" " wisno wood furniture finishing: Spraying the shellac.

Monday, April 25, 2011

Spraying the shellac.

Shellac is a finishing material that is widely used since the year 1800's. Shellac is the traditional finishing materials that can provide protection to the wood substrate. At this era Shellac used to be very popular because it can produce finishes that produce a thick film and a high gloss finish. One of shellac finish that was famous is the French varnish, a finishing with a layer of thick film and high gloss that is very special in that era. Now the similar finish looked with french varnish can be obtained easier by using the coating such: as NC or PU coating.
Shellac is a finishing material that is used when the spray technology still not been used for finishing application. The shellac traditionally is applied by padding or brushed. Until now  many peoples still apply shellac with brush or rag.  But with the development in the finishing technology, now more people prefer to apply shellac by spray.  With spray application we can better do control of the shellac application. Spray shellac principally is about the same with spray the lacquer or other clear coating. What we need to do is to adjust the shellac to fit with the spray gun requirement. We also need to understand the character of shellac is little bit different with other clear coating.





                                                       shellac wood finish



The shellac application by spray.
  • Prepare the shellac
Shellac is mostly traded in the flakes  form and its must be reconstituted into liquid form when it is applied. Put the pieces of shellac into alcohol and stir it until it is all dissolved to form a viscous liquid.  Shellac solution may contain dirt ingredients settle to the bottom of the can.  Separate the unsolved solid compound with the liquid shellac. Filter the liquid shellac and check the viscosity. Make sure the viscosity of fluids is accordance with the standard viscosity of the spraying equipment.  For the air spray,  the viscosity should be about 10 to 14 seconds with the NK 2 cups, or 16-21 seconds with Zahn cup No. 2.  (see our previous post: The viscosity of finishing material)
Choose the
proper shellac according with the desired color.  Shellac will build a yellow brown film color. If we want to finish in white or light color, then the bleach shellac is needed.  Consider the finish color resulted with the shellac, make some color panel to make sure we can identifies the finishing resulted.
Use the dewaxed shellac since it can provide a better film. The wax in the shellac is helping in the padding application, but in the spray application this wax is not needed.
  • Preparation on the unfinished wood.
The wood that will be coated with shellac must be well prepared. Make sure it has been sanded properly and has even and smooth surface. Fill the every holes and gap if any. We also can apply filler to fill the wood with big pores and grain.
Consider the finish color and the basic color of the wood. Shellac will more act as a film former. Although shellac is also form color, but the color produced is relatively limited. Then we may need to staining the wood to make a certain finish color. If the wood base color is not even, we need to adjust it with equalizer stain and sap stain.
  • Prepare the equipment and facilities.
The spray applications require a spray gun and its supporting tools. Prepare the spray gun, compressor and its accessories. The spray process is always leave the dust spray, so it should be done in finishing with spray booth to suck the dust. Wear the personal protection equipment sch as mask, gloves, eye protector and work pack when we spray this material.
  • Spraying shellac
Spraying shellac technically is the same with the spray technique for the other coating material. Spray shellac with wet spray technique to coat the wood. Set the spray gun properly and move the gun consistently to get the even wet coat. (See our previous post: How to spray correctly) Spray shellac 1 layer coat,  and let the shellac layer about 30 minutes to dry.  The first layer always leave rough surface since the raised wood fibers. Sand the shellac layer to cut the wood fibers. Then re spray the shellac as the first application. Repeat the shellac application until we meet the desired finishing looked. To make a high gloss finish we need a thick film that can be achieved with 3 or 4 times application of shellac.  

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