Taking Sanding Seriously
Grit, lighting, surface cleaning - pros share views on the perfect sanding job. April 14, 2005
Sanding is my least favored step. I have a question about my technique. Before sanding, I'll wipe with alcohol and use a card scraper to take off any glue spots that I missed before. I use a Random Orbital Sander usually starting at 120 and ending at 180 or 220 depending on the finish. I'll raise the grain and then briefly block sand following the grain with my last grit and use the same paper folded and hand-held on edges and moldings. My last pass is the next higher grit on exposed end grain. I end with dusting it off and blowing it down and out with compressed air.
What am I not doing that I should? What problems should I look for in my ready to finish piece? Is there a good reference to read on how I should be finish sanding?
From contributor A:
Your procedures sound like you know what youíre doing and you do it well. The only thing I'd tweak around is the final grit. I have found that 150 grit is a good place to stop your prep sanding for most finishes. There are finishes or stains requiring that you bring the grit down to 180. Any higher grit sanding is, in my opinion, a waste of time, energy and asking for problems with delamination due to the wood surface being burnished. I also would switch the easing of edges right after my 150 grit is used but that is a matter of semantics. One part that you should reconsider is the endgrain prep. The one thing to try and avoid doing is folding the fibers back into the open grain as these will tend to expand with moisture increase and make your finish rough or worse yet, break the finish integrity. Also be sure that no water or oils are blowing through the blow gun while cleaning off. They make these nice micro-fibre towels now that are great for removing dust and dirt. Finally, be sure to wear gloves when handling during this step and protect from moisture if and when the wood has to sit out over night because grain raise will set you back a bit.
From contributor B:
I always consider sanding any finer than 150 to be strictly recreational. Some WB stains do like 220 better but I still stop at 150 with them. I also sand the endgrain to 150. The best references are your own eyes. Evaluate every piece you do and identify things you need to do better next time. You never stop learning but the mistakes get noticed by a smaller number of people as you progress.
From contributor C:
The cabinetmakers in my shop dread seeing me walk their way with a piece from my finishing room. In my opinion, proper finish prep sanding is a multi-sense process. It has to look right and it has to feel right. Raw wood can look good with no orbital or cross grain scratches but once it has a finish applied to it, it will take the finish considerably differently.
The lights in my room bring out every detail and every flaw and I've had to learn to adjust my anal retentive tendencies to match the specs of the job. KCMA standard for custom grade for example, doesn't mean a perfect finish like I would prefer if I was making something in my own home. If an orbital scratch can't be seen at 3 feet it is acceptable to that standard.
The grade of finishing the customer is paying for determines the extent and detail of what needs to be done for the sanding. We finishers would love to put out a flawless product but we have to be realistic.
On the occasions that I manage to get to finish something to the highest quality, I don't bother the cabinetmakers who prep sanded it. I dive into it and enjoy each and every aspect of the finishing process. Those pieces are what make enduring mass production of 200 kitchen cabinet doors and all their associated cabinet parts a week worthwhile. My boss seems to sense this and just when I feel like I'm about to throw in the tack rag, he gives me a premium custom job that I can truly take pride in.
From the original questioner:
Your responses raise additional questions. To contributor A: I have practiced new phrases as a result of the air hose, but a fox-tail was never enough, I don't like tac-rags, and my vacuum usually ends up generating a rub point somewhere. I'll have to try the micro-fiber towels. Your offhand comment hit home - when I'm done I usually run my hand over everything to catch sharps that I'd missed. I'd not considered that as a contamination source. I don't follow your end grain comment - can 220 paper burnish end grain over enough to cause a problem? Would new or sharp paper be the answer?
To contributor B: It's perverse - I do notice fewer mistakes, but the ones that get through seem to hurt more and reflect a stupid error that I didn't pick up. That's one reason I developed the hand wipe contributor A cautions against.
To contributor C: You've really got my interest. I've been unable to get shop lights to do anything but hide problems, so I have a small, intense light that I can hold to rake the surface. What's your lighting?
From contributor D:
I see a lot of posts on this subject, where guys stop their sanding at 150 grit. Whenever I stop at 150 I still can see sanding marks in the wood, whether itís a random orbital or a palm sander. In the hardwoods I usually don't notice until I have stained it, but in the softer woods like Alder I see it on the raw wood. Is it possible I'm using the wrong type of sandpaper here?
From contributor E:
To contributor D: You are absolutely right! I too can't always stop at 150 grit like the posts says. I've found that it isn't that simple. It depends on the hardness of the wood for one, I sand cherry finer than oak. It also depends on the sandpaper type and brand. I have different ones and they don't produce the same results for any given grit. And lastly, the sander I'm using makes a big difference. I have to go finer with my 1/4 sheet palm sander than my random orbital. So to recommend one grit only is just plain wrong Ė there are too many variables.
