Stairs receive a lot of wear over time. Risers can become loose or cracked and require repair. The risers support the front edge of the stair treads. They can be tightened and reinforced by installing a wooden block on the underside of the staircase. It is important to maintain your stairs in order to keep them in safe condition. A loose or cracked riser can compromise the stability of the stairs and also lead to further damage, in particular to the stair tread above it.
Measure the length of the broken stair riser on the underside of the stairs using a tape measure.
Place the board on a work surface. Mark the length of the broken riser onto the board using a tape measure and pencil.
Rest the board with the 75 by 1220 mm (3 by 48 inch) side flat on the table of a mitre saw with the 25 by 1220 mm (1 by 48 inch) edge flush against the fence. Slide the board along the table until the pencil mark is at the edge of the blade. Guide the saw through the board in a steady motion to cut the board to length.
Fit the 75 mm (3 inch) wide side of the board flat against broken riser. The top edge should be tight against the stair tread above the riser. The board should fit snugly in place between the stringers on either end of the riser.
Drive wood screws every 75 to 150 mm (3 to 6 inches) through the board into the back side of the riser to reinforce the riser with a screw gun.
Apply wood glue to any cracks in the front face of the riser. Wipe most of the excess glue off with your finger. Sand the remaining glue into the surface of the crack with a fine-grit sanding block. The glue will mix with the dust left from sanding to fill the crack. Because the back side of the riser is reinforced, the crack will not reappear. Sand until the surface is smooth and the crack is filled.
Touch up the sanded area of the riser with a matching wood finish using a paintbrush. Allow the repaired riser to dry for 24 hours before use.
Maintain your stairs regularly to keep them in safe condition.
Wear eye protection when operating a screw gun and when sanding.