What is a Sealed Concrete? How to seal Concrete?

There are broadly three types of concrete floor finish, Plain, Polished and Sealed Concrete. Sealed Concrete is also known as the seal and grind concrete. Sealed concrete finish is the most common one.

What is Plain Concrete Finish?

Concrete is a durable material so when concrete is laid as it is and no treatment has been done to improve the surface quality, it is called plain concrete finish. The plain finish is durable, smooth and light grey in colour. The plain finish is breathable, which means that the moisture from the concrete can be removed.

But it has a serious disadvantage. Concrete has pores in it through which the dirt and dust get collected which is very difficult to clean. Thus plain finish concrete is not very good in areas subjected to heavy staining and dusting.

Concrete is also strengthened by steel reinforcement. Absorption of salt particularly chlorides leads to the corrosion of steel reinforcement. therefore it needs some external aid to prevent it from the above defect. Thus sealing is required.

What are Polished Concrete Floors?

This property of concrete can be improved by polishing its surface. By polishing the concrete surface with a coarser grinder and subsequently with finer ones, the shiny surface is achieved. The amount of polishing depends on the desired level of shine (level 1-level 4)

The polished concrete caters to the stains to some extent but it is not chemical resistant. The polished finish is breathable.

Bonded AbrasivePolished Concrete 

The concrete surface is ground, honed and polished with bonded abrasive and subsequently more and more refined abrasive is used to achieve the desired level of shine. This method yields the most durable finish and requires the least maintenance.

Burnished Polished Concrete

The method involves mechanical friction rubbing a concrete surface with or without resins or waxes to achieve the desired level of gloss. This operation yields a less durable finish and requires more maintenance than bonded abrasive polished concrete. 

Hybrid Polished Concrete

This method involves mechanical grinding and polishing with the friction rubbing process by utilizing bonded abrasive, abrasive pads or a combination of both to achieve the desired level of gloss.

 Polished Concrete Shine level indicator

LevelGritSheen LevelAppearance
1<400none to very lowlittle reflectivity
2100-400Low to mediumSatin or Matte appearance with or without reflection
3400-800medium to highThe object being reflected are not quite sharp but identifiable
4>800highMirror-like reflection.
 Polished Concrete Shine level indicator

Benefits of Polished concrete

  • It is more durable than Sealed Concrete or Plain finish Concrete.
  • It requires less maintenace.
  • It gives naturally beautiful appearance due to grinding of aggregates in concrete.
  • Any type of finish, right from matte to mirror like finish can be achived.
  • No harmful chemicals are used.

Drawbacks of Polished Concrete

  • It has lower stained resistance, the concrete surface can be damaged.
  • slower installation time due to grinding again and again.
  • It is labour intensive thus higher installation cost.
  • Can’t be used for industrial or areas prone to chemicals.

What are Sealed Concrete ?

The third type of concrete finish is sealed concrete finish. Sealed concrete and polished concrete are similar in appearance but there is some difference. In polished concrete, the concrete is polished using finer grits of diamond abrasive until the floor reached the desired level of shine. Remember, there is no film on the polished concrete floor. If you compare this finish with a polished concrete floor, it has a shorter life.

But in sealed concrete, the concrete is cleaned, allowed to dry. A thin layer of acrylic, epoxy or Urethane sealer is applied just like paint over the concrete surface. The layer of sealer fills the voids in concrete.

Thus, the desired level of shininess is achieved depending upon the type of sealer. As the sealer forms the thin film over the concrete surface thus, the moisture intrusion under the finished floor is prevented.

Due to the filling of the pores, the water or spillage do not find its way down thus the life of concrete increases. Sometimes the concrete is sealed to prevent the entry of moisture below the floor.

The sealer gets damaged each time the traffic passes by and eventually wear off thus needing resealing. For example, in the driveway, the sealer may get damaged due to the traffic. Sealers are also applied in cold areas where the problem of freezing and thawing is present. The sealer prevents the ingress of water thus no issue of freezing and thawing.

Types of Sealed Concrete

Sealed concrete are of different types mostly they are silicon-based sealer, linseed oil-based solutions, acrylics, epoxy, and polyurethane sealers. The sealed concrete is also known as grit and seal.

