New slab over old slab?

[City Farmer]

Hi guys

I was getting ready to build a new house on my 24 acres and the neighbor approached me and asked if I'd like to buy their house and property. I close in a couple weeks and now have 50 acres, 40 open and 10 wooded. Taking on debt & building a new barn isn't in the budget so fixing what I have will have to do for a while.

I've pretty much settled on the smaller higher building for my new shop.
Now to my question, has anyone poured over busted up concrete before or do I have to remove all the old?
I'd like to pour a new 6" rebar/fiber reinforced slab right over the top.

There are 2 steel sided pole barns on the property.

(1) 23'x40' - 10' Ceiling - trashed/busted up cement floor and one slider

(2) 25'x50' - 8' ceiling - animal barn with 2 sliders and a dirt floor.

Any help is appreciated,
Andy

 

[747driver]

I assume it is the 23' x 40' building ? How busted up is the old concrete floor? Is it just cracks but still level or really busted up where the floor is out of level ? How good are the pole barn posts...are they showing signs of rot ? If you just pour 6 inches on top of the old i don't see it lasting. You need to make it so the new slab floats on top of the old....meaning you make a footer around the edges so the new slab rests on solid ground. Pictures would help !

Chuck

 

[RNeumann]

If it's busted it's likely things are moving. Typical slabs are 4". It would be good to have a few inches of sand between the two layers to provide cushion and decoupling. This MAY help the cracks from below telegraphing up.

You should also do rebar. You are already having to redo substandard work- don't replace it in kind.

 

[crackerjack222]

I would not pour a new slab over an old busted up slab. there is probably a good reason the old slab is busted up and the new slab may suffer the same fate. That said, I have done something similar. When we built my house 24 years ago there was a lot of rock left over from the rock veneer we installed. Since the garage floor slab was about 20" higher than grade, we put the left over rock in front of the garage. I had hired a concrete guy to pour the approach to the garage and the driveway. He was going to just pour over the rock as is. I stopped him and had his guys wheelbarrow some leftover sand over the rock. Again he was going to pour over the loose sand. I stopped him and began hosing down the sand. Of course this meant we needed more sand. Only when it looked like we had as much sand in place as it was going to take did I give him the go-ahead to put the steel in and pour. After 24 years it has no cracks other than a few hairline cracks.

 

[EddieWalker]

I would remove the old concrete. You don't know why it's in bad shape and it's not worth the risk or expense of hoping for the best.

 

[Egon]

It all depends on the quality of the base under the old slab.

You may consider removing the old concrete and busting it up. Then make a proper base for the new slab using the busted stuff and additional crushed rock so the pad is above grade and well drained.

 

[Gary Fowler]

I would remove the old concrete. You don't know why it's in bad shape and it's not worth the risk or expense of hoping for the best.

I agree. Better to rent a heavy chipping gun (concrete breaker) and break up that concrete into small pieces for removal then prepare a good compacted soil / rock/ sand base. If you chip up the concrete small enough, you could use it back in the base for rough fill. Add small pea gravel and sand over the top and compact in to assure all voids between the broken concrete are filled with sand and rock. It is better to crush up the concrete and use it for fill than trying to dispose of it somewhere.

 

[City Farmer]

Thanks guys.
I had a feeling a tear out was going to be the consensus. The posts, trusses and metal are in good shape. I'm kinda surprised for being 40+yrs old theres no leaks or rot in either building. I didn't see how bad the floor was until the 2 cars and tractors were moved out. The building is high and dry but doesn't have any gutters. That's why I think the floor is busted up around the perimeter and by the front door.

 

[Streetcar]

How cracked is original slab and is there differential settlement?
Many roads are placed over the existing concrete. The existing concrete road is cracked and left in place

 

[Billrog]

Any advice may or may not be sound advice we have no idea what was under the old slab ( clay, gravel, sand ) wet area dry area cracks from settling or just poor concrete with no rebar. If it's on solid ground just pour over it with rebar I'd forget the fiber glass reinforcing fiber.