Concrete Overlay Calculator

Overlay Bags scales directly with Surface Area, but two of this calculator's other inputs move it far more than a quick glance at their input ranges suggests. Overlay Type (1-4) looks like a minor style pick, but it swaps out both the per-bag coverage rate AND the per-bag cost from small lookup tables: at the default 400 sq ft / 1/8 in thickness, switching from micro-topping (1) to heavy resurface (4) alone shifts Overlay Bags from 11 to about 17.6 -- a roughly 60% swing -- because heavy-resurface mix covers less area per 50-lb bag (50 sq ft/bag at 1/8 in vs. 80 sq ft/bag for micro-topping), even though heavy resurface is actually the CHEAPER bag by unit price ($40 vs. $45 for micro-topping) -- the coverage shortfall outweighs the lower per-bag price, so total material cost still ends up higher for heavy resurface at the same area. Waste Factor also isn't a rounding afterthought: it's a direct multiplier on every material quantity (bags, primer, sealer, water) and on materialCost, so raising it from 10% to 20% adds roughly 9% more bags, not a token amount.

Overlay Thickness moves bags inversely -- doubling thickness roughly halves the coverage per bag, so bags needed roughly doubles too, since a thicker layer of the same mix simply covers less floor area per 50-lb unit. Because thickness and area both interact multiplicatively with the same coverage constant, a 10% change in either one moves Overlay Bags by a comparable amount near the calculator's defaults; don't assume area alone tells the whole story once thickness departs from the 1/8 in baseline this tool's coverage figures are built around. Primer and sealer scale purely with Surface Area and Waste Factor -- Overlay Type and Thickness never touch them, since bonding primer and protective sealer coverage rates are fixed regardless of overlay style or depth. All coverage and cost figures are generalized planning estimates; confirm bag coverage against the specific product's technical data sheet before ordering, since real-world coverage varies by substrate porosity and applicator technique.