Preparation
Surface preparation: the half of the job nobody quotes
Preparation is where a coating job is won or lost, and it is the line a cheap quote economises on because the result is buried under the finish where nobody can inspect it. This page derives the profile your film thickness needs, then works out which method can actually reach it on your slab and how many machine hours that represents.
Preparation method for this slab
Diamond grind
to reach profile 4, in 2 passes
Profile note At this film the resin has enough mass to peel itself off a smooth slab, so it needs a profile you can catch a nail on.
Why one method and not another
These four are not interchangeable and they are not ranked by price. Each one reaches a different depth of profile, and two of them cannot remove what is already on a slab. Ruling one out is a fact about your floor rather than a preference.
| Method | Profile reached | Removes coatings | On this slab | Why |
|---|---|---|---|---|
| Acid etch | up to profile 2 | no | ruled out | Ruled out: acid does not touch concrete carrying a cure-and-seal or a penetrating sealer. It reacts with the cement paste, and here the paste is covered. |
| Diamond grind | up to profile 4 | yes | usable here | Removes what is on the slab and leaves a controllable profile. Slower than blasting but it works right up to a wall and it works on a slab that is not flat. |
| Shot blast | up to profile 5 | no | usable here | Fast, dry and self-collecting, and the only practical way to reach a deep profile over a large floor. Leaves a striped pattern that has to be crossed and cannot get near an edge. |
| Scarify | up to profile 9 | yes | ruled out | Ruled out: far more aggressive than this build needs, and the damage has to be repaired before coating. |
The acid-etch question, answered properly
Etching is the cheapest thing that looks like preparation, and it is the reason a large share of domestic garage floors peel. Acid reacts with the cement paste at the surface to leave a light texture. That is genuinely useful under a thin sealer on bare concrete. It is useless under a build coat, because the profile it leaves is too shallow for a film with real mass to key into, and it is worse than useless over a sealer or an old coating, where the acid never reaches the paste at all.
It also leaves salts behind, which have to be neutralised, rinsed until the water runs clean, and then allowed to dry completely — and a slab that has just been flooded with water is the worst possible substrate for a moisture-sensitive resin. The time that rinse and dry takes is rarely counted when people describe etching as the quick option.
This site rules etching out whenever the derived profile is 3 or deeper, or whenever anything is sealing the surface. At the settings above, the reason it gives is: Ruled out: acid does not touch concrete carrying a cure-and-seal or a penetrating sealer. It reacts with the cement paste, and here the paste is covered.
Where the hours come from
Machine hours are the machine-reachable area, multiplied by the number of passes, divided by a productivity rate. Hand hours are the strip around every wall and obstruction that no walk-behind machine can enter.
| Quantity | Value here | Source |
|---|---|---|
| Gross floor area | 384 sq ft | Your own measurement |
| Perimeter plus obstruction edge | 80 ft of wall, plus obstructions | Derived from your dimensions and obstruction count |
| Edge band no machine reaches | 4 in | Assumed — machine housings vary |
| Grinding productivity | 180 sq ft per machine-hour, one pass | Assumed |
| Shot-blast productivity | 500 sq ft per machine-hour, one pass | Assumed |
| Hand edging productivity | 45 sq ft per hour | Assumed |
The pass count is derived from what is on the slab: a sealer has to come off before the profile underneath means anything.
The total is those four components added: 3.9 machine hours, 1.4 hand-edge hours, 0.8 hours of clean-down between passes, and 1.5 hours getting the machine in and out. That comes to 7.6 hours, and it is written out because a total whose parts are not all on the page is a total nobody can check.
Things about this slab worth knowing before the machine arrives
- An hour and a half has been added for getting the machine in and out. A walk-behind blaster weighs enough that a step at the door is a genuine obstacle.
Biggest swing factor The pass count. One extra removal pass over a sealer or an old coating can add more hours than the entire coating operation takes.
What to do with this
- The dust this generates is a regulated hazard and a genuine nuisance — the dust control page derives what the federal silica table requires for the method above.
- Cracks and spalls are repaired after preparation and before coating, on the repair takeoff.
- These hours feed the labour lines on the installed cost page at whatever rate you are actually being charged.