new pad, old garage questions

[hoffman912]

my garage is over 100 years old, no vapor barrier and the floor is like the moon -tons of craters, chipping, divots, etc.

I am looking to do a new pad an someone suggested using the existing as fill and to pour new concrete on top of it.

I want to do what is the most economically feasible (cheap but no short cuts i would regret) is pouring new on an existing pad a bad idea? if i do this, how thick should i make the new pad? will 4 inches be thick and strong enough (i like to work on cars so think of cars being on jack stands, or potentially a scissors lift).

I also want to make sure i have a proper vapor barrier, what should i make sure that the concrete guy uses and how thick should that be?

anything i should request as far as rebar/reinforcement etc?

my plan is to put VCT on it eventually.

thanks in advance,

HH

 

[GS-Louie]

I had the same issue some years ago. The contractor jacked up the garage on the old floor. Then they broke out the footings, poured new ones and built up the walls with block. When that was done they lowered the garage, secured it and then broke up the old floor. New floor nice and level and smooth, garage was square and I was a happy camper.

Lou

 

[jeff000]

Why do you want a vapor barrier under it so bad?

I would think pouring overtop would be the most cost effective, and the current slab has probably moved as much as it will ever move. 4" ontop would be probably than needed, we pour 2" over old concrete in gas plants.

 

[radrush]

You could place a topping slab and waterproof it with an admixture in the concrete mix.

Krystol Internal Membrane™ (KIM®)

Made by these guys: http://www.kryton.com/products/

 

[hoffman912]

why wouldnt i want a vapor barrier? i have moisture come up through it and I dont want my cars to rust out.


to be clear there was probably never a vapor barrier installed 50-100 years or how ever long ago that original floor was poured.

 

[ConCretin]

My first question would be how an overlay would affect your door opening. If you can figure that out, an overlay is a good option. If the existing slab is structurally stable a 3-4" overlay would work fine. You might even be able to do less. I'd treat the existing slab like any other base. Lay down vapor barrier over it and you are good to go.

With regard to vapor barriers, their primary function is to protect the adhesion of floor coverings. Limiting moisture intrusion into finished spaces is also a good thing but it's mostly about keeping your floor down. As adhesives have become more environmentally friendly, they have become less tolerant of moisture. If you're planning on VCT, you definitely need a vapor barrier. Personally, I'd opt for a 15 mil system such as Raven or Stego with taped seams and penetrations. If that's too pricey, 10 mil poly will suffice if you're careful.

My last suggestion is to use rebar. It'e easier to properly support than mesh and will maintain the structural integrity of your slab if cracks telegraph thru. Something like #4's at 24" centers would work. I'd rule out fiber in this situation (and most others for that matter)

Hope that helps.

 

[hoffman912]

Hi Gang, sorry was away in Chicago on business. Thanks for the good suggestions and questions.

garage door should be fine. the plan is to dig up the front a little so we can slope it to meet with the driveway. The front 2 foot behind the door or so is actually black top (the garage shows signs of being extended out that far, and i can only assume that was part of the driveway at the time).

do you think i can get away with 3" or is that too dicey and go with 4"? thanks for the tip on the vapor barrier, as well as rebar.

 

[vovka]

It would be great to get more imput on this i am in the same boat with my garage