The Garage That Used to Be a Room
Old adhesive on the slab, fastener holes in a grid, and no fall toward the door. What a converted-and-reverted garage brings to a coating job around Elgin, and the one question that has to be answered before a grinder is switched on.
Yes, a garage that was once finished as living space is usually still a good candidate for a coating - but it is a see-it-first floor, and one question has to be settled before anything touches the slab. Plenty of Elgin houses have a garage that spent a decade or two as a den, a shop, a spare bedroom or a playroom and then went back to holding cars. What that history leaves behind is not the wear a garage slab normally shows. It is adhesive residue, a repeating pattern of small holes where something was anchored down, striped shadows in the concrete, and quite often a floor that no longer sheds water toward the opening because for years it did not need to. Each of those changes the prep. None of them usually rules a floor out.
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TL;DR
Settle the adhesive question first: some older resilient flooring and the glue under it can contain asbestos, nobody can tell by looking, and identification belongs to a qualified professional before any tool abrades it. Once that is cleared, a converted garage is a normal but slower prep job. Expect residue that loads tooling rather than chipping away, a repeating grid of fastener holes to fill, banded staining that a full flake finish hides, and a slab that may be flat or falling the wrong way because it was built as a room floor. A coating follows the grade it is given, so drainage is a separate discussion from finish.
Before anything else: what is that adhesive?
Some older resilient flooring - sheet goods and tile alike - and the adhesive used to stick it down can contain asbestos. There is no way to know by looking at it, and you will not find a home test in this article, because there should not be one.
What follows from that is a single rule and it is not a flexible one: nothing grinds, sands, scrapes, abrades or heats that material until somebody qualified has identified it. Those actions are precisely what turns a material that is sitting quietly on a slab into dust in the air, which is why the identification comes first and the prep plan comes second. The federal EPA guidance on asbestos in the home is blunt about it: badly done sampling can be worse than leaving material alone, and the job belongs to a trained and accredited professional. In this state, licensing information and the directories of licensed asbestos professionals sit with the Illinois Department of Public Health asbestos program.
Practically, this means you raise it on the first phone call, not on install morning. Say the words: this garage used to be finished, there is old flooring adhesive on the slab, and it has not been identified. A contractor who waves that off is the wrong contractor. A contractor who says the material needs to be identified before they will scope the prep is doing their job properly, even though it is the slower answer and the one that delays your quote.
Everything in the rest of this article assumes that question has already been answered and the material has been cleared. Until it has, the sections below are reading, not a plan.
Why adhesive is a different prep problem
This site already covers coating over old paint, a previous epoxy or a sealer in the guide to coating an old or stained garage floor. Those are failed coatings, and they behave in a fairly predictable way under tooling: they are brittle, so they break up and release. Flooring adhesive is not that.
Residue is soft and it is sticky, so instead of breaking away it loads and smears. It fills tooling rather than coming off it, and it can move around under a machine instead of leaving. That is why a slab with adhesive on it is slower and more staged than a slab with old paint on it, and why an honest crew will tell you the exact approach gets settled on the floor rather than in advance.
There is a second reason nobody should be quoting this blind. Flooring adhesive is not one material. Different products from different eras behave differently, and a garage that was finished once and patched twice may have more than one of them on the same slab. A quote written from a phone description of "some old glue" is a guess about which of several jobs this actually is.
The end state is the same as on any other floor, though. A coating has to key into sound bare concrete, so the residue has to be gone rather than covered. Leaving it means the new system is bonded to the glue instead of to the slab, and the glue is the weakest thing in that stack.
The grid of holes and the striped shadows
If sleeper strips, furring or a framed subfloor were anchored down, the anchors left holes. You can usually spot them straight away because they run in rows at a regular spacing rather than scattered the way impact damage is. Sometimes there are also larger anchors where a partition wall met the slab.
Individually each hole is trivial. Collectively they are the story of the prep, because every one of them is a small void that has to be filled and ground back flush before a coating goes down. It turns into patching work by the dozen instead of the handful of repairs a typical garage slab needs. Our walkthrough of concrete crack repair before coating covers how that fill-and-grind step works, and the garage floor repair page covers the wider repair scope.
Two related things are worth flagging to whoever quotes the floor. Fasteners sometimes snapped off below the surface rather than pulling out, so there can be metal still sitting in the concrete. That is much better found by a person walking the slab than by a machine at speed. And where a partition or a stair once landed, the slab may have been chipped, patched or cut, which is a different kind of repair from a hole.
