- Control Joints are not intended to stop cracking but rather control cracking
- It is best to cut joints as early as possible either while finishing with a concrete groover or within 6-18 hours after finishing with a concrete saw.
- Plan out your control joint spacing 24-36 times the depth of your concrete slab
What is the best time to cut control joints?
Control Joints are not intended to stop cracking but rather control cracking It is best to cut joints as early as possible either while finishing with a concrete groover or within 6-18 hours after finishing with a concrete saw. Plan out your control joint spacing 24-36 times the depth of your concrete slab
When to cut control joints in concrete slab?
1 Control Joints are not intended to stop cracking but rather control cracking 2 It is best to cut joints as early as possible either while finishing with a concrete groover or within 6-18 hours after finishing with a concrete saw. 3 Plan out your control joint spacing 24-36 times the depth of your concrete slab More items...
How deep to cut control joints in concrete?
How Deep To Cut Control Joints In Concrete 1 A 4″ Slab = A 1″ Cut 2 A 5″ Slab = A 1.25″ Cut 3 A 6″ Slab = A 1.5″ Cut
Do you need to fill in saw cut concrete expansion joints?
Filling the saw cut is mandatory as control joints are 1/4 the thickness of the concrete. On a 4″ slab, that is a 1″ deep saw cut and nobody want to use that much caulking. Click to see full answer. Correspondingly, should you caulk concrete expansion joints?
When should control joints be cut?
Joints should be sawed as soon as the concrete can withstand the energy of sawing without raveling or dislodging aggregate particles. For most concrete work, cutting should take place within the first 6 to 18 hours and never beyond 24 hours.
How often should you cut expansion joints in concrete?
Usually, expansion joints should be no farther apart than 2 to 3 times (in feet) the total width of the concrete (in inches). So for a 4 inch thick concrete slab, expansion joints should be no more than 8 to 12 feet apart.
Why do you cut joints in concrete?
Saw cuts are a used to create control joints in concrete, which help control where cracking occurs due to shrinkage. The cuts should be made at a predetermined spacing and only after the concrete has obtained sufficient strength but before internal cracking begins.
Where do you cut control joints in concrete slab?
Cut joints 25% of the depth of the slab. A 4" thick slab should have joints 1" deep. Groover tools cut joints in fresh concrete. Saw cutting cuts joints as soon as the concrete is hard enough that the edges abutting the cut don't chip from the saw blade.
What is the difference between expansion joints and control joints?
Control joints can be isolated within the plane being treated (brick facades, concrete sidewalks) while expansion joints must bisect the entire structure thereby creating a gap throughout all of the building elements—foundation, walls, curtainwalls, plaza decks, parking decks, floors, and roof.
How far apart should control joints be?
Concrete control joints should be no less than ¼ of the total thickness of the slab (1” deep for a 4” thick pour) and placed no less than 2-3 times (in feet) the thickness (in inches) of the slab (8-12 feet apart for a 4” thick pour).
Do I need to cut lines in concrete?
When concrete is poured, it is very important to cut expansion joints in the concrete. By cutting control joints in the concrete you can better control the random cracking that inevitably occurs in concrete slabs soon after the concrete is poured and set.
Do I need expansion joints in concrete?
Concrete expansion joints are particularly important where there have been consecutive concrete pours and are also useful when laying concrete within an area bordered by walls or buildings or if objects such as manhole covers need to be incorporated.
How far apart should the control joints be for a 6 slab?
Rule #5: For better crack control keep the maximum distance between joints in feet at 2 to 2.5 times the slab thickness in inches. For a 6 in. thick slab, the maximum joint spacing should be limited to 12 to 15 ft. Exceeding a joint spacing of 15 ft.
How do you cut control joints?
0:0410:52Saw Cutting Contraction Joints In Concrete Floors & Slabs (Does It ...YouTubeStart of suggested clipEnd of suggested clipSo what we do is we saw cut down about a quarter of an inch as you can see in this picture here onMoreSo what we do is we saw cut down about a quarter of an inch as you can see in this picture here on my website. And what that does is it makes the slab crack in that saw cut.
What happens if you don't put expansion joints in concrete?
Concrete expansion joints give the slabs just enough room to move which helps prevent cracks & buckling. Without these joints, even a little movement creates pressure and stress on the concrete. Eventually weak spots can crack or buckle.
Should concrete control joints be caulked?
Caulking Concrete Cracks and Expansion Joints Caulking the joints and cracks is the best way to stop this from happening. Even expansion joints in your concrete driveway should be caulked. They can be the biggest culprit of water under your slabs.
Why do you need control joints in concrete?
Before you answer this question, you need to answer; what causes concrete to crack? There are a couple of reasons why your concrete surface will crack.
How to cut control joints in concrete
When cutting control joints, you need to consider a couple of crucial specifications. For instance, you need to get the depth right, timing, and the location of the cut. If you get one wrong, it messes with the whole process.
When should you cut control joints?
The perfect timing heavily relies on several factors. For instance, you need to consider the weather, concrete mix, how hard the concrete is, the kind of machine you will use to make joints, among others.
How deep should you cut control joints?
Besides cutting too fast, people often make the mistake of not cutting deep enough. That can lead to uncontrolled cracking.
Where should you place the control joints?
For a better and more desirable outcome, you need to place the joints in the middle of the concrete slab. That way, you will be dividing the concrete into equal sections.