From contributor C:
My finishing room is 18'x 24' and has 8 fluorescent light fixtures with two bulbs in each. They are 8 foot GE high output F96T12-CW-HO-CT Cool White. I'm thinking they are 800 watts each since there is a big 800 right next to the part number on the bulbs. The room walls are covered with white Tyvac housewrap so basically with nearly 13,000 watts of lighting, I can see a 150 grit orbital sander mark at about 5 feet away on raw wood, where as under normal lighting, the customer wouldn't be able to see it at arms length with a stain and lacquer finish.
It's taken me a little adjusting to know what I can let go so I don't look like some prima donna who has to show the scratch to the cabinetmakers using a magnifying glass and a 1000 watt floodlight held 2 feet away.
When I feel like being picky, I have them come into my room and show them the scratches or defects. It can be kind of funny to watch their reaction and hear them say, "How the heck did I miss that!?"
From the original questioner:
It could be your knowledge as well as your lighting. I find that with uniform lighting like that I cannot find defects anywhere near as easily as I can with a directional light. There are areas where I can spot a problem at a glance - finishing is not one of them.
To contributors D and E: Contributor Cís earlier comment on the KCMA standard was a real eye opener. If you cannot see it at 3 feet the scratch doesn't matter. The differences in final grit could be a function of that definition; commercially acceptable practice versus personal preference.
At what grit final sanding would I begin to enter into adhesion problems? As long as I'm below that point, does the finer sanding cause harm other than changing a stain's tone?
From Paul Snyder, technical advisor, Finishing Forum:
That's a lot of sanding steps. You shouldn't have any sanding related problems with that routine. The pre-finish sanding I do is almost always a one pass deal; P150 grit on a random orbit for 95% of the surface, a little hand sanding where needed. It takes a while to get a good technique down so that there aren't any swirl marks or obvious sanding scratches and nothing is missed. A pigmented wiping stain will make every mistake stand out like a neon sign. Most of the finishing I do is production oriented so sanding has to be done quickly but well.
From contributor A:
It is also A.W.I. standards for defects such as scratches or touch-up and repair work - the 3' rule. This is only to protect workers from the customers inspecting with a jewelers loop in hand and complaining about microscopic defects that are naturally found in wood. I have found that too much lighting works against me. If you really want to know the best way to prep wood prior to finishing, it would be to scrape the surface with glass or a super sharp cutter. This is obviously impossible to keep all areas even and not practical to do. I wish I was an engineer so I could make a finish belt sander where the belt is running on a square flat surface with sides that are flush front and rear. To sand until you see no more scratches is overkill and if overdone can lead to delamination of coatings if finer sandpapers get to the point of polishing surface. A lot of the new papers out today are made so that the grit doesn't break down upon use which is good for removal of quantities of material but bad for finish prep. I prefer paper that gradually breaks down when I sand so in effect is like changing the grit of sandpaper as you go. There is definitely a science to sanding because there are so many things that have to be taken into consideration - wood, sandpaper type, machine or tool used, finish/stain/dye used, time allotted, sander pad hardness or softness, etc. This is an area where you need to put in the time to find your optimal schedule for this technique.
From contributor D:
To contributor A and Paul Snyder, technical advisor: Thanks for the insight! I didn't know about the 3' rule. I'm just such a perfectionist I wanted to get all those little scratches out of the wood. I do use wiping stains and like Paul said that is going to make it stand out because of the pigment lying in the scratches. I did some test pieces this afternoon stopping at 150 grit and stained as usual. But then I applied some toner to it (according to Paulís recipe) and it seemed to mask 90% of the scratches. I was very happy with outcome. I guess I'm going to have to break down and put a spray stain into my finishing schedule. Believe me I hate to sand, so the less sanding I have to do, the happier I am.
From contributor G:
To the original questioner: You've already gotten great comments here. To those I'll add our finishing schedule. With every job we have a sample piece that we take through the sanding and finishing steps first.
Paint grade, 120 then 150
Stain grade with clear coats - 120/150 and depending on wood 180, then water wet and 180 to knock off fibers.
Furniture, jewel boxes, humidors and others that are often oil finished - here we go through 320 and the see how the sample piece looks. It is not unusual for these high end projects to see grits going on up to 1000 / 2000. However I assure you they pay for all that sanding.
The comments below were added after this Forum discussion was archived as a Knowledge Base article (add your comment).
Comment from contributor J:
I think I am an oddball after looking at this thread. I do very little staining because of the finish I desire. I end up working to a 600 grit or sometimes (in rare occasions) up to a 2000 grit and oil it in steps between grits until I get the hue that I want. Then I either lacquer it, or if it is a show piece instead of a utility piece I will coat with Elmerís and lightly burn until the glue dries a clear gloss finish on it.