WHEN SPECIFYING A COATING SYSTEM

Introduction:

                    Coatings are formulated and designed according to their usage, applications and functions. Aside from aesthetic purpose, coating must have protection capabilities to the substrates or structures that the coating being applied. Coating properties strongly depend upon the quality and integrity of the coating film that relies on polymer chemistries, chemical makeup, formulation variables and surface characteristics of the substrates.

                   Specifying a coating system suitable applications and its purpose is a complex task. A specifier with limited understanding of the technical requirements associated with the coating selection and surface preparation will end up costly not only to the owner but to the reputation of paint contractor and the paint manufacturer.   Profitability is the main objective of each individual in the coating business, but specifying an unsuitable coating system for a certain project will lead to great loss. The specified coating system should offer long-term durability that will ensure the design life of any substrates, building materials or structures to which it is applied.

Role of Coating Specifier:

               In order to meet expectation and provide the customer with a quality product, it is necessary for a coating specifier to be well versed in all specification and requirements relevant to a coating system. Before a specifying a coating system for a certain project, it is best to do an actual substrate evaluation whether it is new or existing substrate, location assessment, environment condition, and function of the substrate or structure.

               Aside from location, environment condition and function of the substrate/structure, the following factors should be considered during actual evaluation of the structure or substrates to be coated:

-         Preventative maintenance coat inherent with the structure

-         If it is previously coated, the condition of the existing coating system should be evaluated: presence of toxic pigment, film thickness, adhesion acceptable for top-coating, importance of the aesthetic appeal, presence of recurring mode or type of coating failure.

               After the assessment has been done, the coating specifier can then refer to published standards and literature for potential coating system. When specifying a coating system, it is critical that the coating specifier will discuss to the owner of the property the performance criteria for each coating system possible to suit what the owner desires. A coating specifier should be able to present a relative comparison of the coating systems for specific characteristics and performance. The coating systems must comply with all current regulations and standards.

               When specifying, a coating specifier should consider the following:

1.      Acceptable initial cost – the estimated cost when possible must at least fit within the costumer’s budget.

2.      Minimum acceptable anticipated service life of the coating system – depending on the owner’s desire, different choices of coating system with durability comparison should be presented to the owner of the property or his building contractor once assessment has been done.

3.      Method of surface preparation – the most appropriate and suitable surface preparation based on the assessment should be included in the specification.

4.      Easy Maintenance by touch up and maintenance topcoat - when it is necessary a coating system should be easy to touch up

5.      Easy application under field condition utilising equipment that is ready available to the paint contractor.

6.      Recoating window that provides flexibility for anticipated delays - In many cases, a project has a very tight installation schedule. This limits many systems in how long it takes to install a given material. Temperature of the surface at the time of installation is critical in selecting a material. Some systems, such as epoxies, are very temperature-sensitive and can vary widely in cure time at lower temperatures.

Technical Requirements:

               The choice of optimum coating system that fits for purpose is essential to ensure the maximum life expectancy of the coating is realized and the cost of maintenance is optimised. To be able to deliver this, a coating specifier must have at least basic understanding of benefits and limitations of different coating systems and be well-versed on technical requirements when specifying a coating system for a certain projects. This includes the following:

1. Familiarising the industry standards and regulations.

              Standards and regulations were put in place to ensure coatings are designed accordingly to their functions and methods of application. Standards provide guidelines, mandatory requirements, common frame of reference and comparison. A coating specifier must ensure that the coating system and application being specified must meet and comply with certain standards that are relevant to its intended application. He has to be clear and specific which Standards and warranties are applicable. Standards relevant to the building and construction industry can be found and purchased via SAI Global. A test certificate of the product that conforms to relevant Standards must be shown to customer when requested.

                For elastomeric wall coatings, AS 4548.1 is the standard that performance criteria are set as shown on table below:

                 For acrylic roof coatings, ASTM D6083 is the standard that performance criteria of acrylic roof coatings should conform:

2. Choosing the right coating system for a certain project.

                If a specifier lacks technical knowledge of the products, it is best to seek advice from the technical personnel/chemists to learn the benefits and limitations of certain coatings. Choosing coatings based on Polymer type becomes more difficult and may require assistance to review data and compare performance.

