A rear kitchen extension is one of the most common renovations in London — knock through into the garden, add an orangery or flat-roof extension, and suddenly you have the open-plan space the house always needed. The flooring question almost always follows: should it match the existing house or make a statement?
Polished concrete keeps coming up as the answer. It’s durable, it works with underfloor heating, it handles the transition between new and existing space cleanly, and it looks good in a way that’s hard to achieve with other materials at the same price point.
We install polished concrete overlays across London and the South East, and kitchen extensions are one of our most common jobs. Here’s what you actually need to know before committing.
The practical case for polished concrete in a kitchen
Kitchens are hard on floors. Dropped pans, spilled liquids, constant foot traffic, chairs dragging across the surface — most materials show wear within a few years. Polished concrete doesn’t. The grinding and densifying process creates a surface harder than most natural stone. A properly maintained polished concrete kitchen floor should look good for 20–30 years.
Cleaning is straightforward: a damp mop and a pH-neutral cleaner. No specialist products, no grout lines to scrub, no worrying about bleach splashes. For a family kitchen, that matters.
Polished concrete is also seamless — no joints, no edges, no grout. Crumbs and spills have nowhere to hide, which makes it noticeably easier to keep clean than tiles.
Underfloor heating in kitchen extensions — does polished concrete work?
Yes, and it works well. This is one of the most common questions we get from clients planning extensions, and the answer is consistently positive.
Concrete has high thermal mass — it stores heat and releases it slowly. For an underfloor heating system, the floor acts like a slow radiator: it takes longer to warm up than a tiled floor, but once warm, it stays that way. The system runs more efficiently because it’s not constantly cycling.
For our overlay installations, we pour the 5–8mm concrete screed over the UFH pipes as part of the process. The pipes are encapsulated in the overlay, which sits directly above them — good thermal contact, good heat transfer. Just make sure your builder has allowed the right floor depth in the build-up so there’s room for the overlay on top of the screed.
One note: don’t rush heating a new polished concrete floor. Wait at least 28 days after installation before running the UFH, and bring the temperature up gradually over the first week. Thermal shock can cause cracking in any cementitious floor.
New extension vs existing floor: getting the level right
This is where most of the complexity lies in kitchen extension flooring projects. You have two zones — the existing ground floor of the house and the new extension — and you want them level, or at least at a manageable transition.
The new extension will typically have a concrete slab poured as part of the build. In an ideal world, your builder leaves this at exactly the right depth for a polished concrete overlay on top, which brings it flush with the existing house floor. That takes coordination between the builder and us — ideally we’re specified on the project before the slab is poured.
In practice, we often come in after the build is complete and work with what we’ve got. If the extension slab is slightly low, we can adjust the overlay thickness. If there’s a level difference between old and new, we can taper the overlay to create a flush transition. The best outcome is when we’re involved early — if you’re at planning stage, get in touch before your builder pours the slab.
Can polished concrete span both the old and new space?
Often, yes. A common brief we get is: “We want polished concrete throughout the back of the house — existing kitchen, new extension, and the hallway if possible.”
An overlay can go over most existing substrates — existing concrete, screed, or a well-prepared subfloor. Running a continuous polished concrete surface from the old part of the house into the new extension is achievable. The floor reads as one space, which is exactly the point of an open-plan extension.
What you won’t get is a perfectly identical appearance across the whole floor. Concrete has natural variation, and new pours will look slightly different to existing concrete even with the same mix. Most clients find this adds character rather than being a problem, but it’s worth knowing upfront.
Typical costs for a kitchen extension polished concrete floor in London
For a polished concrete overlay in a London kitchen extension, budget £90–£130/m² for a standard finish. Complex finishes, higher gloss levels, or awkward site access can push this higher.
A typical rear extension runs 15–25m². That puts most kitchen extension polished concrete jobs in the £1,500–£3,500 range before VAT. If you’re extending the floor into the existing kitchen and hallway, the area increases and the per-m² rate typically improves.
For an accurate figure, our polished concrete floor cost guide gives a detailed breakdown, or call us on 07730 584 748 to talk through the spec.
What finish works best in a kitchen?
Most kitchen clients choose a mid-sheen finish — something between fully honed (matte) and mirror gloss. A high-gloss kitchen floor shows every footprint and watermark. A completely matte finish can look flat in a large, light-filled extension space. The middle ground gives you the warmth and depth of polished concrete without the maintenance anxiety.
Colour comes down to aggregate exposure and pigment. Natural grey is the most popular, but we can work with pigmented mixes if you want something warmer or cooler. A coarser aggregate exposed at a lower grind gives a more textured, industrial look; a finer aggregate at a higher grit produces something closer to stone.
Frequently asked questions
How long does installation take for a kitchen extension?
For a standard kitchen extension overlay, typically 2–4 days: one day to prepare the substrate and pour the overlay, a curing period, then grinding and sealing. The extension needs to be weather-tight before we can start, so coordinate with your builder on timing.
Can polished concrete go under bifold or sliding doors?
Yes — this comes up regularly with kitchen extensions. We can take the floor right up to the door threshold. For external doors, we seal the edge carefully and make sure the slab edge is well protected. You may want a flush threshold strip at the door opening for aesthetics.
Is polished concrete slippery in a kitchen?
A polished concrete floor has a slip-resistance rating comparable to most stone and porcelain floors. When dry, it’s not slippery. When wet — a spill, or wet feet from the garden — it can be, like any hard floor. We apply a slip-resistant additive to the sealer for kitchen floors as standard, which brings the rating up to R10 (suitable for domestic and most commercial kitchens).
Will polished concrete crack in a new extension?
New extensions go through a settling period. We cut control joints in the overlay to manage any movement — these are planned as part of the design and can be positioned discreetly. In a well-built extension with a properly cured slab, cracking is unusual. If the build has underlying issues, those will show through any floor covering, not just concrete.
Do you cover all of London?
Yes. We cover London and the wider South East. Most of our kitchen extension work is in inner and outer London, but we regularly travel further for larger projects.
Ready to plan the floor for your kitchen extension? See our polished concrete floor cost guide for detailed pricing, or call us directly on 07730 584 748. We’re happy to visit the site and give you a proper assessment.