How to Repair Stairs
The most common problem with stairs is that they creak. However, they may also suffer from physical damage and from missing parts, especially beneath the treads. The ease with which stairs may be repaired will depend partly on whether you have access to the underside. In some cases, plaster or boards may conceal it, which means working only from above.
How stairs are built
The flat parts of stairs that you walk on are called treads; the vertical sections connecting them are called risers. Treads and risers are joined to one another by various means: butt joints, housing joints or tongued-and-grooved joints. Both treads and risers are joined to the side timbers (strings) by butt joints if the strings are “open”, that is shaped to follow the line of the treads and risers, or by housing joints if the strings are “closed”, that is having parallel sides. The housing joints in closed strings are reinforced by long, thin glued-in wedges, while in both cases the joint between the front of each tread and the riser below is usually reinforced by small glued-in triangular blocks.
Blocks
Reinforcing blocks can work loose, and some may be missing altogether. If blocks are missing, you can make new ones by cutting diagonally down through a piece of 50mm (2in) square timber. When fitting new blocks, or refitting old ones, screw them to both tread and riser as well as applying wood adhesive. With an existing loose block, it may be possible to prise open the joint to squeeze in some adhesive.
Wedges
Tapered wedges are used to hold the risers and treads firmly in closed strings, but with age, the wedges may become loose. It is best to remove all loose wedges so that you can clean them and the grooves they fit in of all traces of old glue. If any wedges are missing, make replacements by cutting tapered strips from a piece of timber cut to length, using an old wedge as a guide.
Apply glue to the wedge and its groove, then hammer the vertical wedges home first, followed by the horizontal ones, which should make contact with the vertical wedges at the bottom.
Securing treads
If the joint between the back of a tread and the riser above is loose, you can insert reinforcing screws from below, through the back of the tread into the bottom of the riser. Where access to the underside is impossible, reinforce this joint from above with a couple of L-shaped brackets recessed into the back of the tread and the front of the riser. Make the recesses slightly deeper than the thickness of the brackets and screw them in place.
If the joint between the front of a tread and the riser below is loose, and you cannot get below to reglue the blocks and/or wedges, you can reinforce the joint with screws. Drill pilot holes down through the tread into the riser, making sure they are centred in the riser, and enlarge the holes in the tread to clearance size before driving countersunk screws through the tread into the riser.
If possible, prise the joint apart with a bolster (stonecutter’s) chisel, brush out any dirt and squeeze in some glue before screwing the joint together.