). The paint works as a building envelope but still it is affected by nature's elements like wind, rain, mist and dirt and dust. Water and moisture are the major things which affects the performance of interior and exterior paint applied on the building. In general the paint performance related problems are increasing due to increasing complexity in construction practices. The performance of both interior as well as exterior paints can be improved significantly by using proper waterproofing solution along with a recommended painting system. If water seepage coming from groundwater, rainwater and surface water can be adequately controlled, it would prevent damage of coating system and avoid requirement of unnecessary repairs to building envelopes. In fact water is the most destructive weathering element of concrete, masonry and natural stone structures and its damage continues until the structure is destroyed completely. Waterproofing techniques preserve the structural integrity of the building. Recommendation of waterproofing system involves understanding of natural forces affecting the performance of coating system as well as various designs of waterproofing material.
This paper involves, in solveing the problems arising in interior paint due to water and moisture seepage or ingress using combination of proper coating system by combining it with proper waterproofing solution.
Keywords: Waterproofing, Paint defects, Dampness, Efflorescence, Waterproofing technologies, Nano- materials, Nano-silica, Nano-technology.
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WATERPROOFING is a combination of materials or systems that prevents water intrusion into structural elements of building or its finished spaces. Basic waterproofing and paint system design involves things such as understanding water sources likely to be encountered, designing systems to prevent leakage from these sources and finalizing the design by proper application of the whole system.
Water is likely to penetrate building envelopes either from rainwater, groundwater or from other sources such as leakages from plumbing or water holding tanks. Available water is moved into the interior surface of the structure by numerous forces that include natural gravity, surface tension, wind/air currents, capillary action and hydrostatic pressure etc.
One of the challenges in construction industry today is obtaining a defect free construction work and avoiding ingress of moisture in the buildings. Buildings should be designed to ensure that buildings are free from unwanted moisture/water through dampness, seepage and leakage.
The conventional techniques of waterproofing are being used since the time of construction technologies for buildings are known to exist and have
served the purpose to a great extent. Nowadays the scale of construction in India has gone up and construction material for certain areas like deeper basements, wider slab areas, high rise buildings facing rain and storms at high pressure, coastal side buildings, and pre cast elements etc. has changed significantly. The use of wide variety of materials in such structures pose more challenging problems. Many conventional techniques of waterproofing are available but it need to be supplemented by the new developments in this field. The traditional methods of lime terracing, mud-phuska with clay tiles, tar felt/bituminous treatment etc. are slowly replacing with newly developed waterproofing materials and systems to check the ingress of water in buildings.
The new development in science and technology has allowed using the latest nano-technology to produce eco- friendly organo-silicone products to waterproof practically all the different kinds of building materials. The nano- technology has ensured that service life of this approach will lead to life cycles beyond 20 years at very economical cost. Another advantage of using waterproofing solution is to prevent loss of structural strength of concrete building materials, particularly due to alkali silica reaction, acid rain and sulphate attack etc. It also prevents chloride penetration which can result in corrosion reinforced steel bars.
In this paper we have particularly focused on the nano-technologies based silane waterproofing solution, their performance for effective waterproofing treatment to enhance the performance of coating system to protect the building structures.
Problems caused by water
Unwanted water is a hidden enemy to paint performance. Water enters into surface, either as liquid water, as water vapor, or as a carrier for chemicals dissolved in water. It causes dampness, paint peeling, masonry efflorescence, spalling, rusting, staining and corrosion of the surface, hence affecting the aesthetic and durability of building structure.
Dampness is arising due to a) leakage of rainwater into the building structure through cracks present in vertical wall and roof or moisture from ground (outdoor sources), b) moisture from humans and indoor activities e.g. cooking, bathing, human expiration, humidifiers (indoor sources), c) Retained moisture within building materials due to poor storage of construction material or due to insufficient drying time before painting. d) water leakages from pipes, e) flooding and other types of accidents. Dampness is most common problem for any house particularly in walls near kitchen, and bathroom etc. Dampness spoils the look of the interior paint and also creates many serious problems if continuous for many days and can be susceptible mold growth into the house which creates unhealthy environment in the house.
