It was the mid-eighties, when I was at the cross roads. With a bleak future fretting at me, I was frantically tussling to establish my company’s roots in the Indian market. At that time, I used to call on my handful customers to promote PU anticorrosive coatings and could get a few opportunities to peep at their plants. I had then observed that their bare concrete floors looked very dark, dusty, and untidy and could see many shabby patches in the unkempt floors. I perceived that they paid least attention to it and to them, the floor was deemed to be a place of neglect, a place to be broomed and dedusted every day. A fatuous thought arose abruptly into my mind about metamorphosing these murky areas into livelier milieu by a colourful coating. Sensing that a flood gate may open up, I thought, this was my final call to shape my destiny, which was otherwise sliding to a doomed end: I need to unearth a product to protect and decorate the concrete floors.
I fathomed, I would have to embark on an alien path where others had not trekked so far. It was a challenging quest as the product demanded massive features like wear resistance, adhesion, tensile strength and aesthetics so as to sustain the physical and chemical abuses the industrial floors endure every day. I was, at that time, indulged in polyurethane prepolymers, with TDI as the isocyanate component. The experiments to develop a floor coating based on TDI ended in debacle as it lacked the performance elements worth to be a floor coating. I had read in books that MDI based prepolymer would be a starting raw material for formulating a floor coating, but regrettably, MDI was not available in Indian market. While contemplating whether to abandon this utopian dream, I got a call from my friend who was working in Jagat chemicals (representing Bayer, Germany) and was told that one of his customers had some 50 Kgs of MDI to dispose off. He told me that he would sell @ 50 per Kg, which meant that I had to shell out Rs 2500, a whopping sum for me at that point of time. After a few days of deliberations, I gambled with Rs 2500, bought MDI and started my ordeals. I did numerous experimentations but was nowhere near the goal. Frustration was creeping in and one day, I did another attempt of synthesising MDI prepolymer using a polyester polyol. While transferring the adduct into an empty container, a few drops had accidently spilled on the floor which I forgot to wipe off. Next day, when I came to the lab to gaze at the adduct, my eyes tumbled over the hardened resin on the floor, which I had mistakenly dropped a day earlier. Incredibly hard, it was very difficult to pull off from the floor, as it was well glued on the substrate.
Eureka!, that was the birth of India’s first floor coating.
The first step was admirably crossed over, but now the strenuous challenge came when I comprehended that I had to create an altogether new space in the crowded coatings’ market. I had to first enlighten my prospects why they required a coating on concrete. I strived hard to convince them that concrete floors were their capital investments that were meant to last for decades under tough working conditions. But they rebutted that concrete is very tough, strong and coating is a prodigal exercise. I explained the way the concrete was laid and how it was deficient in certain features and elucidated the point that though the concrete looked solid, it is a permeable structure and is subject to staining, cracking, dusting and absorbing of oil and chemicals.
What is Concrete?
In 1824, an English mason, Joseph Aspdin invented the first true artificial cement by burning ground limestone and clay together and patented as Portland cement, which was coined because of its similarity in colour to Portland limestone, quarried from the English Isle of Portland. The composition of a typical Portland cement is listed in Table 1.
When water is added to cement, each of the components undergoes hydration and hardens to form concrete. Tricalcium silicate is responsible for the early strength, whereas dicalcium silicate reacts slowly, and contributes to the strength at later stage, both of which are hydrated to form calcium silicate hydrate(C-S-H), which is called concrete.
Why do we need a coating on concrete?
Cement is mixed with more water than is needed for the hydration reactions in order to give the mixture sufficient workability. The unconsumed water in the hydration reaction remains in the microstructure pore space which makes the concrete weaker due to the lack of strength-forming C-S-H bonds. Concrete, cured in 28 days, contains numerous capillaries and porosities, which concede absorption of liquids, stains and dust, thus creating an unsightly appearance. Further, concrete generates dust with vehicle traffic because of its poor tensile and flexural strengths, which we call concrete dusting. And so I emphasized that, in order to block the porosities of the concrete so as to mitigate the undesirable dusting and penetration of liquids, the concrete floors needed to be coated.
