Curing Concrete

WHAT IS CURING Curing means to cover
the concrete so it stays MOIST.
By keeping concrete moist the bond between
the paste and the aggregates gets stronger.
Concrete doesn’t harden properly if it is left
to dry out.
WHEN TO CURE Curing is done just after
finishing the concrete surface, as soon as it
will not be damaged.
Precautions When curing leave the formwork in place to help reduce water loss. In hot
weather (above 30°C), or during high winds and low humidity, concrete can dry out easily.
In these conditions take extra care while curing.
See CHAPTER 12 Hot and Cold Weather Concreting
WHY CURE Concrete that is cured is:
LESS LIKELY TO CRACK.
More DURABLE.
Cured concrete has a surface that wears
better, lasts longer and better protects the
steel reinforcement.
Stronger The concrete can carry more
weight without breaking.



HOW TO CURE Concrete is cured by:
APPLYING EXTRA WATER to the surface of the concrete, or
STOPPING water loss from the concrete.
Methods The most common methods of curing are explained below.
The simplest method of APPLYING WATER is to put a
continuous fine, misty spray of water over the concrete.
BEWARE: The spray must be a very fine mist or
else it will damage the surface of the concrete.
Concrete will dry out more quickly in hot weather.
Keep the concrete continuously moist.
The most important thing in curing is to keep
the concrete moist at all times. Hosing in the
morning and again at night and letting the
concrete dry out in between is no good.
Another way to cure concrete is to cover with PLASTIC SHEETS to slow down water loss.
This method is easy and cheap. The only problem
is that the sheets may cause concrete to become
darker in places. To avoid this keep concrete
EVENLY moist.
The sheets must be held down to stop them
blowing away and the concrete surface drying out.
The sheets can be overlapped and stuck together
and/or held down with sand, timber or bricks.
Always check under the plastic from time to time
to make sure the concrete is EVENLY moist. If it
feels dry, sprinkle with water and put back the
plastic sheets carefully. Condensation on the
underside of the plastic is a good sign.



Concrete may also be cured by applying a CURING COMPOUND which slows water loss.
This should be applied soon after finishing. Always follow the manufacturer’s instructions
carefully. Curing compounds may be sprayed or brushed on.
BEWARE: Some types of curing compounds may later make it harder or impossible
to apply a surface finish to concrete such as paint, or to stick down floor coverings.
When using a curing compound, check with the supplier to ensure compatibility
with surface coatings or adhesives for future overlay finishes such as vinyl or tiles.
In rapid drying conditions (ie high wind, dry air and/or hot air) the use of an EVAPORATION
RETARDANT minimises the rapid loss of surface moisture and as such reduces the
incidence of early age plastic cracking.
See CHAPTER 16 Cracking in Concrete
These products contain a fugitive dye and are applied after initial screeding and floating,
and reapplied after each successive surface working until finished. In severe conditions
retardants will require reapplication. Evaporation retardants are not curing compounds;
their effect is temporary therefore once the concrete is finished, normal curing techniques
should still be used immediately.
HOW LONG TO CURE Concrete keeps getting HARDER AND STRONGER over TIME.
Household concrete jobs MUST be cured for at least 3 DAYS.
For better strength and durability, cure concrete for 7 DAYS.
The LONGER concrete is cured, the closer it will be to its best possible strength and
durability.
See CHAPTER 2 Concrete Properties and
See CHAPTER 3 Concrete Testing)