How to apply the bath to avoid stains in the knot and twisted fibre area

Color spots appear in the knot area or on certain portions where the fiber is twisted. How can I avoid this in the future? This îhis question has generated a lot of comments about the natural beauty of wood, its uniqueness, with many saying that this is the way it should be and this is its charm. This is true, wood has its own personality and for many of us, it is this unique coloration that makes us love it. But there are few people who go out and buy wooden furniture in the store and accept that it has stains and uneven color, no matter what the explanation for it. With mass-produced furniture, today's furniture should look like yesterday's or tomorrow's, even if the wood used (and we're talking about the same species) has differences. Find out what methods are used to avoid stains in problem areas of wood below.

Even if it's a different absorption problem, just sanding doesn't help

Problems when staining wood with wood stain occur because of different absorption. The wood is not properly sanded, not properly sanded, is not well sanded, is bruised, scratched or covered with grease or other substances that prevent absorption. A wood surface that has areas of different absorption will color unevenly. It will absorb different amounts of color into the wood and color differences or stains will occur.

To avoid this wood must be sanded correctlyin steps, with successive granulation. Sand along the grain, abrasives should be chosen according to the wood (hardwood or softwood), the final grain of the sanding paper should not be very fine (max. 180, possibly 220 for very loose wood) and it will release very well at the end. Unfortunately, sanding does not help with natural growth defects such as twisted fiber, crimped fiber, knotted area. Even if properly sanded, the wood will still absorb differently and the area will stand out. Differences can be mitigated by reducing the absorption and subsequently smoothing the varnish film.

An example of uneven staining without improper sanding or defects is the staining of resinous. The effect is particularly visible when the wood is cut tangentially to the annual ring (flanged or cathedral wood). Absorption is very different between latewood and earlywood, and the appearance is mottled in staining, with latewood almost uncolored and earlywood dark. Very seldom is resinous wood left this way, it is generally uniformed later.

Reducing absorption in wood is the safest way to achieve even staining - HOW TO DO IT

In the case of wood with natural defects, the reduction of absorption in the wood will result in a more uniform surface coloration. The disadvantage is the partial loss of the wood's natural pattern, the surface coloration diminishes the natural differences in the wood.

Absorption is reduced by applying a first coat of special materials, called insulators, to the wood before staining. Insulators, like primer or varnish, contain resin which penetrates into the wood and hardens, blocking the penetration of the colorant deep into the wood. The resin content is low so that the sealers do not film. After application and drying, the appearance of the wood is almost unchanged from its original appearance. It must be sanded, but be careful, sanding no longer starts at 60 or 80, but 150 or even 180. The goal is to even out the absorption in the surface layer of wood so that the color settles evenly. There are several types of sealers and they must be compatible with the system used (water-based, solvent-based, UV-cured, polyurethane, etc.).

An improvisation often used in factories is to apply a first coat of primer. This is much more diluted, even 1:1 with the water or solvent used, and applied in a smaller quantity so as not to film. Experience is needed because too much can reduce adhesion to subsequent coats, and too little can be insufficient to prevent different coloration.

The use of color-uniforming materials reduces color differences

In this case, there are two kinds of uniforming materials, some that color uniformly and others that reduce color differences. Uniform coloration is achieved with special coloring baths, also called uniformizing baths. They contain resins which prevent deep absorption and pigments which, in this case, do not dissolve with the solvent to color the wood but float in it and settle on the wood surface. As with the above methods of reducing absorption, the disadvantage is the blurring of the natural design.

The method is often used in factories, even to even out the natural color of wood. You have probably often seen furniture that is said to be natural, i.e. it has the natural color of wood, but is very uniform. It is that way because it has a layer of uniformizing bath. For example, ash wood is first treated with a very light (yellowish-white) evening varnish that reduces the color difference in the grain. The pores are then marked with a patina very close to their natural color. The varnish applied over is very transparent and so the effect is that of wood left in its natural color.

Uniforming materials that reduce color differences are applied between finish coats. These are a different kind of leveling beads, sort of correctors that you use as you go. They make the color of the furniture very uniform in the end so that you can, for example, put table legs on any countertop without any differences. The downside is that the finish loses transparency, with the wood taking a back seat. The same effect is achieved by using colored varnishes, i.e. varnish mixed with a small amount of stain.

Apply the bath by methods that avoid deep absorption

Absorption can also be aided or hindered by the application methods of coloring materials. If the stain is applied in abundance and then the surface is wiped to remove the excess, the wood design will be brought out, with all the differences in the area of natural defects. But if the stain is applied very sparingly, by spraying, it dries on the surface, does not get absorbed, and colors evenly, blurring the defects.

As a general rule of thumb, wiping off the stain will always bring out the natural wood design, while spraying with a stain based on fast volatile solvents (acetone) will even out and fade out the color differences within the wood.

In the case of hand spray application, the way the nozzle opening is adjusted, the air pressure, the mixing of air and the mixture of air and water will lead to different results. If you want low absorption, i.e. uniform staining, the stain must reach the wood surface almost dry. This means smaller particles of wood stain (nozzle as closed as possible), more air in the mixture (quarter or half the stroke) and higher pressure (4-5 atm.).

I hope you find the information useful. As always, additions are welcome. And if you have any questions or queries, please leave them below in the dedicated space. I will be sure to reply.