Preparation and Application – A Good Finish Requires BothPosted on April 12th, 2011 No comments
Preparation is a huge part of finishing. Failing to prepare the wood will surely lead to a bad finish no matter how good your equipment or coating. So let’s talk first about sanding.
You must start with a completely dry piece of wood. If you have stripped it, let it dry, preferably overnight. Then give the wood a light sanding. We suggest 180-grit sandpaper, or any grit up to a 220 will work just fine. Anything finer will affect the ability of the stain to penetrate into the wood, especially on closed-grain woods such as maple, cherry, etc. Even if you don’t plan on using a stain, you want a little texture on the surface to promote the adhesion of your sealer or finish coats.
My personal preference is for white colored papers. The Free Cut or No-Fill by Norton or 3M are just a couple of examples. The black, wet-dry papers in similar grits are acceptable but are more costly. Any other brands of the silicone carbide papers (white colored) will work just fine. Some of the new sponge block type sanders are also among of my favorites and are available in all grits. Sometimes these sponge blocks are not labeled by grit but are sold as “fine” or “extra fine.” The blocks are handy as they are easy to hold and will flex in your hand so that you are less likely to sand through the patina on the edges. They will conform to the contours on spindles and curved surfaces. No matter what you use, you absolutely must sand with the grain whenever possible.
Next step is to remove all sanding dust before applying finish. This can be done with an air nozzle on the hose from your air compressor or shop-vac, but you must be careful not to get any oil or water blown from the compressor. My favorite method is to attach the new Blow Off Tool by Apollo to the air hose of my HVLP turbine. This handy tool replaces the air blow off tool that you use with your air compressor. The only difference is that this air tool runs from your turbine system so you will be assured of always having warm, dry air that is free from the contamination typically found in many air compressor lines. This is also handy in cleaning off my workbench, power tools, and also for blowing any sanding and sawdust off my clothes before leaving my shop. I prefer my turbine for this task as it is a gentler stream of air and doesn’t raise such a cloud of dust. It uses less power too.
The hardest, and often the most tedious, part of finishing is proper preparation. Again, if the above steps aren’t followed, your end results could turn out less than satisfactory. Once your piece is “squeaky clean” you can begin the finishing process. We strongly urge you to do a little testing before jumping into the entire project. If you plan to use a stain, do a small color test on the bottom of a chair, inside of a drawer or bottom of table top. Always allow the stain to dry for an hour if it is a water based or overnight if it is oil-based. Then apply a little of the topcoat that you plan to use to make sure it has the proper sheen. This is critical with a water base finishing system as you don’t see the final color and sheen until you have applied a coat or two of the topcoat. To save time I usually rub on a thin coat of finish with my finger if it is water based, or with a rag or brush if it is not. This will dry in 15 to 20 minutes and then you can brush or wipe on a second coat. The stain and final complexion and appearance of the finished wood will then be visible for your approval. If you do this, you will never be disappointed with the final results. When applying topcoat, closely follow the manufacturers application instructions listed on the labels or in their application guides.
We will cover all of the various applications of finish techniques in future articles and will also cover the often-misunderstood “hybrid” methods of using both oil-based and water-based products on the same project. A helpful hint: if for any reason you have problems with the finish sticking or having any imperfections such a “fish-eyes” or poor adhesion, I suggest a coat of de-waxed shellac to lock in any residual surface contamination left on the piece from stripping. This could include waxes from furniture polishes or silicones from the modern spray can furniture polishes.
Today’s water-based coatings are much more tolerant of these finishing gremlins than their solvent- based predecessors, but they still don’t like any oily substance left on the piece, especially petroleum based products.