" " wisno wood furniture finishing: The common problems in the varnish application..

Wednesday, February 9, 2011

The common problems in the varnish application..

No matter how expert you are there is always possibility to find problem during the process finishing with varnish. The problem in varnish application however is also part of the job as finishing people. The problems sometimes are very situational. Therefore, to solve these problems we should know and consider the circumstances and the condition in the finishing process. There is no such perfect formula to solve the problem since it may depend on the condition and time when the problems come. But, to help to find the solution we may learn for the peoples in the past. 

Here are some common problems that often arise during varnish application.

  • Runs, sags, crawl.
A varnish layer can run, sag or crawl on the surface when it applied. This problem mostly caused since the application is too thick, or could be due to the varnish that too slow dry. To prevent this problem then avoid application of varnish too thick. Apply varnish with normal thickness every time application. If a thick films is needed then apply the varnish in many coat. Apply a layer of varnish; wait until it dry, sand it and re varnish it. Do it many times until we meet the thickness we need.
A sagging varnish layer can be cleaned by cut it and sand it well. Make sure that the layer of varnish is completely dry and always use a sharp cutter and cut it carefully until we obtained a flat surface. Then we have to sand the varnish layer until an even and smooth surface is obtained. Then we can re varnish the surface in the correct way to build the smooth surface.
Crawl can also be caused by oil on the wood surfaces; it is when the varnish does not stick on the surface. If it is happened then we have to wash and clean the varnish layer and repeat the application the varnish. Make sure that the wood surface is clean from some contaminant such oil, wax or other chemical before application of varnish.  Clean the wood surface with acetone or mineral spirit before applies the varnish.

  • Bubble.
This problem is the emergence of the bubbles in the varnish layer. Bubble is usually caused by the application of varnish is too thick or the finishing room that is too hot. Avoid too thick application of the varnish to reduce the risk of bubble. In the hot finishing room the risk of bubbles is higher, so use the less thick varnish and apply it in the rightly layer.  
Bubble has been happening is rather difficult to be handled, but often can be cleaned without having to wash the varnish layer. Wait until the varnish is completely dry, then do a good sanding until the bubble is cut off and cleaned. This is sometimes a bit difficult work since the risk of oversanding. To prevent the oversanding then we have do the sanding to as much as we can but with no oversanding. Then we apply the varnish on it. If the bubble is still there then repeat the process of sanding and varnish application until all the bubble is cleaned.
  • Varnish does not dry.
The varnish is a take quite long time to dry, but the correct material will always dry. If the varnish does not dry, then it is usually caused by the material problem. In the varnish there is an additive to accelerate the drying process called drier (Japan drier). A varnish is not containing drier in the right formula will take a long time to dry. We can add some more drier to the varnish to solve the not dry varnish, but it should be done carefully. It is better if we consult with the supplier to adjust the material to solve this problem
Varnish layer can also take a very long time to dry when the temperature of the room is too cold. The ideal temperature for the application of varnish is between: 70 F to 90 F. If it applied on the room with temperature below 70 F, then drying varnish can take a very long.  Heating the room with a good air circulation can be done to solve this problem.
  • Varnish does not flow
Varnish need a good flow to produce a smooth film layer. Varnish with no good flow will result on the uneven surfaces, the brush marks, orange peel, etc. The flow problem can be caused by the varnish is too thick, or it could be because the varnish is too cold. The varnish that is too cold can be heated to lower its viscosity. Varnish can be heated by heat it with the warm water. Put the varnish cans in the water and then heat the water slowly, the varnish in the tin the will be hot and thin. Do the warming varnish carefully; do not ever heats the varnish by directly object it to the fire. Varnish is a flammable material, when it is subjected to the heat or direct flame, he can burn or explode.  
Also avoid heating the varnish too high temperature, too hot varnish set too quickly off the brush and prevent tipping off. Too high a temperature difference between the varnish and the room temperature will also make the varnish dry too quick and resulting in the imperfect flow.
  • Rough surfaces.
The varnish application usually needs relatively long drying time. If there any dust in the room, then the dust will fall and stick to the wet varnish and produce a rough surface. To make the finishing room is clean and totally free of dust may be is not possible, but we have try as far as possible to minimize the dust problems.
If the varnish application has to be done in a dusty room conditions and rough surface can not be handled in the application, we may consider doing rubbing to the varnish layer when it dry.


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