Solid wood furniture is highly prized, and some people don't want to have any furniture other than solid wood. Stains, waxes and oils can be used to beautify and protect it, but synthetic varnishes are also used, which are more resistant but more demanding. If certain conditions are not respected, the finish can fail over time, the cause often being independent of the quality of the varnish. Let's take a look at the problems varnish coatings can have on solid wood, what causes them and how they can be avoided or remedied.
Incorrect or incomplete drying of wood leads to varnish film defects
Sometimes on the finished surface of the furniture appearfine cracks along the wood grain. The first reaction is always "it's the lake". Sometimes - quite rarely - the lake can play a part, but in most cases cause is solid wood that has not been thoroughly dried.
To be properly dried solid wood must be left in the kiln, respecting the specific drying time and cycle, until it reaches equilibrium at a moisture content of 8-12% for wood used indoors. This is for forced drying. In the case of natural drying, the timber must be left to dry for at least 9 months in the stack, during which time water is removed from the wood until it reaches equilibrium moisture content.
Forced drying (by increasing the temperature in the kilns or keeping the wood directly in the sun) can cause cracking, but also a differentiated moisture content in the wood, higher inside and lower outside. Over time, the wood will try to balance its moisture, and during this process it will move. If this movement continues after finishing, the varnish will 'feel' it and if it is not elastic enough, fine cracks may appear along the grain throughout the varnished surface.
This is why outdoor varnishes are very elastic, even if this is at the expense of hardness. Outdoors, where the wood should have moisture in the range 14-18%, the possibility of the wood being influenced by the variation in humidity in the atmosphere is much greater. The result is a movement of the wood which, in the absence of an elastic varnish, would lead to cracks in the veneer.
Bad sanding is the cause of many finishing defects
Finishing defects that originate from the correctness with which the wood is prepared before varnish application are lack of adhesion, differential absorptionand tarnished appearance. All this is caused by incorrect sanding of the wood before the finish is applied.Polishing should be done in stages, using increasingly fine sandpaper. Also, the sandpaper should be changed when it gets dusty or when the sandpaper sandpaper starts to fade. If the wood is not sanded well the raised grain is not broken but pressed, forming so-called mirrors. In these areas the wood does not absorb properly, resulting in stains or lack of adhesion.
Defects can also occur due to differential dye uptake in splice areas (straight or finger joints), where there are fibre ends that absorb more dye (even 100 times more). This makes the splice stand out, which is not accepted by everyone. Differential absorption can be avoided by using an isolator before applying dye. A solution may also be to apply a very thin primer, after which the dye is applied.
Poorly chosen construction solutions can also have an effect on the varnish film
Sometimes the constructive solution for wooden doors is to embed a board in a frame. The battens do not need to be glued in place precisely to allow the wood to vary in size if the humidity outside drops or rises. If the skirting were glued to the frame, the system would become very rigid and movement would be much more noticeable, which can lead to cracks in the varnish film. However, it should be borne in mind that in very low humidity (as can happen in winter) the frame may shrink and the previously hidden part may become visible. If it is not finished in the same way as the whole door, that part will stand out. To avoid this the edges of the frame should be stained before it is put into the frame. This is a tip we add to the others about staining, varnishing and painting of wooden doors.
The application technology must be in accordance with the wood used to avoid the appearance of film defects
In the case of large-pored wood such as oak, mahon or nuc, small holes may appear in the film shortly after the furniture has been finished. The phenomenon is also called pore drop. Basically the pores become visible again. If the aim is a very good coating with complete closure of the pores, their rediscovery is not acceptable. "Falling out" can be avoided by using an isolator or hardener varnishes such as polyurethane varnishes. The pore drop phenomenon is especially common when finishing with nitrocellulose materials. Another option would be to apply the first coat of primer very thinly so that the primer "wets" the pores.
![wood pores](https://revistadinlemn.ro/wp-content/uploads/2016/03/pori-inchisipori-deschisi.png)
Solid wood furniture is not as easy to make as derived wood panels and it is not enough to know how to mechanically process wood. You also need to know about wood species and their behaviour over time, their main characteristics and 'weak' points, drying, the influence of humidity and temperature and other such information. This is useful for producing quality furniture that will last for a long time.
If you have any questions or concerns you can leave them in the comments below, and if the topic is helpful to others you can share it.
Hello, I have a question, I have in my house a solid wood cabinet and a solid wood TV table, but they are of different colors because one is made of oak and the other I really don't know. I would like to sand and refinish that furniture and bring them both to the same color. But it should still be the colour of the wood. What steps should I take? (I was saying sanding, bath, then varnish. Is that ok?) it would help me enormously if you could give me some advice. Thank you in advance for your reply.
Good evening.
First of all you should know that if they are made of very different species of wood, for example oak and fir, it will be difficult to make them look alike, because the texture of the wood is different and has a different effect.
To remove the varnish layer you must sand with coarse abrasive sponges or 80 or 100 grit paper, then wipe the surface of the wood with a rag dipped in thinner. You can also try removing the varnish with paint stripper. You can find it at DIY stores like Dedeman, Hornbach, Practiker, BricoDepot, etc. I got some time ago Decanol made by Policolor, but there may be other brands. Apply the substance with a brush and let it work, then remove the soaked layer with a squeegee or scraper. Wipe off afterwards with thinner.
After you have cleaned well and the wood has dried after the thinner apply bait if you want to stain the wood. It will still be visible, but it will have a colour - walnut, cherry, oak - or whatever colour you want. After it dries you can apply clear varnish. Do not apply a thick coat. It is much better to apply 2 thinner coats. Thick coats crack over time. Apply the second coat after the first one has dried.
Good luck!
Hello. Excellent article, thank you.
I have two questions for you:
1. I want to make a bamboo edging that I can knock into the ground to support the difference in level between the flower border and the path. What varnish/type of varnish/other solution do you recommend I use to protect the wood from moisture and eventually rotting, but still maintain the natural colour of the wood?
2. I want to make a table in oak/European walnut for outdoor use, but I mention that it will be placed in a gazebo, protected from rain, but still exposed to temperature and humidity variations in the air and eventually probably to sunlight. And in this case I want to use a varnish/lacquer to keep the natural colour of the wood and highlight the fibres, but I want to get a smooth, dark pore look?
Good evening!
Thanks for your appreciation.
Bamboo wood is more special. Varnish adhesion is low due to the glossy surface and it absorbs hard as it is very dense. For outdoor use these are considered qualities. However, protection is needed for a better resistance.
1. Any product you use (oil, varnish, varnish), if it is totally transparent, does not provide UV protection. It must contain a small amount of pigment (5%). A very good protection against humidity is linseed oil. I would use an oil-based varnish, pine colour, for protection. It is semi-transparent, very bamboo-like in colour and is oil. To increase absorption sand the wood beforehand. You can also use water-based exterior varnish. In this case you have to make sure that the varnish is applied on all sides (including the edges) to prevent water absorption. Apply 2-3 coats.
2. And in this case I would still use oil. Oak, but especially walnut, looks great oiled. But oil does not make a film and does not work the pores. For such a finish you have to use exterior varnish. The ones with the highest resistance are the water-based ones. Apply 2-3 coats according to the instructions. For a smooth, silky sheen, use a 40-50 gloss varnish.
Good luck!
Thank you very much for your advice! Have a nice day!