High Gloss Processes

Q. We manufacture custom metal parts, and lately we have been asked to start buffing parts to a high gloss. We have tried this in the past, but had a difficult time getting a high gloss polish look with the finish material we are using. What should we be using as a proper coating? Then what are the best products to use to achieve the high-gloss look?—R.D.

A. I am asked this question quite often. There are several things we need to understand about the nature of coatings and application before making the best decision., such as hardness, sheen, clarity, drying times, impact resistance, chemical resistance and so on. To help you better understand what you may or may not need for the high gloss process, let us first dive into the coating itself.

What is sheen? Sheen is measured on a scale from 0–100 with zero being the lowest possible reading, typically using a sheen meter with a 60° degree prism. Before each use you need to first calibrate the meter, then sheen can be measured to ensure it is to your specifications.

I do not know what your target is, but typically 70- to 80-degree sheen paint material or clear is what I like to start with before a high gloss buffing process. So why is this gloss range important? People often try to bring a coating to a high gloss with a coating that may not be designed for high gloss processing. You did not mention what sheen product you were trying to achieve a high gloss with, but typically you will want to use a coating that is high in gloss and formulated to be buffed. So why is this important? Not all products are designed to be brought to a high gloss. Lower sheen products and even higher gloss products use silicas and other additives to control sheen levels and other attributes in their coating products that will not let you achieve high gloss ranges. It is best to consult with your current coating supplier to see if the product you are using is designed specifically for high gloss buffing.

The next equally important step is the sanding sequence before the actual buffing process. Generally, I use the following wet/dry sand paper sequence while continuously dipping my paper into water or using a misting bottle to spray the surface as I sand:

• 600 wet/dry paper with water to remove the coarsest debris and any possible orange peel. If the paint is fairly smooth you can skip right to the next paper listed.
• 1000 wet/dry paper with water to remove the previous 600 grit scratch pattern.
• 1500 wet/dry paper with water to remove the previous 1000 grit scratch pattern.
• 2000 wet/dry paper with water to remove the previous 1500 grit scratch pattern.
• Finally, 3000 wet/dry paper with water to remove the 2000 grit scratch pattern.

The surface is now smooth and ready to buff with the proper compounds. But first, if you have not already, you will want to invest in a buffing machine with a variable rpm range, which can be air or electric. I use an air orbital sander retro fitted with the “Hook It” pad (basically Velcro) to hold the foam pad in place more aggressively. The buffer should have an RPM range of 1500–2500. The wool pad typically can be used at 1800–2500 rpm for the heavy cutting process, and a foam pad can be used at around 1000–1500 rpm for the final polish.

There are several schools of thought as to the best buffing bonnet to use. Lamb’s wool vs. foam pad?

It really comes down to a personnel preference, but here are some observations I have made regarding the two options. The wool bonnet is good for the heavier cutting compound stage. It does tend to absorb or load the rubbing compound more than its foam counterpart. So why is this not a good thing? During the process, the wool pad begins to burnish the surface more than it buffs when it loads up. This is caused by the friction and resistance between the loaded pad and the surface. You really do not want to do all that tedious sanding to start burning the surface. Even using a misting bottle with water can still cause this to occur. They can also be laundered for continuous use. The foam pad loads as well, but the nubs on the pad keep it from loading too heavily. It also does not seem to build up heat and friction like its wool counterpart. There are now various densities of foam for each step of compounding and final buffing, and they can be washed out and reused. My preference is the foam pad because it gives you the best final buffing look. Lastly, “The Compound.” There are many products out there that claim to be the greatest and best, and while we do not promote specific products at Products Finishing, the best thing is to do is look for a compound that will remove a minimum 1500 grit scratches without leaving swirl marks. You may want to do some trial and error testing to find the best product for you. Often, your coating supplier will be a good resource for the proper compounds to use with their products.