Wet sanding

[Aragorn]

Hi all
I just want to check I'm doing wet sanding right, simple though it may be!
Would some kind soul talk/walk me through what they do from bare wood when wet sanding.
Much appreciated.

 

[Anonymous]

Hi Aragorn

Never heard of wet sanding of bare wood. I use fine (600grit) wet and dry paper to sand back an oil finish after 5-6 coats before the final coat. Water slows the cloggin of fine paper with debris from the sanding process. I simply dip the paper into water very regularly to clear away any bits that may mark the surface. I occasionaly 'flush' the surface with water too, again to make sure that no bits of finish etc get rubbed against the smooth surface. Keep sanding until the surface is uniformly smooth and dull, just like I used to do when spray painting stuff in my youth (mostly motorbikes)
Rub the last coat of oil on this to get a really smooth glossy finish

Cheers

Tony

 

[Chris Knight]

Like Tony I have not heard of wet sanding bare wood - unless you are referring to the practice of sanding in an oil finish as some folk do. If you have an already prepared surface say to 240 or 320 grit, you can then use say a 400 grit paper and a finishing oil like Liberon or Organoil and sand that into the wood. The very fine slurry you create will be partially carried into the pores of the wood and be lodged there as the oil sets. So you are in effect combining two finishing steps - grain filling and a finishing coat.

The surface you produce in this fashion will be wondrously smooth and very tactlile but rather duller in appearance than if you had used oil alone. It will therefore be more suitable for some woods than others.

Apart from this, sanding a finish is as Tony says, often done with wet and dry paper used wet. You can use water or white spirit or oil (mineral oil - often sold as polishing oil), depending on the finish you are working on. Using water as a lubricant produces a somewhat more aggressive cut than using white spirits or oil.

You have to be careful sanding a finish in this manner because the lubricant wets the surface of any bare wood you may accidentally expose by sanding through a finish and disguise the fact that you have just damaged the finish - you only notice when the area is dried off.

I take it that your question was not about pre-raising the grain of wood prior to using a waterborne finish?

 

[Adam]

I sometimes skim a light coat of water across on a reasonably damp cloth to lift the grain - and almost immediately sand with a very fine 'paper.

This was after a demonstration by Mike Humphries when he went through getting an optimum finish on french polishing.

Dampening the grain lifts the fibres, without raising the troughs (you need to look under a microscope to see) you then sand the raised grains, which provided you don't soak them :shock: are dry a few minutes later - and the subsequent finish is much smoother - with less visible "troughs".

Adam

 

[Aragorn]

Thanks for your replies.
Chris - I like the sound of sanding an oil into the grain! Haven't heard of that before.
I'm OK with raising the grain it was just the wet sanding that I wasn't sure about. I've always used dry sanding up until a few months ago. I get it now though!
As for raising the grain, I have found that dampening one side of a board (like a table top) can make the panel warp slightly. This is usually corrected by dampening the underside afterwards, once you can turn the piece over. Has anyone else had encountered this?
I'm always a bit worried that all that work that goes into getting a panel lovely and flat could be wasted by raising the grain for a really smooth finish.

 

[Chris Knight]

Aragorn,

Certainly wetting one side of a panel can cause it to bow. For grain raising, one does not use a huge amount of water - I use a crumpled-up wet paper kitchen towel usually.

If thin, a panel can still warp from only a small amount of water but usually flattens when it dries off. If worried, by all means wet both sides. In any case, it usually pays to finish both sides of a panel in the same way (precisely to have a balanced condition vis a vis moisture content changes), so similar wetting to raise the grain is by definition a good idea/required.