Can I efficiently brush polyurethane without bubble formation? This is a daunting question to many while doing the varnishing work. The appearance of bubbles interferes with the general outlook of a wooden surface. Therefore, avoiding them from the first place is the key. As you do the brushing, employ much care on every inch.
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You stand a chance of reducing the bubble development by avoiding much turbulence in the application process. The spraying of the finishes perfectly deals with this as compared to the brushing work. Even so, the spreading of polyurethane can be game-changing when you do it smoothly. It curbs the chances of trapping air films in between the varnishes. Remember to use some medium to high grit sandpapers for the sanding work.
Before the application of the polyurethane, prepare the wooden surface well. Most old wood at times has rough surfaces which require some leveling. Sanding every inch makes you create a proper runaway for the finishes. Start by the low-grit sandpapers as they are coarser thus get deep into the surface well.
As you progress, use higher-grit papers such as 120-grit and 180-grit. This smoothen the surfaces well. Afterward, do the wiping of the wood dust. It may be a nice idea to use an air compressor here. Brushing polyurethane at such a surface minimizes the chances of bubble formation in a great way.
In-Between Coats Sanding
After successfully applying the first coat of polyurethane, the battle is not over yet. The bubbles can develop from the consequent layers to make. It is therefore necessary to remember the sanding procedure each time you brush a film of the finish. Give enough time for the dry-up of every coat before adding another.
Each time you do the scrubbing of a layer, let it be followed by a proper wiping of rub offs. This removes any particle which may be stuck in the films hence interfere with the whole project. I find the use of two clean clothes for the whole wiping being significant. Going for a paper towel or dampened rag is a wonderful idea.
Most finishes are thick as you open them in the cans. As much as this is helpful in the coating of surfaces, there is a downside to it. Smearing thick polyurethane maximizes the possibility of puddling, running, and bubbling. Therefore, the trick is to not apply one thick layer at once but rather several thin coats on a surface.
Thinning the polyurethane in the ratio of three to one may work well for anyone against bubbling on the varnishes. For oil-based polyurethane, the mineral spirit needs to be your pick. Water will serve you well if the finish is water-based. What you need is to be gentle with the mixing to avoid trapping air into the mixture. From the thinning, you make the spreading of the finish easy thus scrapping off the chance of bubbling.
Brushing polyurethane on a wood surface is at times faced with drawbacks such as bubbling. The good thing is that one can be safe from this by being gentle with the spreading. Before then, prepare the wooden surface well through sanding work. Make the polyurethane possess the right thickness by adding solvents in the right proportions.
Here is an article which will help you decide what can work for you between Spar Urethrane and Polyurethrane.