The floorings’ journey since1985
FK 909, the first PU floor coating of the country, had all the attributes to be a floor coating. It penetrated deeply into the floor, sealed the porosities and delivered a smooth, colourful, seamless, hard wearing and easily cleanable surface. It had enhanced the light reflectance of the floor, transmuting to a cheerful working environment. The first job with FK 909 was done at Crompton Greaves, Nashik and it had a dramatic impact on employee morale, as they relished working in a safer, brighter and healthy environment. A new era had thus begun when this novel concept of Floors from Cans had metamorphosed Indian industrial floors from a place of ignore to a place of brilliance. From just Rs 80,000 market volume in 1985, this segment has grown into a 600 Cr strong market with a CAGR of 12-15 %. From 1985 to 2018, during the last 33years, the country had witnessed many inventive technologies emerging in the market and numerous varieties of floor coatings are currently available in the market place, with distinct advantages as well as few disadvantages.
Sealers are largely classified as penetrating thin coatings which are of 10-25 microns in DFT and designed to impede absorption of liquids into the concrete. Acrylic sealers are the most generic type of sealers that are inexpensive and easy to install. PU based sealers are tougher, wear resistant and more durable. Whether it’s a stamped concrete, a terrazzo floor, an interlocking paver driveway, an acid-stained floor, or an exposed-aggregate walkway, sealers will keep it looking stunning.
Densifiers such as sodium, potassium and lithium silicates penetrate, react with free lime in the concrete and form C-S-H bonds. Densifiers are predominantly employed in ware houses, raised floors, and non-critical floor areas. An emerging trend in this segment is the polished concrete where the concrete substrate is densified, ground and polished to expose the aggregates, thus imparting a terrazzo look.
Coatings have higher film thickness than sealers and build a thick film on the concrete that is hard and wear resistant. The coating thickness varies from 100 microns to a few mm thicknesses. Epoxies are the industry’s workhorse floorings as the majority of floorcoating companies are involved in them. Epoxy resin is produced by the condensation reaction of epichlorohydrin (ECH) with diphenylpropane (DPP or bisphenol A) in the presence of a catalyst. Polyurethane is the reaction product of a hydroxyl containing polyol (OH) and polyisocyanate (NCO) and the resultant polymer delivers a highly cross-linked film having excellent abrasion resistance, while the linear polyols in the PU chain renders flexibility. The moisture-cured urethane (MCU) is single component and cures by reaction with atmospheric moisture, generating polyurea linkages. Epoxy-urethane hybrid coatings, called as urethane modified epoxy or EPU, have made a surgical strike in the Indian flooring industry, where urethane linkages are infused into epoxy polymer matrix to provide enhanced elongation and wear resistance. Epoxy phenol novolac (EPN) resins which contain more than two epoxy groups per molecule are synthesised by reacting a phenolic novolac resin with epichlorohydrin. Novalac epoxy renders excellent resistance to strong alkalis, acids, and solvents. Polyaspartic is an aliphatic polyurea coating where the–NCO terminated prepolymer is reacted with secondary or hindered aliphatic diamines. Polyaspartics have exceptional UV stability, gloss, and wear resistance and furnish some of the finest properties of epoxy as well as urethane resins. MMA floorings are based on PMMA (polymer derived from MMA monomer), which is cured by benzyl peroxide catalyst (1-2% of PMMA). Rapid curing is a great advantage of MMAs, specifically at very low temperatures, which are routinely used in cold stores, chillers and freezer rooms. Vinyl esters are produced by the esterification of an epoxy resin (Bisphenol A or Novalac type) with an unsaturated monocarboxylic acid, which is then dissolved in styrene at 35-45% by weight. Vinyl ester resins cure by free radical polymerization and are best promoted as chemical resistant floorings.
