Thursday, December 30, 2010

Understanding Key Issues Affecting Long-term Wall System Performance

Jim Hendley
Impact, thermal shock, abrasion, chemical staining agents, water exposure, and UV lights are a few of the things that can damage vivarium walls. Selecting the right high performance coating can improve the appearance and longevity of wall finishes in these demanding environments.
When you look at your vivarium walls and ceilings, it probably isn’t apparent that a lot of work goes into selecting those finishes. Most people talk about what type of paint they have on these surfaces when in fact, there is more to it than that. The high performance coatings used in vivariums withstand a wide array of operating conditions. This article reviews useful information affecting the selection and longevity of your high performance wall and ceiling coating systems.
Paint versus High Performance Coatings – the Differences
Protective coatings come in many chemistries, performance properties, and thicknesses. For the sake of this article, I’ve divided them into two classifications, paints and high performance coatings (HPCs). Changing from light to moderate duty surface protection to more demanding environments requires the use of HPCs to insure adequate performance.
Paints are thin-mil (a mil is a thousandth of an inch) systems designed to provide uniform pigmentation/color/hiding of the color beneath it. They typically are between 0.5 to 3 mils in total film thickness. Paints are typically used in offices, break rooms, and other areas not subjected to abuse, wash down, or regular water exposure. They are normally standard acrylics or water-based acrylic epoxies. Thin-mil coatings offer a cost effective solution in less demanding environments.
HPCs range from 5 to 50 mils, and often involve multiple coats and a range of reinforcement options. Materials range from 100% solids epoxies, high build hybrid acrylics, water-based, and/or high solids urethanes. HPCs are used in wet areas, spaces subjected to wet sanitization, impact zones, surfaces subject to thermal shock, and walls and ceilings subjected to flexing.
Paints are typically in the “catch-all” paint section of architectural specifications. HPCs often have their own architectural specification section because of the special skills required to install them. When HPCs are specified, one contractor is often responsible for the installation of the resinous floor, wall, and ceiling systems. This helps insure all of the architectural detailing associated with these systems are installed properly.
Substrate Considerations
What you put your paint or HPCs on top of matters. Vivarium substrates can consist of standard drywall, moisture resistant board products, cast in place concrete, precast concrete, and concrete masonry units (CMU). Standard drywall should only be used in dry areas with minimal risk from impact damage. Moisture and impact resistant board products are good for occasionally wet applications. When board products are hung on the wall, the screw heads and seams need to be filled with special drywall compound to cover these imperfections. The degree of fill and number of steps taken is referred to in the industry as level of finish. Level of finish is an important consideration for both standard and moisture resistant board products. Too low of a level of finish can result in telegraphing of the screw heads and seams through paint or HPC systems. Too high of a level of finish can cause delamination of wall and ceiling systems with even light impact or thermal shock.
For areas subject to frequent wash down and wet conditions, concrete masonry units (CMU), or cast in place and/or concrete are used. CMU substrates require correction of surface voids and imperfections prior to paint or HPC application. Filler options include: pure acrylic resin coatings applied in multiple coats, acrylic modified cement, epoxy cement, or epoxy gel.
Selection of the CMU filler depends upon the degree of fill, smoothness, and levelness required along with consideration of impact, wash down, and thermal shock exposure of the area. Typically, the higher the level of cleanliness required, the more filled the surface of the CMU must be and the higher level of skill required to install it.
Below grade poured concrete substrates can be placed utilizing self-compacting concrete to minimize bug holes. These substrates should be tested for moisture content prior to application of non breathing paint or HPC systems. If moisture content is high, topical treatments can be utilized prior to application of the protective coating to address this condition.
Detailing for Success
Surface intrusion of water or sanitizers into and behind wall and ceiling protection systems can cause substrate damage, peeling, blistering, and, in certain cases, back-side mold growth. In addition, proper allowance for building movement and expansion and contraction of dissimilar materials can prevent cracking. To address these conditions, proper treatment of architectural details is critical. Areas of concern include: proper detailing of expansion joints, utilizing appropriate caulk, treatment of inside corners, wall ceiling transitions, termination at door frames and embedded fixtures and penetrations, and top of cove base transition. Standards for proper treatment of these conditions should be clearly documented in the architectural drawings as part of the contractor bid package. A final check point to insure the subcontractor selected for your project is capable of properly installing these details is the project mockup. Project representatives should inspect and sign-off on the mockup prior to installation of significant square footage of the HPC on your project.
Project Planning – the Cross Functional Team
Understanding how your current vivarium wall and ceiling finishes are performing is an excellent starting point in planning a new or renovation project. A project team consisting of facilities planning and design, vivarium management, space users, and maintenance staff can document both pros and cons of the systems currently in use. Gather historical information on the type and location of each finish and how they have performed. Note cracking, peeling, blistering, loss of gloss, pin holing, chalking or yellowing, problems with impact damage, cutting, gouging, and staining with the corresponding coating used in each type of space (clean corridor, dirty corridor, specific types of holding areas, necropsy, etc). Maintenance department input concerning difficulties associated with certain finishes due to cure time, odor, complexity of repair, need to recoat an entire room due to discoloration, etc. should be taken into consideration.
Anticipated usage condition information for your current project can also be gathered. This can include anticipated impact, thermal shock, abrasion, chemical and staining agents, and water exposure, UV lights, and possible damage from certain types of animals, caging systems carts, etc. The more detail by area the project team can provide to your outside design team, the better. For example, typically, the cage wash is considered separately because it is one of the toughest performance environments for wall and ceiling systems. Compilation of the information the team has gathered, including must-have and “would like to have” HPC performance requirements by area, prepare the project team for discussion with the design team.
Wall and ceiling coating systems in vivariums can provide lasting protection and aesthetics. A critical look at your current situation and the use of the areas can dramatically impact the type of system needed to completely protect your wall. Remember the difference between paint and high performance coatings—it will impact your decision how to best guard against mold, cracking, or any other areas that would jeopardize a safe, clean workplace.

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