Garage Floor and Concrete Slab Repair in the Syracuse Area

Because it takes the same salt with none of the rinsing. NRMCA's written advice is that when conditions permit homeowners should hose off the accumulation of salt deposited by cars on driveways and garage slabs, and it warns that magnesium-based salts, which are used for pre-snow de-icing of roads, can be tracked by cars and accumulate on concrete surfaces. A driveway at least gets rain and snowmelt across it. A garage floor gets neither, and behind a closed door it dries slowly, so the solution sits on the surface and concentrates as it evaporates. NRMCA also names poor drainage that lets salt solutions accumulate as increasing the severity of the exposure. Add that the garage floor is usually the one slab that was troweled smooth, and that excessive finishing reduces the entrained air in the surface layer, and the pattern stops being a mystery.

It depends on what is under the pitting. NRMCA's position is that light to moderately scaled surfaces can be repaired but that the repaired surface will only be as strong as the base surface it has to bond to, that the unsound material has to be removed first by hammer and chisel, sandblasting, high-pressure washing or jack hammer, and that the surface receiving the repair must be sound. Where scaling is excessive and progressing, it says repair may not be feasible at all. There is a second test worth doing on a garage floor before anyone quotes a resurface: tap it. NRMCA's own method for finding delamination is a hollow sound under a hammer or a heavy chain drag, and a hollow slab has nothing sound to bond a new topping to.

NRMCA states that de-icing chemicals composed of calcium chloride and sodium chloride, which is rock salt, are considered acceptable for concrete, and that ammonium sulfate, ammonium nitrate and magnesium-based salts should never be used as a de-icer because they are chemically aggressive and destroy concrete surfaces. The awkward part is that magnesium-based salts are used for pre-snow de-icing of roads, and NRMCA notes they get tracked in by cars and accumulate on concrete surfaces, so some of it arrives on the tires whatever you buy for the driveway. There is also live research on this: Purdue University's Joint Transportation Research Program reports that some chloride-based salts react with the calcium hydroxide in cement paste to form calcium oxychloride, an expansive phase that can damage concrete. That sits in genuine tension with calcium chloride being called acceptable, and the honest position is that it is an open question rather than settled. What is not in doubt is the practical answer: nothing at all on a new slab in its first winter, clean sand for traction, and a rinse when the weather allows.

Three respectable sources give three different figures, so it is worth seeing all of them. The Residential Code of New York State, Table R402.2, asks 3,500 psi with air of not less than 5 and not more than 7 percent by volume in its severe weathering column for garage floor slabs, and footnote f lets a steel-troweled floor drop to not less than 3 percent air if strength is raised to at least 4,000 psi. NRMCA, consistent with ACI 332, the code for residential concrete, recommends ordering exterior slabs that will be continuously moist, exposed to freezing and subject to de-icing chemicals at 4,000 psi with about 6 percent air at 3/4 or 1 inch aggregate. ACI 318's severest freezing and thawing class, which is the condition of concrete that is frequently wetted, freezes and has de-icing chemicals applied to it, sets a 0.45 maximum water to cementitious ratio and 4,500 psi for plain concrete, and deliberately matches its requirements to the class for concrete exposed to an external source of chlorides. A garage floor in this county is doing the hardest version of that job, so the top of the range is the sensible read rather than the code floor.

There is no published figure for this county, and anyone who quotes you one is guessing. In the Residential Code of New York State, Table R301.2(1), the climatic and geographic design criteria, is published with every column blank and the values are established by the local jurisdiction. Its footnotes direct that jurisdiction to fill in the weathering index for concrete and the frost line depth itself. New York's own regulation on the point, 19 NYCRR 1202.12, makes the owner responsible for providing those criteria as established by the city, town or village with a permit application, and where local criteria have not been established, for obtaining them from a registered architect or professional engineer. The code adds one useful rule: where weathering requires a higher strength concrete than the structural requirements need, the weathering requirement governs. So the number comes from your municipality rather than from a chart on the internet, and the figures that circulate for New York have no statewide basis behind them.