Does it matter when you sand in relation to applying a finish?

Question

When I was building my first piece of furniture I remember reading a SO answer or forum post where someone made a special note of how sanding has some effect on opening up the grain, and either should or should not (I can't remember which) be done within an hour or two of spraying lacquer. At the time I made no special note of it because they said it as though it was industry standard knowledge that everyone would be talking about in other articles.

Now I'm trying to remember what the advice was and understand it for use in my projects, but Google is turning up no results for timing sanding in relation to finishing. Is there actually any difference between sanding 15 minutes before spraying lacquer and sanding several days before? Assume that in either case the surface is properly cleaned just before spraying begins.

Answer 1

Does it matter when you sand in relation to applying a finish?

Yes, sometimes.

Is there actually any difference between sanding 15 minutes before spraying lacquer and sanding several days before?

As always there are variables but as a general thing consider it best practice to sand (or otherwise work the surface of the wood, e.g. by plane or scraper) just prior to finish application to help ensure best results.

This is not to say if you apply finish to a surface that was sanded four weeks ago you will have a problem, it depends on the species of wood, the storage conditions (dust, cycles of change in RH) and above all the type of finish being used. When using a waterbased finish (any type) it is highly advised to apply it to a freshly-worked surface for exactly the same reason it's important when using glue — older wood surfaces aren't properly wetted by water-based products, while with shellac or oil-based varnish for example their solvents will tend to cut through the surface contamination. But it's still advisable to freshly work show surfaces just prior to finishing with shellac or varnish, especially critical areas like a tabletop.

Answer 2

I have never heard of anything regarding finishing soon after sanding. Leaving wood set for a long time might cause some oxidation that could affect the color.

I have heard of gluing issues on very oily woods (teak) if they are not wiped down right before applying the glue, so that may where the idea comes from.