An undermount kitchen sink is a sink that is placed under the countertop.
The advantage of placing a sink under the countertop is that there are no seams or sealant visible at all. Because there are no extra edges, dirt will not be able to accumulate at the edge of the sink on the countertop.
The undermount installation of a sink or sink can be placed under the countertop in 2 different ways. The possibilities depend on the type of sink you have.
It is not always possible to place a sink under the countertop. With the following kitchen worktops it is not possible to place the sink under the kitchen worktop:
- Plastic Kitchen Countertops
- Wooden Kitchen Countertops
- Concrete kitchen Countertops
Which countertop/kitchen top does allow an undermount sink to be installed:
- Composite kitchen worktop
- Granite kitchen worktop
- Stainless Steel Kitchen worktop
- Solid Surface Kitchen worktop
- Ceramic Kitchen worktop
- Glass Kitchen worktop
Installing stainless steel sinks underneath
The rim of a stainless steel sink also called flange is placed under the countertop. The flange is glued with acid-free silicone glue and propped up before the glue cures. After the silicone glue hardens, you can use the sink. Make sure that the underside of the worktop and flange are completely clean and free of grease so that the acid-free silicone glue maintains its maximum strength.
Our Stainless Steel Favorites
Seamless stainless steel sink, designed for sleek undermount installation
Ceramic and other heavy undermount sinks
The weight of a ceramic sink is certainly already 20kg, when the sink is completely filled with water it will be up to 60kg. To support this weight properly, additional support is needed to place the sink undermount. This is done by mounting metal brackets under the sink. In addition, the ceramic sink will also be secured at the top with silicone glue to create watertightness and extra support.
It is best to install an undermount sink flush with the saw size of the kitchen worktop, however, a small overhang of the countertop is also common. In practice, composite countertops with a sink made from the same material and color and glued underneath are often used. Unfortunately, these composite sinks are not very sturdy and often break down. Because the size is often very different from a standard stainless steel sink, it cannot always be replaced. Therefore, we recommend that if you do purchase a composite sink, a "standard" size is made so that this will not be a problem in the future should it be replaced.
How is an undermount sink held in place?
The sink rim, or flange, sits against the underside of the worktop and is bonded with a bead of neutral-cure, acid-free silicone. While it cures, the bowl is propped or clamped from below so it stays in firm contact. On heavier sinks, mechanical supports take over for the long term: metal brackets, a rail, or epoxy-set studs with clips.
Do undermount sinks need brackets or clips?
A stainless steel bowl is light enough that the silicone bond plus support during curing is usually enough. Heavier ceramic and granite composite bowls do need mechanical support, either metal brackets fixed under the bowl or a clip-and-stud system spaced roughly every 25 cm around the rim, so the cabinet carries the weight rather than the adhesive alone.
Which worktops can take an undermount sink?
Solid worktops work well: quartz and composite, granite, stainless steel, solid surface, ceramic, and glass. Laminate, wood, and concrete tops are not suitable, as their core cannot reliably hold an undermount bond and the exposed cut edge is left open to water.
How long does the silicone need to cure?
Leave the props or clamps in place until the silicone has fully cured, commonly around 24 hours, before filling or loading the sink. Check the cure time on your specific silicone, and make sure both bonding surfaces are grease-free and dry first so the bond reaches full strength.
Why do heavy sinks need extra support?
A ceramic bowl alone weighs about 20 kg, and filled with water that can climb to 60 kg. Even a stainless sink with water and dishes can pass 45 kg. That load is too much for adhesive on its own, so brackets or a support frame transfer the weight to the cabinet.
Can I install an undermount sink myself?
Yes, if your cutout is accurate and you support the bowl while the silicone sets. Stainless steel is the most forgiving for a first attempt because it is light and bonds cleanly. The two steps people most often get wrong are skipping the propping during curing and trying to undermount into an unsuitable top like laminate.