                Table below is a performance comparison of sealers/coatings based on polymer type:

                 On epoxy coatings, the type of curing agent also dictates curing time and film properties:

3. Clarity on its scope and use

                 Selection process does not limit to aesthetic appearance: both functional and decorative; and finish which either smooth or textured. Most important is the performance capabilities of the coating which is suited to the location and use of the substrates/structures. Different coating products from different manufacturers will achieve different outcomes. Coatings have certain benefits and limitations, so it is important to know them. Choosing the wrong product could lead to costly recoating as a result of coating failures like blistering, cracking, peeling, delamination, fading and whitening. Those failures can also be associated to poor surface preparation and application.

                  When specifying coating system for concrete floor, Polyspartic or Novolac type Epoxy coating is best recommended for Concrete floor that subject to cold temperature, heavy foot and wheeled traffic, spills and chemicals. Water based low-solid acrylic sealers could not withstand with those conditions. Although, the durability of Concrete Stain is dependent on its chemical makeup and polymer type, the Stained concrete floor must be regularly treated with waxes or other sealers to maintain the aesthetic appearance. A failure to regularly care for stained concrete can quickly result in a wearing away of the coloured surface in high-traffic areas, leaving patches of bare concrete that begin “dusting” as well as absorbing contaminants. Repair of such areas can be difficult. On the other hand, if the floor is light to medium general service and will not be exposed to harsh chemicals, extreme pH substances, wet processing, food production or packaging, toxins or potential environmental contaminants and the like, then polished concrete may be an adequate. However, because polished floors require regular re-polishing or other professional maintenance, they may not be ideal for constant critical traffic operations.

4. Suitability to Exterior Application

                 Coatings are formulated according to its specific applications and intended use of surface to be coated for a given environment. Coatings that are designed for interior applications cannot be specified for exterior applications. A coating specifier must have a clear understanding between interior and exterior application.

                 For example, styrene butadiene rubber (SBR) type coating has excellent abrasion resistance and water resistance, but it has poor UV and weathering resistance. UV attacks the polymer, which leads to coating weakening and causes extensive cracking. So, therefore, SBR membrane coatings must not be specified for exterior application.

                 Epoxy based coating is another type of coating which has poor weathering resistance. Epoxy coatings do tend to chalk and yellow in direct sunlight. Therefore, for exterior application, Epoxies are often top-coated with two- pack aliphatic urethane that offers outstanding colour and gloss retention as well as chemical and abrasion resistance.

                 Coatings for vertical application on masonry substrates should pass the Wind Driven Rain Resistance Test in accordance with ASTM D6904- 03 (2013). This is an evaluation of the ability of coatings to resist the passage of water through masonry block when exposed to continuous water spray and a dynamic pressure equivalent to a 98 mph wind velocity without exhibiting water leaks or weight gain, or both.

5. Colour Durability.

                For exterior application, specification of colour should be done in accordance to the colour lightfastness and weather resistance of pigments. The colour development is based on desired shade/hue and is achieved by combining at least two pigments, maximum to four pigments either organic or inorganic or combination. Colour warranties are based on amount of inorganic pigments versus organic pigments used to create the final colour. Not all pigments are suitable for every application. The pigment component in any formulation can enhance or degrade the overall performance of the protective colour coating and is important to choose correctly either inorganic or organic pigments. Inorganic pigments have high hiding power, superior colour stability, heat resistance and chemical resistance but produced less bright colour while organic pigments have low resistance to fade, low heat resistance, allow UV and oxygen to penetrate in and less hiding powers but produce very bright and vivid colours. The colours are developed to withstand the weathering and environmental condition preventing from fading and chalking. UV (sun) exposure, moisture, humidity, high temperature and temperature fluctuation lead to colour changes and fading. Bright colours such as yellows, oranges and reds fade faster.

                 Heat reflective pigments give a cool effect and reduce absorption of heat, which helped in extending the life of the binder/resin used in the coating.

                  The Australian Standard AS2700 “Colour Standards for General Purposes” presents reference colours for use in choosing colour schemes in the industrial, architectural and decorative areas with particular emphasis on paints and related materials.

6. Managing Safety, Risk and Health Factors associated with the coatings.

                    When specifying coating system, safety and health factors are also considered. The specifier will need to determine which environmental regulation must be satisfied. A coating specifier must also consider the VOC content of a coating system and its impact on the environment. Environmental regulations addressed the VOC released into the air during painting operation, amount of metals, organics and microbiological growth. Coatings with Green Star Rating and APAS certification comply with Volatile Organic Compound Criteria.

