Granite Shower Curb Dimensions: You Measure the Finished Height, the Factory Cuts the Blank
Granite shower curb dimensions are three numbers, not one: section height, section width and length. The one buyers get wrong is height — the tape on site reads the finished face above the tile, while the factory needs the blank that still includes the depth buried in the mortar. Most projects sit at 15–25mm visible, 100–150mm wide, with length taken from the tiled opening less a joint at each end; glass-door curbs go to 40–50mm visible. That is trade practice, not a mandatory standard.
Granite shower curb dimensions: which of the three numbers do you fix first?
Granite shower curb dimensions are not one number but three, and each is settled by a different thing: section height runs vertically, section width runs front to back, length runs along the opening. Trade practice puts the visible height at 15–25mm, the section at 100–150mm and the length at the clear opening after tiling, less a joint at each end. Those are conventions, not mandatory figures, so every one of them still has to be derived from your floor build-up and your glass fixing. Where a glass door hangs, the visible height goes to 40–50mm, which is still practice rather than a standard; sections 5 and 6 give the reason. The mistake is rarely in the range. It is in which face was measured: the site reads the finished surface, the saw cuts a blank that has not gone into the mortar yet, and the difference is the embedment.
Why can't the factory make the height you measured?
Because visible height is not carved out of the slab, it is stacked. The curb sits on the structural floor and the tiles run up to its flanks, so the thickness of the finished floor — levelling, waterproofing, adhesive and tile — decides how deep the curb is buried. Blank height = finished floor thickness + visible height. A 35mm floor with 15mm showing needs a 50mm blank, which is why a curb is cut from a thick block rather than sliced from a 20mm slab. Say only "15mm high" and the factory has to guess your floor build-up; guess 10mm out and the curb either sits below the tile face or disappears down to a lip.
| Finished floor thickness | Visible height | Blank section height | Build-up |
|---|---|---|---|
| 30mm | 15mm | 45mm | Thin-bed adhesive, shallow levelling |
| 35mm | 15mm | 50mm | Mortar bed with 10mm tile |
| 40mm | 20mm | 60mm | Deep mortar bed, large-format tile |
Why is the width derived from the finished wall tile instead of chosen up front?
Because the outer face of the curb has to stand in a fixed relationship to the finished tile face: flush with it, or a few millimetres proud so water clears the tile edge and drips to the floor. Fix 120mm first and tile afterwards, and a 20mm build-up eats into that width — the curb ends up either a step sticking into the room or a recess that collects dirt. Work backwards in four steps: first, fix the finished tile face on both sides, structure plus levelling, waterproofing, adhesive and tile, never the bare wall; second, decide the outer face, flush or 5mm proud; third, fix the glass centre line so the clamp base sits wholly on stone, with at least 10mm from the base edge to the curb edge, or the clamp will chip it; fourth, what is left is the width. Example: tile face 20mm proud, glass line 70mm in from the outer edge, 50mm kept on the shower side, giving 120mm. Single-lip and double-lip profiles follow the same logic rather than taste: a single lip is raised on one side and flat on the other and relies on clamps and adhesive, a double lip carries a groove down the middle with a lip each side and takes the glass directly. Settle how the glass is fixed and the profile follows.
Should the length match the shower opening or the wall?
The opening — the tiled opening rather than the bare one, with a joint taken off at each end. Length = tiled clear opening minus one joint at each end (5–10mm). A 900mm gap between structural walls loses 25mm a side to tile and mortar, leaving 850mm clear; an 850mm opening takes an 830–840mm curb, not 850mm. The order sheet carries the curb length, not the opening width — write the opening and the factory cuts 850mm, and 10mm then comes off each finished end on site. Leave 5–10mm at each end for a joint and fill it with elastic sealant, never cement: wall and stone move by different amounts, and a rigid joint either spalls the edge or cracks the tile. Where there is a door, the end has to clear the frame and the swing, so no hinge lands over the curb. A curved opening cannot be built from straight lengths forced into an arc — curved pieces are set out by chord, with the radius back-calculated from chord and rise.
How high should the curb be to hold water without becoming a trip hazard?
Height does not stand alone; it belongs with the floor slope. A shower floor falls to the drain at 1–2%, which is 10–20mm per metre, so a 2m shower can carry a 20–40mm difference from the far corner to the drain. What the curb holds back is water arriving across the strip of tile immediately inside it, so the visible height only has to clear that strip — and the top must not pond. Drain position moves the number: with the drain against the curb, water stands deepest at the curb foot and the height goes up; with the drain at the far end, the curb side is already the high point and the height can come down. The ceiling is tripping: above 40mm people step over it, which rules out elderly users and accessible projects, and there the answer is a linear drain and a flush transition rather than a taller stone. The 40–50mm visible height used at a glass door is one concession to that ceiling: the leaf has to seat on the curb, and a low sill lets water run out under the door. Above 40mm the entrance normally already carries a step, or the owner accepts the rise; otherwise the number stays inside 40mm. One detail is routinely missed: the top should fall slightly outward, or carry a drip groove on the outer edge, to cut the film of water that otherwise creeps under the stone and out onto the bathroom floor.
What has to be written into the order before the pieces are cut?
Six items. Section: for a shallow threshold order the blank height worked out above, floor build-up plus visible height; where a glass door hangs, take the visible height to 40–50mm and add the floor build-up back on the same formula, which on a 35mm floor lands at a 75–85mm blank, with enough width for the whole clamp base to land, because the panel weight and clamp loads sit on this stone. Surface: polished is slippery when wet, so most projects cut two anti-slip grooves in the top, or flame the top and keep the flanks polished for cleaning. Edge: square-cut ends, with a 2–3mm round on the outer corner people step on, never a sharp arris. Water: seal all six faces against efflorescence, and bed the curb on a full mortar joint with no voids. Measurement: order by linear metre, not square metre — a 100×50mm section weighs about 13.5kg per metre (0.1 × 0.05 × 1 × 2.7). Loading: work from metres and section — 346m² is the theoretical ceiling for slabs in a 20ft container, holds for slabs only and does not transfer to long stock. At our plant these orders are not scheduled until the floor build-up, the glass fixing method and the clear opening are all on the sheet.