Finishing a new staircase: whose job it is

Supply, fit and finish are three different things. You can buy one, two or all three, and the mistake almost everybody makes is assuming that buying the first two gets them the third. It does not. Worse, a lot of firms do not offer finishing at all, so on many jobs there was never a box to tick in the first place, and the reader who assumed it was covered finds out months later.

So a staircase is normally supplied bare. Finishing it is a separate job, it happens on site once the stair is fitted, and unless your order explicitly says finishing is included, it is yours to arrange and yours to pay for. Check your paperwork rather than assume, because the moment to find out is not the moment the timber has already moved.

None of that is a manufacturer being awkward. A stair leaves the workshop as bare timber because the fitting itself involves cutting, scribing and fixing, and a finish applied before all that would be damaged by it. But "it happens later" quietly becomes "nobody did it", and that is where the trouble starts.

It is worth being straight about how this usually plays out, because it is one of the most common things a customer will blame their maker or their fitter for. In fairness to the trade, it is not a stitch-up. You agree to terms and conditions with most firms, that is entirely normal, and the finishing position is usually written into them. So it is a position you accepted rather than one that was sprung on you, which is exactly why the time to read them is before you sign and not after the timber has moved.

Where firms differ is how easy they make that. Our own terms sit on the quote itself rather than in a separate document, so the price and the conditions arrive in the same place and you can see what you are agreeing to while you are deciding. Ask for terms up front if they are not in front of you.

The argument itself is not really the point anyway. By the time anyone is having it, the timber has already moved, and no outcome to that conversation puts a twisted string back straight. See what a good fit looks like for the fitting side of the same job.

Why bare timber does not stay still

Timber is not inert. It takes moisture in and gives it back out with the air around it, and it changes size as it does so. A finish does not stop that completely, but it slows the exchange down enough that the timber moves gently and evenly instead of quickly and unevenly. Leave it bare and it warps, twists and splits. A staircase that went in straight can be out of true within weeks if nothing is sealing it.

Where the moisture actually comes from

People picture a leak or a wet winter. On a new stair it is almost always the plastering. Plastering puts a very large amount of water into a house, and it goes into the air before it goes anywhere else. Bare timber sitting in that air will absorb it. By the time the walls look dry and everyone has moved on, the damage to an unfinished staircase is already done, and it is done in a way you cannot undo by finishing it afterwards.

The faces nobody finishes

Most people finish what they can see and stop there. That is the mistake, because the faces that matter most for movement are the ones that disappear.

• The underside of the treads. Out of sight under the stair, so nobody thinks about it, and it is the face most exposed to damp air. On anything that is not MDF, this one is not optional.
• The wall side of the wall strings. Do it before the string goes tight against the wall. Once it is fixed and the wall is plastered you cannot reach it at all, and that is exactly when the moisture arrives.

Where MDF is different, and where it is not

MDF is the exception on tread undersides, and it is worth being precise about why. It does not have the make-up of traditional timber, so it does not take moisture up and move the way a solid or laminated timber component does. That is the whole of the exception.

It is not a claim that MDF is safe. Some grades are moisture resistant, which is not the same as waterproof. Throw a bucket of water over an MDF tread and it is ruined, and no finish applied afterwards will bring it back. Moisture is a staircase's worst enemy whatever it is made of, and there is no maker of stairs who can protect you from that.

Pre-primed is not finished

If your stair arrived pre-primed, that is worth having, but read it for what it is. A primer is a base layer. It is there to be coated over, and it is not a finish in its own right. On its own it will not hold moisture out of the timber for long.

There is a second reason it does not get you off the hook, and it is the one people miss. A primed stair stops being fully coated the moment it is fitted, because fitting means cutting. Strings get trimmed, treads and risers get cut in, parts get scribed to walls that are never quite square. Every one of those cuts is fresh bare timber, exposed on site, after the priming was done. So a pre-primed staircase still needs finishing, and it needs it most in the places the fitting has just created.

What it looks like when it has not been done

Most stair timber is laminated, which is to say built up from pieces glued together rather than cut from one solid section. That changes how it fails. When a laminated component takes up moisture and moves, it tends to give way on the glue line, so what you get is a split running along a joint rather than a crack wandering across the grain.

Oak brings a second problem, and this one is for anyone still working above the stair rather than for the finish itself. Water marks on oak are hard to get out. Get plaster on it and it goes black, and at that point it is close to impossible to shift. If work is carrying on overhead, cover the stair. That is a separate job from finishing it and it does not replace finishing it, but a stair can be ruined by either.

When to do it

There are two ways to do this properly, and either is fine:

• Finish it before fitting, then finish again afterwards to cover everything the fitting has cut.
• Or finish it as soon as possible after fitting.

As soon as possible means a matter of days. Not weeks, and not months. The longer a stair sits bare the more likely you are to have a problem, and the clock is really running once the plasterer arrives.

The tread undersides are the ones to be strict about, and not only because they are the most exposed. They are the hardest thing to put right later. Once the underside of the stair has been boarded and plastered, getting back to a damaged tread means taking the plasterboard off first, and changing a tread or a riser is not a straightforward job even once you can reach it. An hour with a brush at the right moment turns into a small building project at the wrong one.

Which finish you use is a separate question, and it is a real choice rather than a detail: oils and hardwax oils penetrate and can be spot-repaired, films like varnish and lacquer are tougher day to day but wear through at the nosings. See oils, varnishes and lacquers compared. Whichever you pick, the rule on this page does not change. It needs doing, it needs doing on the faces you cannot see, and it needs doing before the plasterer.

So read the terms you are agreeing to, because the finishing position will usually be in them, and go in knowing the onus is on you. That is not a warning about a bill. It is a warning about a staircase you have already paid for quietly going out of shape while everybody assumes somebody else is dealing with it.