How to Seal Concrete: How Many Coats and How Long Between?

Sealing is the last step of every concrete or microcement project, and it’s the one we get asked about most on the phone. How many coats? How long between them? What if it’s cold, or the concrete keeps soaking it up? This guide answers all of it, using the same advice we give customers every week.

Quick facts
Coats	3 as standard; 4–5 on porous or outdoor concrete
Time between coats	At least 4 hours in warm, dry conditions; allow up to 8 when cold or damp. No maximum.
Light use	24 hours
Full cure	7 days
Difficulty	Easy – the measuring is the fiddly bit
You’ll need	Concrete Lab Sealer, the Concrete Sealing Kit, a short-pile roller, kitchen towel

What does sealing actually do?

Concrete Lab Sealer is a two-part, water-based polyurethane. It’s a hybrid: the first coats soak into the surface and the final coats build a thin protective layer on top. That combination gives you stain resistance, chemical and mechanical resistance, and UV stability, without the plastic look of a thick topical coating.

One thing worth clearing up: on microcement, the sealer isn’t what makes it waterproof. Microcement is waterproof on its own. The sealer is there for stain resistance and durability, so coffee, wine and grease wipe off instead of soaking in.

How do I prepare concrete before sealing?

Freshly made concrete or microcement: vacuum away all the dust, then wipe the surface down with a damp cloth and let it dry.

Existing or previously sealed concrete:

1. Sand with an orbital sander to remove old coatings, working up from 80 grit to 200 grit.
2. Vacuum thoroughly.
3. Degrease with a proprietary degreaser.
4. Wash down with clean water and let it dry.

If you’re polishing cast concrete before you seal it, stop at around 240 grit. You can polish to a much higher shine, but the moment the surface gets wet the extra shine disappears – so it isn’t worth the effort.

How do I mix the sealer?

The sealer comes as Part A and Part B. Use our project calculators to work out how much Part A, Part B and water you need for your area and for each coat – the water amount changes from coat to coat.

1. Measure Part A with a syringe into a clean container.
2. Measure Part B with a separate syringe. Part B is quite viscous, which is why we recommend the Concrete Sealing Kit with its syringes.
3. Mix A and B thoroughly for about 2 minutes.
4. Add the water and mix for another 2 minutes.
5. Use the mixed sealer within 2 hours.

Put the lid back on the Part B tub tightly straight away. One customer resealing a seven-year-old worktop told us his Part B solidified after he left the tub loosely closed for a few hours.

How many coats of sealer does concrete need?

Three coats is the standard system, and on our own mixes and microcement that’s usually all you need. But the real answer is: keep going until the surface stops absorbing.

The first coats are simply sucked into the concrete. Think of it like filling a bath – you can’t build a protective layer until it’s full. You’ll know you’ve got there when you can push the sealer around on the surface for five to ten minutes before it soaks in. From that point, each coat adds to the protective film.

Some surfaces need more:

• Home-mixed or lean concrete (more sand and stone, less cement) is more porous. Plan on around five coats.
• Outdoor worktops, BBQs and pizza oven plinths benefit from four or five coats for extra protection.

For coats four and five, simply repeat the coat-three mix from the calculator. Use the website calculator for each coat and you won’t go wrong.

How long should I leave between coats?

Leave at least 4 hours between coats in warm, dry conditions. In cold or damp weather, give it longer – up to the 8 hours stated on the printed instructions. The gap isn’t just about the surface feeling dry; it’s giving the chemical reaction between Part A and Part B time to get going.

There’s no maximum. A day or a week between coats is fine. The only catch is that the surface isn’t protected from stains until you’ve finished.

A typical indoor timetable looks like this: one coat first thing, one at midday and one at the end of the day.

Sealing outdoors

Outdoors, moisture evaporates faster but cold slows the reaction down, so the minimum gap still applies. Wait for a guaranteed dry day. If you’re applying five coats, do three on the first day and two the next.

How do I apply each coat?

1. Roll the sealer on evenly with a short-pile roller.
2. Dab excess off the roller with kitchen towel so you don’t leave puddles or drips.
3. Leave it alone until the next coat is due.

When can I use the surface?

• After about 6 hours on a floor you can walk on it carefully if you really have to – but treat it with kid gloves.
• After 24 hours the sealer has its initial strength and the surface can take light use.
• After 7 days the sealer is fully cured. Until then, don’t clean it, keep water and dirt off it, and avoid knocks and scrapes.

Sealing should be one of the last jobs on any build, after the trades have finished. For more on looking after concrete while it cures, read The Importance of Curing.

Can I seal over an old sealer or recoat later?

Yes. For a maintenance coat, degrease the surface, rinse, let it dry and apply a fresh coat – there’s no need to sand. Our own outdoor kitchen, which has a cast-iron pizza oven and a log burner sitting on sealed concrete, gets this treatment about every two years.

If you’re adding microcement over an area that was already sealed, the sealer acts as a primer. Give it a light sand for grip and go straight over the top. Our guide on how to repair microcement covers patch repairs in detail.

Finished and it feels a bit tacky? See what to do if your sealed concrete feels tacky.

How do I look after sealed concrete?

Use mild detergent and a soft cloth. Avoid scourers and abrasive cleaners. Acidic spills like lemon juice or vinegar can still etch the concrete underneath the sealer, so wipe them up promptly. For outdoor surfaces heading into winter, our outdoor concrete care guide has the full routine.

Frequently asked questions

Is it the sealer that makes microcement waterproof?

No. Microcement is waterproof in its own right. The sealer adds stain resistance and durability, and protects the surface from everyday dirt and moisture marks.

Can I leave a day or more between coats?

Yes. There’s no maximum time between coats. A day or even a week is fine – just remember the surface has no stain protection until the full system is on.

How do I know when I’ve applied enough coats?

When the surface stops drinking the sealer. If you can push a coat around for five to ten minutes before it disappears, the concrete is full and the next coats will build the protective film.

Can I seal concrete I mixed myself?

Yes. Concrete Lab Sealer works on cast concrete, microcement, resin and stone. A leaner or more porous mix will simply take more coats than our own mixes do.

Will the sealer go yellow outdoors?

No. It’s UV-stable and doesn’t yellow, so it suits outdoor kitchens, BBQ worktops and pizza oven plinths.

How often should I reseal?

Indoors, a maintenance coat after several years is usually plenty. Outdoor surfaces benefit from a refresh every couple of years: degrease, rinse, let it dry and apply a fresh coat – no sanding needed.

Still not sure how many coats your project needs? We’re happy to talk you through it – info@concretelab.co.uk

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