Then there is the banding. The concrete directly under each strip stayed dry and clean for years while the concrete between the strips collected dust, spills and whatever came through the floor above it. The result is a rhythm of lighter and darker stripes across the slab, often clearer than the wood ever was. Cosmetically this matters less than it looks like it should: a full flake broadcast covers the substrate completely, so the banding disappears. It matters more if you were leaning toward a solid color or a light flake density, because a thin, quiet film has more chance of letting a busy substrate read through. Our comparison of full flake against a solid color is the right place to make that call, and a banded slab is a genuine argument for flake.
No fall to the door, and a threshold that moved
Garage slabs are normally built to send water toward the opening. A floor that was poured, leveled or re-topped to serve as a room was built to a different priority, because water was not the design problem in a den. So converted garages often come back dead flat, and sometimes they fall gently toward the house wall instead of away from it.
That matters again the moment cars come back. Snow packed in a wheel well, rain off a bumper, and Kane County meltwater all arrive on the floor between December and March, and on a flat slab that water has nowhere to be. It stands, or it travels toward whatever the low side is.
Be clear-eyed about what a coating does and does not do here. It is a film on the surface and it follows the shape underneath it exactly, so a floor that does not drain before it is coated does not drain after either. What does change is that a sealed, non-porous surface stops soaking meltwater into the concrete and lets you squeegee or mop it out deliberately, which on a flat converted slab is a real day-to-day improvement rather than a fix for the grade. Anyone telling you a coating solves drainage is describing something else.
The other thing to look at is the opening itself. If the overhead door was removed and walled up during the conversion and then put back, the threshold and apron at that edge may have been rebuilt, patched, or cast to a different line than the original. The coating has to terminate somewhere along that edge, and on a converted slab that edge is often not the clean, uniform one an untouched garage gives you. It is a detail decided by somebody standing at the door with the light behind them, not from a form.
What you find and what it changes
A quick map of the conditions a converted garage tends to present, what each one actually is, and how it lands on the job. Treat it as orientation for the conversation with a contractor, not as a diagnosis of your particular slab.
| What you can see | What it usually is | What it changes |
|---|---|---|
| Dark sticky residue, patchy or across the field | Old flooring adhesive | Identification first, prep approach decided on site |
| Small holes in regular rows | Fasteners from sleeper strips or a subfloor | Many small fills, ground flush before any coating |
| Metal still sitting in a hole | A fastener that snapped rather than pulled | Flagged before grinding, not discovered during |
| Light and dark stripes at even spacing | Slab under the strips stayed cleaner | Mostly a finish decision; full flake hides it |
| Floor is flat or falls toward the house | Built as a room floor, not a garage floor | Grade stays as it is; water handling is separate |
| Threshold or apron looks rebuilt | Opening was closed up and later reopened | Where the film stops is decided at the door |
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One more thing the conversion did
A slab that spent years under sheet flooring, adhesive or a sealed subfloor has not been open to the air the way a bare garage slab has. That makes the moisture check part of the visit something to take seriously rather than tick off, particularly on a floor with basement or crawl space conditions nearby. Our guide to coating older basement floors covers why that reading matters on any slab with a covered history.
What to tell the estimator before anyone comes out
None of this is hard to describe, and describing it up front saves everyone a wasted visit. On the first call, say what you know:
- That the garage was finished as living space at some point, and roughly when if you have any idea.
- Whether there is adhesive still on the slab, and whether it has been identified by anyone qualified.
- Whether you can see fastener holes, and whether they run in rows.
- Whether water ever stands on the floor, and which way it runs when it does.
- Whether the overhead door, threshold and apron look original or rebuilt.
- What finish you were hoping for, since a banded slab pushes that conversation toward flake.
If you bought the house later and do not know half of it, that is a perfectly good answer. Most people are in exactly that position. It is also the reason a crew wants to walk the slab before they write anything down: a converted garage carries more genuine unknowns than almost any other residential floor, and the honest version of this job starts with looking rather than quoting.
Elgin has a lot of these. The post-war neighborhoods on both sides of the river are full of houses where a garage became a family room, a workshop or a bedroom for a while and later went back to being a garage, and the slab kept a record of the whole thing. Nearly all of them coat well once the prep is honest about what is on them. Our garage floor coating page shows the standard build, and a converted slab simply gets a longer front half. Request your free estimate and we will come and read the floor rather than guess at it.