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Alternatively, glue and screw string blocks (small rectangular blocks of timber) to the corners of the stairs to secure the treads to the strings. These can be used in addition to the glue blocks to give added strength and rigidity.
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The principle of string blocks is essentially the same as glue blocks, but they are used to fix the ends of the treads to the strings.
The screws are fixed at right angles to each other, one pair boring into the bottom of the tread and the other pair into the string. It is recommended that the blocks are glued then moved back and forth on the surface of the tread and string before screwing to eliminate air pockets in the glue.
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2.
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Replacing Worn Or Missing Wedges.
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If the staircase is built into a housed string system, it most likely contains securing wedges for the risers and treads. These wedges would have been placed in the staircase when it was originally constructed.
They are used to butt the risers and treads up against the mortises of the housed string so that no gaps are visible between the strings and the treads and risers.
The drawing below summaries this:
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Over time and extensive use of the staircase, the wedges can slip or become damaged. This can also lead to the dreaded "creaking" or "squeaking".
A slipped or damaged wedge can normally be spotted if there is a gap showing on the staircase between the tread and/or riser and the string mortise:
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If possible, inspect the rear of the staircase for loose and damaged wedges. Gently remove all damaged wedges with a chisel.
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Inject adhesive into the mortise and coat the replacement wedge with adhesive. Use a mallet to gently drive the wedge into place.
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3.
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Insert Small "Slip" Wedges.
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Another method of effectively tightening the joints between the tread and riser is to insert small "slip" wedges into the joints.
The way in which these wedges are inserted into the joint will depend upon the type of joint that connects the tread and risers.
Each wedge should be about 30mm long and tapered down from 3mm to a point. Apply wood adhesive to the wedge, and insert according to the following joints:
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