A frequent question that comes up from spray finishers relates to using the correct nozzle, needle and air cap sizes with HVLP turbo spray systems. Finishers are often torn between paint and coating manufacturer recommendations and those recommendations of the HVLP spray equipment manufacturer. Here are my thoughts on this subject to shed some light on the subject.
HVLP manufacturers offer a range of nozzle, needle and air cap sizes and designs. Theoretically and generally recommended is to use a smaller nozzle, needle and air cap with thin or low viscosity coatings and gradually increase the size relative to the viscosity of the coating being sprayed.
By default, most HVLP manufacturers provide a 1.0mm or 1.3mm nozzle/needle combination as these two sizes will often cover a wide range of common fluid viscosities. Some less expensive and lower powered HVLP will provide a 2.0mm nozzle/needle combination as default to compensate for lower atomizing pressures. Recent product testing with various coatings has shown that smaller nozzle/needle combinations tend to provide better atomization and finish results with higher power turbospray systems regardless of fluid viscosity whereas lower powered turbines tend to work better with medium to larger nozzle/needle assemblies.
Since paints and coatings vary widely in their performance sometimes a bit of experimentation will lead you to the best results. Apollo continues to design new air caps to enhance coating atomization, fan pattern size and pair them with proper nozzles and needles for the best results with various paints and coatings in multiple industries.
Speaking with our knowledgeable technical experts can often save a lot of time in resolving your questions in selecting the best combinations for your individual application and the coating you are using. Give us a call.
Here is a link to Apollo Distributors where you can buy your Atomizer.
Glazing is one of the most versatile and valuable and fun techniques a finisher can possess and Greg tells you his technique.
This Month’s Finishing Article, Glaze Basics, by Greg Williams
The occasional table pictured was purchased in the1960’s and is of a dark wood, hand carved in the orient. It was not an expensive piece, and had a rustic charm in the original finish. Sometime later, it was painted white to “match” some wicker furniture in a bedroom.
The white paint obscured the character of the piece, disguising its texture, both in respect of the wood grain and the profile established by the carving. From a short distance, in many lights, it appears as a very plain, almost featureless table other than for its overall size and shape.
Several choices presented themselves; it could be repainted another color, but the carvings would not become much more visible if it was just another solid color. It could be stripped, stained and finished, allowing the wood’s character and color to be highlighted, but stripping the old white paint off would be difficult and time consuming to do properly. Finally, the white could be left on, and the color modified, the carvings emphasized, and even the original hand tooled texture of the wood could be revealed. It would be necessary only to clean the existing surface, determine if that surface was compatible with a clear lacquer,* and apply a glaze, then a topcoat.
Glaze can be thought of as a product as well as a process. The product is usually a liquid or paste, colored with a pigment, which can be applied over a coating or sealer rather than to the bare wood. It can be wiped off selectively, leaving only a haze of color, or left “hanging” in low places in the surface, such as scratches, dents, holes, the lower parts of the profile of moldings, carvings, or other surface detail.
Traditional “oil” glazes used boiled linseed oil as a binder, and a solvent such as mineral oil or naphtha as a reducer. These glazes do not dry hard but become stiff and mechanically attached to the surface on which they are applied. They do not form a solvent bond with the surface, and can be wiped off entirely or partially, leaving color where it is desired. They can be patterned in a number of ways; striated with a stiff brush, dabbed on with a crumpled cloth to form a mottle figure, brushed along existing figure in the wood to emphasize it, or dubbed off corners and edges which may simulate wear, and “struck out” to highlight areas to which we wish to draw attention.
In the case of this table, we decided to use a burnt umber glaze, applied over the existing white paint with a small stiff brush, then wiped with a soft cloth to make sure we forced the glaze into all of the carving and texture of the wood.
After the glaze had dried about 20 minutes, losing its gloss and hazing a bit we wiped most of the glaze off the surface. Additionally we wiped quite hard on outside edges to simulate wear and to highlight those edges. Using a toothbrush, we removed much of the embedded glaze from the deeper carving to avoid darkening the piece too much, and highlighted the centers of the grapes. Finally we “blended” the color with a badger hair blending brush, to soften the effect, avoiding streaking of the glaze.
After several hours further drying, we applied a very light coat (mist coat) of precatalyzed lacquer to the piece, let it dry for about 10 minutes (Approximately 74⁰ F, 35% RH) and applied a full wet coat of the precatalyzed lacquer.
Total working time was about 45 minutes (not including drying time).
