I’m often asked, “I want to have an undermount sink. How do I fix my sink to the underside of the concrete?”

Now an undermount sink for those who don’t know is a sink that sits under the work surface, beneath a “cutout” which can either have a reveal, no reveal (i.e. flush) or an overhang.

Incidentally this is a small detail but one which can have big consequences with food getting trapped once the sink is in service.

My response to customers when they enquire about fixing the sink is to not fix it at all to the concrete. It ideally needs to either be hung from something beneath or fully supported. 

Don’t get me wrong. It can be hung from the concrete but there are a few conditions (e.g. thickness of the concrete, size of the sink, weight of their sink, weight of the sink when full, sink material, wall thickness etc. etc. etc.) 

Also the get a secure fix involves using resin-bonded bolt inserts on the underside of the concrete and when you add all of this together it’s far simpler to approach it from a different angle. Either hanging or supporting.

Hanging the sink from the cabinet

In all but a few cases where the sink is as big and can sit directly on the cabinet below, the cabinet has to be adapted or added to internally to allow the sink to hang from it.

In the early days we used to make a “fillet” out of plywood for the sink it sit into. This would then be screwed into the cabinet. This works very well but requires quite a lot of accuracy. We have a CNC machine and laser templating equipment which does all of the accurate work required for this. It also requires the cabinets to be in final position so that the sink cabinet interior can be measured, the fillet manufactured and then the sink installed. A bit clumsy if you are making concrete worktops for a client.

You can put a full sheet of plywood over the top of your cabinets and make a cut out for the sink to sit into.

Another method is to build a frame within the cabinet for the sink to sit on. This is functional and the cheapest option but not the most elegant of solutions.

Supporting The Sink

The third way option is a variation on the second, costs approx £100 but is a more elegant and adaptable method.

https://www.the1810company.co.uk/product/sink-support-bars/

The brackets can be raised or lowered allowing for fine adjustments making your sink installation very straightforward. Whilst it adds an extra cost to the project if you’re not confident with any of the previous methods we can highly recommend it because it’s easy to install and also rated up to 180kg.

So hopefully this will give you something to “sink” about (sorry for the dad joke.)