# How to prepare a garage floor before tiles go down

_Published by CAVE4MAN (https://cave4man.com) — storage, workshop and man-cave kit for UK home garages. The shop has not opened yet; nothing here can be ordered today._

_Updated 2026-09-19 · 6 min read_

**The short answer**

Clear the floor, sweep it, degrease any oil, and then look at the slab honestly. Loose-laid tiles tolerate dust, stains, old paint and hairline cracks far better than any coating, so most floors need no more than that. What they will not hide is a hump, a hollow or anything loose left underneath, which they telegraph straight to the surface.

**In this guide**

1. [Clear it, then look at it properly](https://cave4man.com/guides/garage-floor-preparation#clear-it-then-look-at-it-properly)
2. [Sweep, degrease, sweep again](https://cave4man.com/guides/garage-floor-preparation#sweep-degrease-sweep-again)
3. [What is actually wrong with the slab, and what to do about it](https://cave4man.com/guides/garage-floor-preparation#what-is-actually-wrong-with-the-slab-and-what-to-do-about-it)
4. [How flat is flat enough](https://cave4man.com/guides/garage-floor-preparation#how-flat-is-flat-enough)
5. [What to leave alone](https://cave4man.com/guides/garage-floor-preparation#what-to-leave-alone)

## Clear it, then look at it properly

Nobody has seen the whole of their garage floor for years. The shelving, the bikes, the mower and the pile in the corner have been on it since the day they moved in. Everything comes out: it is the only way to find out what the slab actually looks like, and a floating floor cannot be laid around a loaded unit anyway. Do it on a dry day and put the contents on the drive.

With the floor bare, walk it slowly. Look for cracks and whether the two sides of a crack are level with each other. Look for humps, hollows, old adhesive from a previous covering, patches of a different colour where a repair was made, and the white powdery bloom that means moisture has been coming up through the concrete. Sight along it from the door at floor level, where a hump shows up that you would never see standing.


## Sweep, degrease, sweep again

The slab does not need to be clean the way a floor about to be painted does, because nothing is going to bond to it. It needs to be clear of anything that will sit under a tile and rock it, and anything that will migrate up through the joints. That means grit, loose paint flakes, dried mud, the small screws and washers that have collected along the walls, and above all oil.

Oil matters not because it stops tiles working but because a fresh spill on bare concrete keeps spreading under the tiles for months, and a solid tile over an oily patch is a tile you cannot get a grip on when you want to lift it. Soak up anything liquid with an absorbent first, then a degreaser and a stiff brush, then rinse and let it dry. An old stain that has soaked in and dried is not a problem under a loose-laid floor; leave it.

Sweep again once the degreaser has dried. The first sweep moves the dirt, the second collects what the water lifted. Pay attention to the strip along each wall and the corners, where a broom does not reach and where a decade of screws, washers and dead spiders has collected. That strip is where the expansion gap will be, and anything left in it ends up under the edge row. A dustpan and a hand brush do the corners properly; a vacuum does them better.


## What is actually wrong with the slab, and what to do about it

The most useful thing to understand is that a loose-laid tile tolerates a bad-looking slab far better than a coating ever could, but it is not forgiving of an uneven one. Stains, dust and colour are irrelevant. Shape is not. A tile spans a small hollow and clicks when you stand on the corner; it sits on a hump and rocks; it bridges a loose flake of paint and crunches. The table sorts the common faults into the ones you can ignore and the ones you cannot.

For the ones you cannot, the fixes are ordinary. A hump is ground down or knocked off. A hollow is filled with a floor repair compound or a levelling compound, whichever the depth suits, and given the time the tub says to cure. Loose material is scraped off until what is left is solid. None of this needs to be pretty, because nobody will ever see it.

| What you find | Under a loose-laid tile | What to do |
| --- | --- | --- |
| Dust and old stains | Irrelevant | Sweep and move on |
| Sound old paint or sealer | Irrelevant | Leave it; scrape only what is flaking |
| Hairline cracks, both sides level | Bridged without a trace | Nothing |
| A crack with one side higher | Tiles rock across the step | Grind the high side or fill the low side |
| A hump | Tiles rock and the joint lifts | Grind or chip it off |
| A hollow or a dip | Tiles click underfoot in that spot | Fill with repair or levelling compound |
| Flaking paint or loose material | Crunches and shifts under the tile | Scrape to sound surface |
| White powdery bloom | A sign of moisture; not a defect in itself | Brush off; read the damp floor guide |


## How flat is flat enough

There is no magic figure, and anybody who gives you one has not seen your floor. The honest test is a long straight edge, a spirit level or a length of straight timber, laid across the slab in several places and both directions. Where daylight shows under it, that is a hollow; where it rocks, that is a hump. Run a hand along under it and you will feel the depth. A gap you can slide a coin under is nothing to a rigid tile. A gap you can get a finger into is a click every time you walk over it.

What you are looking for is not perfection but the absence of sudden change. A slab that falls gently to the door across its whole length is fine; the tiles follow it and you never notice. A slab with a ridge where two pours met is not, because a rigid tile cannot bend over a ridge and instead sits on it and rocks. Fix the sudden changes, leave the gentle ones.


## What to leave alone

Do not repaint or seal a floor that is about to be tiled. It gains you nothing under a loose-laid floor and it costs a weekend. Do not grind a whole slab smooth for the sake of it; grind the hump. And do not fill the movement joints, the deliberate straight cuts across a larger slab. They are there so the concrete can move without cracking somewhere worse, and a rigid tile bridges them without any help.

The one thing to look at rather than fix is moisture. A slab with that white bloom on it, or one that darkens in patches in winter, is bringing water up from underneath. Tiles will go down on it perfectly well because they are not bonded, but what happens under them afterwards is worth understanding before you decide between a solid tile and a perforated one. That decision has its own guide.

## Common questions

**Do I need to level a garage floor before laying tiles?**

Not the whole floor, no. Loose-laid tiles follow a gentle fall to the door without complaint. What they will not tolerate is a sudden change: a hump, a step across a crack, or a hollow deep enough to get a finger into. Fix those with a grinder or a repair compound and leave the rest alone.

**Can you lay garage floor tiles over painted concrete?**

Yes, as long as the paint is sound. Nothing bonds to the paint, so it does not matter that it is there. What does matter is paint that is flaking, because loose flakes sit under a tile and crunch and shift. Scrape anything loose back to a solid surface and leave the rest.

**How do you get oil off a concrete garage floor?**

Soak up anything still liquid with an absorbent such as cat litter or sawdust, sweep it up, then scrub the patch with a degreaser and a stiff brush, rinse and let it dry. An old stain that has soaked in will not come out entirely, and under loose-laid tiles it does not need to.

**Can you lay floor tiles over cracks in a garage floor?**

Over a hairline crack with both sides level, yes, and a rigid tile bridges it without a trace. A crack where one side sits higher than the other is a step, and a tile rocks across it. Grind the high side or fill against the low side before tiling. Leave the deliberate movement joints in a larger slab alone.

## Kit that does the job

- **Interlocking garage floor tiles** — £59.99, not yet on sale (https://cave4man.com/product/interlocking-floor-tiles)

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Guide page: https://cave4man.com/guides/garage-floor-preparation