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Get great results with the least amount of work.
T.Think about it: what’s the first thing you do when judging someone else’s woodworking? You throw your hand over it, of course. If it looks really smooth to you, you admire the work. If it looks rough to you, you’re not that impressed, even though the woodworking can be spectacular.
The way to get the smoothest, tactile finish is to “wipe off” the last coat with sandpaper and abrasive compounds. Methods for doing this are often written. It is a mechanical process that does not differ much from wood sanding.
Start with coarse enough abrasives to remove problems efficiently without creating unnecessarily large scratches. Then work through the abrasive grits until the desired shine (luster) and look is achieved.
But elimination is a lot of work. You might be willing to do this on a critical high-end table, but you’re not likely to want to bother on a set of kitchen cabinets, for example.
So how do you get the smoothest possible results without having to go through the erasing process? Here are five ways to get a smooth finish with the least amount of work.
Step by step
You can’t get a completely dust-free room, nor can you get your finish or application tools totally dust-free. But you can get close. So the first trick is to get everything as dust-free as possible. Here are some easy tips to do:
1. Wait several hours after sanding a surface before starting to finish to allow the dust to settle.
2. Remove the dust deposited on the surface, preferably with a vacuum cleaner. Adhesive cloths also work well on flat surfaces, but should not be used under a water-based finish because sticky residue hinders adhesion. Don’t brush off the dust or you’ll have to let it settle again.
3. Drain the finish unless you have just opened the can. Always filter the water-based finish.
4. Make sure the cloth, brush, or spray gun is clean. Clean it if it isn’t.
5. Just before starting to apply the finish to a horizontal surface, run your hand over it to check it is clean and to remove any small particles of dust that may have settled.
Waiting for the dust to settle and then removing it from the project also applies when sanding between coats.
Sand the first coat
The most important thing you can do to get even results is to sand the first coat. Except that there is a lot of dust and dirt in the air when you are doing your finish, the main cause, by far, of rough results is not first coat sanding.
The first coat, called the “sealant” coat, of any finish raises the grain of the wood and locks it in place. If you don’t sand this coat well, the roughness will pass through to all coats and make the final finish look rough.
The reason why it is better to sand the first hand, rather than a subsequent hand, is that it is thin. The thinner the finish, the easier it is to sand without gluing the sandpaper.
Use a grit of sandpaper that removes roughness efficiently without creating larger scratches than necessary. Usually this means # 320 or # 400 grit. Both of these grits are available as stearate (dry lubricated), which resists clogging better than non-stearated ones. Lightly sand if the sealant layer is very thin and there is a stain underneath so as not to sand and remove some of the color.
Water-based finishes increase the grain more than solvent-based ones, so you will probably need a coarser grain to be efficient. I suggest starting with # 220 grit and see how it works. You can move finer or coarser from there. As long as the finish is completely dry, non-steared sandpaper usually works well without clogging.
On turned and uneven surfaces, abrasive pads with foam backing may be useful. They adapt well to curved surfaces. Using mechanized sanding tools will require some practice during which you will likely experience a few sand passes while learning. I always chart the first hand by hand for the best control.
All that is needed when sanding the first coat, or when sanding between coats, is to make the surface smooth. It doesn’t have to look perfect. In fact, it rarely does. You just want the next hand to go on a flat surface.
Penultimate layer sand
If you are applying more than two coats in total, you may find it helpful to sand the penultimate coat before applying the last coat, either by spray or by brush.
The sanding roughens the surface, favoring a better leveling of the next finishing coat. (Think water dripping on shiny surfaces of cars or tables versus leveling water on concrete.) So orange peel and brush marks will be reduced.
Thin the last hand
The finer the finish, i.e. the lower the viscosity, the better it levels to reduce brush marks and orange peel. You don’t necessarily feel these flaws, but they look bad in reflected light.
You don’t have to lose much weight to have a significant effect, usually only 5 or 10 percent. But, with the exception of water-based finishes, which may not flow well if you add too much water, you can dilute as much as you like without having any negative effect on the finish.
The reason some instructions on solvent-based products say not to dilute is to comply with VOC regulations in the most restrictive areas of the country. Thinning is not detrimental to the finish.
Scrub with a brown paper bag
This trick is effective enough to remove small nibs of dust without leaving scratches on the finish. However, it is not effective for smoothing a surface on which the sealant layer has not been sanded.
Fold a small brown paper bag from a supermarket and rub it on the finish after it dries well. Finishes harden at different rates, and temperature significantly affects speed. So you may have to experiment a little to find the first time the finish has hardened enough so that the bag doesn’t leave scratches.
The paper bag is rough enough to level most of the dust nibs. Leveling these nibs is not the same as removing them completely. You may still see flaws in a reflected light, but the finish should look significantly smoother.
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