Finishing a wooden staircase: oil, hardwax oil, varnish and lacquer

Once you have chosen the timber, the finish decides how the stair looks, how it wears and how easy it is to live with. This is about clear and natural finishes on bare timber, oils, hardwax oils, varnishes and lacquers. If you are painting the stair, the material underneath is a different question, covered in painting your stairs.

Oils and hardwax oils

An oil, or a hardwax oil, soaks into the timber rather than sitting on top of it. The look is natural and matt to low-sheen, close to the raw wood. The big practical advantage on a staircase is repair: because there is no film, a worn patch or a scuffed nosing can be cleaned and re-oiled locally without stripping the whole flight, and it blends in. The trade-off is that oils need occasional recoating in the busy areas to keep their protection up, so they ask for a little upkeep rather than none.

Varnishes and lacquers

A varnish or lacquer builds a film on the surface, and it can be had in anything from matt to high gloss. A good film is tough and needs less frequent attention day to day. The catch is what happens when it does wear. Stairs wear hardest at the front edge of the tread, the nosing, and once a film wears through there you cannot simply patch it invisibly: the repair shows as a line, and doing it properly means sanding back and recoating the whole tread or flight. So a film is lower maintenance until the day it is not, when it is a bigger job than topping up an oil.

Slip: measured, not assumed

Slip is the part people worry about and the part most often talked about loosely, so here is how it actually works. In the UK, slip resistance is measured with a pendulum test that gives a Pendulum Test Value (PTV): broadly, a PTV of 36 or above is treated as low slip potential, 25 to 35 as moderate and below 25 as high, tested in the relevant wet or contaminated condition, and a higher value is expected on stairs and on routes used by the frail or elderly.

The important point is that this is a property of the finished surface in use, not of the finish out of the tin. No oil or lacquer has a fixed slip rating you can quote for your stair, because it depends on the actual surface once it is applied, worn, cleaned and, on a stair, sometimes dusty underfoot. What can be said fairly is that smooth high-gloss films tend to feel more slippery, especially when wet or dusty, and that a matt oil, a little surface texture, or added grip such as anti-slip stair nosings and a runner all help. If slip really matters on a particular stair, the honest answer is to have the finished tread pendulum tested, not to trust a number on a label. Ratings you may see on flooring products, the R9 to R13 scale, come from a different German oil-ramp test and do not convert reliably into a PTV.

Colour, ambering and site versus factory

Two last things worth knowing. First, colour shift: oil-based finishes and some lacquers amber over time, warming and yellowing the wood, which flatters oak but can surprise you on a pale timber like ash or maple; waterborne finishes stay closer to the raw colour. Second, where it is done. A stair finished in the workshop, in clean, controlled conditions, usually comes out more even than one brush-finished on site in a dusty house with people walking past. Site finishing is sometimes unavoidable, but a factory finish is one less thing left to chance. See also what a good fit looks like.