![]() ![]() ![]() These instructions are very clear on the need to let a coat dry for 3 to 4 hours before lightly sanding the entire surface with 220 grit sandpaper. Here’s an extract from the Minwax technical data sheet relating to their Fast-drying Polyurethane 550 VOC. Oil-based polyurethanes are less fussy regarding when to apply the next coat, but most will require sanding between coats. If you apply the next coat within the 2 to 24-hour time, the drying coat can still merge with it, creating a good bond. These then begin hardening off when they come into contact with the air.Īfter 24 hours, the surface hardness and gloss have progressed to a stage that compromises adhesion with a further coat of polyurethane. First, the water-based carrier liquid evaporates, leaving behind the urethane resins. The reason behind this relates to the curing process that polyurethane undergoes once applied. However, if you miss the 24-hour window, you must lightly sand the coat with 220 grit sandpaper before applying the next coat. If you observe this drying time, no sanding is required. Take a look at the following instruction from a Minwax technical data sheet relating to their water-based polyurethane, Ultimate Floor Finish.īefore recoating, the instructions advise you to let your coats dry for at least two hours, but less than 24 hours. However, a lot depends on your timing for recoats. As a general rule, you can get away without sanding between coats when using water-based products. #Rejex wait between coats how toRelated: How to Fix Common Polyurethane Mistakes Do all types of polyurethane require sanding between coats? While some people suggest that using a foam brush helps, this only assists in reducing brush marks, it does nothing for the other sources of surface contamination and defects. By the time you’ve applied three coats and failed to sand between each, the surface finish is rough when you run your hand over it, with a lower quality appearance. As wet coats of polyurethane dry, they pick up dust from the atmosphere, and bubbles or small imperfections develop. The surface finish will also be of lower quality. Instead of achieving a surface life of four to five years, you will find yourself reapplying the polyurethane in 12 to 18 months. Once your surface is in use and exposed to temperature and humidity changes, the layers will begin to delaminate, separating and flaking off in patches, making the surface rough, and look unsightly while removing the surface protection. Instead of the coats combining, each dries independently, creating layers. If you fail to sand polyurethane that requires it, you will compromise the adhesion between the coats. What happens if you don’t sand between coats Giving each intermediate coat a light sand smooths the surface in preparation for the next coat and avoids locking in defects that detract from the final finish. Sanding between coats also removes brush marks, bubbles, dust, and surface imperfections on the previous coat. The surface protection is compromised, and your project will look unsightly. Over time, the layers will begin flaking off with expansion, contraction, and use. If the new coat does not integrate and stick to the old coat, you won’t get the life you expect from the surface finish. ![]() When recoating polyurethane, you want to ensure maximum adhesion between the coats. ![]() There are two reasons you might sand polyurethane between coats. Why sanding between coats of polyurethane is necessary However, aside from the technical aspects, you should consider sanding between coats for aesthetic reasons. Most manufacturers of oil-based polyurethanes do require sanding between coats. Some manufacturers of water-based polyurethanes do not require sanding between coats, as long as you observe specific recoating times. The answer depends on the manufacturer and type of polyurethane you are using. Do you have to sand between coats of polyurethane? ![]()
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