This problem is usually caused by water getting entrapped behind the paint film. If the paint system is not sufficient to resist water for the actual exposure, water can penetrate the surface in sufficient amount to cause the paint peel. The most common cause of paint peeling is breaks in the painted surface due to cracks in the wall or open joints that are not properly caulked. Openings around doors and windows are special source of trouble because improper caulked joints.
A second serious cause of paint peeling is the moisture present in the space behind the painted wall. Moisture condensed into liquid water and gets into unpainted side of the wall behind the paint. Then from behind it pushes the paint off the wall. If the excess moisture comes from inside the building, it usually caused by insufficient ventilation to the outside plus a wall paint system that is not waterproof. Another common cause of paint peeling is moisture or water seepage from moist ground under a house or other structure.
Efflorescence is the deposit of water soluble salts on the outside of painted masonry surfaces such as stucco, concrete, volcanic ash cinder block and mortar between bricks. The water soluble salts are migrated out of the masonry by water and these salts come to the surface from inside. The water evaporates from the painted surface, leaving a deposit of salts. Although the salts can be washed off with stream of water, they will form again unless the source of water behind the paint is stopped. Many times the source is leaking roof. If the efflorescence is only about 16 inch of ground, it is probably due to the capillary action groundwater by masonry walls. Capillary action stopped by waterproofing the foundation with tar or waterproof paint for 2 feet below ground level and few inches above ground level.
Water soluble corrosives
There are the water soluble compounds affecting the performance of the paint system. Dissolved compounds of iron will rapidly deteriorate the decorative function of paint. Rust stains are formed on the surface, spoiling its appearance. These stains are difficult or impossible to remove without damaging the paint film. Seawater contains large amount of dissolved salts. These salts accelerate water penetration of the paint film so that water comes into contact with substrates.
Types of waterproofing systems available
Bituminous and modified bituminous membranes.
Single ply sheet membranes.
Cold applied liquid membranes.
Polymer modified repair mortars
Cementitious coatings (Negative side waterproofing)
Bituminous and modified bituminous membranes
Bituminous membranes are still considered as a backbone of waterproofing because of their effective cost and they are available in various forms which can be either cold or hot applied. The major drawback of bituminous and coal tar based products is their black colour and fast degradation under the exposed condition. However these shortcomings are now overcome by their modification with certain elastomers like SBR, SBS, ABS, polyurethanes and plastomers like APP, PE and thermoplastic elastomers. The addition of elastomers and plastomers in bitumen provides them flexibility and elasticity on the dried film. It also ensures better resistance to fracture over a wide range of temperatures and moisture variations.
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| Fig. 1: Modified bituminous membrane |
The modified bitumens are prepared by adding certain amount of polymers through heat and mechanical action. Majorly atactic polypropylene (APP) and styrene-butadiene styrene (SBR) thermoplastic rubber used for modification. Modified bitumens have excellent flexibility at low temperatures, the elastic recovery is also high and considered best suited for colder climates. The APP modified bitumen have excellent UV resistance and exhibit high durability.
The most important achievement in the area of modified bitumen membrane which contributed to improved performance of roofing membranes is the development of new non-woven fabrics. Some of the manufacturers now started using two types of mats i.e. glass fiber lightly reinforced with polyester non-woven and polyester non-woven lightly reinforced with glass fiber mesh which provide dimensional stability of glass fiber with good mechanical properties.
Single ply sheet membranes
Single ply synthetic roofing membranes are the latest addition in the area of waterproofing. In last 20 years number of new roofing materials has been developed. Flexible PVC membrane is most popular in thermoplastic category and EPDM (ethylene propylene diene monomer) is the most popular in elastomeric category. Although polychloroprene, polyisobutylene and chlorosulphonated polyethylene elastomeric membranes are also available.
Single ply membranes can be used in loose laid, adhered or mechanically fastened systems with insulation above or beneath the sheet. Because it is free floating, it can accommodate movement of the substrate and small amounts of entrapped moisture. However, it should be weighted down with smooth river gravel, pavers or concrete blocks to prevent wind uplift. The limitations of this system are that it can only be used on flat roofs and only on buildings that can structurally support the weight of ballast, otherwise sagging and ponding may occur.
The membrane may be attached with adhesive used alone or in combination with mechanical fasteners. Fully adhered systems may be used to advantage for covering sloped roofs. Depending on the type of the membrane, joints are made between sheet by heat fusion, torching, solvent welding, and tacky tapes or with adhesives.