Different types of concrete joints
When cutting joints in concrete slabs, there are three distinct types that you can consider:
Tips for cutting control joints
Here are some of the tips you need to keep in mind while cutting control joints:
How long after concrete is poured can you cut?
In hot weather conditions, saw cutting may start as soon as four hours after the concrete is poured. In cooler weather, sawing may not start for 12 hours after pouring. 1 The best way to determine whether the slab is ready is to make trial cuts to check for raveling. Saw cutting should start as soon as the raveling stops during these trial cuts.
What happens if you cut concrete too early?
Cutting too early causes raveling, an effect created by the saw blade pulling the aggregate out of position, leaving a messy, weakened edge along the cut. This also causes undo wear on diamond concrete saw blades. Sawing too late can result in uncontrolled cracking as the concrete contracts during curing.
How far apart should joints be on a concrete slab?
Joints shall be spaced at 24 to 36 times the slab thickness but this need to be confirmed by a structural engineer. Joint spacing normally ranges between 10 to 18 feet depending on the amount of reinforcement the slab has. 1 If you are using high shrinkage concrete, you might want to decrease the cut spacing.
Why delay sawing concrete?
Some contractors delay sawing to protect their equipment and saw blade to reduce blade abrasion. There are several types of saw blades that can be used, depending on the concrete type and how soon the cuts can be started. Other factors that can lead to excessive blade wear and joint raveling include:
Why do we use saw cuts in concrete?
Saw cuts are a used to create control joints in concrete, which help control where cracking occurs due to shrinkage. The cuts should be made at a predetermined spacing and only after the concrete has obtained sufficient strength but before internal cracking begins. Therefore, the timing of saw cuts is critical.
How to cut joints with water?
Once you've laid out the joints to be cut, mark them using a chalk line. If you're using water cutting equipment, make sure that the water is running all the way down to the blade. Allow the blade to reach the required depth, then start walking or moving the equipment following the chalk like mark.
Is it better to have smaller cracks or larger cracks?
It is better to have smaller cracks than to increase cost by having and maintaining several joints. Under hot weather conditions, you might want to try forming a larger square and then cutting interior joints. By doing this you will be controlling fast setting concrete cracks in larger areas.
How soon after a concrete saw can you cut off a joint?
Here is a quick recap of what you need to know. It is best to cut joints as early as possible either while finishing with a concrete groover or within 6-18 hours after finishing with a concrete saw. Always cut off of your corners as soon as possible because this is usually the first place cracking starts.
What happens if you cut concrete too early?
If you cut to early though you can cause your concrete to ravel on the edge of the cuts but if you cut to late you will end up with uncontrolled cracking. There are many different factors that come in to play when it comes to timing of administering cuts such as. Tools used to cut concrete. Blade type. Saw speed.
What happens if you don't cut your concrete?
If this step is not done properly then you are essentially wasting your time. You will find that your concrete is still going to crack wild in an uncontrolled manner. To plan out where you are going to puts your cuts it is going to be important to know the depth of your concrete slab.
How much does concrete shrink?
As concrete goes through it’s curing process it shrinks as much as 1/2″ over 100′ which of course will cause it to pull apart resulting in hairline cracks. It is also important to know that the more water used in the placing process, the more likely it is to shrink and crack.
Why don't engineers specify the time to see joints?
Engineers don't specify a time to saw joints because they don't know what time of year the concrete will be placed or even what time of day the contractor will decide to place the concrete. Unfortunately, the time to saw joints is based on experience and trial and error.
Can you cut concrete before a saw?
Sometimes concrete cracks before the saw can cut the joint without causing raveling. In these cases, consider using a lightweight saw that allows you to cut within a few hours after final concrete finishing. Using this equipment, you can place concrete in the morning, then cut the slab during regular working hours the same day.
What determines when to cut concrete?
Factors such as concrete mix, weather conditions, hardness of concrete and types of machines used for making the control joints determine when to cut the concrete slab. When the concrete is sawed with the help of blade before it has reached its initial setting time, the aggregates may strew out of the concrete slab and leave a messy, ...
How long after concrete is poured can you saw?
In hot weather conditions, sawing can be started 4 hours after the concrete is poured. In cold weather conditions, sawing can be started 12 hours after the concrete is poured. The best way to determine whether the slab is ready is to make trial cuts to check for ravelling.
How to determine control joints?
If you are using high shrinkage concrete, you might want to decrease the cut spacing. The factors that determine the location of control joints are : 1 Continuity: The joints must be continuous. 2 Square Pattern: They must form segments in square patterns. 3 Reinforcement: The ideal location of placing the control joints is where the steel reinforcement is less or not found. 4 Size of the segment: The square segments formed in the hot climatic conditions are larger than conventional segments due to the fast setting of concrete in a big area.
Where to place control joints?
Location of Control Joint. It is recommended to place the control joints in the centre of the slab dividing the concrete into equal segments. The spacing of the joints is in the range of 24 to 36 times the thickness of the concrete slab. If you are using high shrinkage concrete, you might want to decrease the cut spacing.
What determines the location of control joints?
The factors that determine the location of control joints are : Continuity: The joints must be continuous. Square Pattern: They must form segments in square patterns. Reinforcement: The ideal location of placing the control joints is where the steel reinforcement is less or not found.
