Importance of Scratch Pattern

Greg Mihaich, Application Engineer III, DIY/Contractor Markets, Norton | Saint-Gobain

The final look of any fully finished floor depends greatly on the scratch pattern left by the last round of sanding. However, ensuring the highest quality finish begins the very first moment a sander touches the surface. Even while using a coarse grit sandpaper in the early stages of floor preparation, you can significantly impact your final results.

When sanding a floor, you are most likely standing upright over your equipment. From that position, it can be hard to see the finer details on the surface. It would be helpful to know that the sandpaper you’re using is removing marks and leaving the finest scratch pattern possible. That’s why the recently improved coarse grits of Norton Red Heat® are so important.

Measuring Scratch Patterns

In modern construction, scratch patterns have become more visible. Newer homes and offices incorporate more light, with bigger windows and recessed lights all coming down on the floor. In older, darker homes, you couldn’t see the floor surface quality as well. Plus, there are new types of finishes, including the current popular trend to use oil wax finishes that give the floor an almost raw, unfinished look.

Unlike oil-based polyurethane finishes that sit on top on the floor and mask some of the sanding marks, the newer finishes actually penetrate the wood and don’t leave a film to hide surface flaws.

Because scratch patterns are visible, you can compare them with the naked eye. There are, however, more objective methods for measuring scratch patterns. For Red Heat, we use a technique known as laser profilometry. This is a non-destructive testing method used to scan and map a surface. Lighter green and blue indicates a finer scratch while the redder colors indicate a coarser, deeper scratch.

The image above shows the laser profilometry results of Red Heat (R955P) vs a competitor after using a 36- and 50-grit sequence on maple wood. The evenly striped blue and green color for Red Heat compares favorably to the erratic red colors of the competitor. Below the color swatches, you can also see a two-dimensional cross-section of the scratch, showing the Red Heat is much more uniform and consistent.

The Time vs Quality Quandary 

Most professionals start with an aggressive coarse-grit abrasive in order to work faster when removing old finish from a floor. While most of these strong abrasives increase early productivity, they also create deep, unsightly scratches. The time saved in taking off the old finish is then needed later in the process when the operator has to work doubly hard to eliminate the scratches.

This dilemma drove the Norton engineering team to redesign the coarse grits in the Red Heat portfolio. The goal was to increase the aggressiveness and durability of the product while maintaining the product’s reputation for having the cleanest scratch pattern available. To accomplish this, the manufacturing process was modified to improve the grain orientation. Doing so gave the new belts and rolls more cutting points and made the grain more available on the surface. This, in turn, improved the initial cut rate by 30%.

Said Alex Caracci, a contractor who owns Olde Tyme Hardwood Floors in Doylestown, Pennsylvania, “We love Norton paper. The new [coarse-grit] belts worked great. They were fast and effective and seem more hardy and aggressive. We were sanding prefinish and it was not an easy sand.”

Constructed for Consistency

Red Heat uses a ceramic alumina abrasive. While silicon carbide or zirconia abrasives lose their shape and break down more readily, ceramic grains maintain their shape throughout the life of the belt, roll, or disc. The recent changes to Red Heat also improved the grain orientation to have more cutting points down, delivering that tighter, more consistent scratch pattern.

In an effort to maximize productivity and efficiency, contractors will push products as long as they can. As some of the other types of abrasives begin to deteriorate, they become dull. This changes the scratch pattern and can burnish the wood. In comparison, Red Heat products will maintain the same uniform scratch pattern throughout their entire life. Said Michael Comnaire, a Contractor from Ann Arbor, Michigan and an early user, “I was able to sand almost 2,000 sq ft with one 60-grit Red Heat belt on new red oak. And it had a much finer scratch pattern than [a competitive product].”

Overall, the engineering changes made Red Heat a very easy product to work with because operators don't have to work as hard to get the core scratches out and they can have peace of mind that those unwanted scratches are just going to be removed. Then, when stain is applied, there aren’t going to be any big swirl marks or sanding marks, just a clean, consistent surface that lets the wood quality gleam.