Engineered Slab Void Forms for Structural Isolation
Slab void forms are used to create a controlled separation between structural concrete slabs and expansive soil conditions. This separation protects the slab from soil movement, allowing the foundation system to perform as engineered.
At Carton Forms LLC, our slab void forms are hand-assembled in Denver, Colorado and built with a clear understanding of engineering intent, soil expansion, and real-world jobsite conditions.
When slabs are part of the design, proper isolation is not optional. It is structural insurance.
Why Use Slab Void Forms
Slab-on-grade systems built over expansive soils are vulnerable to uplift pressure. As soil moisture changes, volume changes with it. Without isolation, that movement transfers directly into the concrete.
Slab void forms are used to:
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Create a compressible void space beneath structural slabs
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Prevent uplift pressure from transferring into the slab
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Reduce cracking and long-term structural stress
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Maintain separation between soil and structural elements
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Support engineered foundation performance in expansive conditions
When expansive soils are present, isolation is what allows load paths to behave as designed.
How Slab Void Forms Work
Slab void forms are placed over prepared subgrade prior to reinforcement and concrete placement. The corrugated carton structure supports the weight of wet concrete and reinforcing steel during the pour.
After the concrete cures and becomes self-supporting, the form gradually weakens from moisture exposure, as designed. As soil expands, it moves into the created void space rather than pushing upward into the slab.
The result:
Load goes where it is intended. Movement goes where it is allowed.
Construction & Materials
Carton Forms pier void forms are manufactured using the same proven methods as our slab and wall forms to ensure consistent, predictable performance.
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Wax-coated exterior cover to resist moisture during placement
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Corrugated cellular interior designed to support fresh concrete loads
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Water-based adhesives selected for controlled degradation
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Precision-cut geometry to maintain proper clearance around pier tops
Each form is hand-assembled for consistency and inspected before delivery.
Applications
Slab Forms are commonly used in:
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Structural slab-on-grade foundations
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Residential foundation systems in expansive soil regions
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Commercial foundation systems
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Post-tension slab systems
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Elevated structural slab designs requiring void space
They are suitable for both residential and commercial construction where soil movement must be managed.
Installation Considerations
Proper installation ensures slab void forms perform as designed. Common best practices include:
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Confirm soil conditions and engineered void depth requirements
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Prepare level, properly compacted subgrade
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Install forms tightly but without compression
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Protect from premature moisture exposure
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Coordinate reinforcement placement to avoid crushing or displacement
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Verify edge conditions and transitions at grade beams or piers
If project conditions differ from standard details, we are available to review specifications before the pour.
Compatible With Protection Board and Soil Retainers
Footing void forms are often used in combination with:
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Protection Cover Board to shield forms during reinforcement and concrete placement
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Plastic Soil Retainers to prevent lateral soil movement into the void space
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Pier void forms when slab and pier systems intersect
These components work together to maintain clean, functional void conditions beneath structural slabs.
Why Contractors and Dealers Use Carton Forms Pier Void Forms
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Built to meet engineering specifications
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Designed for predictable isolation performance
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Hand-assembled quality control
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Consistent sizing and dependable fit
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Jobsite-aware design
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Technical experience you can lean on
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Reliable delivery and clear communication
Nothing is assumed. Everything is earned.
Availability & Support
Carton Forms slab void forms are available through local concrete supply dealers. If questions come up around specifications, or take-offs, we work alongside our dealers to offer optional product and installation methods, that help ensure the right solution is quoted and supplied.