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How to Manipulate Coating Viscosity for Better Application

Applicators will manipulate coating viscosity for satisfactory application results.

What is the first thing any painter does when having application issues? Nine times out of 10, that painter reaches for thinner, adding it to the coating with the care of a 16-year-old filling his or her gas tank for the first time. Thinner is the first trick every applicator tries when it comes to poor application properties, as most problems arise from very viscous, or thick, industrial coatings. Thinner will reduce the viscosity of the coating, making it significantly easier to spray.

This blog post explores the concept of fluid viscosity and the role it plays in the application of high-performance industrial coatings. It covers how an applicator can manipulate viscosity to achieve better application properties, as well as the importance of the relationship between pump fluid capacity and viscosity.

What is Viscosity?

Oversimplified, viscosity relates to the thickness of a fluid. The viscosity of a liquid will change with the temperature of that liquid. This concept is fundamental when it comes to the application of industrial coatings. To illustrate this point, consider a freshly made milkshake. Now, think about how much easier it is to drink that milkshake after it melts for a minute. But why? At no other point in its life will it be as cold or as thick as it is at the moment of inception. This phenomenon is no coincidence—fluid mechanics teaches us that temperature and viscosity are closely related. The colder a liquid gets, the more viscous it gets. As the milkshake begins to warm up or melt, its thickness begins to lower, becoming fluid and easier to pull through the straw.

The Impact of Viscosity on Coatings

So, what does this analogy have to do with coatings? Like the milkshake, coatings are fluids and subject to the same scientific laws. As you heat coatings, their viscosity naturally lowers. Conversely, when coatings are cold, they are thick or highly viscous. This notion explains why material stored overnight at a job site during cold weather months can be harder to apply first thing in the morning, until the products warm back up. The applicator may have trouble moving the paint through his or her equipment, even to the point of starving the tip—leaving an incomplete, or even worse, no fan pattern.

On the other hand, hotter material can provide some application benefits. Lower spray pressures, better atomizing attributes and a superior final appearance are all examples of the benefits of applying coatings at lower viscosities. All of these reasons and more are why thinner is typically used with coatings. Because of these temperature effects on viscosity, thinner recommendations are provided in ranges. For instance, an applicator in the Texas summer might not need as much thinner as someone in Canada using the same coating at the same time.

Using Heat to Lower Coating Viscosity

When thinning is not appropriate, it is common for applicators to apply heat to reduce the viscosity of the material. If cold material is being applied with resulting issues, heat may just be the solution to your problem. Remember—heat can be your friend by increasing the workability of a coating, but it can also shorten the pot life significantly. The practice of using heat in this manner can be a handy tool in your box but, like all tools, one must know how to use it.

If heat is used to lower the viscosity of the material, there are several factors to keep in mind. First, viscosity is not the only coating attribute affected by the introduction of heat. Pot life can be drastically impacted as well. For this reason, heat should not be used to lower the viscosity of material that has a short pot life in a single-leg application. Conversely, almost all plural-component spraying procedures include the use of heat to improve the viscosity of the coatings. This viscosity improvement makes the product sprayable, with an aesthetically appealing finish.

Applying Industrial Coatings with Short Pot Life

When purchasing a spray pump for high-performance coatings with a short pot life, it is essential to consider all performance specifications of the equipment. One of the most common mistakes is paying attention only to the power output of a pump, while completely neglecting other factors. Though the output pressure, or power, of a spray pump is an essential factor, it is not the only factor to consider when purchasing equipment for industrial coatings.

Equally important is the fluid capacity of the pump. Capacity, or output, is the amount of material a pump can expend at a time. Measured in gallons per minute (GPM), this factor usually exists independently of output pressure ratings. It is common for a pump to have the pressure required to atomize industrial coatings, but not have the necessary fluid capacity. Take commercial electric spray pumps as an example. These pumps provide plenty of pressure, with capacity severely lacking. The phenomenon that explains this entirely is viscosity.

Let’s go back to the milkshake for a minute. The thickness of the shake is only one factor slowing the ride to satisfaction—viscosity also deals with the internal friction within a liquid. Putting a liquid into a closed channel, like a straw, further complicates our analogy. The flow of the milkshake is virtually non-existent at the point of contact with the inner walls of the straw. The majority of movement comes from the internal cross-section of the milkshake—a space that is scarce with a typical size straw.

This factor is why fluid capacity is one of the most critical factors when choosing a spray pump. As the viscosity of a coating increases, the capacity requirements for equipment increase parallelly. The relation of the fluid with the fluid wall is the reason why pump capacity is debatably more critical than the pressure rating of the equipment. Typically, equipment pressure ratings will increase as the pump capacity increases, eliminating the concern of not having enough system pressure. In other words, the pump capacity is the size of the pump’s “straw.”

Because the viscosity of coatings has such a significant impact on their application, knowing how to manipulate it while improving its application properties can go a long way in ensuring a successful project outcome despite any challenging situations that may pop up.

Want More Best Practices for Industrial Coating Application?

Contact a local sales representative from Carboline’s Technical Service team.

