Question
Recently I have been sanding doors with 150 grit sandpaper on a bi orbital sander. I noticed that there are consistent swirl marks after sanding is completed. I always hold the sander the right way. Is there anything i can do to prevent this?
Forum Responses
(Finishing Forum)
From contributor B:
You should not be getting swirl marks with 150 grit. If your down to 150, maybe you’re using too much pressure. Is the wood real soft or is dirt collecting on the sandpaper? Other than that its usually bad sanding technique that does it.
Not all sandpaper is the same. 150 grit from one manufacture will be slightly more or less coarse than 150 from a different manufacture. Even within the same brand, different types of paper can vary in actual coarseness for the same number grit. Technique has as much to do with swirl marks as anything else.
The biggest mistakes people make when sanding are going too fast, using too much pressure and tilting the sander off level. All of these mistakes can cause sanding marks that may not be evident until after staining and finishing.
Finally, knowing what grit is the best for the wood you are using also helps. 150 is a good all around choice but it can be overkill for some hardwoods like ash and hickory, while other woods seem to like a finer grit. For instance, I go all the way to 180 or even 220 with walnut. It seems to show marks from anything coarser, especially when stained.
The only times I seem to get swirls is if I sand too fast. I like the 3M silicon carbide paper for both raw wood sanding and sealer sanding. I’ve been sanding sealer coats with 280 for quite awhile and it seems to work for me. With raw wood I might use150-180 and like contributor J I like 220 on walnut.
