Adding layer of concrete to existing slab

[bmarshall1]

Hello,

I have a 30x60 block outbuilding that the previous owner must have done a DIY concrete job. It is unlevel, has footprints, and worst of all, actually slopes IN from the doors. Living in SW Florida combined with the rainy season and roll up doors means that water is always in the garage. I am working on sealing the doors but what is the feasibility on adding a 2" or 3" concrete cap to the existing slab and getting the right slope and adding drainage channel from the center. The current slab appears to be in good shape with no cracks despite the lack of relief cuts. Any tips or things to look out for when talking with contractors??

 

[DCarr2]

What your suggesting is called white topping.

I did something similar in my shop, though my shop had asphalt.

I laid down a 6mil plastic moisute barrier, 2" reclaimed foam insulation, 6" wire mesh, PEX tubing (for heat) and then went with 6" of concrete over the entire shop.

This ofcourse, created a new problem: a now 8" ledge from my driveway into my shop.

Last summer I poured a ramp in front of my main OH door, 3' wide, 14' long (the width of the door) Im super happy with it.

Everyone here will tell you to rip out the old floor, and install new. That can get pretty expensive.

 

[bmarshall1]

Thanks DCarr - living in FL and since I already have a concrete floor that is solid, the prep should(?) be negligible, if any. Would I have to tie the old floor to the new floor with anchor bolts for any reason? I would not mind a small 1 or 2 inch ledge to help keep water out.

 

[rsanter]

What you are proposing is not really the ‘right’ way to do it.
However, if you do this there are several things you can do to make it ‘more right’ than wrong.
first off I would be sure the exsisting concrete is as clean as it can be.
If you need to acid etch or grind it then do so. You also want it to be rough.
Then I would apply a concrete bonding agent.
When you pour the concrete I would go with 3-4” over the top. Less than 3” of concrete has very little strength other than for basic walkways and even then it is a bit questionable as you get down toward 2” thick

 

[ConCretin]

If the existing slab is structurally sound, there is no reason you can't do an overlay. You'll just need to deal with door openings and such. 2 or 3 inches of concrete will be fine. Wet down the existing slab over a period of time to get the concrete saturated but remove any standing water. This will prevent the water from being sucked out of the new concrete and help the overlay bond. Cure the new concrete well and you should have a durable slab that performs better than what you have now for minimal cost.

 

[bmarshall1]

Yes - although I would love do do the 'right way', I have to weight budget and effort. I have been working to un*uck everything the previous owner did. He's dead now but it's as if he said to himself "hey, I'll be gone in 5 years, let see how crappy I can do things so the next owner hates me".

Example - the garage floor, a half assed self contained septic for the garage, did not run the roofing past the eaves and now the roof edge has sagged and the water runs into the eves, there is a buried bulldozer by the back building, a 33 foot Donzi style boat he towed to the neighbors woods, buried car parts EVERYWHERE, installed a used well pump, wired a 110 outlet with 220. The garage WILL flood every hurricane as he dod not build it up.

I could go on for many paragraphs but you get the idea.

 

[bmarshall1]

Thanks Willy, I'll be making some calls on Monday, any particular needs I should express to the contractor or simply explain my goal?

 

[TractorJeff]

They did an overlay in a basement on "This Old House" recently.
Which means if its good enough for them to show on Television, it must be OK!
As far as the buried Bulldozer, how deep is it and is it an old Caterpillar? Guys collect them and a few down that way might be more than happy to dig it out if they get to keep it!

 

[larry4406]

What you are proposing is not really the ‘right’ way to do it.
However, if you do this there are several things you can do to make it ‘more right’ than wrong.
first off I would be sure the exsisting concrete is as clean as it can be.
If you need to acid etch or grind it then do so. You also want it to be rough.
Then I would apply a concrete bonding agent.
When you pour the concrete I would go with 3-4” over the top. Less than 3” of concrete has very little strength other than for basic walkways and even then it is a bit questionable as you get down toward 2” thick

+++1! I agree completely.

After capping the slab, check you garage door head height.

Had a problem in a production home where excavator dug too deep and we had adverse grade to the street for the garage. We capped the garage slab just like described above but we also had to raise the garage header so the door would work. Then fix the driveway.

 

[MikeF2316]

I've seen this done, and I've seen it delaminate and create a big mess. But on the other hand, there are several spots in my commute to and from work where overfilled concrete trucks have spilled a little of their load on asphalt roads, and that stuff is stuck there through boiling hot summer days, sub zero temperatures, heavy trucks, snowplows hitting it. And no surface preparation!

 

[6768rogues]

In SW Florida, it will work.