" " wisno wood furniture finishing: How to spray stain to the wood furniture

Monday, September 26, 2011

How to spray stain to the wood furniture


spray stain

Stain is a finishing material that is used to make color of the finishing. Failure in the stain application will affect the resulting color of the finishing. The uneven stain will produce an uneven color, while the wrong stain will make the wrong color. In the modern finishing industry, most of stain is applied by spray. With the right technique, the application stain by spray will produce the best coloring results. The spray application will give an even color staining with high speed and high flexibility adjustment. By spray we can control the thickness of the stain layer.  Nevertheless, the proper technique and good preparation is needed to produce good results.

There are several things that must be considered in spraying stain.
  • The sanding at the unfinished wood.
Sanding the wood is very important factor that will greatly affect the staining result. The purpose of sanding is to produce a clean, even and smooth wood surface. The sanding process should be started with the coarse grade followed by finer grade sandpaper until a smooth surface is obtained. The final sanding for the unfinished wood should be end up with a 180 or 240 sandpaper. The sanding with coarser grade sandpaper will leave scratch marks that will appear in the finishing looked. While the sanding with finer grade is also not recommended since it will tend to polish the wood surface and producing too smooth but uneven surface that would interfere the absorption of stain. Too smooth sandpaper sanding will make the wood is too slick, and make the stain is not well absorbed by the wood. Finally the uneven coloration or blotchy stain is resulted.
The stain absorption by the wood will be highly influenced by the porosity of the wood surface, since  that we need to make the wood surface has uniform porosity. The porosity problem is rarely happen at the hardwood such as: oak, mahogany, teak, etcWith the proper sanding process a uniform, even, smooth wood surface will easily obtained. But for some soft wood such as: sengon, maple or pine, porosity could be problem and more intention should be done at the sanding process. We may need to do "glue sizing" to produce the even and smooth wood surface.
More about wood sanding can be viewed in our previous article: how to sand the wood  furniture
  • The basic color of the wood
In wood finish, the final color is always determined by two things: the color of stain and the color of the wood base. The final finishing color is the combination of the wood base color and the color of the stain layered on. The color of wood is already exists and cannot be changed. The stain color is the adjustable factor to produce the desired color finishing. To get the required color then we have to find the right stain color to obtain the final color. The proper stain color is the key to get the right finishing color. To find the right stain color we can use the "color wheel diagram"
But
usually we meet the furniture product that has uneven base color. Wood is a natural substrate from the live creature, its character is highly depend on how the condition when he was alive. The most common problem is the color variation. Its color may vary from the sap wood to the heartwood, or there may be some red part or blue stain partly at the wood surface. The uneven wood base color will result to the uneven color of the finishing. To overcome this problem we need to do some treatment to the wood.  If the variation that is not too contrast, we can adjust the wood base color with sap stains and equalizer stains. The wood with light color is darken with sap stain, whereas some small disturbing such as: light red color or blue stain colors are covered with equalizer stain. The adjustment wood base color with sap stain equalizer stain work when the color variation is not too contrast.  If the difference is too contrast then we may need to bleach the wood to get the even color.
See our previous article:  how to match color in the wood finishing
  • Preparation of stain.
The right stain color is essential. Make sure that we use the correct stain color to match the final finishing color. We can use the triangular color diagram theory to find the right stain color. Check the physical properties of the wood stain and make sure it is in the good condition.
If there is any slurry then we need to stir the stain to let all pigments in it perfectly mixed. View and check the appearance of stain, make sure that the stain in the uniform liquid mixture. If there is dirt or sediment then it should be filtered.

  • The spray equipment
The proper spray equipment is needed to get the optimum result. There are many type of spray gun and not every type is suitable to spray the stain. The air spray gun is the most appropriate equipment to the stain application. The air spray gun can produce stain layering with the perfect atomization and has the most flexibility at the adjustment. The HVLP spray gun can also be used, it can produce good atomization stain with higher efficiency, but it  has a lower flexibility. The airless is not recommended to spray stain, the L.V.L.P spray gun could be okay but the best choice is the air spray gun.
Make sure that the equipment function properly. Choose the nozzle size that suits your needs. Nozzle size varies from each brand, but essentially we need to choose the nozzle size that is big enough to produce a sufficient spray width according to the product.

  • Spray techniques
The stain should coat the wood evenly.  To do that we need a proper spray technique. A skillful operator is needed to do the proper spraying technique. Set the spray gun correctly, the volume of material, the air pressure and width spray should be adjusted according to the wood surface. Make sure that a perfect material atomization is obtained.  
Then the correct movement of the spray gun is needed to get the even and wet spray coat of the stain. The spray technique should also be conducted with due regard to the form of the furniture product. The complicated form product such as: chair, leg and carved form product is quite difficult to be sprayed but the form will hide some imperfectness staining. While the flat panels let the spray gun can be moved more freely, but if there some unevenness at the stain layering, then it will obviously appeared. 
To see more about spraying technique you can go to this link: How to use spray gun correctly 1 and : how to use spray gun 2

  • Layering with clear coating 
The wood stain layer is always followed by clear coating application. Some layer of sealer and top coat is needed to protect the stain and produce the smooth finish. Before it is coated with clear coating the stain is still very easily to be wiped off. The removal stain that has been coated with clear coating will be more difficult. Since that we better check the stain before it is layered with clear coating.  Check the staining result, make sure the stain is even with the right color before apply clear coat on it.
For small color problem we can remove the stain with steel wool or sandpaper. If the problem is too big then we may need to wash the stain layer with  thinner .
If the
staining is properly done; the even stain layer with the right color is obtained then we can continue the process with the clear coating application.  
Make sure that the stain is dry before
layered with a clear coating. Usually the wood stain is a  thin material that will be dry within a few minutes. But there could be some special stains that require longer drying time. Read the specification of the stain and make sure that follow the stain specification. 

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