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Joint Filler vs. Crack Repair
Concrete joint filler supports joint edges against wheel impact. Crack-repair material repairs a defect in the slab. The materials can share similar chemistry while behaving differently when the concrete moves.
At Craftsman, we select the material around the opening’s function, expected movement, traffic, and finished appearance. We then coordinate preparation and installation with that material’s requirements.
Material selection is part of our polished concrete repair and joint-filling process.
Compare how each material handles movement
Semirigid joint filler supports joint edges under wheeled traffic but should not rigidly bond adjoining panels, and it is not a substitute for an expansion-joint sealant. Crack-repair materials are not all rigid, and a strong bond can become a problem where concrete keeps moving, so we check the selected material’s movement limitations before using it.
Joint filler supports the edges without locking the slabs together
- Material
- Semirigid polyurea or epoxy
- Movement
- Formulated to tear or lose adhesion
Semirigid polyurea or epoxy joint filler helps protect contraction and construction joint edges from damage caused by pallet jacks, material-handling vehicles, and other wheeled traffic.
The filler needs sufficient stiffness to support those edges. However, it should not rigidly bond the adjoining slab panels together and prevent them from moving independently.
The Concrete Polishing Council explains that semirigid fillers are formulated to tear or lose adhesion when substantial drying shrinkage opens the joint. They have limited ability to stretch laterally.
Semirigid joint filler is not a substitute for an expansion-joint sealant. For example, Euclid Chemical specifically excludes EUCO QWIKjoint UVR and EUCO QWIKjoint 200 from use as expansion-joint sealants.
Select crack-repair material for the expected movement
- Material
- Not all rigid; varies by system
- Movement
- Strong bond can become a problem
Crack-repair materials are not all rigid. The condition of the crack and the selected system determine which material is appropriate.
A strong bond is useful in a repair, but it can become a problem when the material bridges concrete that continues to move. Metzger/McGuire specifically prohibits using Rapid Refloor as a floor joint filler: its high adhesive and tensile properties can restrain movement and may cause concrete tearing if substantial movement occurs after installation.
We check the selected material’s movement limitations before using it. A product suitable for a stable surface defect should not be assumed suitable for a moving crack or joint.
What ACI specifies for polished floors
Where ACI SPEC-310.1-20 is incorporated into the project documents, it sets separate requirements for crack-repair materials and joint fillers.
Unless otherwise specified:
| Requirement | Crack-repair material | Joint filler |
|---|---|---|
| Material | Two-component semirigid or rigid polyurea or epoxy. | Two-component, 100% solids, semirigid polyurea or epoxy. |
| Appearance | Approximates the specified color and can be polished. | Closely approximates the specified color and can be polished. |
The specification permits rigid material for crack repair; its joint-filler provision calls for semirigid material.
Match joint-filler hardness to traffic
ACI SPEC-310.1-20 also sets the following joint-filler properties unless otherwise specified:
| Floor use | Minimum Shore A hardness, ASTM D2240 | Elongation, ASTM D638 |
|---|---|---|
| Pedestrian traffic | 60 | Above 25%. |
| Hard-wheeled traffic | 80 | Above 25%. |
These are requirements of the adopted specification, not universal selection rules for every project. Project-specific contract documents govern conflicts with ACI SPEC-310.1-20.
Material selection and installation must agree
Choosing a suitable filler does not settle its preparation or installation details. Joint depth, backing, surface preparation, and processing times still need to follow the selected system.
Our joint preparation, fill-depth, and backing guide covers those decisions.
Later separation also needs context. Concrete shrinkage can open a joint and stretch the installed filler until it tears or loses adhesion. Our joint separation and maintenance guide explains how to evaluate that condition.
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Frequently Asked Questions
Sometimes a product is approved for both, but the uses are not interchangeable by default. Check the manufacturer’s intended uses and movement limitations, along with the project specification.
A strongly bonded rigid material can restrain movement between adjoining concrete sections. If substantial movement continues, the concrete itself may tear. The selected product must be suitable for the movement expected at that location.
It supports joint edges against impact and helps reduce edge damage. Its relative stiffness serves a different purpose from a flexible joint sealant.
No. Semirigid filler can tear or lose adhesion as drying shrinkage opens a joint. Material selection, preparation, installation timing, and slab conditions all need to be considered.
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