Fitting stair treads

The difference looks small, but it changes how the staircase looks, how the work is done and how good the base has to be. Decide before you order the treads, because the joiner sets the nosing overhang and the shape of the front edge based on that choice.

• Fitting stair treads (this item) suits an open staircase on a steel spine or stringers, where there is open space between the treads. It also suits a concrete staircase where the vertical faces get a different finish: plaster and paint, ceramic tiles or a skim coat.
• Fitting stair treads with risers is the choice when you want the whole staircase in timber, including the vertical faces. The joiner then has to deal with the joint between tread and riser, the fitting order, and more careful preparation of the concrete faces.
• The nosing overhang matters more on treads without risers. The front edge either covers the top of the concrete face or, on an open staircase, forms the only visible edge. So it has to be even along the whole flight.
• The concrete faces stay visible with this item. If they are crooked or chipped, repair them before fitting. Once the tread is in place, they are much harder to put right.
• Time on site is shorter with treads alone, because there is no measuring, cutting and gluing of risers. On an open staircase, though, each tread takes extra time to set exactly on the spine.

In practice: if you have a concrete staircase and already know you want timber on the vertical faces too, order the version with risers straight away. Adding risers later under treads that are already glued down is fiddly, and the result is rarely as clean.

The method depends on what the tread sits on. At the survey, the joiner asks about the base first and only then about the timber.

Concrete staircase

This is the most common case in houses. A cast concrete staircase carries the load by itself, and the timber tread is only a cladding. It is glued down over its full area with a flexible adhesive and sometimes also secured with anchors. The advantage is that the tread feels solid and does not creak. The drawback is that concrete is never perfectly accurate. Steps tend to vary in height and depth and are rarely quite level.

Steel spine stringer

This can be a central spine, often called a mono stringer, or two steel side stringers. Here the tread carries the load, so it must be thick enough for its span and for what the maker of the steelwork specifies. It is screwed on from below through steel plates, often with a flexible pad that dampens footstep noise and stops creaking. The holes in the plates and in the timber must line up exactly, or the tread ends up skewed.

Timber strings

Treads are either housed into grooves in the strings or sit on top of them. A staircase like this is usually made as a complete unit in the workshop, and fitting the treads is part of assembling it. Fitting treads as a separate job mainly comes up when worn treads are replaced on an older timber staircase.

Cantilevered treads fixed into the wall

These treads look as if they float out of the wall. Each tread carries its full load from the wall alone, so this needs concealed anchors, a loadbearing wall and structural calculations. It is not ordinary cladding work. A firm with a structural design should carry it out. If the wall is not loadbearing or is built from lightweight blocks, this solution may not be possible at all.

If the staircase is being built new or its structure is changing, the job is no longer just cladding. Check with your local building authority what local building regulations require for the change. In a block of flats, a shared staircase is not altered without the consent of the building management or owners' association.

Most problems with treads start before fitting, when the trades are not properly coordinated. Before the survey and fitting, the following should be true:

• The concrete is dry. A fresh concrete staircase needs time. It keeps giving off moisture for weeks. Timber glued to a damp base swells and warps, and the adhesive may not hold. The joiner will usually measure the moisture. The required value comes from the adhesive manufacturer.
• Plastering is finished and dry. Wet trades indoors raise the air humidity, and timber absorbs it. Treads go in after plastering and screeding.
• The floors at top and bottom are known. More precisely, you know the finished floor level at both ends of the staircase. After fitting, the first and last steps must be the same height as all the others. If the floor is still to be laid, the joiner needs the exact build-up of the floor, not a guess.
• The electrician has done the first fix. If you want LED step lighting, cables and boxes must be in the wall or the concrete before fitting. A qualified electrician does the electrical connection, not the joiner.
• The balustrade is agreed. Whoever makes the balustrade needs to know whether it fixes into the tread, into the concrete face or into the wall. Fixing through a finished timber tread has to be planned so the holes go in the right places.
• The concrete faces are repaired. With this item they stay visible. The plasterer or tiler either prepares them beforehand, or it is agreed that they will be finished after the treads, with the timber protected.
• The space is accessible. There must be power on site, room to cut, and no other trades using the stairs during fitting and while the adhesive cures.

Measuring and templates

On a concrete staircase, each step is measured separately. The joiner measures the length at the back and the front, the depth at both ends and the height of every step. For winders on a turn, templates are made from card or thin plywood, because the wall angle and the shape of the step change from one to the next. The treads are numbered from the bottom up so they do not get mixed up.

On an open staircase on a spine, the joiner checks the spacing of the plates, their height and whether they are flat. If a plate is bent, a metalworker corrects it. The joiner should not pack it out.

Levelling the heights

Why does this matter so much? Your foot gets used to the rhythm of a staircase within two steps. If one step is higher or lower by even a few millimetres, people easily trip on it. So the joiner evens out the differences in the concrete. Low steps are built up with levelling mortar or a thicker bed of adhesive, as far as the adhesive allows. Larger differences call for adjustable packers or packing boards. The aim is for every finished tread to have the same height and depth.

Preparing the base

The concrete is cleaned of dust and leftover plaster and mortar, and sanded if needed. Then it gets a primer that matches the adhesive system. Adhesive does not hold on a greasy, dusty or crumbly surface.

