How to install and protect polished concrete floors

Polished concrete flooring is an increasingly popular flooring choice because it’s both beautiful and durable. Polished concrete is also versatile, it works well indoors and outdoors, and in both residential and commercial properties.

Clients love it.

Clients get excited about it.

In fact, we’ve known people to actually swap over builders specifically so they can have polished concrete done within the pre-handover build process.

Choosing to install a polished concrete floor is a smart design choice, but at what stage in your build is it best to have the polish done? And how do you look after it until your client takes possession?

Find out everything you need to know about polished concrete flooring below!

At which stage of the build is Concrete Polishing best?

As large polishing machines can only reach up to within 10mm of a straight edge, the most consistent and the most cost-effective time to polish is at soft lockup, when the walls are up and roof on. Being watertight is crucial.

It’s preferable for installation to happen prior to plaster, paint and cabinetry as well – The machine is close to half a tonne, if it swings around unexpectedly it can go straight through plaster, and it can damage paint or cabinetry which then must be rectified or redone. Working around cabinetry means smaller machines or a great deal of hand grinding and corner tooling. All this is time and dollar hungry, and steals efficiency from the schedule. As we all know, time is money, especially on a build site where a wide variety of trades are working intermittently on the same area.

Polishing is best done at soft lockup

Here is what you need to know before installing a polished concrete floor

At Grind and Seal, we don’t supply concrete mixes nor do we pour concrete. We specialise in mechanically polishing concrete. But if you’re interested in knowing the specifications for installing a polished concrete floor, here is what you need to know:

Preparation

If you’re a renovation specialist or shopfitter working with an existing slab and your client wants a polished concrete floor, you may be able to use the existing concrete, currently hidden beneath tiles, carpet, timber or vinyl. You’ll need the concrete assessed first, as not all concrete is viable for polishing. If there is no existing concrete, there are some details for the new topping slab you’ll need to know.

• If you’re needing a new topping slab or decorative screed, it will need to be 32mpa. If your client likes the industrial look, with no aggregate visible, the concrete will need to be 40mpa, or even 50mpa.
• If we’ve assessed the existing concrete and found it to be viable for polishing, we can densify it several times throughout the process to bring it up to 32mpa strength. However, this adds additional time, labour and product, so it may be a higher price per m2 than a new slab concrete polishing price, which has been specifically purpose poured.

Pouring

A high level of care needs to be taken at the time of the concrete pour. Aggregate placement is more important to the finished product than you may realise, and it all depends on what your client wants.

• If your client wants a decorative finish, they’ll want to see the aggregate, similar to a terrazzo floor. They won’t want to see footprints, screed bar marks, or leaf imprints throughout their floor.
• If your client wants the industrial-nil-aggregate look, such as a Surface Polish, they won’t want to see any aggregate or shapes in their floor at all!

So the main objective is to get that slab as level as possible, from edge to edge. Using a Profilograph an FF reading of no less than 50 and a FL reading of no greater than 30 is required.

Regardless of which finishing technique they favour, a Standard Class A slab where there is a maximum deviation from a 3m straight edge of 3mm is needed. For an industrial-nil-aggregate finish, burnishing is needed. For all levels of aggregate exposure, the slab can always benefit from a light burnish when finishing the wet slab.

It generally takes 28 days for the slab to cure enough to mechanically polish, regardless of its size. This is good to know, so you can incorporate the polish between other trades.

Sealing & Drying

The beauty of mechanically polished concrete (MPC) as opposed to replica forms of polished concrete with topical coatings is that the MPC sealer is fully penetrating, and the work of turning the concrete into MPC has essentially been completed. The sealer is simply the last step for an MPC, sealing in that finish. This step is quite quick.

You can’t walk across a wet floor, but downtime in this stage is almost non-existent as the penetrating sealers used in mechanical polishes only take around 15-30 minutes to dry (great!). Keep in mind though that Melbourne’s weather is famously unpredictable and quick to change. Even this sealer can still be affected by moisture, concrete temperature and air flow – perhaps taking as long as an hour (still great!). Once the concrete has been polished and sealed, water should be kept away from the floor for a minimum of 72 hours to allow the sealer to cure fully. Once dry, your polished concrete floor will be good to go.

Replica forms of concrete polishing are called ‘grind and seals’. If you have a grind and seal finish, the sealers are topical coatings of epoxy or polyurethane. The cure time for these finishes is between 7 to 14 days, or in cold wet seasons, up to 21 days (keep an eye out for our next blog to get the down low on these finishes).

How to protect a polished concrete floor throughout the build

While polished concrete is an extremely durable finish, there are still some steps required to protect it throughout the remainder of your build process.

Protecting your polished concrete floor investment throughout construction

During construction, it’s highly advisable to protect polished concrete. Although polished concrete is very durable, construction often presents many unique challenges, for instance: if a heavy tool with a sharp edge is dropped from height, a chip can occur. Of course chips can be repaired, but in most cases the repair compound will not match the rest of the concrete or aggregate colour. Adding colour oxide to repair compound weakens the bond, so for a permanent repair, odds are it will be somewhat noticeable.

Here are some other common things on construction sites that can damage a polished concrete floor. To ensure the floor is not damaged during the build, and to save needing it repaired, ensure your team know the following products should be wiped up immediately.

• Petroleum – this high viscosity substance can stain the floor
• Paint and timber stains – once dried paint can stain your floor, and timber stain will stain it immediately!
• Acids – these can damage concrete
• Adhesive tapes – the glue ingredients on adhesive tape can damage polished surfaces so never tape anything to the floor
• Paint thinners/paint removers can damage polished surface

To avoid damage, make sure you lay Ramboard (a commercial grade breathable cardboard protection) over
your floors and clean up any spills immediately after they occur. Ramboard should be laid by taping each piece of
Ramboard to the adjacent piece. Once all pieces are taped together there is  no need to tape it directly to the floor.
The weight of this 100% recycled cardboard is enough to prevent it
from shifting, thus it’s able to be walked across and worked on.

The Pre-Handover Clean – Cleaning the polished concrete floor before handover

Ensure your commercial cleaners have access to the pH balanced product we leave on the floor at polish completion. Grind and Seal gift a full complimentary container of pH balanced cleaner for you to give to your clients. We also email you directly a PDF Care Instruction document, to send to your client. It’s definitely in your best interests to ensure your client receives both the container of pH neutral cleaner and the PDF so their floor will stay in the same condition as when they took possession. You wouldn’t want them to unknowingly ruin their floor and blame it on the build.