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Which sander should you choose for sanding stairs?
For a staircase you usually need two machines: a random orbit sander for the flat parts of the treads and risers, and a detail sander for the corners and edges. Sand back to bare wood with 80 to 100 grit, then finish with 120 to 180. If the stairs are covered in thick layers of old paint, take most of it off first with paint stripper or a paint scraper.
What will you learn in this article?
- Which sander suits which part of the stairs?
- Sand the stairs or strip them first?
- What do you need to sand stairs?
- Step-by-step: how to sand stairs
- Which grit should you use for stairs?
- Finishing the stairs after sanding
- Common mistakes when sanding stairs
- Frequently asked questions about sanding stairs
- In short: choosing a sander for stairs
Which sander suits which part of the stairs?
A staircase is full of corners, short flat surfaces and edges, so no single machine does everything well.
| Sander | Good for | Less suited to |
|---|---|---|
| Random orbit sander | Flat treads and risers, removing paint and varnish | Tight inside corners |
| Detail (delta) sander | Corners between tread and riser, edges along the wall | Large flat areas (slow going) |
| Multi-sander | Interchangeable pads for corners, edges and spindles | Heavy stripping back to bare wood |
| Orbital (sheet) sander | Light sanding between coats of varnish | Corners |
| Belt sander | Very old, thick coatings on wide treads | Too aggressive for most stairs, quickly leaves dips |
| Drywall sander | Not for stairs | Designed for walls and ceilings |
For most stairs in the home, a random orbit sander plus a detail sander is the most practical pairing. On a staircase you are constantly moving up and down, and the nearest socket is often a long way off. A cordless sander, for example a random orbit or detail sander from the Maxxpack 18V range, saves you running extension leads across the treads. Do check that you can connect the sander to a vacuum cleaner for dust extraction.
Sand the stairs or strip them first?
That depends on what is on the stairs now.
- Clear varnish or oil: you can sand straight away.
- One or two coats of paint: sanding works, but the paper clogs quickly. Use a coarse grit and change the paper often.
- Many thick layers of paint: stripping or scraping first saves a lot of sandpaper and time.
If you use a chemical paint stripper, work in a well-ventilated space, wear chemical-resistant gloves and safety glasses, and follow the instructions on the tin. Leave the stripper to work, scrape the softened paint off, then neutralise or clean the wood as the manufacturer directs. Let the wood dry thoroughly before you start sanding.
Watch out for old paint
If your home was built before the 1960s, the stairs may have been painted with lead paint at some point. Do not dry sand it, and do not remove it with an angle grinder or a heat gun on a high setting. If in doubt, test it first with a lead test kit or have it tested. Asbestos can also turn up in old carpet adhesive or floor coverings on stairs in buildings built or refurbished before 2000. Do not remove suspect residue yourself: have it tested first.
What do you need to sand stairs?
- Random orbit sander and detail sander
- Sandpaper in 80, 120 and 180 grit
- Vacuum cleaner with a hose, ideally connected to the sander
- Paint scraper or filling knife
- Paint stripper and an old brush, if needed
- Wood filler for holes and cracks
- Masking tape and dust sheets or plastic sheeting
- Soft brush and a slightly damp cloth
- FFP2 dust mask, safety glasses, ear defenders and gloves
Step-by-step: how to sand stairs
Strip the stairs bare
Take up any carpet, staples, gripper rods and adhesive residue. Punch any protruding nails below the surface.
Mask off the surroundings
Tape off the walls, skirting boards and the floor at the bottom of the stairs.
Clean and degrease
Clean and degrease the stairs so that grease does not get into the sandpaper and clog it.
Remove old paint if necessary
Take off thick layers of old paint with paint stripper or a scraper first.
Start at the top
Work from the top down. That way you are not constantly walking over finished treads, and the dust falls onto steps you have not sanded yet.
Sand the flat surfaces
On each step, sand the tread first with the random orbit sander and 80 grit, then the riser.
Sand corners and edges
Do the corners and edges with the detail sander.
Fill holes and cracks
Fill holes and cracks with wood filler and let it dry fully.
Sand with finer grits
Go over everything again with 120 grit and then 180 grit. On the final pass, sand with the grain.
Remove all dust
Vacuum the stairs thoroughly and wipe them with a slightly damp cloth.
Which grit should you use for stairs?
- 60 to 80: sanding old paint and thick varnish back to bare wood.
- 100 to 120: removing the scratches left by the coarse grit.
- 150 to 180: the final pass before varnish or oil.
- 220 to 240: light sanding between two coats of varnish.
Do not skip too many grits as you work up. Going straight from 80 to 180 leaves scratches you will only see once the varnish is on.
Finishing the stairs after sanding
Once sanded, the wood is unprotected. Choose a finish that stands up to wear, because stairs take a lot of punishment:
- Stair varnish or floor varnish for a hard, hard-wearing finish. Usually apply two to three coats and sand lightly between coats with fine paper.
- Primer plus a hard-wearing gloss or satin paint if you want painted stairs.
- Hardwax oil for a natural look. This needs touching up more often.
An anti-slip additive in the varnish, or anti-slip strips on the treads, makes the stairs safer, especially with a smooth varnish.
Rags soaked in oil or wood stain can heat up by themselves and catch fire. Let them dry laid out flat, or keep them in a sealed metal tin filled with water.
Common mistakes when sanding stairs
- Using a belt sander, which rounds off or flattens the nosing of the tread unevenly.
- Sanding too long in one spot, especially on veneer or a thin top layer.
- Skipping the corners, which leaves a visible edge of old paint.
- Not removing all the dust before varnishing, so grit ends up in the finish.
- Not wearing a dust mask. Wood dust and old paint particles are bad for your lungs.
Frequently asked questions about sanding stairs
Can I sand stairs with just a detail sander?
You can, but it takes a long time. A detail sander has a small sanding pad and is meant for corners and edges. On the flat treads, a random orbit sander is much faster and gives a more even result.
How long does it take to sand a staircase?
That depends on the number of steps, what is on them and if they need stripping first. A staircase with a clear finish can often be sanded in a day. With thick paint, filler that needs to dry and several coats of varnish, you can easily spend a few days on it.
Should I sand stairs with the grain?
With a random orbit sander the direction matters less, because the pad spins and oscillates at the same time. On the final pass, and when sanding by hand, do work with the grain. That prevents cross-grain scratches that show up after varnishing.
Can I sand stairs with veneer or a thin top layer?
Carefully. Veneer and the top layer on some stairs are very thin. Start with a fine grit, do not use a belt sander and keep checking that you are not going through the top layer.
In short: choosing a sander for stairs
Sand the flat parts of a staircase with a random orbit sander and the corners with a detail sander. Start at 80 grit, work up through 120 to 180 and begin at the top. Strip thick paint first, get old paint or adhesive tested if in doubt, and finish the stairs with a hard-wearing varnish.