Pouring concrete over concrete

[millstreaminn]

Hi. I'm doing a major overhaul on my beef barn and have a question about pouring concrete over concrete. My concrete guy says the minimum he is comfortable with is 3 1/2" for the over pour, but the concrete company said they would pour it down as low as 2". The existing concrete is solid, with just your normal cracks. This over pour would be 3500PSI with fiber in it.

I have only ever poured concrete over concrete at 4", but that was just to add heat to the floor.

I don't want to spend $5,000 for new concrete if $3,000 will work.

Thanks-Scott

 

[ALACOWMAN]

ive seen it done over a driveway and it crumbled all to he$# ..... hope that helps

 

[skyhightree1]

personally I would go thick as possible .. ALA is right I have seen that happen as well when it was thin.

 

[Limomike]

It can be done. . but as was said before, it should be thick. Surface has to be clean too, no peeling or spalling. I think they put some type of adhesive down before they pour the new surface too. Good luck.

 

[CottageFarm]

Ask the concrete company if they will warranty a 2" pour....they'll start chuckling.

Go with your concrete guys recommendation. I wouldn't do anything less than 3" and I'd be a whole lot more confidant about closer to 4"
Acid etch the existing and neutralize. If the exiting has a steel trowel finish (unlikely) it will need to be scarified. I haven't worked in that field for almost 20 years. There were some good bonding agents available, but at that time they weren't really up to the task of a large surface recoat. They were acrylic based, and needed to be covered before drying completely. The fiber will help ALOT. I would also inquire about the cost difference for a 4000-5000lb mix. 3500lb doesn't seem strong enough for cattle.

I understand your desire to not spend more than needed, however you also don't want to spend $3000 and have it fall apart and have to spent another 7000 to fix the mistake.

 

[millstreaminn]

Thanks for the information. I wasn't planning to try and bond the new pour with the old, just kinda let them move-crack independently of each other. Was goon saw cut the slab into 10'x15' blocks, to try and minimize irregular cracks. The slab that is in there now is 4" of 3000 PSI that I poured in 1991.

3500 with fiber is $114 a yard and you add $3.00 a yard for each 500 PSI, thus 5000 PSI would be $123 a yard. I'm kinda leaning towards 3" of 5000 PSI...

 

[ALACOWMAN]

if the old slab is still in good shape. why do you need it??

 

[millstreaminn]

if the old slab is still in good shape. why do you need it??

When I built the barn in the early 90's, it was set up to hold holstein heiffers. The pens and headlocks were sized for them. I'm taking the headlocks out and replacing them with adult cow sized ones, as well as moving the feed alley from one side of the barn to the other. We jack hammered a lot of curbing out etc. Instead of patching all of that, I just want to pour over the whole thing.

 

[Named'em Tamed'em]

I've been stuck in the concrete industry for the last 30 years. A 2" slab would be a waste of money. I would pour a 4" slab 4000 psi. Any cracks you have in the existing slab will more than likely transfer through. Wire mesh or a #3 bar grid would help hold it together. If you choose fibermesh, don't go with the "stealth" mesh get the heavy comercial mesh fiber. As for a bonding agent, a 4 inch slab shouldn't need any since it will have it's own structual integrity and not need to bond. Have the ready mix co. add a mid range plastcizer (water reducer) to the mix. This will allow you to place the concrete at a more user friendly slump and help reduce shrinkage cracks and add strength (lower water to cement ratio). As soon as allowable seal the new concrete with a cure and seal product to slow the hydration process.

 

[millstreaminn]

Thanks for the info. I appreciate it! :clap:

 

[denvermartinfarms]

I've been stuck in the concrete industry for the last 30 years. A 2" slab would be a waste of money. I would pour a 4" slab 4000 psi. Any cracks you have in the existing slab will more than likely transfer through. Wire mesh or a #3 bar grid would help hold it together. If you choose fibermesh, don't go with the "stealth" mesh get the heavy comercial mesh fiber. As for a bonding agent, a 4 inch slab shouldn't need any since it will have it's own structual integrity and not need to bond. Have the ready mix co. add a mid range plastcizer (water reducer) to the mix. This will allow you to place the concrete at a more user friendly slump and help reduce shrinkage cracks and add strength (lower water to cement ratio). As soon as allowable seal the new concrete with a cure and seal product to slow the hydration process.

+1, a 2" cap is not going to work. Your guy that said 3 1/2 is doing you right.

 

[TennesseeTuxedo]

Shouldn't the concrete be scored in such a fashion as to facilitate better footing for the cattle?

 

[millstreaminn]

We're gonna rough up the finish before it sets completely. Kinda like a "broom" finish on a sidewalk, on steroids.

 

[CottageFarm]

Thanks for the information. I wasn't planning to try and bond the new pour with the old, just kinda let them move-crack independently of each other. Was goon saw cut the slab into 10'x15' blocks, to try and minimize irregular cracks. The slab that is in there now is 4" of 3000 PSI that I poured in 1991.

3500 with fiber is $114 a yard and you add $3.00 a yard for each 500 PSI, thus 5000 PSI would be $123 a yard. I'm kinda leaning towards 3" of 5000 PSI...

It won't work that way. Unless there is an isolation membrane between the slabs, the old cracks/control joints will transfer (eventually) to the top slab. A lot of that will be dependent upon the stability of the original substrate prep and your soil type and conditions. You would have to put your control joints in the new slab in the same locations as the old slab.

As for a bonding agent, a 4 inch slab shouldn't need any since it will have it's own structual integrity and not need to bond. Have the ready mix co. add a mid range plastcizer (water reducer) to the mix. This will allow you to place the concrete at a more user friendly slump and help reduce shrinkage cracks and add strength (lower water to cement ratio). As soon as allowable seal the new concrete with a cure and seal product to slow the hydration process.

Ditto all of this advice.