Concrete FAQ
What is concrete?
Concrete is a mix of cement, sand, gravel, water, and other chemicals. After the water is poured into the cement, hydration happens, and this holds the mixture together.
The finished look of concrete appears to be a solid slab but is slightly porous. Sponge-like capillaries are commonly seen throughout the slab after the excess water in the mix evaporates.
Can I pour concrete in all weather?
It can be challenging for the hydration process to happen in extreme weather. When the temperature is close to freezing, hydration is nearly impossible, and the concrete will not cure properly. Ideally, the ground should be at least 50 degrees or more. However, if the temperature is too hot, evaporation will be quicker, which makes it challenging to keep the concrete wet.
What kind of sub-base should I use?
The topsoil should be cleared, and a sub-base of stone or gravel should be placed and compacted to ensure the slab has a consistent thickness.
Proper grading is crucial to ensure water flows away from any structures. The base should slope ¼" every linear foot for adequate drainage.
How thick should the slab be?
Generally, a 4-inch width for sidewalks and 5-6" for driveways is recommended. For aprons, it is ideal for keeping the thickness to 7" to 8".
Should I use reinforcement in the concrete?
Steel reinforcement is essential to prevent cracks later in the life of the slab. The wire mesh should be elevated to the center of the slab as the mixture is poured. You can add fiber to the concrete to reduce cracking and permeability.
The genetic component of concrete.
There is a unique mix of concrete for every type of application. The market offers different mixes that involve adding more Portland cement that impacts the strength of the concrete. In general, we use 6 ½ bag mix of cement with a compressive strength of 3500 psi for sidewalks and 4000 psi for driveways.
Concrete doesn't need much water to get the desired strength. Keep in mind that too much water will significantly diminish the concrete's strength. The secret to a perfect mixture is the consistency of freshly mixed concrete. To increase the slump, you should add more water to the mixture. For sidewalks and driveways, we typically use a slump of 3" to 4".
Is it true that concrete shrinks?
The concrete shrinks to ½" for every 100 linear feet as it cures.
Does the shrinkage cause the concrete to crack?
Yes. Control joints should be installed in the concrete to allow stress relief. Control joints should be at least 2 to 3 times the thickness of the slab. For instance, a 5" slab's control joint should have control joints every 10 to 15 feet.
The thickness of the slab should be a quarter of the slab. So, for an 8" sidewalk, it should have 2" deep control joints.
Isolation joints, on the other hand, are areas where concrete slabs touch another fixed structure. In these situations, a pre-molded joint filler of ½" to ¼" is required.
Concrete is a mix of cement, sand, gravel, water, and other chemicals. After the water is poured into the cement, hydration happens, and this holds the mixture together.
The finished look of concrete appears to be a solid slab but is slightly porous. Sponge-like capillaries are commonly seen throughout the slab after the excess water in the mix evaporates.
Can I pour concrete in all weather?
It can be challenging for the hydration process to happen in extreme weather. When the temperature is close to freezing, hydration is nearly impossible, and the concrete will not cure properly. Ideally, the ground should be at least 50 degrees or more. However, if the temperature is too hot, evaporation will be quicker, which makes it challenging to keep the concrete wet.
What kind of sub-base should I use?
The topsoil should be cleared, and a sub-base of stone or gravel should be placed and compacted to ensure the slab has a consistent thickness.
Proper grading is crucial to ensure water flows away from any structures. The base should slope ¼" every linear foot for adequate drainage.
How thick should the slab be?
Generally, a 4-inch width for sidewalks and 5-6" for driveways is recommended. For aprons, it is ideal for keeping the thickness to 7" to 8".
Should I use reinforcement in the concrete?
Steel reinforcement is essential to prevent cracks later in the life of the slab. The wire mesh should be elevated to the center of the slab as the mixture is poured. You can add fiber to the concrete to reduce cracking and permeability.
The genetic component of concrete.
There is a unique mix of concrete for every type of application. The market offers different mixes that involve adding more Portland cement that impacts the strength of the concrete. In general, we use 6 ½ bag mix of cement with a compressive strength of 3500 psi for sidewalks and 4000 psi for driveways.
Concrete doesn't need much water to get the desired strength. Keep in mind that too much water will significantly diminish the concrete's strength. The secret to a perfect mixture is the consistency of freshly mixed concrete. To increase the slump, you should add more water to the mixture. For sidewalks and driveways, we typically use a slump of 3" to 4".
Is it true that concrete shrinks?
The concrete shrinks to ½" for every 100 linear feet as it cures.
Does the shrinkage cause the concrete to crack?
Yes. Control joints should be installed in the concrete to allow stress relief. Control joints should be at least 2 to 3 times the thickness of the slab. For instance, a 5" slab's control joint should have control joints every 10 to 15 feet.
