Wood staining - recommendations for a stain-free look

Although there are opinions that say that wood should be used uncoloured, the charm being its natural colourMostly we find it coloured, from natural shades of walnut or pine to the most unusual colours. It is also preferred because the colour brings out its natural design much better. But staining wood is not a simple operation. Wood is an inhomogeneous and anisotropic material, with different properties from species to species, within the same species and even within the same piece of wood depending on the orientation of the grain. This makes achieving a uniform, stain-free stain quite a difficult task. But not impossible.

Why stains appear when staining

The main cause of staining is the different absorption of colour in the wood. It happens because of the quality of the wood or the way it is processed before staining. If we refer to the quality of the wood we are talking about its density, how easily it absorbs the staining solution, resin or tannin content or growth defects (knots, twisted fibre). That is, a wood like poplarFast-growing and very lanky, it absorbs colour quickly and differently and spots can appear very easily. Oak but it is dense and harder which makes for even absorption and stain-free staining.

Related to processing is the important way the wood is cut and sanded. Clean cuts, without jagged or jagged edges, made with sharp quality tools, make for a more even absorption. Sanding is one of the most important processes for the final appearance of the product. Uniform colouring, adhesion of the varnish, and a pleasant tint to the film depend on how much attention has been paid to sanding. I consider sanding so important to achieving a quality end product that I put it at the top of my recommendations for stain-free wood staining.

1. Sanding wood before staining is very important for stain-free staining

Sanding smoothes out those ends of the grain that result when cutting wood. It is through these fibres that food enters the tree before it is cut. This is why the penetration of colour here is natural and if not controlled can lead to staining.

Sanding is first done with sandpaper or coarse abrasive sponges - grit size 80-100. Then you move on to finer grit to give that pleasing tuft. On hardwood - oak, frasin, fag - The finer grit is considered 150, sufficient to achieve a quality surface. If the wood is soft, loose and uneven - poplar, lime, arineven molid - 180 or 220 grit is needed to "soften" the stained fibre and achieve the most uniform colouring.

Sanding also removes any adhesive or grease stains (greasy fingerprints from food or products used in production) or fine scratches. If these areas are not sanded, stains will appear after staining. On wood they are not visible before staining. Sanding, however, removes them and thus removes the risk of stains.

Don't ignore this step if you want to get a quality product. The more time you spend at this stage, the better the colouring and later the finishing will be. More information on white sanding can also be found at here.

2. Choose the staining solution taking into account the wood essence

It may seem strange, but not all wood species behave the same when treated with a particular type of stain solution. For example, oak and beech are both hard, high-density species. However, when treated with a staining solution made from pitch and white spirit (P43 - famous decades ago) behaves completely differently. While oak stains beautifully and evenly the wood on beech, no matter how well it is sanded, will be full of stains. That's why a little research into the staining behaviour of wood can save you a lot of trouble.

Staining solutions (baths) can be water-based or solvent-based, with or without added resin, made from soluble dyes or pigments. Although, generally speaking, each has its own type of behaviour (pigments even out, stains bring out the natural pattern, etc.) interaction with wood can produce surprises. This is because wood contains tannins, resins, dyes and many salts that can influence staining and absorption in wood. This is why in factories, tests are always carried out with the chosen wood stain on the wood that will be used in production. In this way the behaviour of the wood can be seen and the wood stain adjusted as required.

A few "tips" on staining wood:

• Water-based stains penetrate deeper into the wood and are more likely to stain. But the colours are more vivid and the natural pattern better highlighted;
• Solvent-based baths behave differently depending on the solvent mixture used. They can be juggled more easily by making them dry faster or slower or penetrate more or less into the wood. Everything is adjusted by varying the proportion of solvents in the thinner mixture;
• a stain made with acetone is evened out, staining only the surface of the wood (acetone evaporates very quickly);
• acetone and ethyl alcohol (technical alcohol) are miscible with water. You can speed up the drying of water-based baths by replacing some of the dilution water with acetone or alcohol.

Regardless of the type of wood, always check on a small area for compatibility with the wood used. You can only see what it looks like when the wood is completely dry and coated with varnish (or primer). These reveal defects, even those that are less visible.

3. Choose an application method that allows greater control of the amount applied

Stains occur mainly as a result of the absorption of the staining solution into the wood. If in one place the wood can absorb more colour in that place it will stain. If the stain loaded brush is placed directly on the wood without reducing the amount by wiping the edge of the container, a dark stain will appear there. That's why controlling the amount applied can reduce the risk of staining.

