What can we help you with?
Technical flooring, delivered directly
- ESD flooring, urethane cement, terrazzo, and polished concrete
- In-house W-2 installation crews and experienced field leadership
- National service coverage with project-specific staffing plans
- Testing, documentation, and defined project closeout
- Dedicated support for corporate procurement and multi-site contracting
Phone: +1 (844) 687-1961
Suspended Slabs
Suspended slabs can develop different grinding depths and aggregate exposure across the floor. Deflection, surface hardness and the difference between normal-weight and lightweight concrete affect the result. A mockup on the suspended slab provides a more representative sample than one placed on the ground.
American Society of Concrete Contractors (ASCC) authors writing in Concrete Contractor describe these appearance risks and recommend locating the mockup on the suspended slab itself.
Our new concrete slab specification guide covers the broader placement and polishing decisions.
Plan for conditions that affect appearance
According to the ASCC authors, flexible structures can have high spots over beams and low spots at the middle of a bay, changing how deeply each area is ground and how much aggregate is exposed. Differences in density and surface hardness between lightweight and normal-weight concrete also affect grinding depth, and surface cracks remain visible after polishing.
Account for high and low areas
The ASCC article describes how flexible structures, including concrete on metal decks, can have high spots over beams framing into columns and low spots at the middle of a bay. Those differences change how deeply different areas are ground and how much aggregate becomes exposed.
The authors also compare suspended-slab deflection with curling in slabs on ground. They report that deflection in many suspended slabs exceeds the upward movement at curled ground-supported slabs, potentially producing larger areas of non-uniform aggregate exposure after polishing.
Our flatness at placement and before polishing guide explains why the slab’s condition when grinding begins matters to the intended finish.
Set expectations for lightweight concrete and cracks
According to the article, differences in density and surface hardness between lightweight and normal-weight concrete affect grinding depth and final appearance. A finish achievable with one may not be achievable with the other.
The authors also state that surface cracks in a suspended slab remain visible in the polished floor. Include those appearance considerations when selecting the finish.
Coordinate the mockup and project requirements
Because a ground-level mockup does not reproduce the suspended slab’s flatness, cracking or deflection, the ASCC authors recommend placing it on the suspended slab itself. ACI SPEC-310.1-20 applies to suspended slabs as well as slabs on ground once incorporated into the Contract Documents, and project-specific requirements govern conflicts.
Put the mockup on the suspended slab
A ground-level mockup does not reproduce the suspended slab’s:
- Flatness and levelness.
- Random cracking and variable crack widths.
- Deflection.
The ASCC authors therefore recommend placing the mockup on the suspended slab itself.
Our mockup planning and approval guide covers sample construction and approval before production polishing.
Use ACI requirements within their stated scope
ACI SPEC-310.1-20 applies to both slabs on ground and suspended slabs. It takes effect when incorporated into the Contract Documents, with project-specific requirements governing conflicts.
See our ACI specification guide for the specification’s role in project requirements.
Project Gallery
Frequently Asked Questions
It cannot reproduce all the relevant conditions. The ASCC authors identify differences in flatness, cracking, crack widths and deflection, and recommend placing the mockup on the suspended slab itself.
Do not assume they will produce the same result. The ASCC article explains that differences in density and surface hardness affect grinding depth and final appearance. It does not establish that one concrete type always produces a better finish.
The cited appearance guidance does not establish an allowable grinding depth. ACI SPEC-310.1-20’s applicability to suspended slabs is not structural approval for a particular depth of grinding. That determination belongs with the project’s structural designer.
Polished Concrete Knowledge Center
Resource links
Performance & Safety
Design & Aesthetics
Installation Guidance
Economics & Sustainability
Maintenance & Aftercare
Comparative & Decision-Making
Blog
Craftsman Publishes 2026–2027 ESD Flooring Technical Guide
ESD Epoxy Flooring Case Study: 34,000 SF Dallas, TX
