ACI Decorative Flatwork common mistakes
ACI Decorative Flatwork · Understand the traps and how to avoid them.
Treating decorative flatwork as ordinary flatwork and skipping the pre-placement substrate and moisture check before applying a topping or overlay.
Candidates learn standard slab placement first and assume the decorative surface is forgiving; they underestimate how bond failures, vapor drive, and curing differences drive most decorative callbacks.
What to do instead
Before every decorative placement, state the substrate preparation and moisture-verification step explicitly (clean and profile the surface, confirm it is sound and at an acceptable moisture condition for the product), then describe the bond coat or primer and the timing between steps.
Specifying or accepting a mix design or water addition without tying it to the decorative finish and exposure, then finishing on the wrong schedule.
Candidates memorize generic slump and strength targets and apply them to stamped, broomed, or exposed-aggregate work where workability, set time, and bleed behavior must match the finish.
What to do instead
Describe the intended finish first, then justify the mix and placement choices from it: consistent water-cement ratio, no water added at the truck beyond what the mix design allows, and a finishing window planned around set and ambient conditions.
Placing control joints only after the decorative pattern is laid out, so joints conflict with the stamp or score pattern and get omitted or misplaced.
Candidates focus on the aesthetic layout and treat jointing as a finishing afterthought, forgetting that joint spacing and depth are structural requirements independent of the pattern.
What to do instead
Plan joint locations before layout: establish panel spacing and depth per slab thickness and reinforcement, then design the stamp or score pattern to align with or conceal those joints rather than replace them.
Finishing too early or overworking the surface with a trowel or float, especially in hot, windy, or low-humidity conditions.
Candidates want a smooth, closed surface and keep working it, which draws bleed water up, traps it under a densified layer, and produces delamination, crazing, or dusting.
What to do instead
Wait for bleed water to disappear and the surface to support finishing without rutting; use the minimum passes needed, avoid wetting the surface to extend workability, and use evaporation-control measures (windbreaks, fogging, curing compound timing) when conditions demand.
Applying color hardener, stains, or sealers without confirming surface moisture, temperature, and cure state for that specific product.
Candidates generalize one product's application rules to all decorative products, but broadcast hardeners, reactive stains, and film-forming sealers each have different moisture and cure windows.
What to do instead
For each product, state the manufacturer's required surface condition (moisture, cure age, temperature range), test a small area, and adjust application and recoat timing to actual site conditions rather than a fixed schedule.
Skipping or mistiming curing because a sealer or decorative treatment is assumed to cure the concrete.
Candidates see a glossy sealed surface and assume curing is handled, not realizing sealers are not curing compounds and that curing must begin before the surface dries.
What to do instead
Identify the curing method separately from the decorative finish, start curing as soon as the surface can accept it without damage, and verify compatibility between the curing method and any later sealer or coating.
Ignoring ambient conditions (temperature, wind, sun, humidity) when scheduling placement and finishing of decorative work.
Candidates plan by clock time rather than by evaporation rate, so rapid surface drying causes crusting, plastic shrinkage cracking, and stamping that tears rather than imprints.
What to do instead
Estimate evaporation rate before placement, adjust start time, use set retarders or accelerators as appropriate, and have shade, windbreaks, or evaporation retarder ready before the surface is at risk.
Placing reinforcement or establishing slab thickness without relating it to the decorative finish and joint layout.
Candidates treat reinforcement and thickness as fixed inputs and don't connect them to crack control, joint spacing, and whether the decorative surface can tolerate the resulting crack pattern.
What to do instead
State slab thickness, reinforcement type and position, and joint spacing as one coordinated system, and explain how the chosen finish and pattern accommodate expected crack locations.
Applying a sealer or coating over a surface that is too wet, too green, or contaminated, then blaming the product when it blisters or peels.
Candidates want to protect the finished look quickly and apply sealer as soon as the surface looks dry, without checking moisture or removing curing residue and dust.
What to do instead
Verify the surface is at the product's acceptable moisture and cure condition, remove curing compound residue and contaminants per the manufacturer, and test adhesion on a small area before full application.
Failing to describe a repair or remediation path when a decorative defect appears, instead describing only the ideal installation sequence.
Candidates rehearse the successful sequence and have no plan for the deviations exam scenarios describe, so they cannot distinguish cosmetic fixes from structural ones.
What to do instead
For each defect, state whether it is cosmetic or structural, the appropriate remediation (surface prep and re-bond for delamination, patching or replacement for structural cracks), and the acceptance criteria before sign-off.