4 Best Practices to Avoid Common Concrete Pitfalls

A resinous flooring installer slopes the floor to drains.

Coating concrete can be one of the most challenging applications in the industrial coatings market. Contrary to the relatively straightforward process of coating non-porous surfaces like steel, concrete can pose a variety of unique challenges that spontaneously require attention.

To use an analogy with which most parents are all too familiar, imagine the stark difference between going to the grocery store alone and bringing along a toddler. On a solo trip, execution of your plan is generally quick and painless, with only minor speed bumps or inconveniences along the way. However, when you throw a toddler into the mix, anything can—and will—happen.

The same idea applies when it comes to coating concrete. It is essential for an applicator to not only understand the potential pitfalls that can occur during a concrete coatings project, but to be able to remedy these problems quickly to avoid costly, time-consuming mistakes.

Here are four best practices to help avoid these common concrete coating pitfalls:

  1. 1. Understand the Composition of Concrete

    Understanding the composition of concrete will help you spot and address potential issues before they arise during the application process. Concrete contains about 6% of air, which takes the form of capillaries throughout the substrate. Concrete is similar to a sponge in the way these capillaries form, as well as their absorbency. This network easily transports water, chemicals and contaminants throughout the concrete, which can lead to potential problems.

    For instance, as the temperature of concrete increases, it expels the air through the pores at the surface. With exterior concrete projects in particular, this outgassing can cause blisters or pinholes in the coating. Because of this phenomenon, coating projects are often completed at night when the temperature of the concrete is lower. Tenting can also be used to prevent the sun from warming up the concrete.

  2. 2. Test the Moisture Content of the Concrete

    Water can travel through the capillaries of concrete in both liquid and gas forms. When water transfers through concrete as a gas, it is commonly referred to as moisture vapor transmission (MVT)—a problem that typically presents itself with concrete slabs on grade. Warm, dry air above the slab pulls moisture from the soil through the concrete as the environment seeks equilibrium. There are three methods to test for MVT in concrete, which all provide a snapshot of its existing moisture content:

    • Plastic sheet test, which involves taping polyethylene film onto a concrete slab and examining the sheet’s underside for signs of moisture after a 16-hour period
    • Calcium chloride (or MVER) test, which involves sealing a small dish of calcium chloride on a clean section of concrete under a plastic dome and measuring the weight gain after three days
    • In situ probe test, which involves drilling a hole into the concrete slab and using an electronic relative humidity probe to measure its moisture content

    Most manufactures will recommend that applicators perform two of these tests to gain an accurate picture of the moisture content in concrete. Moisture-resistant coatings, like our Carbocrete cementitious urethane mortars, are another effective remedy for issues resulting from MVP.

    On the other hand, hydrostatic pressure occurs when water transfers through concrete in the liquid state, leading to excess moisture that creates pressure buildup in the concrete slabs and connected flooring systems. As with the folk story of the little Dutch boy who saved his town from a flood by sticking his finger in the dam, a simple coatings job will typically not be sufficient when hydrostatic pressure is present. Instead, concrete repair is usually warranted in this situation.

  3. 3. Remove the Laitance Before Coating Application

    Expanding on the composition of concrete, it is essential to recognize that concrete contains about 20% water in its original form. Concrete installers measure the amount of water by examining the concrete slump. They fill a cone—similar to a cheerleader megaphone—with the concrete mix, then turn it upside down and remove the cone. Next, they observe if the concrete maintains its cone shape. The distance that the concrete flattens is considered the concrete slump.

    As concrete cures, the water moves to the top of the pour and creates a weak layer at the top called “laitance.” This layer is fragile and brittle, making it easily susceptible to damage. With this in mind, it’s critical to remove the laitance before the application of a coating in order to avoid premature failure of the coating system.

  4. 4. Take Time to Prepare Your Surface

    As with any coating application, surface preparation is the most significant step of applying a concrete coating. One method for preparing a concrete surface is mechanical abrasion, which is used to create the desired surface profile and open the porosity of the concrete—thereby promoting better coating adhesion. Grinding, scarifying and blasting are the most commonly used forms of mechanical abrasion. With this method, the surface should be free of any contaminants, debris, dirt and dust, as their presence will lower the adhesion of the coating system.

    When it comes to preparing your concrete surface, industry standards are your best friend. The Society for Protective Coatings (SSPC), together with NACE International, developed an SSPC SP-6/NACE 13 “Surface Preparation of Concrete” joint standard, which offers a complete road map for the preparation of concrete surfaces before the application of protective coating or lining systems. In addition, SSPC recently introduced its new CAB standards that set values for the cleanliness of abrasive-blasted concrete. Both of these standards are invaluable for concrete applicators.

Though there are a variety of factors that can affect the application of concrete coatings, having an understanding of the potential problems that can arise during the application process, as well as how to prevent or mitigate them, is the best defense for concrete applicators.

Want More Best Practices for Coating Concrete?

Listen to Carboline’s recent podcast episode that discusses the various moisture content tests used for concrete in the coatings industry.

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