Some “dry” glazes have been introduced more recently. You may hear names like “Amazing Glaze”, “Break-Away Glaze”, and “Powder Glaze”. They differ from standard oil glazes in that they dry very quickly, and are wiped off with abrasive pads, steel wool, cloth or brush. They may or may not contain solvents that establish a solvent bond with the sub coat, but are generally easier and faster to use than traditional glazes. Some which don’t bond well with the sub coat must be treated gently to avoid removing too much. They can usually be top coated almost immediately after wiping to color, and generally don’t require locking in with vinyl sealer.
Traditional oil based glazes are tricky to work with in a water based coating system, and water based products are continuing to gain acceptance; so many manufacturers have water based glazes. The water based glazes tend to dry a bit faster than oil glazes, and are not usually removed just by wiping with a cloth, but require an abrasive such as Scotch Brite or steel wool. Practice before committing to an important piece.
A “clean wipe” removes the entire glaze that can be removed without picking into corners, leaving just a haze of color over the paint or stain below, adding interest and depth. Conversely, a heavy glaze on a raised panel door can be wiped quite clean in the center of the panel, and wiped less vigorously toward the edges of the panel for a “sunburst” effect, drawing attention to the lighter center.
The finisher can use 4/0 steel wool or a synthetic abrasive pad to “highlight” areas, such as edges or corners that would have, in use, received more abrasion. The process of removing the glaze in this manner is called “dubbing off.”
Glazing is part of the process of replicating wear patterns on a reproduction piece, or of retaining much of the character of an older piece being refinished, by preserving those wear patterns. Glaze is also used to emphasize the figure of certain woods, or to add interesting pattern to woods such as poplar or basswood that have little visible figure of their own. It is even used on non-wood products such as RTF and embossed hardboard to achieve a “woody” appearance. There are graining tools that can reproduce the look of wood on a piece of painted hardboard by “dragging” through the glaze, removing the glaze from the surface in selected areas.
White or off-white glazes are used to do pickled or whitewashed finishes, and dark glazes over white or very light backgrounds, wiped fairly clean, soften and warm those pieces. A very popular look in furniture, and becoming more prevalent in kitchen cabinets, is a highly physically distressed wood (with simulated cracks, chips, wormholes and fly speck, and even a crackle), all emphasized by one or more applications of glaze. Van Dyke Brown, Burnt Umber, Raw Umber and Black are popular glazing colors for this.
Once the basic pattern desired is established, the surface may be blended with a brush, often an expensive badger hair blender, or other soft-bristled brush, to make the pattern more subtle. The liquid glaze can be sprayed or “flicked” off the bristles of a tooth brush to simulate flyspecking. It can be dabbed onto the surface with a cloth or sponge for a mottled effect, or brushed into reveals on a cabinet door. The glaze remains in cracks, holes and lower grain, emphasizing them. Over a crackle finish the emphasis can be dramatic.
Glaze can also be used to create subtle changes in the color of a piece, much as toning with a colored lacquer would do, but with more control. For instance, a surface can be darkened with a black glaze, wiped clean. The clean wipe does not remove all the color, so an almost undetectable layer of the black glaze remains, darkening the original color without being obvious.
Burnt Umber (the reddish side of brown) and Raw Umber (the greenish side of brown) can be used, respectively, to add richness to a piece, or to neutralize excessive red, as they are complementary to each other.
Glazing is one of the most versatile and valuable, and fun techniques a finisher can possess. Properly used it is an effective way to add value to a finished piece, and helps to distinguish your craft from the ordinary.
Greg Williams 3/16/2016
Q&A from theFinishingStore.com
Q. How many coats of finish do I need to put on wood?
A. It takes at least two coats to create sheen on the wood. The first coat will probably seal the wood. The following coat or coats will create the sheen. After the first two coats it is up to the finisher to decide if he/she wants to do more. Are you planning to sand it with a very fine grit? Does the surface need more protection? Does it need more depth?
Just be sure each coat is dry before the next coat goes on.
Q. I need to apply my finishes outside. Now that spring is here and the weather is getting warmer and the sun is strong, how do I still finish outside.
A. When spraying in direct sunlight the surface of the finish will skim over leaving the underlying finish still soft. The finish can then blister; this is most predominant in solvent base finishes. The surface dries and the air that is trapped in the pores of the wood cannot readily escape.
As the air rises it must now break through the dried film and forms a blister. It is a situation where the direct sunlight is the culprit and being able to shade the surface makes a huge difference.
Another issue as a result of the surface drying rapidly is called “blushing”, particularly in hot humid areas. Again, the moisture is trapped within the finish as with blistering. The solution once again is to shade the surface from direct sunlight. If using compressed air, make sure your air is dry and filtered. Turbine systems are the best solution to ensuring clean dryer air.
Take a Break and Have Some Fun!
See how many words you can find. Look for words horizontally and vertically. You can print this page, including the puzzle, work offline and then highlight words as you find them.