Finishing reveals, particularly if staining is involved, every flaw. It is a heartless bastard that points out everything you didn't do right, or just didn't do. So a good finish starts with careful, contentious woodworking from the beginning. Every gouge, scrape and nick will have a spotlight shone on it, so take the time to do everything right, and fix mistakes and problems as you go. Trust me, it's much easier to fix it when you do it than later.
Once everything is assembled, I go over the entire project very carefully, filling nail holes, small knots and any other flaws with a sandable, stainable wood based putty. I personally like Famowood, which has a good assortment of colors, dries fast and accepts stain well. If the holes you're filling are small, they will virtually disappear by the time you're done.
Next comes sanding. Since this project is red oak, I hit all the really rough spots with 80 grit to remove any saw marks, router chatter or burns. But, since there's also a lot of plywood in the project, I have to be very careful not to sand through the veneer. As a rule, I never use anything rougher than 120 grit on plywood, I use the 80-grit on the hardwood.
After the first sanding, I vacuum everything off and look over it again. Often there will be holes that need more putty, so I fix them. Then I sand everything with 120 grit, followed by 150 and 180 grits. This will be the last sanding before staining (I sand up to 220 for painting, but that's another issue).
The thing about sanding is that most people don't understand what they're trying to achieve and what sanding actually does, so they spend way too much time on it. Sanding is tedious, so why spend hours and hours doing it if you don't have to?
The point of sanding is to reduce everything to a relatively smooth surface and remove surface imperfections. The 80 grit should remove machining marks, but leaves visible etching in the wood. 120 grit will remove the etching from the rougher paper, and leave a surface that will accept stain and finish well. From there I like to progress up to 150 and then 180 grit. If you progress much past 220 grit on most woods you will start polishing the grain, which seals it up so it doesn't accept stain very well, this can lead to uneven coloring and splotches.
Most people think if they must sand the raw wood very smooth to get a very smooth finish. That isn't true. How fine a grade of paper you sand to depends on the particular wood and finish process, but on most of my projects, 150 or 180 is fine.
The goal of each finer grade of sand paper is to remove the etching left from the previous grade. Once you've done that, you're done with that grade, so stop. A low angle light source placed shining across the piece toward you helps to see the surface texture better. Wiping the surface down with mineral spirits (not water, unless you're using a water based stain, but that's a whole other animal.) also helps. Once the project is consistently smooth, the sanding is done.
Now clean the project very thoroughly. I use a vacuum with a brush attachment, which helps work dust out of the grain. If you don't have one, I recommend getting a cyclone vacuum attachment for your shop vac, it will really help improve the vacuuming process by preventing the filter from clogging up with the fine dust, and it's good for your health.
I also always wear a respirator mask with replaceable filters when sanding and spraying, even when using water based finishes. This is a health issue. Prolonged exposure to wood dust can cause all sorts of health problems. If you only sand one project a year it's probably not going to matter, but if you're a regular woodworker, buy a respirator and use it.
Since I spray my finishes, I set up a four walls of plastic sheeting to create a "spray tent" using a set of 3rd Hands. I also have an explosion proof exhaust fan in my shop ceiling which accepts furnace filters. The tent and vent help reduce dust problems by sucking air out. This is NOT a fume management solution, I always use a VOC rated respirator when spraying finishes, even with water based finishes! I can't stress this enough. Just because a finish is water based does not mean having it's microscopic particles embedded in the walls of your lungs won't harm you, there are all sorts of materials in finishes that are best kept out of your body.
There are a number of ways to apply finishes, since I do a lot of large projects, consistency, efficiency, time and cost all important to me, that's why I invested in an HVLP system. High Volume Low Pressure spraying is much more efficient than standard spray guns. In fact some test say it's 85% efficient, which means 85% of what you spray ends up on the project. I don't know about the numbers, what I do know is that I stained this ENTIRE project, inside and out, front, back and top, including 5 doors and 4 shelves (both sides) with roughly a half quart of stain! A half quart! If I brushed it on I would need at least three times that and most of it would end up in a rag after the wipe off. I only needed two rags to wipe down this entire project. HVLP is that efficient. Plus it's consistent and fast.
Spraying stain is pretty straight forward, assuming you're familiar with your gun (if not, take 10 minutes to practice on scrap). HVLP sprayers use so little finish to get good coverage, that some users just let the stain dry, they don't bother to wipe off the excess. I find that applying a little extra and wiping it off after a couple minutes produces a smoother looking color. Since HVLP produces warm air, I make a point of to stop spraying every 2 -3 minutes and wipe off what I've just sprayed. Leaving it much longer allows it to begin drying. If that happens just spray on a little more and wipe off.
Once everything is stained, let the stain dry. How long depends on the stain and the top coat, so read the directions and make sure you understand them.
BTW, professional paint supplies, will usually have much better quality stains and finishes available if you ask. I typically us Sherwin-Williams products, but the stuff I buy isn't on the shelves, they keep it in back for the pros. Just ask and they will help you figure out a good finishing system that will be much better than the stuff you find on the shelves of big box hardware stores.
After the stain has dried sufficiently, I apply the sealer coat, also usually with HVLP. It's important to make sure your stain, sealer and top coat are compatible, and that you understand the system. On this project I used an oil stain, with a solvent based vinyl sealer and a high build lacquer. The stain needs at least 2 hours to dry before applying the sealer, but can wait longer. The sealer needs 45 minutes to dry before sanding, but needs to be top coated withing 4 hours, or the top coat might not adhere, which will cause problems later (like crackling or peeling). The top coat needs 20 minutes to dry and has no critical re-coat time. Also important to know is that if I want a higher build (thickness) of finish, I need to apply more coats of lacquer, not sealer, but that I shouldn't apply more than 3-4 coats of this particular lacquer.
Freaked out yet? I was too when I first started using pro quality finishes. They really aren't that difficult. The manufacturer has already figured out the system, just tell the sales person what you want to do with the project and they will help you figure out the system. Then try it on a sample piece before committing.
So, after the stain has dried, I spray on the sealer and start a timer. When spraying clear coats less is better. You can always go back over an area if you think it's too thin, but if it drips, sags, runs, pools up or "orange-peels" you're in trouble. So practice on scrap, get the gun dialed in and take your time.
After it's dry, I sand everything again. That's the point of sealer. Everything you sanded will feel rough after the sealer dries. That's normal. Lightly sanding the sealer coat with fine sanding paper or pads is the critical step amatures miss that separates a good finish from a do-it-yourself finish. The key here is LIGHT sanding. Us a fine grit, I like 320, and just brush it over the surface a couple times to smooth out the roughness. No need to scrub it or even use a powered sander, just take the edge off it. Rub your hand over the surface to check it, when it
feels smooth, it is. Sanding sealers, by their nature are designed to make this process easier than sanding hardened lacquer or varnish, so take advantage.Then vacuum the dust up again, or use a tack clothe, or both, and spray on the top coat. The sealer has 24% solids, which means it produces a relatively thick coat, and the lacquer is also high solids content, so I typically use only one coat of that and I'm done. If I want a higher build I can add more coats, but that usually isn't necessary with this system.
There you are, a nice, smooth, tough finish, and it didn't take 2 weeks of rubbing in exotic oils. There's a reason no one uses those antique oil and wax finishes anymore.
After letting the last coat dry completely (usually overnight) I put it all together. Hand the doors, install drawers, etc. And it's ready to go!
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