These membranes are advantageous and preferred choice for lightweight constructions, work with single ply roofing proceeds cleanly and quickly and large areas can be closed in under range of climatic conditions, the single ply roofing provides the architect with new degrees of freedom in colour and design.
Cold applied liquid membranes
The cold applied liquid membranes are one of the modern techniques used for the waterproofing of buildings. These protective coatings are based on various polymeric systems such as silicates, silicones, polymer modified bitumens, plastic emulsions like PVA, SBR, SBS, acrylic emulsions, epoxies and polyurethanes. The advantages of using these polymeric membranes for waterproofing are particularly with regards to their suitability as per various requirements, ease of application, efficiency and reliability. They are available as one component as well as two component systems. The single component systems are solidifying by evaporation of solvent or water while two component systems solidify by chemical reaction. These can be applied by brush, roller or spraying to form seamless waterproofing membrane. They are advantageous over other waterproofing systems in case of their continuity on horizontal and vertical planes as well as around the projections and geometric angles. With the complete adhesion of membrane material to substrate, water cannot easily travel beneath the membrane, laterally or vertically. Therefore, leaks can be isolated and thus can be found and repaired easily.
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| Fig. 2: Liquid applied waterproofing membrane |
Out of all these membranes water based coatings are becoming more popular nowadays, water based coatings are used to check dampness and efflorescence in building. These coatings are based on different types of homo- polymers or co-polymers like PVA, SBR, SBS, acrylics etc. and water dispersible epoxy and polyurethanes etc. The performance of these coatings are superior to other coating systems, as they allow concrete to breath i.e. allow entrapped water vapour to permeate out without allowing diffusion of oxygen, carbon dioxide, rain water, chloride ions etc. from outside. Coatings based on acrylic emulsions have been found to show better results because of their better compatibility with substrates and weatherability.
However epoxy resin is also widely accepted in construction industry, epoxy based products providing solution to various construction problems in the form of coating, adhesives, sealants, mortars, injection grouts and so on. Epoxy based coating are mostly used as waterproofing, damp proofing and protective coatings for interior applications.
Integral waterproofing compounds are powder or liquid materials generally mixed with cement at prescribed dosages to get a waterproofing by producing a concrete which has reduced permeability. There are many types of integral waterproofing compounds which are broadly classified as finely divided solids such as fuller earths, talc, bentonite and other siliceous powder which are inert pore filling materials, chemically reactive finely divided solids such as mineral admixtures and conventional chemical admixtures such as water reducers, accelerators, air entraining agents and superplasticizers. The combination of these admixtures results in lower water content, highly workable and dense concrete with reduced permeability.
Polymer modifier used for cement are organic polymers dispersed in water are used widely because they impart better flexibility, reduces water permeability, increase tensile strength and bonding behavior of cement particles and hence provide excellent waterproofing properties.
Nowadays crystalline waterproofing introduces another set of chemicals to the concrete. The chemical composition of each brand of crystalline waterproofing is different but the basic Cementitious membranes, which are usually self-curing, are pre-packed, technology is the same. In presence of water, the product reacts with calcium hydroxide and other by-products of cement hydration to create a microscopic non-soluble crystalline formation that fills the pores and micro-cracks in concrete. The crystalline formation can only occur when moisture is present hence the crystalline forms in pores, capillary tracts and shrinkage cracks only. Whenever water goes, crystalline waterproofing will form filling the pores, voids and cracks. Instead of reducing the porosity of the concrete, like water reducers and superplasticizers, the crystalline formations fills and plug the voids in concrete becoming an intergral and permanent part of the structure.
Crystalline waterproofing and protection technology is available in powder form and it can be applied by three different ways
Applied as a coating to the surface of an existing concrete structure like foundation wall or floor slab.
Mixed directly into the concrete at the batch plant as an admixture.
Shaken as a dry powder onto fresh concrete and trowelled into the surface.
Polymer modified repair mortars
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| Fig. 3:Polymer modified repair mortar |
These are ready to use mortars in dry form. The properties are suitably modified using polymer bonding agents, plasticizers, shrinkage compensating admixtures and waterproofing admixtures. On site only specified amount of water is to be mixed with dry mortar. They result in a mortar with improved cohesiveness, strength, bonding and free from shrinkage. The repairs made with these mortars are watertight.
