Sanding Between Coats of Polyurethane: Is it Necessary?

By MWB-Team •  Updated: 06/10/23 • 

Polyurethane is a durable finish with heat-, water-, solvent-, and scratch-resistance. Poly is a film-building finish, meaning multiple coats must be applied to the wood for better protection. When applying each coat of polyurethane, it is usually advised to sand the previous coat before applying a new coat.

In this article, we’ll discuss why you need to sand between the coats of polyurethane, which sandpaper grit to use, how to sand, and lastly, how to sand the last coat of polyurethane.

However, although it is not a must, sanding between coats of polyurethane removes dust nibs that might have settled as the finish dries, removes blemishes, smoothes the surface, and improves the adhesion of the next coat to the previous one.

Sandpaper Grit for Sanding Poly Coats

When sanding coats of poly, you need to use a fine sandpaper to avoid leaving larger and more visible scratch marks showing after applying the next coat. After sanding the first coat, you can use finer sandpaper grits on the other coats.

After applying the first coat of polyurethane and it has dried, you can use #320 grit sandpaper to sand it smooth. This will eliminate most surface imperfections, such as brush marks and other surface imperfections. The first coat should be sanded properly so that the other coats go on smoothly.

For the other coats, you can progressively use finer sandpaper grits. From #320 grit, you can move on to #400 grit on the next and #600 grit on the other coat. Check out our guide on sandpaper grits for an informative reading.

How to Sand Between Coats of Polyurethane

Polishing the Final Coat of Poly

For the final coat, you can wet sand the polyurethane to get a smoother finish and a higher sheen. However, unlike the other coats of polyurethane, you’ll have to wait for the finish to fully cure. Curing time is usually longer than drying time and means the finish has undergone all the chemical processes and is not ready to be used.

Once the polyurethane has fully cured, wet sand using finer sandpaper grit or steel wool for a higher sheen. Wet sanding involves using a lubricant like mineral oil or soapy water to polish the surface to a smoother and desired sheen. Check out our guide on polishing polyurethane for an informative read on how to do it.

MWB-Team

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