Sherwin-Williams says non-moving joints should be filled flush with a rigid filler compatible with the flooring system before that system goes over them. This guide covers how joint fillers differ by hardness and intended movement, and what a written scope should spell out so the repair holds up once the coating is applied. It is written for the facility manager, property owner, or general contractor who is scoping and bidding a floor-coating project, not for the crew doing the installation. It covers non-moving joints and how fillers differ; see the Colorado Concrete Surface Preparation contractor hub and the Colorado Commercial Epoxy Flooring contractor hub for related services. Expansion and isolation joint treatment is a related but separate subject and is only mentioned here in passing.
FloorSpec's surface-preparation scope lists crack repair and joint filling as steps to create a sound substrate for the coating.
Concrete slabs also keep moving after they are poured and cut. SASE's installation timing guide states that as slabs shrink, joints widen — a joint originally cut at 1/8 in. may open to 3/16 to 1/4 in. or more, and SASE notes that about 20-30% of total shrinkage tends to happen in the first 30 days after placement. SASE ties joint-filling timing to slab shrinkage; SASE and Simiron each state a minimum concrete age for their own product: SASE's own FlexJoint 85 data sheet calls for a minimum concrete age of 28 days, depending on curing and drying conditions, and cites ACI and PCA guidance to postpone joint filling 60 to 90 days after slab placement, longer if conditions permit; Simiron's 860JF calls for concrete at least 28 days old.
Commercial slabs generally include a mix of the following:
ACI's abstract for ACI 224.3R (a 1995 report, reapproved 2013) describes it as a state-of-the-art review of joints and joint sealant materials across many structure types, including slabs-on-grade; the abstract does not mention coatings.
Manufacturer data sheets and tech tips describe parts of this sequence: confirm slab age against the product's minimum, fill with a compatible filler, and bring it flush; check the filler's data sheet for cure timing before coating.
ASTM C881/C881M is a specification for two-component epoxy-resin bonding systems for concrete, classified by type, grade, class and color. If a product is cited as meeting ASTM C881/C881M, ask for its type, grade and class; the standard does not cover cement-, aggregate- or fiber-modified epoxy systems or address creep. It is a material specification, not a joint-filling method.
Each product's data sheet sets its own application and cure conditions.
Simiron states both hardness and joint type for its product. The table below summarizes publicly documented examples; always confirm current values on the manufacturer's current data sheet before specifying.
| Product | Hardness | Minimum concrete age before filling | Intended joint type | Source |
|---|---|---|---|---|
| Simiron 860JF (fast-set semi-rigid polyurea) | Shore A 91 | At least 28 days old | Control and construction joints | Per Simiron 860JF product data sheet |
SASE's FlexJoint 85 data sheet similarly calls for a minimum concrete age of 28 days, depending on curing and drying conditions, and cites ACI and PCA guidance to postpone joint filling 60 to 90 days after slab placement, longer if conditions permit. Sherwin-Williams' general tech guidance is that non-moving joints should be filled flush with a rigid filler compatible with the flooring system before that system is installed over them.
Which product fits a given project depends on the joint type, the coating system planned over it, and the slab's actual age and condition — all of which should be confirmed in writing before work starts. For budgeting, see the Concrete Surface Preparation Cost in Colorado guide.
A written scope for joint and crack repair ahead of coating should itemize, at minimum:
If the floor is a distribution or logistics facility with heavy forklift traffic, the scope should also note that joint and crack repair is being coordinated with the broader coating system planned for that use, which can be reviewed through the Colorado Warehouse Floor Coatings contractor hub and the Colorado hub for Warehouses & Distribution Centers facilities. For general price context, see the cost calculator and the Commercial Epoxy Flooring Cost in Colorado guide.
Questions to ask each contractor before you sign:
Joint and crack repair before coating addresses non-moving joints and cracks in an otherwise structurally sound slab — it is not a substitute for other repairs the slab may need. Expansion and isolation joints, which are designed to accommodate significant movement, are treated with different methods and are outside what a standard joint-filling scope covers. Spalled, delaminated, or otherwise deteriorated concrete at the surface is its own repair category and needs to be addressed separately from joint and crack filling. Sherwin-Williams describes filling non-moving joints flush before the floor system goes over them; if a contractor proposes a different treatment for a control joint, ask them to show the coating manufacturer's data sheet allowance in writing. If a slab shows ongoing movement, joint-filler guidance for non-moving joints does not apply; ask the contractor and design professional how the condition is being addressed.
Which joints move is a judgment for the design professional, and the classification should be documented in the scope. Sherwin-Williams says non-moving joints should be filled with rigid filler. If there is any doubt, ask the contractor how they classified each joint and what they are basing that on.
SASE and Simiron each state a 28-day minimum concrete age for their own fillers, and SASE cites ACI and PCA guidance to postpone joint filling 60 to 90 days after placement, longer if conditions permit. The exact timing depends on the specific filler product and the slab's actual curing and drying conditions, so confirm the figure on the current data sheet for the product being proposed.
Manufacturers publish hardness for their fillers: Simiron 860JF is Shore A 91. Confirm the proposed filler's hardness and joint-type limits on its data sheet, so this should be specified by name in the written scope rather than left general.
Sherwin-Williams says that not honoring moving joints can lead to cracks in the coated surface. Joints and cracks are listed as their own line item in surface-prep scope, so confirm they are included in the quote.
See the Colorado Warehouse Floor Coatings contractor hub for how joint and crack repair is coordinated with the coating system for that use. The underlying repair steps — classifying the joint, confirming slab age, filling flush, and allowing proper cure before coating — are the same process described throughout this guide.
What concrete surface preparation costs per square foot in Colorado, how it scales by market, and why prep scope often decides the final coating price.
What warehouse floor coatings cost per square foot in Colorado, how it scales by market, and what drives the price of a distribution-center floor.
How moisture mitigation systems work on slab-on-grade concrete, when a coating project needs one, and what to put in the written scope.
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