When to wet sand wood and what are the advantages

Wood sanding is an important part of the finishing process. No matter how good the finishes, varnishes or paints used, without proper sanding, you will not achieve a stain-free, durable and pleasant to the touch surface. By the time it reaches the sanding stage, the wood has already gone through natural or forced drying in kilns and mechanical processing. In the vast majority of cases, sanding is done dry, on the wood as it comes from mechanical processing. There are, however, situations where a slight wetting of the surface is needed to achieve the desired results. What these situations are, how wetting and sanding is done, what the advantages are and when not to use this method, find out below.

What does wet/hot sanding involve

Wet sanding is done to sand the wood more finely, to remove some defects that have occurred during machining or to reduce the amount of dust that results. Very fine sanding of the wood is not always desired because undesirable consequences such as poor adhesion and staining may occur. We have written extensively about these consequences here. Typically, successive dry sanding with 80 and 150 or 120 and 180 grit paper is sufficient to achieve uniformly coloured surfaces and good varnish adhesion.

But there are times when wetting helps lift the fibre for better sanding in difficult areas. Difficult areas in terms of sanding are considered to be those with fibre ends, i.e. milled areas. In the past, factories used to moisten these areas - called churns - with a small amount of water containing a small amount of aracite. The finer sanding of the raised grain and the hardening of the absorbed aracite in the wood limited the absorption of the berry and the staining was more uniform.

Wetting the wood will also reveal any scratches and impressions that may have occurred during mechanical processing. Otherwise invisible, scratches appear after beating and the surface must be sanded to remove them and beaten again. In the case of prints, water can help remove the defect, provided the fibre is clogged, not broken. Simply run an iron a few times over a wet cloth laid over the print and the wood will recover. If the print is deeper, the operation will have to be repeated.

Wetting the wood involves a light sprinkling, like ironing laundry, followed by immediate wiping of the excess with a cloth. A fine water spray system can be used. Another, much safer way is to wipe the surface with a cloth soaked in water and wrung out thoroughly. The wood should not be over-wetted. Too much water can do more harm than good - it attacks the glue, loosens the joints, stains the wood, swells the veneer. In addition, water-soaked wood does not sand well because the sandpaper loads very quickly.

When it is good to wet sand

Here are some of the products whose quality increases when wet sanded:

• shredders end grain,
• the bowls or pens obtained by turning,
• jewelry boxes,
• wood embedded in epoxy resin,
• musical instruments

Choppers need a very fine working surface to be of quality, and this is more difficult to achieve when the fibre ends form the surface. In order for the sanding to be done very well, and for its smoothness to prevent strong absorption, sanding is done with wetting. This results in a much finer sanding than dry sanding.

In the case of turned elements, the fibre ends exist practically all over the surface of the object. The very thin walls of a bowl, for example, need to be very fine, and this smoothness can only be achieved by wet sanding. And the wood that is resin-bonded to form a tabletop or decorative object must also look very fine, and be finely sanded. And in this case wet sanding is the best solution.

Wet sanding is also recommended for exotic wood or wood whose dust may be toxic. Wet sanding greatly reduces the resulting dust, thus reducing the danger of allergies or other side effects for the sander.

When wet sanding is not recommended

There are situations when wet sanding is not the best option, even if the way of obtaining the object or the destination would recommend the method. Here are some of them:

• The object has many joints,
• are cracks in the wood,
• the adhesive used is not waterproof,
• The design of the object allows water to reach areas where wiping is cumbersome or impossible.

Dry sanding is recommended for furniture parts. A very fine sanding can lead to reduced varnish adhesion and bath absorption. In such cases, ordinary sanding with sandpaper up to 220 is sufficient to achieve good results. However, the quality of the abrasive materials is also important. Read more about how to choose them here.

Also, if the exhaustion system is good dust problems disappear and dry sanding can be used.

How to achieve very fine surfaces using water sanding

There are 2 ways to sand using water as an aid. The most commonly used way is moistens the surface, wait a little while for the fibre to rise and become soft, then sand dry with ordinary sandpaper. The waiting time depends on the conditions in the working environment (humidity, temperature, air currents) and can be up to an hour. If the surface is coarse, it is better to sand initially, without wetting, with 120 grit. Then dampen and allow to soak, then sand with 180. Remove the dust and wet again. After polishing, sand with 240. Repeat the operation using paper 280, 320, 360 and 400. A very fine surface with a discreet sheen is obtained.

The second method is the one in which dampens sandpaper. In this case, special water-resistant sandpaper should be used. The paper is moistened in a bowl of water and used wet. The difference with the above method is that the grain of this paper is much finer. Start with 200 grit and continue with 500, 1000, 1500 and so on until the desired fineness is reached. You can go up to 4000, 5000 and even more and the result is a very fine surface whose gloss makes the wood look varnished. The paper must be wet throughout the sanding process. If it appears to have dried out it is put back in a bowl of water for a while. Unlike the other method, this does not produce any dust because it is retained by the sandpaper. This method is often used by wood turners.

In both cases it can be sanded either manually or with hand sanders. In wet sanding, circular sanding is also possible, but when wet paper is used it is recommended to move along the grain. When using wet sanding machines you must ensure that there is no danger of electrocution.

I hope you find the information interesting. If you have used this method to sand wood, please share your experience with us. And if you have any questions or queries, leave them below in the space provided. I will certainly answer them.