First, what you are looking at: three different problems
How a pro assesses a slab before quoting repairs
A good assessment is unhurried and mostly low-tech. The installer looks at the pattern: a single straight crack that follows a joint is a different story from a map of intersecting cracks, which can point to subgrade or curing issues worth discussing before any coating is promised. They check whether crack edges are at the same height — a lip where one side sits higher suggests movement that a rigid fill will not hold. They tap and probe spalled areas to find where the weak concrete ends and sound concrete begins, because patch material only holds when it is bonded to a solid base. And they ask about history: when the cracks appeared, whether doors have started sticking, whether water pools in one corner. None of that appears in a square-foot price, and all of it shapes the repair plan.
That assessment also happens alongside two checks covered elsewhere on this site: moisture testing, because vapor moving up through a crack can lift a repair and a coating together, and a full diamond grind, because grinding is what reveals the true extent of surface damage once the weak top layer comes off.
How cracks and spalls are actually repaired
- Cracks are opened, not just filled. The standard approach is to chase the crack with a V-shaped cut so repair material has clean, sound edges to bond to, vacuum out the dust, and fill with a compound matched to the crack's behavior — more flexible fills where some movement is expected, rigid fills where the crack is dormant and a hard, grindable surface is needed.
- Spalls are cut back to sound concrete. Loose, flaking material is removed until the patch will sit on solid slab, the cavity is cleaned, and a repair mortar or resin patch is troweled in slightly high, then ground flush after it cures. Skipping the cut-back is why DIY patch jobs pop out — the patch was glued to the same weak surface that failed in the first place.
- Everything is ground flush. A repair that sits even slightly proud or low will telegraph through a glossy coating and catch light across the whole floor. Grinding the repair level with the surrounding slab is the step that makes it disappear under a full-broadcast flake finish, which is the most forgiving finish over repaired concrete. A smooth metallic finish is the least forgiving — see metallic care and durability for why pattern choice matters over repairs.
- Repairs cure before coating. Patch materials need their own cure time before a base coat goes over them. Rushing that window to keep a one-day schedule is a false economy your installer should flag, not hide.
Control joints: fill them flush or honor them?
This is a genuine judgment call, and a trustworthy installer will walk you through both options rather than deciding silently:
What matters most is that the joint is not simply bridged with rigid coating and forgotten. A rigid film stretched across a moving joint is being asked to do the one job it cannot do. In valley-floor homes in Lincoln, Roseville, and Elk Grove, where slabs sit on soils that swell and shrink with the wet and dry seasons, that conversation is especially worth having in person, with your actual joints in view.
What happens if you coat over damage without repairing it
Coatings are thin films. They follow the contours beneath them faithfully — which is their virtue on a well-prepped slab and their problem on a neglected one. An unfilled crack shows as a dark line and can become a path for moisture and tire-borne grit to work under the film edge. An unpatched spall reads as a crater, holds dirty water, and its weak rim keeps flaking outward under the coating, enlarging the failure from underneath. A joint bridged without a plan tends to announce itself as a straight crack in the finish within the first few seasonal cycles. In each case the fix later is harder than the repair now: the coating has to be ground off in that area, the concrete repaired properly, and the system rebuilt and blended — the same grind-off logic described in fixing a failed DIY epoxy kit.
Questions worth asking any installer about your slab
- Which of my cracks look active, and how does that change the fill you would use?
- Will spall repairs be cut back to sound concrete and ground flush, or surface-patched?
- For my control joints, do you recommend filling flush or honoring them — and what should I expect to see in a few years either way?
- Is stem-wall and step damage included in the repair scope, or only the flat floor?
- If a filled joint re-cracks in the finish, how is that addressed under your warranty — as a defect, or as expected slab movement?
The answers matter less for any single phrase than for whether the installer has clearly looked at your slab as a specific slab. Vague reassurance before the quote becomes vague accountability after it.
Cost context
As clearly-general guidance only, most professional 2-car garage coating projects in our region land between $2,400 and $6,000 — see the cost guide for what moves a project within that band. Repair scope is one of the biggest movers: a clean, newer slab with a few dormant hairlines sits very differently from an older slab needing extensive spall work and joint decisions. That range is not a quote for your garage — your installer confirms exact pricing after assessing the slab in person.
The bottom line
Cracks, spalls, and joints are not reasons to skip coating a garage — they are the normal condition of real slabs, and repairing them is core professional work, covered in overview on our prep and repair page. They are reasons to choose an installer by their repair plan, not just their color chart. Get the assessment in writing, decide the joints together, and the coating on top has the foundation it needs to last.
More homeowner guides
Prep, grinding & crack repair · Grinding vs. acid etching · Polyaspartic deep-dive: UV stability and cure times · What a garage floor coating costs in Northern California
Not sure what shape your slab is in?
Describe the cracks and damage honestly on the quote form — that detail helps your matched pro arrive with the right repair plan, not just a color deck.
Educational note: this guide is general information only. Repair methods and materials vary by installer, product line, and slab condition — your installer's in-person assessment and written scope for your floor govern.