Sealed concrete is either a Stained Concrete or Commercial Coating. All stained concrete is essentially sealed concrete. In stained concrete, colour is added in the concrete to match the theme. Thus to prevent the layer of this shade or tint, from getting scratched a film of sealer is required. Thus, all stained concrete is sealed.

If we compare the working of different types of sealers they are generally of two types. The first one is Silicon based the second one is organic resins such as acrylics, epoxies, or polyurethane.

The silicon-based sealers penetrate the concrete surface to a slight degree and form a thin film on the concrete surface. Hybrid sealers are also produced which are based on silanes or siloxanes and incorporate organic resins such as acrylics.

Sealed concrete floor.

Epoxy Concrete finish

In epoxy sealer, a layer of epoxy material is used over the concrete. The concrete surface is first cleaned and allowed to dry. A thin film of epoxy is applied which will fill the voids in the concrete.

The drawback of epoxy sealer is that it has a high potential for failure. You must be thinking how can it fail. What happens is that epoxy later over the concrete surface starts to separate from it.

Another drawback of this finish is that due to the 100 percent sealing of the concrete surface, it will not be breathable. The vapour starts building inside the concrete and doesn’t find its way out. Thus it creates vapour pressure, especially in humid areas.

Polished concrete floors cannot fail due to the vapour pressure because they release moisture naturally without any impact on their finish. The epoxy finish has a tendency for showing scratches and wear in high traffic areas. The coating material is not as durable or strong as concrete thus it wears down.

The major advantage of epoxy sealer is that it allows patching of surface defects, cracks and joints which is not possible for other types of sealer.

Acrylic Sealer

A thin film of acrylic sealer is applied over the concrete surface just like an epoxy sealer. Acrylic sealer is water repellant. It is very easy to clean the concrete. And most importantly it is breathable. It does not seal the concrete entirely that is why the concrete remains breathable. The whole surface needs to be resurfaced and resealed because it is not a repairable installation.

Silicon-based Sealers

Silicon-based sealers are most common. They resist oxidation and offer good heat resistance and thermal stability. They also offer good resistance to UV rays and water making them ideal water-repellent materials. It is also called densified Concrete.

Silicon-based sealers consist of silanes, siloxanes, and silicates. While Silas and siloxanes function by penetrating the concrete pores and filling them, silicated function differently.

It reacts with the calcium hydroxide in the concrete and essentially blocks the pores. These silicate sealer products are also called densifies since they harden the top surface of the concrete.

Why do we need Concrete finish

The plain concrete is very porous or spongy. It could get damaged due to staining and dusting. We need the finish to prevent the concrete from abrasion and staining. Sealed concrete is always better than the Plain finish or even polished concrete. The epoxy finish is expensive to repair. the entire floor must be stripped or ground and a new coating is applied.

Advantages and Drawbacks of Sealed Concrete

Sealed Concrete has high stain and Chemical Resistance. Installation time is fast. It gives a high gloss surface and it has a low installation cost. If we talk about the drawbacks, it has a high potential for failure.

The sealed concrete is impossible to repair the entire surface needs to be repaired. Sealed concrete shows scratches and becomes slippery when wet due to high gloss.

The Concrete on which a thin layer of sealing compound generally acrylic, epoxy or urethane is applied and allowed to dry is called sealed concrete. The application of the sealing compounds is similar to the painting. This gives the shiny surface due to the pores of concrete getting filled with the chemical.

Pros Cons
High stain and chemical resistantHigh potential for failure
Less installation timeDifficulty in repair
Glossy and smoothEasy scratches and wear
Low costSlippery when wet
Less labour intensive than polished concreteNot breathable thus vapour pressure builds up.

How to apply Sealers to Concrete

  • First of all the concrete surface to be treated is cleaned. The surface preparation consists of a clean concrete surface. The surface should not be rough because the sealer penetrates into the concrete rather than adheres to the outer surface.
  • Thus clean surface is needed. If the surface is coated with oil or grease it prevents the sealer from absorbing into the concrete. The surface can be cleaned with pressurized water or using cleaning detergents that are recommenced for cleaning concrete.
  • Then the concrete surface is ground. The grinding of the concrete floor using concrete grinders to remove the contaminants.
  • The cracks if appears are filled using patching material. Depending on the desired finish requirement the concrete floor may be ground again with grinders having finer blades.
  • Then the floor is cleaned thoroughly. After that, the sealers are applied in a coat and allowed to dry.
  • Grind and sealed concrete has more consistent appearance because the desired shine is not due to grinding process but due to the sealer compound.