In factories, staining is best controlled when applied by spray gun. Spraying starts outside the staining surface and ends outside the staining surface, so as not to deposit more or less colour. You can adjust the amount coming out of the gun so that a certain amount/m² is applied. The staining will be more even and stains will only appear if the wood is not well prepared in white.

Trafaletus also allows fairly good control of the amount applied. The choice of the type of material that coats the drum is important. In the case of sponges, these can be of different qualities. The smaller the quantity incorporated or the more controlled the quantity released, the more uniform the colouring will be.

When staining with brush, cloth or sponge care must be taken that they are not put loaded with solution on the wood because a stain will appear there. They are always wrung out first. Put the entire piece of wood into the flush jar and squeeze it out. Do not soak it only partially because over time it will accumulate more and more colour which it will transfer to the wood, the colour being lighter at the beginning and darker at the end.

Whatever the method, do not partially overlap the colour layers because a stain will appear there. That is, do not go twice with a brush, a charcoal, a trowel, a gun over a portion where the wood has already absorbed colour and has become a little faded. There the wood will absorb double and the area will be darker.

4. Blocking deep absorption when wood is soft and absorbs unevenly

There are situations where no matter how careful we are with the application, no matter how well we control the amount applied, stains still appear because the wood is too soft, too loose and uneven. In this case the solution is to keep the colour as close to the surface as possible so that the wood has as little influence as possible.

We saw above that one way to do this is the use of baths based on rapidly volatile solvents, i.e. acetone. When applied with a spray gun, the wood is almost dry and the stain is very uniform. The disadvantage is that the natural pattern of the wood is less emphasised and, above all, the working environment becomes very difficult to handle because of the solvent.

Another method is "thickening" the bath so it's harder to absorb. It can be done by adding resin to the berry. A simple method is to add nitro varnish (primer) to simple solvent-based varnishes or water-soluble varnish (primer) to water-based ones. Compatibility should be checked beforehand by mixing small quantities. Do not add a very large amount because it turns into a coloured varnish which can give a plastic look to the wood.

Tot de primer we can use to create a barrier in the way of the berry. The primer (varnish) to be used is diluted 50, even 100% and applied to the wood before staining. It does not need to film. After drying sand the wood again and apply the stain. Absorption will be less and the staining more uniform and stain free, but lighter in colour. For a darker stain use a more concentrated stain or apply 2 coats of stain.

Areas where there are fibre ends and absorption is high (milling or turning) can be blocked with a diluted aracite solution (arachnid in water). The solution will be absorbed, harden and block the fibre. It should not be thick and filmy. After drying and before applying the wood stain, sand the wood white.

5. Use smoothing solutions

If, however, the staining is uneven and there are spots on the surface of the wood, but they are not very noticeable, the defect can be reduced by using methods to even out the colour. This method is very common in furniture factories, but it is not complicated and can be used for smaller projects or even diy projects.

The levelling can be done with a stain solution similar to the one used to stain the wood, but more diluted, which is applied in a very thin layer on the stained surface or after the first coat of primer. The solution should be solvent-based, preferably acetone-based. The coat should be very thin so as not to change the colour (the evenness will darken the original colour a little) and not to affect the adhesion of subsequent coats (if applied over the primer coat). The layer over which the levelling coat is applied must not be sanded to avoid altering the colour.

Another way to even out is by lightly staining the first coat of primer. In this case, too, the addition of colour should be small so as not to change the colour too much and give the finish a plastic look. To be added to the primer the bath must be of the same nature. That is to say, in solvent-based primer, solvent-based and in water-based primer, water-based. Be careful, not all of them are compatible even if they have the same nature. That's why a test should be done beforehand.

Wood staining is an important step and if it is not done well the whole project can be ruined. I've always said that wood is very important, but what sells furniture (or other wooden objects) is the design and finish. Furniture made from the best wood, even if it has an attractive design will not be bought if it is full of stains.

On the other hand, we have to learn that wood is a special material with a personality that we cannot always tame. But that's its charm. A wood that absorbs differently and has a less than uniform final appearance can be much more appreciated and desirable than one whose uniformity can be considered monotonous. I'm not talking about ugly stains, but about the appearance of wood that absorbs more on one side and less on the other. It is its signature that we must learn to respect.