Pouring over old concrete floor


Old 05-05-13, 02:08 PM
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Pouring over old concrete floor

Hi all,

As you can see from the picture, the concrete floor of my detached garage is in pretty bad shape. In fact, what you see is after I swept away the bulk of the loose material. I say 'most' because it feels like you could sweep away most of the remaining material.

I was wondering about the possibility to pour new concrete right over it. Except for the face where the door is, the rest is enclosed by the footing which could act as the form. The surface is about 20' by 20'.

What thickness of what kind of concrete would you recommend? How would you prep the surface beyond removing the loose stuff? Would you take the time to lay down a mesh? And would you screw it to the existing surface to help adhesion?

Thanks in advance for any guidance,

P.S. sorry for the picture rotation. I'm puzzled.

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Old 05-05-13, 06:16 PM
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Pouring over loose concrete is not a good idea. If you want an easy way out, consider rubberized flooring. You could lay that on top of it.
Old 05-05-13, 11:02 PM
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Hey Pulpo,

Thanks for the insights. Rubberized flooring is what they use around skating rinks, right? I wonder if that would work given that those cracks, gaps, soft spots I have are up to 2" deep and maybe 15" across. I think I've seen those mats at the local hardware store, they are about 3/4" thick and fairly heavy, but I'd still want to somehow tie them together so they don't move around when I drag a trash barrel, park the car or do other manly jobs.

What's the biggest risk in pouring over old/loose concrete? I'm trying to understand how different from pouring over packed dirt it really is. Is retention of moisture in the old concrete what we're worried about?

Old 05-06-13, 12:16 AM
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I'm not in this line of work just making some observations.

One difference is when you pour a floor over dirt it is usually the desired finished thickness. Maybe 4-5." Maybe with mesh or re-rod. The thickness of the concrete supplies the strength.

Now you are pouring a thin coat over existing cement. You don't have that thick amount of concrete for strength and since you have loose cement you are losing even more of your finished strength. The layer you pour may just crack and come right back up.

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