concrete slab

My garage roof also serves as a patio. It is 8" thick, built in 1950, and I don't have any specs or drawings for it. In other words, I don't know how/if it is reinforced. It seems to be a one-way span, 12' ea., with a cast-in beam down the middle.

I would like to remove 2" off the top, in order to resurface the patio w/ a flagstone finish w/o raising the patio finish level.

My contractor can do this, but is understandably reluctant to do so w/o a hold-harmless say-so from me. Is this a no-brainer, or is this something a structural engineer needs to site-verify?

My house is in Chevy Chase, MD. If you can't advise me based on my description, can you recommend an engineer in my area who might look at this?

As always, thanks in advance.

 

[AJUK]

By the fact that the slab is still there after 50 years will tell us that the slab is reinforced. Concrete just doesnt span such distances without reinforcement.

However, DO NOT REMOVE TWO INCHES FROM THE TOP without consultation with a structural engineer, it will most likely fail.

I'm in the UK so obviously I can't recommend a local professional but I'm sure someone will help you out.

 

[JAE]

Agree with AJUK - get yourself a structural engineer and he/she can evaluate the slab. You can remove some concrete from the bottom surface of the slab to reveal the reinforcing bars and get a handle on what it was designed for and what condition the reinforcing is in.

 

[oijammu]

Hi, I am in Tanzania.Knockout a 1'x1'hole in the slab and find the rebar location/spacing.you can always make good later.
I'm sure a structural eng.can make a good guesstimate of the structural stability from the exposed section.

 

[shahid1]

dont worry make a hole just 9"x9" and find out the location of reinforcement
okay and tell me the result

 

[jeg]

I should like to know how your contractor will remove 2 inches from a 12 inch suspended slab without damaging the integrity of the slab and probably causing collapse!!!
What will it cost???
If you must retain the existing patio level and need 2 inches of new surfacing, it may be less expensive to demolish the slab and rebuild.
Have you considered 8mm, fired clay or ceramic tiles set in a thin epoxy mortar bed? These should not add greatly to the loading on the roof though it would be advisable to test load the roof and check the deflections to see if it is overloaded by any new work.
Good Luck

 

[Trussdoc]

There are electronic detectors available which would find the rebar and give a fairly reliable idea of the size. It may be better than cutting a hole.

I think you should seriously consider jeg's suggested demolition option. Replacing the existing deck with a steel ribbed pan deck is a possibility too.

I hope its OK to recommend AE firms here. If you still feel you need a local consultant, you could try Smislova Kehnemui Assocs. in Rockville. I have had good experiences with them.

 

[LPPE]

You could shore the slab and then remove the 2 inches, but I dont think putting flagstone back there will restore your compression block.