                   Good environmental Choice Australia (GECA), which is an Australian Ecolabeling in accordance with ISO14024, set a standard specification for ecolabeling that includes environmental and social criteria. Below are GECA criteria but not limited to (visit GECA website for full list):

A. GECA Criterion 7: The total content of volatile organic compounds in the product must not exceed those stated in the table below:

Maximum VOC content for base or untinted products:

B. Criterion 16: The product must not contain or be manufactured using Prohibited substances that can have detrimental effects to the health of manufacturing staff and users of the finished product as well as the health of the environment:

• ·        Formaldehyde, formaldehyde donors and aldehydes;
• ·        Phthalates;
• ·        Isoaliphates;
• ·        1,3 butadiene;
• ·        Bisphenol A;
• ·        Toluene and toluene compounds;
• ·        Crystalline quartz silica (CAS 14808-60-7) **; or
• ·        Alkylphenolic compounds including alkylphenol ethoxylates and alkylphenol alkoxylates.

             Submission of coatings to be certified is voluntary and only few coatings are Greenstar, GECA or APAS certified, thus displaying Greenstar, GECA Ecolabel and APAS label on the product. If uncertain, a coating specifier may ask the coating manufacturers for copy of certification that confirms their claims. List of Certified coatings products are found on GECA and APAS websites.

               GECA Certified paints meet the requirements of the VOC credit under indoor environment quality, as part of Green Star.

                Whenever possible, water-based coating products with minimal characteristic odour are preferred to be specified especially in enclosed or indoor application.

                 Coatings for floors /pavements should not alter or reduce the slip resistance of the surface being coated. Most building materials like travertine, marble and terrazzo when polished or coated to attain the ’wet’ look effect, the slippiness of these materials may increase significantly when wet and thus increasing the risk of slip. In areas where surfaces are subject to be constantly wet like pool areas must not be coated with the film-forming sealer/coating that alter the profile of the substrates’ surface and its slip resistance. Slip resistance of sealed/coated floor/pavement surfaces are assessed  in compliance with AS 4586 (for new pedestrian surfaces) and AS4663 (for existing surfaces) whichever is applicable.

Final Run

               Once a suitable coating system was determined for its intended use, a proposal is submitted and be agreed by the owner of the property. Test patches of surface preparation, and coating works should be undertaken to determine compatibility with a pre-existing coating. Test patches also provide a visual and tactile representation of the specification requirements. They establish the appearance of building repairs, the degree of surface preparation required and quality of paint application required. Once the test patch has been applied, the job must be inspected and approved.

Summary:

                Coatings are used to protect the substrates from deterioration. Using the proper coating system will protect the overall system for the life of the project. Correct choice of colour also contributes to the optimum protection and functions of coatings in a project.

                In summary, thorough assessment and careful consideration on the requirements of area of use, substrate/surface preparation, right application method and conditions are the key factors for successful installation of coating system. Planning, monitoring and review, inspection scheduling, documenting the installation process, maintenance, and repair program should be established for continued performance and satisfaction of the coating system.

                This article serves as a helpful guide not only to the coating specifiers but also to coating product salespersons, architects, paint contractors, builders, renovators and to the building/structures owners.

 

References:

           1. Selecting the Proper Coating for Concrete Floors by Robert Cain

           2. Specifying Concrete Floor coatings & Treatments by Tom Murphy

           3. Guide to Concrete Flat Wall Finishes by Cement Concrete and Aggregates Australia

           4. GECA Paints and Coatings version PCv2.2ii-2012

           5. ASTM D6083.05e1 – Standard Specification for Liquid Applied Acrylic Coating used in  Roofing

           6. AS/NZS 4548.1 – Guide to long-life coatings for concrete and masonry Part 1: Wall Coatings – latex extensible

           7. AS 2700 - Colour Standards for General Purposes

           8. AS/NZS 4586 – Slip Resistance Classification of New Pedestrian Surface Material

           9. AS/NZS 4663 – Slip Resistance Measurement of Existing Pedestrian  Surfaces

           10. ASTM D6903-03 (2013) – Standard Practice for Resistance to Wind Driven Rain for Exterior application on Masonry

 

 Written by:

ZF Czora, ChE, ATSC