Sanding isn’t cut and dry where the procedures and grit selections are always the same floor to floor, particularly if you are working with a variety of wood species. This blog is just too short, and too general to meet the universe of variations and permutations of species, mineral type, grit size and other variables. All I can do is give general ideas on why changing to certain selections and procedures may be better for the situation you are in.
Just consider that if you are doing the same exact procedures on different hardwoods (36g rough cut for example), you may be working harder than necessary and the results may not be what you are looking for. So, with the many species with different characteristics, all the mineral choices and grits available, you might overthink it and have difficulty figuring out what is the most effective way to execute a good floor, but it isn’t really.
Regardless of the species, there are three major factors to consider: mineral, grit selection and pace over the floor. These are not mutually exclusive and they need to be used in a balance to yield a good finished floor. So, despite what species you are talking about, these tips will help you get a better product for your client.
Denser species will show scratch marks more if you were to start with too coarse a grit. Sappy materials need a coarser grit due to pitch build up (rendering a 36g equal to a 50 or 60g). Softer woods need finer grits than normal because the wood fiber is removed so easily.
When choosing the correct mineral, the best outcome is to not put deep scratches in to begin with. For the first cut (of 2!) use a longer lasting, sharper mineral but in a finer grit for initial big machine and edger work.
For medium to dense woods, if you are used to using a 40g or 36g to start a 3-cut floor, try starting with a 50g or even a 60g paired with a deliberately slower pace and smaller advancing passes (2-3” per pass) at 7-15° on the BM. Drop the standard 45 over the floor (unless it is way out of whack). The shallow angle will not place noticeable scratches in the wood fiber. Matched with a tighter, smaller advance at a slower pace allows more contact time per area under the paper to be sanded clean because this doesn’t engage the mineral deep into the wood fiber like a courser mineral would. Try this out. You will likely never buy 36g paper again for every day floor work!
For medium to dense woods, when the 1st cut is done, the next challenge is on the next cut and this is also why the 1st cut selection is very important. The sanding characteristic of dense hardwoods is that the finer grits won’t sand (remove) substantial material downward to get the deep scratches out that are left by heavier grits previously used. If you get the 1st cut done with 60g, move to a 100g paper but select a softer friable mineral, such as SiC. Repeat the same pass advance and light pressure, but slightly straightening out your path to 4-7°, allowing the mineral to work over the floor as before. The reason for the slight angle is to not introduce drum marks from changing densities at end joints. This is very commonly seen in wider planks of any species if sanded straight with the boards and it’s just more work to get out.
For sappy woods, too fine a grit selection that stays too sharp will just load up while leaving deeper slashes in the face. It’s possible that you will “fine” cut with a 60g SiC but certainly no higher than an 80g. The pitch load will lift the mineral over the floor and only the grain points will be sanding. That’s what makes the printed grit number not act like that number. Sappy woods turn a 60g into 100g or 120g. Also expect to change the paper a lot and clean your machine frequently so work the cost into your bids.
Softer woods may start with an 80g SiC BM 1st cut and a SiC 100g final pass. For these, a brisker pace but still tight overlaps will help sand the floor flat. Edging is a challenge because these woods tend to dent under the wheel pressure. A solution is to wet the wheel track zone after edging to puff the wood fiber up, then buff with a hard plate or use your multi-head at the walls. Buffing (clocking properly) with a very fine grit (120-180) on a stiff plate is better than on a driver with a pad as it will reduce or even eliminate dishout.
As always, the edger should be properly clocked to align the scratch pattern to the wood fiber. The goal here (and this is the same for ALL floors) is to not put cross scratches in you don’t have to take out.
All the above are general suggestions for unfinished woods. If you have a cupped floor or are trying to remove finish, dropping a grit or 2 and using a stronger, sharper mineral will help in the finish removal. But after that, go with a soft mineral and finest grit possible to get to a nicer finished floor.
I hope this brought you some ways to think about how you can make adjustments to your normal processes to become more effective and bring a better product to market.
Good Luck out there!!