When it comes to refinishing wood, polyurethane is one of the most popular choices. It’s an easy-to-use option that is perfect for beginners and experts alike. However, knowing how to sand the existing coating of polyurethane or other finishes properly can make all the difference in achieving a beautiful finish. To help you learn more about this process, we’ve put together an article with everything you need to know about sanding polyurethane or other finishes, before refinishing!
1) Sand Your Work Piece
First, you’ll need to determine the best way to prep your workpiece. There are a few different methods for this, and it will depend on what type of finish you want. For instance, if you’re working with wood that has been polyurethaned, lacquered or varnished previously, most experts recommend sanding first with 60 grit paper before moving to finer grits. If you want a glossy finish, it’s best to sand with 180 or 220 grit paper after thoroughly cleaning the surface of any residual grease/polish.
Always sand in the direction of the wood grain, never against. You can see the grain when the paint or finish is sanded from the wood surface or the beginning when the existing finish keeps the grain visible as done by water-based poly or acrylic.
2. Remove Dust after Sanding
Dust is a key enemy of any finish at any stage. They cause an unsmooth finish and lead it to be less sticking to woods. When you sand woods already coated with a finish, dust must be there and you have to essentially remove that before recoating. An air compressor to blow off or a floor brush to brush the dust may still result in an unsmooth or wet finish (for a long time).
Use a bristle attachment added to a vacuum cleaner to capture all the dust safely. Using a damp cloth to wipe the dust is also effective, but you might wipe more than once for better results. However, make sure there is no dust before recoating.
Here you will find the most efficient dust collection system for woodworking and bristle attachments.
3) Apply Stain and Polyurethane
Next, you’ll want to apply stain and polyurethane. The first step is staining the wood with a paste or liquid finish that matches its color. Once the surface has been treated in this way for about 20 minutes, you should lightly sand again with 60 grit paper to remove any excess residue from your workpiece.
4) Sand Again Before Putting On the Final Polish
You’ll want to apply a polyurethane finish by brushing on two or three coats. It would be best if you waited at least an hour before applying your first coat. The secret is that this will allow it to dry and give off fewer fumes and leave a smoother surface for subsequent layers of polyurethane to adhere to.
Once that’s dry, you should sand the first coat lightly with 100 grit paper to remove any excess residue and then begin applying the second layer of polyurethane. You will want to wait at least an hour before applying your third and final layer of finish after this one has dried.
Is There Any Way Other than Manual Sanding?
There are automatic machines used to remove the existing finish, for instance, buffers, that help you get rid of manual sanding. You can use any of them for steps 2 and 4. However, we suggest using a buffer only for the 2nd step, where you entirely remove the existing finish, no matter that’s polyurethane, varnish, lacquer, paint or anything else. Sanding for the 4th step should be mild, and the use of hand and sandpaper is better there. Last but not least, use such a sanding device only if the wood is wider enough, for example, a floor or deck. Smaller or trickier surfaces like cabinets or tables should be very carefully sanded by machine while refinishing.
However, how to sand with a machine?
- Put on a dust mask before starting sanding.
- Stick a buffing pad to your buffer.
- Move the buffer from one side to the other across your floor in the grain direction. Every course should be overlapped by 6 inches.
- As you go, the existing finish will turn to powder. Check the area covered and continue buffering with an interval every 5 minutes to vacuum or wipe the dust.
You may check a list of compatible floor buffers.
If you want to ensure a beautiful, rich refinish on your project that will last for years to come, then you should follow these steps of sanding and recoating.