prep before finishing

[Brian Runau]

I keep seeing I should use 120, 180 & 220 to finish sand before applying my finish. I have always just used 220 on the surface after it comes off the planer. What am missing by not using the other grits? Thanks Brian

[Prashun Patel]

If your planer has fresh, perfectly set knives and your finish is matte, going straight to 220 may be perfectly acceptable.

However, planers will frequently leave a scalloped surface that is not visible until you start building a glossy finish. To remove those scallops, people may want to start at 120 or 150. 220 can get them out, but you may need to sand longer than you think appropriate.

But I agree with you. My planer has a helical head and I too can start at 220.

I suggest (apologies to others who see me say this a million times) in fact, that you may be missing something not by starting at a lower grit, but by finishing at 220. If you go to 400, 600, or 1000, the initial coats often go on more even. This can help you achieve a thinner finish that is often more nice to the touch than 220. My opinion only.

[John TenEyck]

Planers leave scallop marks and compress the wood as they cut. Even is you can't see scallop marks under raking light the wood could still be compressed beyond what 220 grit will remove in a reasonable amount of time. You might not see any defects if you are just clear coating but dyes and stains will often show little bands of dark/light/dark/ etc. across the board when those compression marks haven't been removed.

Regardless, what you definitely are missing is that not every wood or application should be sanded with or to 220 grit. Paint grade projects don't and shouldn't be sanded beyond about 150 or maybe 180 grit. Going finer doesn't improve the finish and makes it harder for the paint to bond. Woods like oak, ash, and other really porous species generally don't get better after 150 or 180 grit either, whether they will painted or clear coated. On the other hand really dense woods might look much better after sanding up to 600 grit or even higher when using an oil or wax finish compared to 220 grit.

John

[Edward Dyas]

220 is way too fine to be sanding surfaced wood. The planer makes ridges across the wood as the knives cut. You need to start with a coarser paper like 80 to remove the marks made by the planer and then sand with 120 and finally with 180 for most wood. If you are working with very soft wood or you are going to use an oil finish then it should be sanded to a finer grit. Just keep in mind that when you get to very fine paper the sander tends to wallow out the soft wood and leave the hard grain so it tends to have a washboard appearance if you stay at it very long.