Scratch Marks from Hand Sanding

      Basic advice on appropriate hand sanding technique to minimize visible scratch marks. December 29, 2008

Question
How do you get sander marks out of wood before staining?

Forum Responses
(Finishing Forum)
From contributor M:
Don't know if you're referring to hand sanding or large production sanders, but the method is pretty much the same. I usually start with 100/120 grit and work my way through each successive grit (100, 120, 150, 180, 220) up to about 180 grit. Usually when you go above 180 you begin to compromise the ability of the stain to penetrate the wood. Good way to check for sanding marks before staining is to wipe the wood with lacquer thinner or mineral spirits and view with a high angle light source.



From the original questioner:
Thank you very much. Is it still okay to go back and use different grits after you have already tried 220? And they are production sander marks.


From contributor M:
Shouldn't be a problem unless you are working with thin veneer (1/32") on a substrate. Each successive grit removes the scratches from the previous grit and leaves a finer scratch pattern which is then removed by the next finer grit sanding... and so on and so on.

So yes, as long as you don't think there is any danger of sanding through, you should be able to start over again with no problems.

Is this on a wide belt Timesaver type machine? What type of material are you sanding? What type of finish are you using? Could probably give you a little better direction with answers to these questions.



From the original questioner:
Thank you. Actually, it was a 1/3 sheet sander. Not sure if it was the right tool to work with. I am working with oak. I am looking to use a stain from Zahr to finish it.


From contributor S:
1/3 sheet sander is fine. Pigment stain doesn't penetrate the wood exactly the way a dye would, but the pigment hangs up in the grain and sanding scratches, hence the reason for minimizing them as much as possible.

When using a 1/3 sheet (or 1/4) vs. an orbital sander, there is an easy way to know that you have removed all the previous grits scratches. It does go against logic and the usual teaching and you have to pay attention to being thorough. You will be alternately sanding with the grain and against the grain of the wood.

Decide what is the final grit you are going to sand to and that grit will be sanded with the grain of the wood. If you want to sand to 220 and you are starting with 120, 150, 180 then your sanding schedule would begin by sanding against the grain with the 120. With the grain with 150, against the grain with 180, and with the grain for your final 220.

This makes it very clear and easy to know when you have removed all of the previous scratches. It is important to change your paper frequently especially on the finer grits, and make sure you do not allow junk to build up on the paper, which can leave deeper scratches.

It should take just about half the amount the sanding time on successive grits (to remove the previous) as it took for the previous coarser grit, but again, keep your paper fresh. One of the toughest points I ever have had to get across in training others is that their labor involved in overuse of a piece of sandpaper far outweighs the cost of the sandpaper, not to mention it simply stops being effective when overused. Try it on a sample first and see if it works for you.



From contributor G:
Depending on the wood, you can get away from a lot of sanding by hot water-popping the wood, which will swell up the fibers and raise out the swirls. After it dries, you can sand with the grain and get rid of them all with 180.


From contributor N:
A good high-speed orbital sander shouldn't leave sanding marks visible to stain even at 120 grit. It is not necessary to have a five-step sanding process to eliminate scratches.


From contributor G:
Use an inspection light properly and you can see all sanding marks plainly, even sanding marks you don't need to see and won't show. Nothing special about the lights - a car headlamp will work. You need it bright. The light should be at a very low angle across the top, shining across it, not down. You'll know when you get the proper angle - all the details in the top will jump right out.

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