Controlling Gloss in Wood CoatingsI took my camera with me on my trip to Victoria and Vancouver, B.C. this week. During a quiet moment, I found some great pictures on my memory card that I had forgotten were there. One of those that inspired me anew this week is included here. I took it at IWF 2012 in Atlanta in August.

On one of my strolls through the aisles at IWF, I came across something that previously I had only heard about; a gloss meter.

I know. Seeing a gloss meter may not be something on your bucket list. But as a wood coatings guy, I spend a lot of time explaining and dealing with gloss. Gloss is a big deal in my circle. You also know that I love tools. Remember, I’m “Tool Time Bernie.” I was so excited that I took pictures of this device. I was surprised to find that it was about the size of a 6” sub sandwich.

There was a company exhibiting in Atlanta that was demonstrating their ability to adjust gloss in flat line applied coatings. Their machinery was set up in their booth. They were running samples through the machine. To validate their results, they had a digital gloss meter to quantify what they had accomplished.

Controlling Gloss in Wood CoatingsHere’s what I knew going in the door that day. I knew that gloss was measured with a gloss meter. I knew that the process involved shining a light on the coating at a specific angle and then measuring the intensity of the reflection from that light. Obviously, the more light that is reflected, the more glossy the coating. In clear coatings, where reflections can come from within the coating itself, the unit of measure for the reflection is given in terms of the percent of light that returns to the gloss meter.

Also referred to as sheen, there are no strict standards across the industry. However, there are some general ranges that can be referred to. A dull sheen is usually around 15% reflection. Satin is around 35%. Semi-gloss is approximately 65% and gloss is usually 80% and higher. Of course, within the opaque coatings it is not unusual to see different sheen names including eggshell, flat, and wet look. The latex paint on the walls of my house is considered a satin eggshell sheen.

Let’s jump ahead to the next issue. That would be how we manipulate gloss or sheen in a coating. There are pastes and powders available to modify sheen levels. The pastes are the easiest to use because they are already pre-liquefied. If you’ve ever tried to evenly disperse a dry powder in a liquid, you can appreciate the tendencies for clumping which can be problematic. The significant ingredient in these flattening pastes is silicon dioxide otherwise known as silica.

Coatings manufacturers create flattening pastes for their coatings that are totally compatible with their products. It would be safest to use the correct paste for the coating you are working with and to know how much of that product can be added. There are finite limits to these modifications. Going beyond them will cause problems such as softening of the coating and increased susceptibility to nickel mars.

Therefore, to keep the amount added to the minimum, it would be best to start with a coating that has the closest sheen to the target you are aiming for. Or, looking at that from another direction, it would be best not to start with gloss if you want to go to satin or a sheen that is duller than that. At the same time, there is only so much that a coating can be flattened. Going below 15% is possible but only to a point.

Then too, all flattening paste is not created equal. Some coatings, as I’m sure you know, are cloudier than others. That’s probably the flattening agent. After all, the particles are suspended throughout the coating. Its level of concentration increases as the coating cures and shrinks back. The more course the particles in the flattening paste, the more that cloudiness becomes obvious. It is this phenomenon of concentrating more as the coating shrinks back that creates the change in sheen level that we experience within the first 24 hours after a coating has been applied. It takes time for the coating to achieve its final sheen.

It stands to reason then, that if clarity is an issue, perhaps the answer is to spray initial coat(s) with a gloss product and only use the final coat to create the sheen level that you want. Doing so enhances the clarity. Gloss contains little if any flattening paste. The top layer, then, is the only one that contains the silica at the target sheen. That top layer acts as a lens to bring us to the desired sheen.

Until next time…spray on!

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