# Pouring over existing decent slab



## Stultzlawncare (Jan 16, 2018)

I have a 15 x 20 foot garage floor poured about 12 years ago. It isn't in bad shape it just wasn't poured smooth and I'd also like a drain on it. I'd like to add 3 foot to the front also. It has one hairline crack on it but that's it. Could I rough the surface up and pour 3 inches over the existing slab and pour the new part 5 inches thick?


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## greg24k (May 19, 2007)

Enclosed garage... Go ahead, you don't need to rough anything up since heaving is not a concern. If you want Concrete Bonding Adhesive to the existing floor, other than that the slab is not going anywhere.


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## Stultzlawncare (Jan 16, 2018)

Ok thanks man. Since the front of the new slab will only be covered with stone up to it level should I dig down 2 or 3 feet to avoid lifting in the winter?


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## Fishindude (Aug 15, 2017)

Tear it out and start fresh or you will have problems. Any cracks in the existing slab will telegraph up thru the new slab.


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## Stultzlawncare (Jan 16, 2018)

Even if I use the fiber mesh 4000 psi?


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## Windycity (Oct 3, 2015)

A Concrete contractor that I know bought an old building to use as a mechanic and storage shop for their equipment and did just that since the mechanic wanted a smooth floor instead of the pitted, cracked and uneven floor that was in there. 

I believe their pour was 4 inches right over the top and they drive heavy trucks (semis) on it...


Sent from my iPhone using Tapatalk


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## PennCoat (Apr 15, 2014)

make sure the existing concrete is sealed. dump some water on the surface and see if it beads up. If it does, then it's sealed. If it gets absorbed in the concrete, then whatever you top it with will likely dehydrate. And if the new pour dehydrates, then it likely won't bond very well, and you could hear some hollow spots down the road. Or you could get some alligatoring in the finish.


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## Fouthgeneration (Jan 7, 2014)

Option B: Polish/ grind old surface, caulk crack. Rent a terrazzo grinder and edger. Use the welder outlet or electric dryer plug in?

Leave old crete, drill (as far out of plumb as practical) in 1/4" holes with hammer drill, install a U-shaped, galvanized 1/4" wire 'Staple' between two holes that the is about 1.5" above the old floor to mechanically bond the slabs together. 

Two pieces of material fastened together are twice as strong in bending as two pieces just laying on one another....

At some point it is cheaper to demo the old crete, dig down the rock/ sand base, (for max load capacity, at least 2 x concrete thickness for base material) for the replacement products.


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## Stultzlawncare (Jan 16, 2018)

Thanks for all the replies. I ended up tearing it all out and it is kinda muddy under and was actually frost under the first 4 feet. I'm thinking I'm going to dig down to solid ground then add Maybe 6 inches of 3a modified with a power tamper then my 2b then concrete. Also dig down around the edges about 2 foot for frost.


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## parkers5150 (Dec 5, 2008)

PennCoat said:


> make sure the existing concrete is sealed. dump some water on the surface and see if it beads up. If it does, then it's sealed. If it gets absorbed in the concrete, then whatever you top it with will likely dehydrate. And if the new pour dehydrates, then it likely won't bond very well, and you could hear some hollow spots down the road. Or you could get some alligatoring in the finish.


nope:no:


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## fjn (Aug 17, 2011)

Stultzlawncare said:


> Thanks for all the replies. I ended up tearing it all out and it is kinda muddy under and was actually frost under the first 4 feet. I'm thinking I'm going to dig down to solid ground then add Maybe 6 inches of 3a modified with a power tamper then my 2b then concrete. Also dig down around the edges about 2 foot for frost.




2 " High density foam made specifically for placement under concrete would give you better results. It would work as a vapor barrier and insulation.


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## JBM (Mar 31, 2011)

Is there a frost wall there?


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