Can someone explain 'rubbing out' a finish?

[Chris Hedges]

Pretty self explanatory title. Whats the purpose?

Chris

[Howard Acheson]

"Rubbing out" is the process of abrading a finished surface with ever finer grits of sandpaper and/or powdered grits to produce a particular level of smoothness and sheen. You can create non-gloss flat sheen up to high gloss sheen. It's typically only done on the "money surfaces such as top and front doors of cabinets. It created a formal look to the furniture item.

[Scott Holmes]

To add a bit more info to Howies answer...

Rubbing out is using finer and finer grits of sandpaper and WET sanding the surface. First timers are better of using mineral oil to wet sand... after you get the hang of it mineral spirts cuts a bit faster. Using a power sander is faster AND also easier to burn through the finish.

[Alan Lightstone]

Power sanding with mineral oil is incredibly messy. It works quite well, as Scott said, but make sure everything is covered. Personally I like water with a very small amount of dishwashing liquid in it. Don't use a regular ROS with that. Water and electricity don't mix :>

A polisher (random orbital is safer than a rotary) used for car detailing works quite well, and won't electrocute you.

It's amazing how wonderfully smooth a rubbed out surface can feel and look. But unless you are very careful, and depending on the finish you are rubbing out, you can easily rub through it and get witness lines, which will ruin your day/week/month. Really learned that lesson recently.

[Chris Hedges]

Is this a process reserved for when a finish is less than perfect when brushed or sprayed? It seems with all the technology that goes into developing these finishes, they should lay out flat smooth and as prescribed by the sheen on the can/bottle. I am certainly not a stranger to 'rubbing out' a finish I just found myself wondering why on earth we spent all this money on our finishes and then have to spend so much time making them more perfect.

Chris

[Howard Acheson]

>>>> Is this a process reserved for when a finish is less than perfect when brushed or sprayed?

No, in fact, the surface must be perfectly flat to work the best. If you rub out a finish it will highlight any uneven parts of the surface. The first step in "rubbing out" is to sand the surface perfectly flat before the first coat of finish. Then maintain that flatness with the application of subsequent coats. You need to build up a sufficient film thickness so that the sanding for rubbing out does not go through the film.

It's not a process that you first attempt on a real project. Set up some test boards, prepare them flat and smooth and apply a finish. Then learn how to rub out on these boards. Never learn rubbing out on a real project.

If you are somewhat new to finishing let me suggest you buy Jeff Jewitt's Taunton Complete Guide to Finishing. Amazon will have it. It will give you all the info you need to become a proficient finisher.

[sheldon pettit]

Is this a process reserved for when a finish is less than perfect when brushed or sprayed? It seems with all the technology that goes into developing these finishes, they should lay out flat smooth and as prescribed by the sheen on the can/bottle. I am certainly not a stranger to 'rubbing out' a finish I just found myself wondering why on earth we spent all this money on our finishes and then have to spend so much time making them more perfect.

Chris

To answer your question Chris, If you notice when you put your last coat of finish on wet, it looks nice and smooth and glossy right? Or at least it should if sprayed correctly this is due to being in a state of liquid consistency that includes not only the resins, but the additives and diluents also. as the film dries by loss of diluents etc., the film shrinks and the shrinkage causes the initial smooth look to become distorted. It no longer appears to look like a sheet of glass etc..

when the film becomes bone dry hard, especially when it's a gloss finish that's been applied, it no longer has the glass flat smooth shiny look as it did when wet, thus the need to apply further steps to bring the glass smooth look and shine it originally had when sprayed ok?

There are exceptions to the rule as always, such as casket lacquers etc, that do the same thing as cold spray lacquers do, but are made up of acrylic resins which when heated, re-melt the dry resins and make them flow out glass smooth. but these types of spray and bake finishes are not meant for either commercial or even residential use as they are to soft to hold up to either, they are merely for appearance sake only, but look as good as any perfectly sanded/compounded/ and polished surface would or does look.

Anyway, that's the gist of why it's necessary to rub out the bulk of coatings we use.