5 finishing tips to avoid rough and rough surfaces

It is not enough to use quality products to achieve smooth wood surfaces that do not scratch to the touch. How the wood is prepared, how the primer or varnish is applied and sanded, how the dilution is done, the dust in the area where the varnish is applied are all factors that influence the quality of the film. Medium quality varnishes can be used, but by sanding the wood and primer correctly and applying the finish with a suitable trowel, brush or gun, very good quality surfaces can be achieved. Varnishes and primers, no matter how good they are, cannot work wonders.

Recently, someone asked me, describing the whole process of refinishing an old solid oak floor, why the result was a surface that was unpleasant to the touch and scratchy. The answer may be useful to others, so here are a few tips that can help you achieve smooth surfaces with a pleasing tuft.

1. Sand the wood properly before applying wood stain or primer/lacquer

Wood sanding is essential to achieve quality surfaces. I say it over and over again every chance I get. Don't neglect this step because it will pay off later and it will be much harder to fix defects.

Sanding raw wood is done in stages. Ideally, 3 sanding levels should be used, but if this is not possible and the wood is fairly well processed, it can also be sanded using a single grain. But it must be done painstakingly and thoroughly, without missing any corners or profiles. To identify defects more easily, the surface can be moistened before sanding (wet sanding). It can be done with solvent or water. If water is used, the surface should only be wiped with a wrung-out cloth to avoid increasing the moisture content of the wood.

Use specific wood grain. Don't go for very fine grain, usually used for varnish, because you won't get the desired result. On the contrary, other problems will arise, which you will find described at length here. Use as final grain 150 for hardwood (oak) and 180 for softer wood (plop, brad).

Sanding is done to remove defects and to bring the fibre ends resulting from the flow to a common denominator. This ensures uniform absorption, no stains and good adhesion to the substrate.

2. Always sand after the first coat of primer or varnish applied

After the first layer that makes the film, sanding must be done to remove the raised wood grain. The wood is not sanded after application but only after it has been coated with a primer/lacquer. This first coat must be absorbed by the wood for the film to adhere. During absorption the ends of the fibre lift up, are "coated" with varnish and dry out so becoming very unpleasant to the touch. The better the sanding of the wood has been done the smaller the raised fibre is and the easier it is to remove by sanding.

Sanding the first coat of primer or varnish is made with sandpaper with a grain min.240. Sanding with a coarser paper (below 240) will remove a large amount of primer or varnish. This leads to losses and increased costs. Another drawback is that the curl from sanding with coarse paper becomes visible on the final film.

As with sanding wood, the sanding of primer must be done with care and attention. This is the stage when varnish-laden wood grain is removed. Later it will be harder to remove because each layer will deposit a new amount on the raised grain and make it harder and harder to re-sand. You will have to use coarser paper and end up with the above problems. If this step is done well and no problems occur later when applying the final coat of varnish, you will get a quality surface.

3. Dilute primer and varnish as directed. Do not apply thick coats

Don't apply thick coats hoping to finish faster because problems will occur:

• the first coat will not be well absorbed into the wood and adhesion problems will occur (the film will peel off the wood when knocked and scratched, giving the appearance of broken glass or bleaching);
• the air embedded in the film does not come out much heavier. The coating will dry on the surface and block the air inside. The film will get unpleasant "wrinkles" that can only be removed by sanding;
• a thick layer may not be well spread and may dry with bumps. In order for the final film to look good the surface will need to be sanded well to get a smooth appearance again;
• thick coats obtained in one application run the risk of cracking over time. The same thickness must be obtained from several thin coats for the film to be elastic and resistant over time.

Both DIY and professional products have indications on labels or datasheets about the dilution percentage. Don't think you are saving money by removing thinner. The problems that can arise will make you spend a lot more.

4. Use application tools/appliances that will trap as little air as possible in the film

Primer or varnish can be applied with a brush or trowel for DIY applications, or with a spray gun or other more advanced technology for professional applications. In most cases, more or less air gets into the film. The more there is, the harder it will be to get out before the film hardens and thus those wrinkles I mentioned above will appear.

For DIY applications I recommend using hard sponge pads so that as little air as possible comes out when pressed. If you use brushes, buy soft ones that are easy to handle. Don't get very thick brushes because the risk of bringing more air into the film increases. If you use simple compressor pressure guns, don't increase the pressure to get a strong jet. You'll feel like you're working faster, but the final quality will suffer. Gassing occurs and you will have to sand again and again to get a nice surface.

For professional applications I recommend using Airmix or Airless. The air supply is very low and the appearance of the film is much better compared to a conventional application.

5. Work in the cleanest possible premises with the least amount of dust

Dust is the enemy of the lake. After applying varnish, it takes some time for the film to dry on the surface. This time is even referred to as dust drying. During this period dust from the atmosphere that has fallen on the film is absorbed and the unpleasant appearance and scratchy effect to the touch occurs. Especially when mechanical processing is carried out nearby and the dust in the atmosphere is wood dust, which is much coarser than that normally found in the air.

Work in areas separate from mechanical processing areas or after the area has been cleaned and dust and sawdust removed. Finally water the floor - dust will be attracted to the wet surface.

If at the end, after the last coat, there are still dust particles stuck to the surface of the film, you can remove them by polishing (polishingPolishing should be done on the whole surface because it can change the gloss (the polished area can become shinier).

I hope you find the above information useful. If you find it useful to others, you can share it. And if you have any questions, additions or concerns, please leave them in the space below.