01The three joints, side by side
Everything else on this page follows from one of these three constructions. Pick the joint first; the price and the drawing follow from it. We weld bowls into 5–10 mm plate, and we also cut apertures for bowls you supply — which of the two you get should follow the joint you want, not the grade of plate that happens to be on the rack.
| Method | What it looks like | Drawing impact | Where it fails |
|---|---|---|---|
| Welded-in bowl | The bowl is fabricated into the plate; no rim, no silicone | Bowl geometry, radii and drain position all on the drawing | A weld that was polished too hard thins the wall |
| Undermount | Plate has an aperture; bowl fixed from below on clips or studs | Aperture size and position to the sink template | Clip tension and a silicone line that is never inspected again |
| Top-mount / drop-in | Bowl sits on the plate with a rolled rim and a bead | Aperture plus clearance for the rim | The bead: it traps water and eventually discolours |
On thin sheet, undermount is the normal answer, because welding 1 mm into a flat top distorts it. On 5–10 mm plate the distortion behaves differently — the plate has enough mass to hold shape while heat is put into it — which is why a welded bowl is a plausible spec at this thickness and not at 1.2 mm.
02A sink run we built, and what it shows
The argument above is easier to trust with a photograph of a bowl that is actually in a top. Both frames are from our own showroom stand, shot close enough to judge the joint.
Two things to look at. The bowl has no rim standing on the surface, so there is no bead to clean around at the edge of the aperture. And the deck continues past the bowl to the end of the run in one plane, which is what a fabricated joint buys you and what an undermount cannot: on an undermount the plate stops at a cut edge and the bowl hangs below it.
To be straight about the evidence: these are stand photographs, so they prove the construction and not the installation. They are also not offered as proof of the edge tolerance quoted elsewhere on the site — that is measured on a machined plate edge, not inferred from a picture. For the installed version, the project photographs show a run on site with the difference between the two kinds of frame labelled.
03Welded-in bowl: what it costs you
A welded bowl has no rim, no silicone and nothing to catch dirt. It is the detail that makes a photograph of a commercial kitchen look expensive, and it is the one buyers ask for before they ask the price.
What it costs is time and tolerance. The bowl has to be fabricated from sheet, welded into the plate, the weld dressed back flush, and the finish re-grained across the joint so it does not show as a halo. Every one of those steps is a chance to distort flat plate — and once a top has been through that, the flatness is no longer the mill flatness on the countertop specification, it is the fabricator's.
Our own rule on these: we will not quote a welded bowl without the bowl geometry, because the radius at the bottom corner is what decides whether the weld can be dressed invisibly. A tight radius in 2 mm sheet welded into 8 mm plate is a different job from the same radius in 1.2 mm.
The realistic question is not “can you weld it”, it is “what does the finish look like across the weld when it is done”. Ask for a photo of a finished joint in the same grain direction you are specifying, at the same lighting, before you approve the order.
04Undermount: the aperture is the whole job
Undermount is the cheapest of the three and the one most likely to be wrong, because the aperture is cut from a template that has to match a bowl you may not have on site yet.
- Cut to the sink maker's template, not to the bowl. The template includes the clip clearance; the bowl does not.
- State the datum. “Centred” is not a dimension. Position the aperture from the front edge or from a fixed end, and say which.
- We hold ±0.5 mm on a cut aperture. The ±0.05 mm edge tolerance applies to a machined edge, not to a plasma or waterjet aperture — anyone quoting ±0.05 mm on a sink cut-out is quoting a number they cannot inspect.
- Substrate or no substrate. On 5 mm plate, a large aperture in a 600 mm deep top removes most of the stiff middle. Tell us the bowl size; we will say whether the plate needs a doubler.
05Top-mount: when it is the right answer
Top-mount gets dismissed as the cheap option. It is also the only one you can replace without removing the countertop, which is a real advantage in a rental, a serviced kitchen, or a commercial fit-out where the bowl will be beaten up in five years.
The cost is the rim. A rolled rim on plate reads as a ledge, and the bead behind it is where water sits. If the top is going into a hygiene-inspected kitchen, that bead is the first thing a torch will find.
Where top-mount wins outright: stainless tops over an existing carcass where the bowl has to be serviceable, and any job where the sink model is not final at the time of order.
06What we need on the drawing
For any of the three, the same five things:
- Overall top size, in millimetres, with the datum edge marked.
- Aperture or bowl position from that datum, in both directions.
- The sink: model number, template PDF, or a measured drawing of the bowl.
- Joint method — welded, undermount, top-mount — stated, not implied.
- Drain and overflow position if the bowl is being fabricated.
Send those and the quote comes back in 24 hours with the joint method priced as a line item, so you can see what the weld actually costs against the clip.
Send a drawing · Countertop specification · Commercial kitchens