Measuring Viscosity

As we now understand viscosity is the thickness of a liquid, let’s understand how to measure viscosity. Because temperature has such a strong effect on the thickness of liquids, the first step to reaching the viscosity of your wood coating is to accurately measure the temperature of your coating. Before taking a temperature or reading viscosity, it’s important to mix the coating to ensure all the material is thoroughly mixed.

To measure the temperature, we can use two devices. The first is a digital surface thermometer which will tell us the temperature of the outside of the material and give us a rough idea of the coating temperature, and the second is a traditional thermometer that we can dip into the lacquer to give us an accurate reading of the internal temperature. Remember in larger containers such as pails and drums the internal temperature could vary greatly.

After recording the temperature, we can fill the viscosity cup per the manufactures instructions and follow their procedure to accurately measure the thickness of the liquid.

We use a Ford number 4 cup so we insert the measuring cup sideways to avoid air bubbles, then we wait for it to fill completely before returning it to an upright position. As we begin to remove the cup from the coating, a stopwatch is started as soon as the top of the cup breaks the surface of the liquid. Holding it steady above the container, we continue to allow it to drain until the stream of liquid is no longer solid and we stop the stopwatch.

Now we know that at the current temperature of the wood coating, it takes a specific amount of time to pass through the cup. In the next section we’ll look at how that information helps us understand the best thickness to spray our material.