Why Does The Slab Need 28 Days To Cure Before Concrete Polishing?

So Why Does The Slab Need 28 Days To Cure Before Concrete Polishing?

The 28-day curing time is standard in the concrete industry and comes into play on almost every project. “Wait for 28 days before application” or “Concrete requires a 28-day cure before this or that can take place” — including the application of most decorative sealers, coatings, stains, toppings, or polished concrete — is a common tagline. That is because the concrete needs to have a certain strength, or is there something else going on?

The 28-day standard comes from decades of testing that determined concrete achieves 99% of its strength in 28 days. The American Concrete Institute, ASTM International, and Portland Cement Association all reference the 28-day time frame as the accepted standard for measuring compressive strength. Really, it’s an arbitrary number based on concrete cylinder tests.

It’s also important because it sets a standard and establishes consistency in testing. Mix design and curing conditions have more to do with strength than a set number of days. According to “The 28-Day Myth” published by the National Precast Concrete Association, it’s estimated that concrete reaches 75% of this 28-day compressive strength in seven days, and its strength will remain stable or even increase over time.

Use a Type III-high early cement in your mix and you can achieve 3,000 psi concrete in 24 hours. Most ASTM testing lists a 24-hour, 7-day, and 28-day time frame. All three are important milestones and provide information on how materials are performing compared to a standard.

If anyone tries to Polish Concrete Floors before the 28-day curing period has elapsed, it’s possible to damage the slab when grinding or to instantly achieve a much fuller exposure than you would like. There are some contractors who only wait a week or two, but we’ve seen areas of concrete that have been ‘ripped up’ by premature grinding.

In some cases, it is possible to grind a slab after 21 days instead of 28 days, and we can assess that on a case-by-case basis. However, we normally recommend the full 28 days to ensure proper curing. We are aware that some contractors are willing to grind a slab after 14 days or even sooner, but we view this as extremely risky.

Being a company that guarantees the high quality of our work, at Concrete Polishing Floors Sydney, we don’t like to take any chances with your slab. After all, concrete slabs are the valuable foundation of your new home or premises, and we truly believe you will find that the 28 days are worth the wait.

– Technically, most commercial concrete is strong enough to be polished just three days after pouring.

As a general rule, the concrete should be cured for 28 days before we actually arrive to do the Polish. Then we can do the Polish all at once, or in 2 stages. If we are to do the procedure all at once, we do the floors after the frame is up and the internals are watertight.

– However, that doesn’t mean you should jump the gun and do it that soon. Part of the polishing process is using a densifier to make sure the slab is hard and dense enough for the grinding and polishing process.

If we need to do it in 2 stages, it requires us to do an initial grind and grout prior to the frame being erected and a protective coating being placed over the floor until works have been completed or just before the plaster. We then remove the protective coating and can Polish up the floor. It is much better for everyone if we come in after the frame is up, but before the skirting and plaster gets done.

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