First-fix setting out for four hotel bathrooms
Four identical bathrooms in a Galle hotel are being renovated. The architect's plan dimensions pipe centres from the finished wall face: the 110 mm WC outlet is 350 mm from the finished wall and 1,000 mm above finished floor level (FFL); the vanity hot and cold supplies are 600 mm above FFL and 150 mm apart. The blockwork is not yet built. The setting-out drawing locates the finished wall face 200 mm from grid line B. The floor build-up is 50 mm screed plus 10 mm tile; the wall finish is 12 mm tile on 100 mm blockwork. A foreman marks the WC pipe centre 300 mm from grid line B and 1,000 mm above the structural slab, saying 'the tiler will adjust'. The first-fix inspection is tomorrow and the pipe brackets are already fixed. The plumber has a laser level, a 5 m tape and a story pole, but no approved setting-out schedule.
1. Calculate the correct setting-out dimensions from grid line B and from the structural slab for the WC outlet and the vanity supplies. Show each build-up.
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Grid line B to finished wall face = 200 mm. WC centre from finished wall = 350 mm, so from grid B = 200 + 350 = 550 mm. The foreman's 300 mm from grid B is 250 mm short; with the finished wall at 200 mm from the grid, it would put the pipe only 100 mm from the wall, which is wrong. If measuring from the blockwork face instead, remember the 12 mm tile: blockwork face to WC centre = 350 + 12 = 362 mm.
Vertically, FFL = structural slab + 50 mm screed + 10 mm tile = +60 mm. WC outlet = 1,000 mm above FFL = 1,060 mm above structural slab; the foreman's 1,000 mm is 60 mm low. Vanity supplies = 600 mm above FFL = 660 mm above structural slab. The hot and cold centres remain 150 mm apart, but check whether the drawing dimensions are to pipe centres or finished valve centres; if to finished fittings, allow for the valve body and tile. Set a datum at FFL and mark all rooms from grid B, not from blockwork, so tiling tolerances do not accumulate.
2. The brackets are already fixed. Describe how you would verify and correct the work before tomorrow's inspection, and what you would record.
Read the worked answer
Set up the laser on a stable datum and establish FFL at 60 mm above the structural slab in each bathroom; mark grid B on the slab and on a story pole. Measure the existing WC centre from grid B: if it is 300 mm, the error is 250 mm. Check whether the bracket holes can be relocated without weakening the wall, or whether the pipes can be offset with approved bends; do not bend the pipe sharply. Reset the WC outlet to 1,060 mm above slab and the vanity supplies to 660 mm. If pipes are already embedded or bracketed, use 45° offsets or re-fix brackets, maintaining fall and support. Check the hot and cold spacing and level.
Record the original and corrected dimensions, the drawing and revision used, the FFL calculation, the date and time, and who approved the correction. Photograph the corrected setting-out with the tape or laser visible. Do not rely on the tiler to correct a 60 mm vertical error; tiles cannot correct a wrong pipe centre without damaging waterproofing.