What is Crazing on Concrete Surface? Causes and Repair

Crazing on concrete is a type of physical cracks that are developed in the form of fine random cracks or fissures on the concrete or mortar surface. These are also called as shallow map or pattern or alligator cracking as they are observed as hexagonal irregular areas that are enclosed by cracks which are mainly between 40 mm to 30 mm across the length. These cracks are generally less than 3 mm deep and found in surfaces that are steel troweled. These are caused due to drying shrinkage and loss of moisture from the concrete surface.

Craze Cracks in Concrete in a Hexagonal Pattern

Craze cracks are formed in early stages of concrete placement or within one week of the placement. It  does not appear until the surface starts to dry out. These types of cracks are more unpleasant and unsightly in appearance which do not have a role in affecting the structural integrity.

Lets look in detail the causes, prevention and correction of crazy cracks in this article.

Also Read: How to Correct Hairline Cracks on a Concrete Surface?

Causes of Crazing in Cracks

The main cause of crazing in concrete is the loss of moisture. Any construction practice or condition that do not allow adequate moisture to retain on the concrete surface for strength gain and hardening would result in such defects. All related practices and causes that result in crazing of concrete cracks are:

1. Improper Curing of Concrete

If there is no continuous curing or when the curing process is delayed, the concrete is prone to dehydrate and result in crazing cracks.

2. Wet Concrete or Mortar Mix

A concrete or mortar mix with high water content that are prone to segregation and bleeding would settle the aggregates down and excessive quantities of cement and fines go to the top of the concrete surface. Which when dries gives crazing cracks.

3. Finishing Procedures

Finishing during bleeding water on the surface can result in more water to raise up and result in further crazing issues after drying out.

4. Sprinkling Cement

When the concrete surface is subjected to excessive bleeding, a measure taken is to sprinkle cement on the surface. This is one of the frequent cause of crazing in concrete. This procedure accumulates fines on the surface, which is not desirable.

Also Read: How to Fix Honeycomb in Concrete Structures?

5. Carbonation

Carbonation is a chemical attack on the concrete, which in some situation can be a indirect reason for crazing. During this chemical reaction between the concrete and carbon di oxide, the surface become really soft and as a result of which, cement is dusted over the concrete surface. Which can result in crazing of concrete surface.

Also Read: How to Identify Serious Wall Cracks?

How to Repair Crazing Cracks on Concrete Surface?

Crazing cracks do not affect the strength and durability of the concrete to great degree. These cracks are really shallow, and are not serious until they let any moisture intrusion. Some remedial measures to remove crazing cracks are:

  1. The monolithic appearance of the slabs can be corrected by the application of epoxy and silica sand. This will change the color and look of the surface, which can be corrected using any re-surfacing products. Read: What is Concrete Resurfacing?
  2. When we need to polish a concrete with crazing, we must grind right down to remove these craze which are generally 2 to 3mm deep or a grout can be used to fill the cracks.
  3. Normal grouts tends to slowly show the existing craze, which can be hence replaced by epoxy or latex based grouts and perform concrete polishing.
If we polish the concrete by keeping the craze cracks as such, the final quality of the surface and look will be different as shown in the figure-2 below. Read on : What is  Polished Concrete ?

Polished Concrete Surface Without Removing the Crazing Cracks
Figure-2: Polished Concrete Surface Without Removing the Crazing Cracks

So, before you perform polishing have a check with the client regarding concrete polishing over concrete craze cracks.



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