best control joint in concrete in 2024

by | Jun 17, 2024 | Blog | 0 comments

Control joint in concrete are considered to be one of the most important props of construction which help in abolishing ugly defects and checking the solidity of constructed buildings and concrete regions. In the areas of concrete slab construction, with the process of drywall installation, and with efforts made to prevent crack formation, the nature of control joints becomes a delicate issue. This state-of-the-art-Handbook will explore all the key issues related to the control joints positioning and layout, as well as, the construction joint requirements in concrete as well as drywalls. If a person successfully implements these sorts of techniques in his or her projects, you are going to produce functional, long-lasting, beautiful structures. 

Control joint in concrete

It is important to know that concrete is basically a brittle construction material and it undergoes shrinkage when it is curing and thermal instabilities. These volumetric changes produce tensile stresses that tend to surpass the tensile strength of concrete hence leading to abnormal cracking. Control joint in concrete enable these cracks to follow a straight path across the path that has been determined by the engineer, this way they do not compromise the strength of the concrete element as well as its appearance. 

control joint in concrete

control joint in concrete

Design Considerations for control joint in concrete

The Design Considerations for control joint in concrete includes: 

  •  Control joint in concrete Slab Thickness : Thus a general rule is applied, and that is that the joint spacing should lie between a minimum of 24 times the thickness of the next slab and a maximum of 36 times the same measurement i. E. , Where the slab thickness is four, then the joint spacing should be between eight and twelve feet at the widest. 
  •  Concrete Mix Design: Shrinkage potential impacts joint spacing in a very similar manner; to reduce shrinkage, high cementitious and low W/C ratios are used with appropriate aggregates. 
  •  Exposure Conditions: Because they relate to a region of globe that undergoes scorching heat at one time and the freezing cold at other times accompanied by cycles of wet and dry periods, there is a need to change the spacing of the joints. 
  •  Control joint in concrete Depth: In general, it is advised to shave joints to ensure that the bar can pass through a quarter of the depth of the slab. This assist in ensuring that direction of the crack extends without changing on the joint plane. 
  •  Control joint in concrete Configuration: Joints can also be arranged in a sequential way; differently configured and positioned, they can be straight lines, L, T, or any other shaped configuration that is considered fitting. This is because the above factors result in aesthetic necessities and the structural layout impact this decision that is made. 

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Crack Control Joint Spacing

The spacing of control joint in concrete is an important consideration in the overall success of control joints a well as the avoidance of random cracking in concrete structures. Lack of spacers or incorrect spacers installation results in either having wide gaps between joints or having an excessive number of joints on the surface and this affects the aesthetics of the surface.

Calculating Joint Spacing

Even though the 24-36 time slab thickness is a good guideline, . The following methods can be used to work out control joint in concrete spacing, The PCA approach and the ACI approach. These methods consider the exemplary concrete attributes, the external conditions that the structure will experience, and the restraints on the joint spacing to identify the most suitable gaps.

Joint Layout and Configuration

In addition to spacing, the layout and configuration of control joint in concrete are essential for their effectiveness. Joints should be placed in a way that divides the slab into panels with a length-to-width ratio of approximately 1:1.5. This helps ensure uniform stress distribution and minimizes the risk of cracking outside the joints.

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Control joint detail

The placement and spacing are critical, and of course the detailing of the joint. Evidently, proper detailing helps to ensure that the joint does its expected work of controlling crack development while at the same time avoiding as much as possible the aesthetic impacts and the penetration of water into the joints. 

  1.  Joint Width: The width of a control joint normally varies between 6 and 10mm or up to ¼ to 3/8 inch. According to the amount of insertion, the wider the joints, the larger the movement and the bigger the chance of debris seizure. 
  2.  Joint Shape: The profile of the joint means the shape of the cross-section can be squared, V-shaped or may be of a semicircular form or even of other shapes. As for the joints, V-shaped and rounded ones are desirable as they offer a softer plane at which the crack starts and advances.  
  3.  Backer Rods: These compressible foam rods are putted at the bottom of the joint to the limiting and containment of sealant depth and creating a bond break. 
  4.  Joint Sealants: These are elastomeric substances that are placed over the backer rod to close up the joint and exclude water in the process. These should be able to bond with the concrete to also withstand the anticipated movement.  
  5.  Tooling: If joints are made with the help of grooving tool, the flap ought to be clean and without any sharp edges. 
  6.  Saw Cuts: Saw-cut joints should be smooth with sharp edge and burst surface. The roughness should be carved before sealing. 

  Control joint drywall

In case of drywall, control joints are used and they function as stress releasing parts. They incorporate a controlled crack path thus enabling the drywall panel to expand and contract as intended without leading for cracking of the drywall panel. It was revealed that an applied force or movement is likely to occur frequently in large surfaces of drywall, here is Placement Guidelines: 

  1.  Wall Height: Hence, control joints of walls longer than the specified 30 feet (9 meters) should be taken vertically every 30 on center. 
  2.  Ceiling Length: In the case of ceilings, favorable joint spacing is about 50 ft (15 m) on center while the spacing is guided by a structural engineer. 
  3.  Corners and Transitions: At inside and outside corners also at change of elevation, where one piece of drywall meets another like • Door and Window frames etc. 
  4.  Long Uninterrupted Runs: For work that spans long distances of uninterrupted DW walls you may require control joints. 

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Types of Drywall Control Joints:

There are the common Types of Drywall Control Joints:

  • Simple Score: There is now a small channel running from the tape-line to the edge of the drywall to offer a point of weakness for the crack to start.
  • Tape and Compound: Hangers are spaced thirty inches on center and the scored line is then capped with a control joint tape and joint compound.
  • Metal or Plastic Trim: Metal or plastic trims can be set with the joint compound where a neater and more polished look is intended while at the same time providing for movement.

Installation Techniques

Consequently, employing a utility knife, you will have to make a light scratch onto the drywall face paper in the line of the joint that is to be taped. It should be to the depth an opposing tool will be able to get and create a weak point but not so far that it penetrates the gypsum core. 

Place control joint tape over the scored line and for it to bond properly apply it on the center. 

Prepare the corner joints with joint compound or caulk or paint and sand the edges for that smooth look. If metallic or plastic trims are used, they should be set into the compound as well as the other components are set and painted. 

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It is important to incorporate control joints as soon as possible at construction stage to provide the necessary expansion and shrinkage allowances during the initial settling down of the building, make sure the side of the tape is bonded to the drywall and also covers any other piece that is adjacent to it, Smooth any joints that were created while working on the joint compound or caulk, in order to have that perfect look.

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