Cementitious coatings (Negative side waterproofing)
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| Fig. 4: Cementitious coating |
Cementitious membranes are special, rigid, hydraulic cement compositions which upon hardening form a waterproofing cement coating. Cementitious membranes, which are usually self-curing, are pre-packed, bagged mixes that require only the addition of water. Some manufacturers offer traffic bearing Cementitious membranes which may be left exposed to commercial and industrial traffic. Materials are available for sealing leaks, cracks, penetrations, cants, coves and fillets. Some Cementitious membranes resist very high hydrostatic pressures with a very low permeability, and therefore can be painted or coated with protective barrier system if desired.
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| Fig. 5: Injection grouting |
Grout materials are cement and sand based products with waterproofing chemicals and bonding agents. Some materials containing metallic additives that may change the colour of substrate when metallic materials begin oxidized. Grout is used to fill pores, cracks and fissures in both joints and masonry, waterproofing an entire wall facade. There are many grouting materials available; during original construction or structure life cycling, cracks often develop that allow water and pollutants to enter substrates. If this crack is nonmoving but structural, it is repaired through injection of low viscosity epoxy. The epoxy seals the cracks and restores the monolithic structure nature of the substrates. Injection epoxies are two component low viscosity materials requiring mixing before application. Low viscosity allows material to flow freely and penetrate completely into a crack area. Chemical injection grouts used for waterproofing substrate which is hydrophobic liquid polymer resins such as polyurethanes they react with water present in crack and substrate creating a chemical reaction. The reaction causes a liquid grout to expand and form a gel or foam that fills voids and cracks. Expansion of materials forms a tight impervious seal against substrate sides, stopping water access through joints.
Use of nano-technology in waterproofing building materials
Nanotechnology is the use of very small particles of material either by themselves or by their manipulation to create new large scale materials. The size of the particles is the critical factor. At the nanoscale material properties are altered from that of larger scales. Another important aspect is that, as particles become nano-sized, the proportion of atoms on the surface increases relative to those inside and this leads to change in the properties. Knowledge at the nanoscale of the structure and characteristics of materials will promote the development of new applications and new products to repair or improve the properties of construction materials.
Most of the building materials are very porous and have surface hydroxyl groups. These hydroxyl groups attract water because of the hydrophilic nature and similarity with the structure of water. Hence, most of the building material easily wet and absorb water in the pores. The size of the water molecule is 0.18 nanometer and size of most of the pollutants like acids, chlorides & sulphates would range between 1 to 2 nm. Even with the dense concrete and stones the pore size is much larger than water allowing easy entry with the hydrophilic nature of the building material. Broadly we can classify waterproofing materials into two categories:
- Film formers
In case of film formers the ease of application has led to widespread use of film forming water repellents. The products like acrylic paint, silicon polymers are commonly used in the world for waterproofing application. These film formers have particle size greater than 100 nm, which will not allow them to penetrate inside the pores of the building material but form a film covering and preventing the surface from water absorption. Generally, these polymer films are hydrophobic but they need to be continuous and defect free and also must be UV resistant. It is found that during application ensuring continuous film on rough surface is not easy which leads to weak points for film former. All the typical polymer films tend to break down under UV leading to crack of the films after couple of years, which leads to failure in terms of losing of hydrophobicity and water repellency.
However, in case of penetrants, these are solvent based, soluble monomeric materials with less than 6 nm size. They easily penetrate inside the pores and sub- branches of the pores. There are two types of pentrant i.e., non-reactive and reactive. Non-reactive penetrants are oils and other low viscous hydrophobic material, which coats the pore of the substrate, and provide water repellency. However, these types of materials are also biodegradable and lose hydrophobicity within a year. Additionally, these products also provide food for molds and fungus growth. The reactive penetrants chemically react with the substrate and provide molecular level hydrophobicity to the treated surface and 3 – 5 mm deep in the substrate. Hence, these types of products provide protection for very long period. Additionally, the product is bonded chemically on a molecular level to the substrate as a result, weathering and natural abrasion have virtually no effect and hence very limited effect on the waterproofing characteristics. The various silanes used for waterproofing are basically alkoxysilanes. As most building materials contains hydroxyl group, these hydroxyl groups chemically react with alkoxy groups of silane forming permanent siloxane bonds with the substrate. The alkyl group provides hydrophobicity to the surface. Therefore, these type of products impart water repellency by modifying surface characteristics from hydrophilic to hydrophobic.
