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I am about to commence work on extending my garage. I will be pouring a new concrete floor and trying to get as smooth a finish as I can. However, this will flow up to my existing garage floor which was very poorly laid.

enter image description here

It looks like when they were installing it, they just tamped it vaguely flat and nothing more. It's very difficult to move things around on castors (tables, wheel dollies, engine cranes) and wanted to know what my options were. As I see it I can:

  1. Break it all up and repour the entire garage as one big (steel reinforced) slab
  2. leave it as is and pour the new extension up to it so there are two surface finishes
  3. pour concrete on top of this to smooth is off

I'm reluctant to go with option 3 as it will raise the height of the floor and the floor is already a little higher than the outside. Much more and I'd have trouble getting cars in. Plus it would need to be thick enough to supports cars on it? Option 1 seems the best, but its a lot of work and double the money.

Are there any other options available to me? Is grinding a thing? I'm in the UK (Scotland) so that limits things a bit.

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    Normally concrete will be finished with a broom to leave a finish that is not slippery when wet. Apr 25, 2023 at 14:21
  • One cheap solution that might help short-term is to replace the castors on your tables with larger wheels. Probably not feasible on specialized equipment like engine cranes, but it's at least something and a lot less work than resurfacing the garage. Apr 28, 2023 at 13:49
  • Are you saying the new floor will be laid over or beside the existing one, or what? Apr 30, 2023 at 17:54

7 Answers 7

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This surface isn't a result of poor workmanship. It has been severely degraded, either by overwatering, a faulty mix, or chemical damage. This is why you see so much aggregate (and aggregate pockets).

Resurfacing it may restore it, but it may also just be a costly delay to replacement of the slab. I would have a local expert take a look in person before going to the trouble.

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Grinding is an option. Many home stores rent them out for a modest fee similar to the one shown below from Home Depot. If the surface doesn't have a lot of aggregate, the grinding would go fairly easy and fast.

enter image description here

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Unless you're married to the concrete look, I would consider doing a resin surface over that. I suppose you could even do a clear resin if you like the concrete look. You can even coat old and new pours and have it look more or less seamless (though obvs not if you use clear resin).

You won't be able to skim concrete on top of that—as you've noted, it will need to be an impractically thick layer.

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  • @JamesDrinkwater You can get also resin coatings in many different colors and designs (finishes?), at least on this side of the pond—do a web image search for resin garage floors.
    – Huesmann
    Apr 25, 2023 at 12:50
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    So the new part of floor should be concrete, with reinforcing rod/rebar/mesh installed up to code (or beyond), and tied into the existing slab with anchors epoxied horizontally. I'd leave it with a deliberately rough finish like the existing floor. Once that's all hardened and cured, probably a month, treat the old floor with muraic acid or something to etch for tooth, and then do a self-levelling resin or whatever is common locally. OP might choose an opaque finish, or a clear finish. Thickness should be whatever the resin maker suggests for the use-case.
    – Criggie
    Apr 25, 2023 at 22:06
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    OP might choose to add workbenches through the resin so they are firmly bolted to concrete before the pour, or even artistically embed some old tools/coins in the clear resin.
    – Criggie
    Apr 25, 2023 at 22:13
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Floor leveler

For example, Davco Lanko-133.

It flows freely and is largely self-leveling. It can be 1-25mm thick which will be more than adequate. It is relatively expensive compared to other concrete products.

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  • +1 Might need an isolation joint, as there will be cracks where the two slabs meet.
    – Martin
    Apr 26, 2023 at 14:09
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I agree option 3 is out. You need a minimum of 2 inches of new concrete over old and that is sketchy if you are placing heavy vehicles on it.

I would go with option 2. It's better to have a joint between the old and new as the new will do some settling. Then cover both with an epoxy coating such as this: Floor coating (Not an endorsement, used only as an example). The old floor may need 2 coats to smooth it more.

A statement of caution here: if the floor is too smooth it can be a hazard to walk on, especially when wet.

Good Luck!

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I'd pour the new slab next to the previous one. Maybe you can connect the two slabs with rebar by drilling into the side of the old one and inserting rebar held in place with chemical mortar.

Then pour some fiber-reinforced self-levelling compound over both slabs to get a uniform finish that's smooth and easy to roll on with caster wheels. These compounds have minimum and maximum thicknesses, so to save on the amount, it would be best to not make the new slab higher than the high points on the old slab, perhaps a few mm lower.

In any case there will be a risk of cracking at the joint, so it is best to create a pre-made straight crack with a diamond disc on the grinder. Not too deep, maybe 20mm. Then fill with polyurethane caulk.

Self-leveling compound is quite smooth but it is porous, so if you do engine work and you don't want the oil stains to sink into it and stay there forever, you can finish with floor paint or two component resin. You can add some anti-slip powder to it, or just very fine sand (<0.5mm) to make it non slippery even when wet. I just painted some stairs and adding some very fine sand costs nothing and really does wonders to the grip.

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Dry shake topping concrete is used when a powder coating is applied to the surface concrete after its been poured and before it has completely dried. It reacts with the concrete mix to create an extra hard surface that can withstand greater impact and wear & tear than your typical concrete floor.

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    As it’s currently written, your answer is unclear. Please edit to add additional details that will help others understand how this addresses the question asked. You can find more information on how to write good answers in the help center.
    – Community Bot
    Apr 26, 2023 at 20:34
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    You're right but OP's concrete has long-since cured. Is this a suggestion for the new slab? Or are you suggesting this treatment on top of a top-slab over the existing slab?
    – Criggie
    Apr 26, 2023 at 21:58

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