Installation on uneven surface

[shaklee3]

I thought I just posted this, but I can't find it. Anyways:

My backyard is covered mostly in poured, dyed concrete with a few slopes going into drains built in to the concrete. I want to build a WFO where there is about a 5 degree slope. Do I need to crush the existing concrete to get down below it and make an even slab, or can I build an even concrete foundation on top of the current one?

[NCMan]

Re: Installation on uneven surface

Having poured way more than my fair share of concrete, I'd say cut out the area you plan to build on and start over. First of all, the concrete slab has way too many unknowns. Such as: the base under the slab. You don't know if it was poured on solid ground or fill. Also, you don't know the mix design of the concrete, slab thickness, whether there is sufficient reinforcement, etc. Put simply, you just don't know what you'd be building on. It's not so much the slope, but the things I mentioned. I wouldn't risk it. I would have the area cut out w/a concrete saw, clean up the mess and start over.

[ncsmoker]

Re: Installation on uneven surface

I would dig down to solid ground and build up from there. My 0.02 cents worth. I would not build on an existing foundation that may be too thin or unreinforced.

So.....basically what NCMan said.

[shaklee3]

Re: Installation on uneven surface

There are two things I know about the concrete:

1) It's 3.5"
2) There is a 3000lb+ hot tub on it.

Is it possible that even with the hot tub it's not reinforced enough? Cutting through the concrete may pose a problem since there are two gas lines running under it to a fire pit and to the bbq. I didn't want to accidentally hit one and cause more damage that I started with.

[stonecutter]

Re: Installation on uneven surface

The pizzamaking.com discussion wasn't satisfactory?

[shaklee3]

Re: Installation on uneven surface

Hi Stonecutter, sorry about the confusion and I didn't want you to think I wasn't taking your advice. I posted the question about the slope around the same time on both sites, and didn't see a response over here until after you had answered there. I didn't want to ignore the answers here either. At this point I think I'll take a gamble and just start building on this concrete since cutting a section out would probably require someone to come assess it.

Thanks for the advice.

[stonecutter]

Re: Installation on uneven surface

Hi Stonecutter, sorry about the confusion and I didn't want you to think I wasn't taking your advice. I posted the question about the slope around the same time on both sites, and didn't see a response over here until after you had answered there. I didn't want to ignore the answers here either. At this point I think I'll take a gamble and just start building on this concrete since cutting a section out would probably require someone to come assess it.

Thanks for the advice.

Oh, it's not that....I wanted to make sure I gave you advice that addressed the question. It is always a good idea too get as much information as possible, then make a decision.

To echo what was said over there.....I think your slab is just fine, based on what you want to do.

[shaklee3]

Re: Installation on uneven surface

Thanks guys. One last thing -- I want the base to be connected to the house since it's already connected on the other side where the BBQ is. It looks like the previous builders didn't do anything special at that joint. It looks like they left a gap for the concrete blocks, then just had grout hitting the stucco at the top. Is this the standard way of doing it, or would it be better to mortar all but a small gap around the edges of the stand, then caulk in the areas around that to allow for movement? Pictures below

[NCMan]

Re: Installation on uneven surface

I would just use a good masonry caulk (SikaFlex, etc). Or you could just mortar it in if the gap is too big, wait until it dries for awhile, then caulk it. Either way, it should be caulked at some point. Mostly for cosmetic reasons, but also to keep out rain, bugs, etc.

[stonecutter]

Re: Installation on uneven surface

Use backer rod, then caulk over that. You want to avoid 3 points of contact with caulk, or an edge can spall.

[NCMan]

Re: Installation on uneven surface

I doubt that you would find a structural engineer anywhere that would advise you to place all that weight on a pre-existing 3 1/2" thick slab, w/so many unknowns. You asked for advice and you got it. I guess you were just going to keep asking until you got the "opinion" you wanted. That's all any of us can give and you've gotten a few. Good luck w/it. Personally, a customer couldn't pay me enough to build on a slab like that. For no amount of money. I'd walk away and tell them so, as I wished them well.

[shaklee3]

Re: Installation on uneven surface

NCMan, I wasn't trying to fish around until I found an answer I wanted. Since I'm probably the least-experienced person on the forums when it comes to concrete, I was just trying to hear all the opinions. I'm planning to try to get a hold of the previous homeowners and see if I can talk to the company that poured this concrete so I'll have a better idea of what I'm working with. I'm still debating even putting the oven there since it would only accommodate a fairly small oven (< 30") when all is said and done. I don't have too much land to work with, so hopefully I can figure out something that works. I appreciate all the opinions on here and the help I've received, and I don't plan on doing something dangerous on a whim.