Why you have to finish your new staircase (and why it is on you)
Written by Scott Jones, The Stair Guys, independent staircase measuring and sourcing specialists·Last updated
A new timber staircase is not finished when it is fitted. It is finished when it is sealed. Skip that, or half do it, and the timber will move, and moving timber is what splits treads and works spindles loose. This is one of the most important things nobody tells you, and it is worth understanding before it costs you.
Timber is alive, and it moves
Wood takes moisture in and gives it back out as the air around it changes, and as it does it swells and shrinks. A finish, whether paint, varnish or oil, slows that moisture exchange right down and keeps the timber stable. Leave it bare and it moves with every damp week and dry week, and that movement is what you see later: split treads, gaps opening up, squeaks, and spindles gone loose in their sockets.
Wet plaster is the worst of it
If your stairs go in and then get plastered around, the bare timber sits there drinking in the moisture from the wet plaster. That is one of the biggest causes of a brand new stair moving. Protect it, get it sealed, and do not leave raw timber sitting next to wet trades.
Seal everything, not just the bits you can see
This is the one even some fitters get wrong. You have to finish every face of the timber, including the underside of the treads, the back of the strings, and the parts nobody will ever look at. If you seal only the top and leave the underside bare, the two faces take on and give off moisture at different rates, and the timber cups and pulls itself out of shape. A stair only stays flat and tight if it is sealed all over, seen and unseen.
Pre-primed is not the same as finished
This one trips people up constantly. A pre-primed stair has a base coat on it, and that is all a primer is: a base for the finish, not the finish itself. Primed timber still needs its final coats of paint before it is actually protected and decorated. Order it primed by all means, but do not mistake primed for done. And if the stair is going to sit around before it is fitted, get a coat of something on it in the meantime, rather than leaving it bare or just primed to soak up whatever moisture is about.
Once the stairs are on site they are like any other piece of furniture: keep them dry, look after them and get them finished, or the consequences are yours, not the maker's. So it is not red tape. Finish it, finish all of it, and do it before the timber has had a chance to drink in the moisture around it. That one job protects everything the stair is made of.
Frequently asked
Do I need to finish or seal a new timber staircase?+
Yes. Bare timber takes moisture in and gives it back out, so it swells and shrinks. That movement splits treads, opens gaps and loosens spindles. A finish of paint, varnish or oil slows the moisture exchange and keeps the stair stable, so a new staircase must be sealed to stay flat and tight.
Whose responsibility is it to finish a new staircase?+
The customer's. Finishing is done on site and is written into almost every manufacturer's terms. If a bare stair moves and splits, it is not a warranty claim, because finishing it, the one thing that would have prevented it, was never done.
Is a pre-primed staircase ready to use?+
No. A primer is only a base coat, not the finish. A pre-primed stair still needs its final coats of paint before it is properly protected. If it is going to sit around before fitting, get a coat on it rather than leaving it primed to soak up moisture.
Why do you have to seal the underside of stair treads?+
Because if you seal only the visible faces and leave the undersides bare, the two sides take on and give off moisture at different rates. That uneven movement makes the timber cup and pull out of shape. Sealing every face, seen and unseen, is what keeps a stair flat.
Related guides
- Cladding an existing staircase in oak: what the kits do and when they workOak stair cladding covers an existing staircase with oak tread and riser boards and a thickened nosing, for the look of a solid oak stair without replacing it. It works well on a straight, closed-string stair, but it adds to the step dimensions and struggles on open strings and winders.
- How to modernise an old staircase without replacing itYou can update most of an old staircase without ripping it out: change the spindles, swap the handrail and newel caps, clad the treads, or paint and strip back. Which of those is cosmetic and which needs building control depends on whether you change the shape of the stair, not just the look.
Ready when you are.
Free and no obligation. The Stair Guys survey the real space, never off a plan.