Selecting Concrete Sealers

There are various types of sealers out there in the market. But the question is how to choose the sealer which works out best for you

Different types of sealers, their coverage rate, and the number of coats required are given in the following table. however, the coverage depends on the concrete surface whether new or old, the roughness of the service, etc.

As suggested by the website the spruce sealers offer 250-300 square feet per gallon and required 2 or 3 coats.

Type of SealerCoverage (square feet per gallon)Desired Coats
Acrylic150-2501 / 2 coats
Epoxy200-300/1st coat,
400-500/2nd coat
2 coats
Linseed Oil300-4002 coats
Polyurethane250-3501 / 2 coats
Silane250-4001 / 2 coats
Siloxane100-2501 / 2 coats
Silicate400-600/1st coat,
600-800/2nd coat
1 or 2 coats
number of Coats required for different sealers.

Application of Sealers

The following table indicates the use of sealers at different locations.

LocationsCharacterised bySuggested Sealer
WarehouseHeavy Traffic is present.Densified concrete
OfficeAesthetics and higher footfall.clear coat epoxy
Restaurant Front EndFootfallClearcoat epoxy/Densified Concrete/Polished Concrete
Restaurant-Back EndHot and cold Temperature.
Heavy chemical cleaning
Epoxy
Wet storage AreaSlipperyEpoxy with traction additive
Manufacturing AreaHeavy traction oil and lubricationEpoxy with chemical resistant
Rent purposesClean up quickly for next tenant, quick restoration for building saleAcrylic Sealer
Application of Sealers

What is the Difference between Polished Concrete and Sealed Concrete?

Polished concrete and sealed concrete are almost similar in appearance. Even some of us can’t distinguish between the two. The only difference is that the shine is achieved by different methods in these two.

Appearance

As I already said it is difficult to distinguish between the two because they look almost identical. Both the Polished and Sealed Concrete can have a matte, satin, or glossy appearance. But the process by which a matte, satin, or gloss appearance is achieved is completely different.

In polished concrete floor, the desired level of shine is achieved by using finer grits of diamond abrasive while in sealed concrete the shine is achieved by different types of sealers. The finish in the case of grind and sealed concrete is more consistent.

Durability

Polished concrete is more durable, it has a scratch-resistant finish and requires minimal maintenance and can last longer if properly maintained. However, the sealed concrete needs resurfacing frequently if traffic is high.

Cleaning

If polished concrete is installed in a place of heavy spill and stain, permanent marks can appear in the concrete. However, it is easy to clean the Sealed concrete.

Cost

Polishing is more labour intensive thus cost more. Sealed concrete is cheaper than polished concrete. However, the frequent repair makes it expensive in the longer run.

Is sealed concrete the same as polished concrete?

No, the sealed concrete and polished concrete are different. In sealed Concrete epoxy, urethane or acrylic is used to achieve the shine but in polished concrete, the shine is achieved by the polishing of the concrete.

What is meant by sealed concrete?

The concrete in which epoxy, urethane or acrylic is used to achieve the shiny surface is called sealed concrete.

What Concrete is sealed with?

Concrete is sealed with a thin layer of acrylic, epoxy or polyurethane layer applied just like paint.

What does sealing do to concrete?

Sealing fills the pores of concrete thus preventing the entry of moisture and dirt to it and increasing its lifespan.

Does sealing concrete make it shiny?

Yes. Concrete becomes shiny after sealing. Any level of shine right from matte to mirror-like shine can be achieved.

How many coats of concrete sealer should I use?

Acrylic- 1 / 2 coats
Epoxy- 2 Coats
Linseed Oil – 2 coats
Polyurethane- 1 / 2 coats
Silane-1 / 2 coats
Siloxane-1 / 2 coats
Silicate -1 or 2 coats

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