Setting the tread

Each tread is first tried dry. The joiner checks that the length fits, the gap at the wall is right and the overhang is even. A movement gap of roughly 3 to 5 mm is left at the wall so the timber can move. Then a flexible adhesive, usually polyurethane or MS polymer based, goes onto the concrete with a notched trowel. It covers the full area or goes on in close beads, depending on the manufacturer. The tread is laid in, levelled with a spirit level and weighted down until the adhesive grabs. On an open staircase, the tread sits on the plates with a pad and is levelled. Then it is screwed from below with screws of the right length so they do not break through the top.

How long it takes

A joiner can usually fit a straight flight with prepared treads in one to two days. Winders, uneven concrete and making templates add time. According to the manufacturer, the adhesive usually needs roughly 24 hours before you can walk on the treads carefully, and full loading comes later. If the treads are oiled or lacquered on site, add drying time for each coat.

Timber species

Treads are commonly made from oak, beech and ash, less often walnut or pine. Oak is hard, durable and copes well with everyday wear. Beech is hard but more sensitive to changes in humidity and moves more. Softwoods such as pine dent easily, so they suit less used stairs, for example to a loft.

Laminated or solid

Most treads are made as laminated panels from glued staves. The staves either run the full length of the tread or are finger jointed. Full-length staves look calmer. Finger jointed staves are a little cheaper to produce and look busier. Both are strong if well made and if the timber has a moisture content of roughly 8 to 10 %.

Thickness

On concrete, treads are usually around 30 to 40 mm thick. On an open staircase, the tread carries the load and the thickness depends on the span between supports, often around 40 to 60 mm. Here the maker of the structure decides, not the look.

Front edge and slip resistance

Without a riser, the front edge is more visible than on the version with risers. It is usually rounded or chamfered, because a sharp edge chips easily. You can have anti-slip grooves routed into the front of the tread or insert an anti-slip strip. This is worth it mainly on oiled surfaces and in homes with children or older people.

Surface finish

Oil brings out the grain, looks natural and can be repaired in patches. It does need renewing as it wears. Lacquer forms a tougher film and is easier to clean, but damage means sanding the whole tread. It helps to have the treads finished in the workshop, so only the last coat, or nothing, is done on site.

This item is priced per tread, so how demanding each tread is affects the whole job. It goes faster and more simply when:

• The staircase is straight and all treads have the same shape
• The concrete is accurate, dry and without large height differences
• The treads arrive finished, cut to size and surface treated
• The finished floor levels are known, so the first and last steps do not need sorting out later
• On an open staircase, the spine plates are accurately placed

The work takes longer and becomes harder with:

• Winders on a turn or a spiral staircase, where every tread has a different shape
• Uneven side walls that have to be scribed onto the tread
• Uneven concrete that has to be levelled step by step
• A staircase open on both sides, where the tread ends are visible and must be perfectly finished
• Extra cut-outs for balustrade posts, lighting or the transition to a landing
• Tight access, for example a narrow staircase in an old house, where long treads are hard to handle

• Gluing onto damp concrete. The timber swells, and treads lift at the edges or crack. This often shows only after the first heating season.
• Spot gluing instead of full bedding. Hollows remain under the tread, it sounds drummy underfoot and starts creaking over time.
• No movement gap at the wall. When the humidity changes, the timber pushes against the wall. The plaster cracks or the tread bows.
• First or last step at a different height. This is the most common coordination mistake with the floor fitter. People trip on such a step, and it is very hard to fix afterwards.
• Uneven overhang. Without risers this shows at once. Seen from below, the line of front edges wanders.
• Timber directly on steel without a pad. Wood on steel creaks when you walk on it and carries noise through the whole house.
• Screws too long or the wrong drill size. A screw tip or a crack around the screw appears on the walking surface.
• Large gaps between treads on an open staircase. With small children in the house, open space between treads can be dangerous. Building regulations often limit the size of this gap, so check what applies locally. The usual fix is an extra bar or infill, not a riser.

If you have a straight concrete staircase, treads made to measure and experience with precise work, you can do the cladding yourself. Leave open staircases on a spine, cantilevered treads and staircases with winders to a joiner. Those depend on load-bearing capacity and accuracy that is hard to correct later. Step lighting must be connected by a qualified electrician.

1. Measure the moisture of the concrete, or have it measured, and wait until it meets the adhesive manufacturer's requirement.
2. Measure the height and depth of every step and note the differences, including the finished floor levels at top and bottom.
3. Clean the concrete of dust and mortar residue, grind down high spots and fill low areas with a suitable mortar.
4. Prime the base to suit the adhesive system and let it dry.
5. Try each tread dry and check the gap at the wall and the overhang of the front edge.
6. Start at the bottom step and spread adhesive over the full area with a notched trowel.
7. Lay the tread, level it with a spirit level in both directions and check its height against the step below.
8. Weight the tread down, for example with bags or weights, and remove squeezed-out adhesive before it sets.
9. Work upwards and keep off the stairs for the curing time stated by the manufacturer.
10. Fill the gaps at the wall with flexible sealant in the colour of the timber or the wall, and finish the concrete faces.

Walk up and down the finished staircase several times slowly, then at a normal pace. Your foot should not hesitate anywhere. At handover, check:

• All steps have the same height, including the first and last relative to the finished floor
• All treads have the same depth and an even nosing overhang along the whole flight
• Treads are level in both directions, checked with a spirit level
• No tread moves, sounds hollow or creaks when you walk on it
• Movement gaps at the wall are neatly filled with sealant
• Surfaces are clean, with no adhesive residue, scratches or dented edges
• On an open staircase, screws are tight, pads are in place on the plates and no screw tips break through
• Fixing points for the balustrade are prepared as agreed
• You have received details of the adhesive, timber species and surface finish, including care instructions