Can You Polish a Liquid Screed Floor?
In short, no, not to a genuine polished concrete finish. Liquid screed, whether it’s a calcium sulphate (anhydrite) mix or a cementitious one, is designed to be a level base for tiles, wood, carpet or another floor covering, not a decorative surface in its own right. Grinding and mechanically polishing it the way you would a concrete slab tends to expose weaker, more porous material underneath and can leave the surface patchy or prone to dusting. If you want that smooth, glossy, exposed floor look, the reliable route is a dedicated polished concrete topping laid over the screed rather than polishing the screed itself.
Why liquid screed isn’t built to be a finished floor
Screed of any kind, liquid or traditional, is what’s known as a wearing or non wearing subfloor layer. It’s formulated to be flat, stable and quick to install, and its finish is deliberately left slightly open and porous so that adhesives, primers and floor coverings key into it properly. That’s the opposite of what you want for a polished surface, which needs a dense, closed material that can take a mechanical grind without breaking down.
Can anhydrite (calcium sulphate) liquid screed be polished
Not really, and it’s generally not worth attempting. Calcium sulphate screed is gypsum based, so it’s softer than a cementitious mix and its natural colour can vary from batch to batch, which makes an even, polished finish hard to guarantee even where the surface can take it. Guidance from Easyflow notes that while a hardener can be applied and the surface mechanically polished, anhydrite screed was never designed to be the final flooring, and covering it with tiling or carpet is usually the more reliable option.
There’s also a practical risk if you try to add a decorative overlay on top instead. Anhydrite and hemihydrite screeds hold onto moisture for longer than cementitious ones, and guidance from Carrcrete points out that trapping that moisture under a bonded topping can lead to delamination further down the line, so any overlay needs the screed properly dried and tested first.
Can cementitious liquid screed be polished
Cementitious liquid screed is closer to concrete in composition, so it holds up better to grinding than an anhydrite mix, but it still isn’t a like for like substitute for polished concrete. Research from British Concrete Polishing found that flow screeds generally aren’t ideal candidates for polishing because the aggregate is much finer than in a structural concrete slab, so grinding it back rarely produces the same depth of finish or aggregate exposure. Some cementitious screeds can be lightly ground and sealed for a smoother, low sheen look, but it’s a job for a specialist who can test the specific product first, since many screeds won’t tolerate more than light grit before the surface starts to fail.
The reliable way to get a polished floor over liquid screed
If the end goal is a genuine polished, glossy floor rather than something to hide under tiles or wood, the better option is a purpose made polished concrete topping installed over the cured screed, rather than trying to polish the screed itself. This is a thin, trowel applied overlay, often laid from around 10mm thick, that’s ground and polished in the same way as a structural concrete floor, giving a consistent, durable, high gloss finish that a raw screed surface simply isn’t formulated to achieve. Our own polished concrete toppings service is designed exactly for this, and can be re-polished multiple times over the life of the floor rather than being a one off finish.
What about sanding or sealing instead
Sanding a liquid screed is sometimes used to knock back high spots or smooth the surface before laying a floor covering, but it’s a corrective step rather than a finishing one. As J&H Lynch’s guide to liquid screed finishes puts it, targeted sanding and specialist sealing can help prepare the base, but polishing isn’t really an option on the raw screed itself. Sealing can offer some protection during the build phase, but on most projects the screed is still intended to be covered rather than left exposed long term.
How to tell what type of screed you have
Since the right approach depends heavily on whether you have an anhydrite or a cementitious mix, it’s worth checking before deciding on a finish. If the screed was installed recently, the contractor should have a record of the exact product used. Cementitious screeds are generally a darker grey and feel harder underfoot, while calcium sulphate screeds tend to be a lighter, more uniform grey and feel slightly softer. If you’re not sure, it’s best to get a specialist to check before grinding, sanding or applying anything to the surface.
Getting the right finish for your floor
If you’re planning a screed and already know you want an exposed, polished result rather than a covered floor, it’s worth specifying that from the outset so the right screed and topping combination gets used, rather than trying to polish a standard liquid screed after the fact. Contact Express Liquid Screeds to talk through your project and whether a liquid screed with a polished concrete topping is the right fit.
FAQs
Can you leave liquid screed as the finished floor without covering it?
It’s possible in some low traffic areas with a cementitious screed and a sealer, but it isn’t what liquid screed is designed for and the finish won’t match a proper polished concrete floor. Most projects still cover the screed with tiling, wood or another final floor finish.
Does polishing liquid screed cost less than a polished concrete topping?
Attempting to polish the screed itself might look cheaper upfront, but the results are inconsistent and can fail early, which often costs more to put right. A proper polished concrete topping is a more predictable and durable route to a genuine polished finish.
Can you polish liquid screed over underfloor heating?
Yes, a polished concrete topping can be applied over a screed installed with underfloor heating, but the screed needs to be fully cured and moisture tested first, and the heating system should follow its usual gradual heat up schedule before any topping work begins.
Will polishing liquid screed remove the trowel marks or texture?
Light grinding can smooth out minor surface texture, but liquid screed isn’t dense enough to take a full mechanical polish without exposing weaker material underneath. A topping system is the more reliable way to get a completely smooth, glossy result.
How do I know if my screed is anhydrite or cementitious?
Check with the original installer if possible, as they’ll have a record of the product used. As a rough guide, cementitious screed is usually darker and feels harder, while anhydrite screed is lighter in colour and slightly softer underfoot, though a specialist assessment is the safest way to confirm it.
