In most cases, a true drop-in sink is not designed to be undermounted. Drop-in models rely on a visible rim that sits on top of the countertop cutout, using the rim to distribute weight and create the primary seal. An Undermount Sink is engineered to be supported from below with mounting hardware and adhesive, leaving the countertop edge exposed for a cleaner finish.

That said, there is an important exception: some sinks are built as dual-mount designs. These can be installed either top-mount or undermount because the rim geometry, flange thickness, and mounting provisions are engineered for both methods. If your “drop-in” sink is actually a dual-mount model, undermounting may be possible with the right countertop and installation process.

Drop-in vs undermount: what changes structurally

A quick way to understand the limitation is to look at how each installation carries load and controls water:

• Drop-in installation

• The rim rests on the counter surface and carries most of the sink weight.

• Sealing is done at the rim-to-counter contact area.

• Works with a wider range of countertop materials because the rim provides support.

• Undermount installation

• The sink is supported from below with clips or rails, plus adhesive.

• Sealing must be reliable along the underside bond line.

• Requires a solid countertop that can hold hardware and maintain edge integrity.

When a “drop-in sink” can be undermounted

You can consider undermounting only when the sink meets all of the conditions below:

• Flat, uniform flange that can sit flush against the underside of the countertop without gaps.

• Adequate flange width to allow clips or a support frame to grip securely.

• Manufacturer-approved undermount method, with mounting points or compatible clip systems.

• Appropriate bowl geometry so the countertop cutout and reveal style remain practical and cleanable.

If the sink has a rolled rim, a thick overhang lip, or a decorative top edge meant to be seen from above, it is usually a top-mount-only product and undermounting becomes a leak and stability risk.

Practical decision table for project evaluation

This is exactly why many projects choose a sink that is purpose-built for the intended method rather than trying to convert after selection.

Countertop requirements that make or break undermounting

Even with a compatible sink, undermounting depends heavily on the countertop:

• Stone and engineered stone are commonly used because they are rigid and can be machined for clean edges and secure mounting.

• Laminate countertops are typically poor candidates for undermounting because the exposed cut edge is vulnerable to water intrusion and swelling unless special reinforcement is used.

• Cutout precision matters more than many buyers expect. Undermount failures often come from uneven edges, poor adhesive coverage, or inconsistent clamp pressure.

If your project involves heavier bowls, deeper basins, or long spans, a support rail system is often more reliable than clips alone.

What it takes to convert an existing drop-in cutout

Converting an installed drop-in sink to undermount is possible only in limited scenarios, and it usually involves trade-offs:

• The existing cutout may not match undermount reveal preferences.

• Removing a drop-in sink can chip or crack the counter edge if not done carefully.

• You may need additional reinforcement to carry weight long-term.

• Resealing is critical, because the sealing plane changes from top surface to underside bond line.

For many renovations, the safer route is to keep the drop-in method or replace the sink with a model engineered for undermount installation.

How LANSIDA supports sink selection for real installations

From a manufacturer and supplier perspective, the best outcomes come from matching sink structure to installation intent at the specification stage. LANSIDA’s catalog includes undermount, topmount, pressed, and handmade stainless steel sinks, plus related Kitchen Accessories, so you can select the correct base design rather than forcing an incompatible install method.

For project planning, LANSIDA can support:

• Material options and consistency for stainless steel sink programs, including common grades used in sink manufacturing across different series.

• Model-based specs with clear dimensions and installation method labeling to reduce install-site ambiguity.

• Program flexibility for OEM/ODM development when you need consistent sizing, finish control, packaging requirements, and stable supply for bulk order planning.

Bottom line

• A true drop-in sink is generally not meant to be undermounted.

• Undermounting becomes realistic only when the sink is dual-mount or explicitly designed for undermount installation, and the countertop and installation plan support it.

• For dependable performance, select the sink based on the intended mounting method early, and align cutout, reveal, and support strategy before production or purchasing.

If you want, I can turn this into a short “spec checklist” you can paste into a product page or a quotation sheet, tailored to the sink series you are promoting on LANSIDA’s site.