Concrete over concrete
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Concrete over concrete (by DonV [OH]) Dec 2, 2021 5:47 PM
       Concrete over concrete (by Dodge [PA]) Dec 2, 2021 7:39 PM
       Concrete over concrete (by Jeff [OH]) Dec 3, 2021 5:46 AM
       Concrete over concrete (by Steve [MA]) Dec 3, 2021 6:01 AM
       Concrete over concrete (by DonV [OH]) Dec 3, 2021 6:03 AM
       Concrete over concrete (by Steve [MA]) Dec 3, 2021 7:00 AM
       Concrete over concrete (by DonV [OH]) Dec 6, 2021 1:44 PM

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Concrete over concrete (by DonV [OH]) Posted on: Dec 2, 2021 5:47 PM
Message:

Has anyone had any luck pouring concrete over existing, structurally sound concrete? This is outdoors and in any situation.

Also very important, if you have had luck how thick was the new (top) concrete?

I have run into situations like this many times as a rehabber and as an engineer - working with the City Engineer on street repair programs. I typically get a "NO" answer but I am sure there is a way - and if not someone could make a fortune figuring out a way to do this. --76.189.xxx.xxx




Concrete over concrete (by Dodge [PA]) Posted on: Dec 2, 2021 7:39 PM
Message:

Bush hammer, pressure wash, wet til saturated-surface dry, bonding agent, new concrete, prayers.

I've never seen it hold up as good as a single pour. --174.198.xxx.xx




Concrete over concrete (by Jeff [OH]) Posted on: Dec 3, 2021 5:46 AM
Message:

Fellow engineer here. I have done it successfully. Spread 1” of sand over entire old concrete, pour new concrete over top…normal (standard) thickness depending on what you are pouring. The goal is not to bond the two, you are just trying to use the old concrete as a base. The sand allows for some flexing and water to dissipate between the slabs. --142.54.xx.xxx




Concrete over concrete (by Steve [MA]) Posted on: Dec 3, 2021 6:01 AM
Message:

We've done it similar to Jeff[OH] but used rigid insulation between the existing & the new concrete. Depending upon what the pad was going to be used for we would install either a grid of rebar or 6x6 wire grid & definitely have fiber added to the mix. --71.174.xx.xxx




Concrete over concrete (by DonV [OH]) Posted on: Dec 3, 2021 6:03 AM
Message:

Thanks! In my current scenario I am hoping for a thin top layer, a couple inches. Basically, skim coating concrete. I cannot raise the grade more than 3 inches, preferably only 2 inches.

The sand idea is GREAT thanks! --76.189.xxx.xxx




Concrete over concrete (by Steve [MA]) Posted on: Dec 3, 2021 7:00 AM
Message:

Don, how big will the new slab be?

Since you only want to increase the height 2-3", you might consider using some building wrap like Tyvek as a slip sheet instead of sand or rigid insulation. Just thoroughly clean the old slab, saturate the old slab with water, blow off any standing water with a leaf blower, lay down the house wrap & smooth with a broom and pour the new concrete. Definitely make sure you have them mix some chopped fibers to the mix. If you're not familiar with using chopped fiber do a Google search.

Depending upon what type of finish look you're going for, I might be inclined to use either PT lumber, 5/4 PVC boards or synthetic decking to make the forms. You could excavate down the sides of the existing slab & permanently attach the new forms to old slab.

--71.174.xx.xxx




Concrete over concrete (by DonV [OH]) Posted on: Dec 6, 2021 1:44 PM
Message:

Thanks! --76.189.xxx.xxx



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