Use of nano-silica in concrete
One of the advancements made by the study of concrete at the nano scale is that particle packing in concrete can be improved by using nano-silica which leads to a densifying of the micro and nanostructure resulting in improved mechanical properties. Nano-silica addition to cement based materials can also control the degradation of the fundamental C-S-H (calcium-silicate- hydrate) reaction of concrete caused by calcium leaching in water as well as block water penetration and therefore lead to improvements in durability of concrete structure.
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Fig 6: Pore blocking of concrete
However there are many commercial products available as waterproofing solutions for building structures. Asian Paints India Limited is a big name in the market of construction waterproofing and it has number of products in a Smart Care range for interior and exterior waterproofing. As going with the GREEN all the products are water-based and environmental friendly that makes them unique.
Selection of waterproofing techniques before painting
These entire product range is useful, when used with various painting systems, it would protect the buildings from damages due to unwanted entry of water in the surface for many years. Of course cost of waterproofing system is a primary concern but if we look to the recurring maintenance cost of re- painting to get the desired performance, it is better to do the waterproofing of the substrate first then paint it.
Various segments of waterproofing based on different chemistries can be used as recommend ed below–
In case of basement and underground structure like raft foundation and retaining wall we can use the deep penetrative, reactive, capillary waterproofing system i.e., basically crystalline technology along with integral waterproofing compound or hydrophobic capillary blocking compound. Also in case of top down construction as well as construction joints, ethylene vinyl acetate (EVA) polymer based spray applied waterproofing membrane for tunnel concrete composite shell linings, re- injectable hose, and specially formulated poly vinyl chloride compound (PVC) or neoprene rubbers can be used.
In case of roof, deck and podium areas we can use polyurethane based waterproofing coatings, single component fibre reinforced acrylic waterproofing cum heat reflecting elastomeric coating, two component polyurea system for exposed roofs and for roof gardens pre formed synthetic liner of thermoplastic poly olefin (TPO), having UV & weather resistance one side and puncture resistance on the other side, bitumen-modified polyurethane based elastomeric membrane can be used.
In case of wet areas or wash rooms, waterproofing can be done by 2K or 1 K acrylic modified cementitious coating, single component flexible mastic system for under ceramic coverings, but in case of plumbing cutouts single component moisture curing pre-polymer which is re- swell able in contact with water is suitable for permanent sealing of construction joints in concrete structures. In case of window frames the gap between window frame and wall can be sealed by various sealants which after curing resists entry of water through it. Skirting areas and walls near to kitchen and bathroom generally affected by the damp patches, paint peeling or flaking or efflorescence due to negative side water penetration or rising ground water which can be treated with 1K or 2K cementitious coating over plastered surface.
In case of water tanks or swimming pools internal waterproofing can be done by 2K acrylic modified cementitious coating, external treatment to be done by using surface applied capillary waterproofing system for concrete and mortar but for potable water tank, non-toxic, solvent free, high build epoxy coatings. Synthetic membranes of plasticized PVC, synthetic liner of TPO with fiber reinforced composite obtained by co-extrusion, the upper layer exposed is characterized by a very high resistance to weathering and UV rays, whereas the lower layer is resistant to puncturing and to roots are the solution for water reservoirs.
To get the leakage control by injection grouting one component polyurethane injection resin cement based injection grout is used for small to mid-volume water ingress in masonry surfaces. However, in case of heavy duty work two component polyurethane injection resin/two component epoxy injection grout to be used.
The benefits of various waterproofing compounds are increasing gradually to the Indian building industries. In order to extend the life expectancy of structure and to retain the aesthetics of the building for longer time, use of waterproofing chemicals as part of the painting system are increasing. Use of proper waterproofing system with right quality paint is not only used to increase the durability of structure but also is cost effective in terms of maintenance. This paper gives insight of various waterproofing systems which can be used to enhance the performance of various painting systems for Interiors of the house.
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