Making the right choices in the abrasives used on any wood floor sanding job is one of the major keys to success. The main idea is efficiency, as any professional will tell you that when you are using the right tool, sandpaper, and grit at the right time in the process, not only is the time expenditure kept at a minimum, but the quality of the finished product will seem to take care of itself. In this article, we will cover the things to consider while using the big machine, edger, and multi-head, so you can get the most out of the choices you make concerning the abrasives you choose.
Big Machine
Choosing the first grit of abrasive to use on any sand job is critical, as it sets the tone for how the job will go in terms of time spent and the quality of the finished product. So, how do we determine what that first grit should be? There are many factors to consider, but first, let’s consider that proper big machine (belt or drum) sanding means that the floor surface ideally will be sanded with four passes of the grit that has been selected. The forward and reverse passes in the same path represent passes one and two. Shifting over (to the RIGHT PLEASE?) with a 50 percent advance (and 50 percent overlap) on the next forward and reverse in the same path represents passes three and four on what is overlapped (and one and two on the advance). In these four passes of the first grit, the result should be a flat, clean, and uniform cut.
On new wood, there should be a uniform dullness from the sanding spanning the entire width of the boards sanded. There should be none of the telltale “shiny corners” or “shiny streaks” found at the boards’ edges. This “shine” that can be left over is from the milling machine that cut these boards flat. If there is a substantial amount of shine left after these four passes, the grit of the abrasive chosen likely is too high, and moving to a lower grit would be advisable. Conversely, if all the shine consistently is taken out prior to pass number four, you likely are starting with too low of a grit. That carries a host of undesirables, such as adding more sanding steps, using more abrasives, and removing too much wood material (which can equate to lesser quality of the final product’s appearance and lifespan).
For resanding an older floor, your focus is on the removal of finishes; again, judge by what gets accomplished in the four passes.
If there are patches of finish left behind, it likely is better to drop down a grit or two. If the finish is gone completely in the first or second pass, you just might do well to switch to a higher grit. A small amount of experimentation with the flexibility to make a change or two is how it’s done.
Big Machine and Edger
After completing your first big machine cut, it usually is prudent to begin the edging process. Oftentimes, the first cut with the edger will be the same grit that was chosen for the big machine’s first cut. Once this first cut with the edger is complete, it likely is time for the next big machine cut. The rule here is to never skip more than one grit over the last grit used. Once this second sanding with the big machine is complete, it is time to bring out the edger and follow up by using the same grit that was last used by the big machine.
Again, consider every job unique and have the flexibility to make any needed changes. Even so, the key point to remember at this stage is that the edger is following the work of the big machine.
Edger and Multi-Head
The floor is now flat, and we have completed at least one additional refining step with the big machine and the edging is of equal grit, and we are looking to finish up by using the multi-head sander. The idea here is that as we enter the true finish-sanding phase of the sand job, we begin with the same grit of abrasive as was last used by the big machine. The other adjustment here is there is no more skipping of grits. Once this first multi-head sanding step (which probably shouldn’t ever be more than 60 or even 80 grit) has been completed, it is time to let the edger take the lead.
Unlike the big machine phase, we bring the edger out first to climb the sanding grit ladder. This is done to minimize the width of the often problematic transition zone from the walls to the field of the floor. It is better to push the multi-head’s work into the edger’s work toward the wall than to push the edger’s work over the multi-head’s work out onto the field. This results in less edging and a narrower transition zone – a huge benefit. So now we have a reversing of the rule we visited in the big machine and edger phase in that the multi-head is now following the work of the edger.
The final grit will have everything to do with the species of wood being finished, as well as the nature of the finish and any colors used. It is usually a choice between 100, 120, and sometimes 150. The screening process often will match the last grit used from the sanding, though conventional single plate buffers often call for one grit higher than the last sanding. Again, being flexible always will be a major key to success.
Russ Watts is in sales and service for Lägler North America in Denver, Colorado. He can be reached at russ.watts@laglersanders.com.