The evolving trend now is environment friendly, VOC compliant, waterborne coatings, where solvent vapours are not emitted and are breathable too. Water borne epoxies are formulated with emulsified resins and hardeners and are used as breathable self levelling floorings. 2K PU waterborne floorings, where the -OH groups of PUD are reacted with hydrophilic isocyanates, deliver performance features on par with solvent borne systems. In PU concrete, a waterborne urethane combines with cement, triggering a dual reaction of forming of both polyurethane polymerization and cement hydration. Designed to exhibit a highly cross-linked density, PU-concrete systems are chemical and thermal shock resistant and the most preferred floorings for F&B industries.
With their inimitable pluses, resinous ESD floorings are increasingly popular in industries where electrostatic discharge is a grave concern. Polymers like Epoxy and PU exhibit a very high surface resistivity( 10^13 ohms), but when they are doped with anti-stats, they become conductive or dissipative. The resistance to the movement of electrons across the materials’ surfaces defines ESD floorings in to two distinct categories: conductive (10^3 to 10^6 ohms) and static dissipative (10^6 to 10^9 ohms). ESD floorings are customarily laid in IT, electronic industry, ordnance factories, hangars, operations theatres to name a few.
Dielectric flooring systems have superior electrical insulation properties and maintain a high dielectric strength while providing a long-lasting and attractive atmosphere for work environments and are engineered to minimize breakdown (BDV) during voltage-induced stress, thus protecting people and valuable equipment from electric shocks. Dielectric floorings, available in epoxy and PU mediums, are frequently employed in high voltage substations, switch gear panel rooms, bus bars, battery rooms etc.
The types of floorings that have mushroomed in the last three decades have positive as well as negative traits and so the expectancies and needs of the customer are of paramount significance in picking up the right product. Let us evaluate the current options one by one. It is a verity that concrete sealers do not proffer long term protection. Densifiers, however, offer short-lived protection, as the closed pores of the concrete by the densification get opened up due to traffic impacts and oils and chemicals start infiltrating into the mother substrate. Epoxy flooring is plausibly applicator friendly, but has severe performance limitations, as it tends to crack and its mediocre wear resistance makes the floors getting easily scratched. Moreover, as the epoxy polymer has an open molecular structure, larger amount of filler loading is possible than any other polymer, and so low-cost, filler-rich variants are engulfed in the market, which are vulnerable to failures. Polyurethanes, on the contrary, are fast curing, wear resistant and considered to be the best bet for topcoats. However due to its sensitivity to moisture, polyurethane may pose hiccups during application in rainy times. This deficiency is overcome by PU-Concrete where one of its ingredients, cement, utilizes this moisture for its hydration. The undesirable feature of PU-concrete is, however, its exceedingly short pot life and the restricted shades. EPU is more or less akin to epoxies, but with upgraded flexibility and wear resistance. Those who look for a high sheen, moderately wear resistant flooring, EPU flooring (pre-filled system, with no filler addition at the site), would be the rightful choice. MMA and Vinyl ester are quick curing systems with admirable mechanical properties, but do not have good aesthetic appeal. Moreover, they give away obnoxious odour during application. Polyaspartic is rapid setting, with outstanding features, but the price is a major discerning factor. Waterborne epoxy has modest compressive strength than the solvent-free and imparts a matt surface on curing. However, the waterborne epoxy self-levelling flooring is the only antidote to floors which are subject to hydrostatic moisture and osmotic blistering, where all other floorings eventually fail. MCU floorings deliver a highly abrasion resistant floor and being single component, there is no chance of mixing errors by applicators. However, as they cure with atmospheric moisture, they need a minimum relative humidity of 50% for crosslinking. Novalac epoxy and vinyl ester systems are functional floorings with no great aesthetic allure and exclusively used for chemical resistant applications. The overview table may be a fair tool for selecting the right flooring system for your facilities.