Want to pour new concrete on my garage floor?

Question

I have a detached 1 car garage on my home that is about 80 years old. The roof is new and the garage is in very good shape so i dont want to rebuild. There is a crack across the floor in one part of the garage. after the crack the cement floor slopes down (like it sank into the ground). When you enter the garge the crack is about 6 feet into the garage running across almost the entire floor. The slope is not very steep (maybe 3/4" over 5 feet). I was thinking of pouring new cement ontop of the existing cement floor and re-leveling it. Good idea? how do I do it?
Thanks!

Answer 1

You have two main problems:-

1. Part of your garage floor is subsiding. Pouring more concrete over the top may hide the crack for a while but if the floor is still subsiding then the crack will re-appear. The additional weight of more concrete on top may well increase the amount of subsidence.

2. You need a way of making the new concrete "key in" to the old concrete - otherwise all you'll get is a slab of new concrete that isn't really attached to the old stuff. This is then likely to crack as the two layers expand and contract independently with changes in temperature and with the car's weight going over it.

Depending on how exactly you garage is situated, you also may end up with your car having to drive up a "step" created where the new concrete is. If you reduce the step then the concrete will be too thin and it will crack.

The only solution to all these problems is to remove a good thick layer (say, 5-6 inches) of old concrete from the entire garage floor and follow the crack all the way down if you can. If an entire portion of the floor has sunk then that will need to come out completely along with any loose material underneath. Use the bits of broken old concrete to form a more solid foundation under the subsiding portion of the floor and make sure it is well compacted down.

You should ideally use steel reinforcing mesh on your new concrete flooor as this will help prevent further cracking. Pour one layer of concrete (say, 3 inches thick) and then lay the mesh on and follow that by another 2-3 inches. Work in sections and have some lines marked out to give you the right levels. The floor should slope very slightly downwards towards the main door so that water dripping from the car runs out of the garage.

Answer 2

Pouring A Garage Floor

Answer 3

That slope may be original. Garage floors need to slope away from the structure and out the door to drain water and keep rain from coming in. I usually slope mine starting at the back of the garage which makes the slope less visible. All concrete cracks. You can only try to control where and how. You can by a crack filler at a home store. as long at both sides of the concrete crack are level and the crack is no wider than 3/8" I would just use a crack filler. Color may not match perfectly but it will smooth it out. It even comes in a caulk tube for easy installation. http://www.quikrete.com/ has some good info.

QUIKRETE® Concrete Repair (No. 8620) is a sanded acrylic formula that is weather resistant, has excellent adhesion and remains flexible. Matches the color and texture of concrete surfaces.

If there has been a major crack other than what I described, you'll want a pro to look at it. At 80yrs old if it hasn't moved any in the last few years, it probably won't move any more.

Answer 4

There was a show on television recently (home improvement show) where they were leveling out a floor in a concrete slab house for the installation of some sort of special floor over it. What they used according to the contractor interviewed was a very special concrete mix that was made specifically to "level" and fill the floor in. I can't say for sure if this particular type of concrete patching mix is good for garage directly but could check with Lowe's of other place and see if you can find that material. If memory serves came in 5 gallon buckets and after mixing they poured it out and leveled some by hand, but most of it leveled itself out. I think there was some sort of acrylic or resin based stuff added in it that allowed it to do the job even though it was a very thin film of concrete as they didn't want it to crack and ruin the flooring they were installing above. The contractor made special mention of this as the host asked him how they could pour concrete in such a thin layer and not have it crack. Wish I had written down the name.

Answer 5

If your garage is that old I think that amount of cracking is normal. To pour a new floor, the old floor should be removed or the crack will reappear. The floors are now made with joints or cuts so the future cracks will follow the line. this way it looks good for a long time.

Answer 6

Not a bad Idea, but I would seal the crack with cement sealer and paint the whole cement floor with an epoxy garage floor paint. It is easier and workes quite well . It is also less expensive and you can pick up a couple of different kinds at the local big box store such as Lowes or Home Depot. Good luck.

Answer 7

well i wouldn't recommend repouring over existing floor. If anything i would jackhammer out floor that has settled, cut a straight line with a diamond blade and then repour floor to existing floor. That is the cheapest way to do it right. Otherwise i would jackhammer up entire floor and repour it. The first way would be correct but might not look pretty. The second way should look beautiful if you hire the right person to finish the concrete properly.

Answer 8

You also need to check and see if any footings are involved under the old floor. If the floor is sagging as you say, it's likely that the footings have failed - or weren't even installed in the first place. You may need to pour new bell-bottom footings to prevent the new floor from sibsiding just like the old one did.

Answer 9

Yes. Use a minimum of one and half inches thick new concrete over stable existing concrete. If the reason you are doing this is because the old slab is breaking up, you need to have a professional to look at it to determine if old slab pieces need to be removed and if you have enough head room, whether it will interfer with doors, etc. Wish you would of added why you are considering it and condition of existing. Post back with more info, please.

Answer 10

I assume being that old, the garage isn't very wide. I'd jack the slab back up and place lean mix (controlled strength material/slurry) under it. Then patch the crack.