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| How
Important is Curing? |
The
hardening of concrete depends on
hydration, the chemical reaction
between cement and water.
The rate of hydration depends on
temperature, time and
moisture. Concrete should
be kept continuously moist for
at least 7 days. This can
be accomplished with fogging or
ponding or application of curing
compounds or covering with a
barrier such as polyethylene
sheeting. Cold and hot
weather conditions require
special procedures to prevent
freezing and shrinkage cracking
due to rapid evaporation. |
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| What
Are Blisters? |
Blisters
are hollow bumps on the concrete
surface, typically from
1/2" to 3" in
diameter. Blisters are
formed by hard troweling the
surface before the concrete has
stopped bleeding. Rapid
evaporation of the surface makes
the concrete appear ready for
troweling, while the underlying
concrete is still plastic.
Some ways to prevent blisters
include:
- Not pouring over
polyethylene sheeting.
- Floating rapidly without
working the surface
excessively.
- Taking measures to prevent
surface drying. (covering
with plastic)
- Delay finishing as long as
possible.
- Avoid using air-entrained
concrete for hard-toweled
finishes.
- Use as low a slump as
possible.
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| Do
I Really Need to put Joints in
the Slab? |
Cracks
in concrete cannot be
prevented...but they can be
controlled. Concrete is
weak in tension, and if that
tendency is restrained, cracking
will occur. Three basic
types of joints include
contraction, construction and
isolation. Each has a specific
application and should be
carefully planned. Depth
and shape of the slab, columns
or other obstructions and
containment (i.e. a basement
slab) are all important factors. |
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| What
Type of Finish Should I use? |
The
two main types used are
hard-troweled and broom
finish. Trowel finishes
are usually used indoors where a
smooth, hard and flat surface is
required. Broom finishes
are appropriate for exterior
slabs such as sidewalks,
offering durability and a slip
resistant surface.
Decorative finishes are also
available, including:
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