The thickness of the slab should be a quarter of the slab. So, for an 8" sidewalk, it should have 2" deep control joints.
Isolation joints, on the other hand, are areas where concrete slabs touch another fixed structure. In these situations, a pre-molded joint filler of ½" to ¼" is required.
Do all concrete crack?
Yes. Concrete will crack at some point. To control and prevent the cracking, the correct mixture and proper installation are crucial.
Wear and tear and stress due to shrinkage are some of the common reasons for cracking. Stress due to poor sub-grade is also a common reason.
How do I deal with apparent cracks in my concrete?
As much as possible, we do not recommend fixing hairline cracks until they are 1/8" to ¼." At this time, we can use a grinder and grind the crack. We will also caulk it with self-leveling concrete caulk. Generally, the caulk should be tack free in two hours and is fully cured in a week or two.
What finish should the concrete have?
A clean and simple "broom finish" is what we typically recommend to allow traction and aesthetic finish.
How long does it take for concrete to cure?
As concrete gets older, it also gets stronger. The process of curing persists for years. The hydration process goes on fast then slows down, so it is safe to say that concretes are rated at their strength on the 28th day since installation. We recommend car traffic to enter the concrete driveway after three days and trucks after seven days, for practical reasons.
What curing compound do you use?
It is crucial to keep proper moisture levels in new concrete and protect it from the sun and wind during the early stages of hydration.
Are concrete sealants necessary?
It depends on your personal preference. We can apply a sealant after the concrete had cured for at least 28 days. Sealants are applied to keep moisture from getting into the slab. The sealant should still give room for the concrete to breathe to allow moisture from the ground to evaporate.
Why is exposed aggregate concrete more costly than standard concrete?
This is because of two reasons: first is that it uses smoother and larger gravel in the mix. The second reason is that it uses a two-step process. After the concrete is at the finished state, a special surface retarder is sprayed over the area. It allows the center of the concrete slab to cure while letting the surface stay malleable. After a day, we will come back to hose off the top layer of concrete with water.
What does "spalling" mean?
Some areas have severe freeze-thaw cycles where water gets into the concrete and freeze that result in parts of the concrete to spall or chip off. Sealants are used to protect the concrete from spalling.
Why should I use salt on my newly-installed concrete?
Concrete can be vulnerable to water damage during its first winter. In times like this, the salt melts ice and lets the water to penetrate the concrete. After the water freezes again, it causes the concrete to expand to as much as 9%, resulting in the spalling off or chipping off the surface of the concrete. The use of cinder chips or sand on the concrete is recommended by the Portland Concrete Association.
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Yes. Concrete will crack at some point. To control and prevent the cracking, the correct mixture and proper installation are crucial.
Wear and tear and stress due to shrinkage are some of the common reasons for cracking. Stress due to poor sub-grade is also a common reason.
How do I deal with apparent cracks in my concrete?
As much as possible, we do not recommend fixing hairline cracks until they are 1/8" to ¼." At this time, we can use a grinder and grind the crack. We will also caulk it with self-leveling concrete caulk. Generally, the caulk should be tack free in two hours and is fully cured in a week or two.
What finish should the concrete have?
A clean and simple "broom finish" is what we typically recommend to allow traction and aesthetic finish.
How long does it take for concrete to cure?
As concrete gets older, it also gets stronger. The process of curing persists for years. The hydration process goes on fast then slows down, so it is safe to say that concretes are rated at their strength on the 28th day since installation. We recommend car traffic to enter the concrete driveway after three days and trucks after seven days, for practical reasons.
What curing compound do you use?
It is crucial to keep proper moisture levels in new concrete and protect it from the sun and wind during the early stages of hydration.
Are concrete sealants necessary?
It depends on your personal preference. We can apply a sealant after the concrete had cured for at least 28 days. Sealants are applied to keep moisture from getting into the slab. The sealant should still give room for the concrete to breathe to allow moisture from the ground to evaporate.
Why is exposed aggregate concrete more costly than standard concrete?
This is because of two reasons: first is that it uses smoother and larger gravel in the mix. The second reason is that it uses a two-step process. After the concrete is at the finished state, a special surface retarder is sprayed over the area. It allows the center of the concrete slab to cure while letting the surface stay malleable. After a day, we will come back to hose off the top layer of concrete with water.
What does "spalling" mean?
Some areas have severe freeze-thaw cycles where water gets into the concrete and freeze that result in parts of the concrete to spall or chip off. Sealants are used to protect the concrete from spalling.
Why should I use salt on my newly-installed concrete?
Concrete can be vulnerable to water damage during its first winter. In times like this, the salt melts ice and lets the water to penetrate the concrete. After the water freezes again, it causes the concrete to expand to as much as 9%, resulting in the spalling off or chipping off the surface of the concrete. The use of cinder chips or sand on the concrete is recommended by the Portland Concrete Association.
Click here for more information.