Load Bearing Garage Floor over a Basement

[yooperdave]

No Strength has been reduced.

There are 2 slabs. The lower slab being the structural slab, and the upper slab being a wearing course. You reinforce the structural slab for all of the superimposed loads. The wearing course is supported by the structural slab. The wearing slab may have temperature and shrinkage reinforcement to limit cracks. The structural slab will have flexural reinforcement as well as temperature and shrinkage reinforcement.

Yooper Dave

 

[Anonymous Poster]

The entire purpose of the membrane is to prevent saltwater from entering the structural slab. Protecting of the steel under the pour isn't a consideration since the steel offers little or no strength after the concrete has cured. The steel is only strong enough to hold the wet concrete, not the load placed on the floor. The wear surface layer above the membrane offers no additional strength to the pour.

The aternative is to use an electricly charged grid of rebar in the pour.

 

[Hoeman00]

What about a 2 part epoxy paint for the concrete to seal it?
My floor has radiant heat and the vehicles dry so fast I don't
know if u get much calcium soaking in.

 

[yooperdave]

Hi Tim,

The epoxy paint will only work if you have very small almost not visible cracks in the concrete which the paint will span over. It just takes a new crack to open up and your defense has been breached. You will not know if many new cracks have appeared or have opened up because they will be too small to see.

The epoxy paint would be a good choice to initially seal the wearing slab. The membrane will always be there to provide the protection if the wearing course ever leaks.

Yooper Dave

 

[Anonymous Poster]

This is one of the deals where you either do it right the first time, or do it over and over. I was on a floor this week that has been coated with epoxy paint 5 years ago, and is now in a condition where the remaining epoxy needs to be removed so the floor can be repainted.
Needless to say, the floor was placed by a brilliant company that knew everything I told the building owner was [censored].
The pour was NOT vibrated, because the masons knew that wasn't necessary (translation, more work + more concrete)
The pour was NOT rebar, it was lightly screned (translation cheaper + less labor)
The pour was NOT fiberglass concrete (translation less labor to place & finish)
The pour was NOT keyed together or bullnosed (less concrete and less labor) NOW, it is cracking at the joynts.
The pour was NOT properly joined to the foundation at door openings, HEAVING from frost.
NOW, the owner asks me how to solve the problems he has with his cheap job. Needless to say, he didn't like my answers.
Epoxy concrete paints do NOT last. It will cost far more to install an epoxy floor covering that will last, such as "Torginol" than it will to do a proper pour, and it will be SLIPPERY WHEN WET.
WR Grace also makes a concrete that will resist salt damage, but they will only sell it installed by their crew with their equipment.
OR, you can protect the floor electricly bw connecting all rebar together, and placing a cathode 1" below the wear surphace.
The bottom line, protect it or loose it.

 

[Makers_Mark]

Wow. Isn't it great that TBN has such knowledgable members. /forums/images/graemlins/cool.gif
So, if my application called for a 3" thick structural slab, I pour that slab, let it cure, membrane it, then pour the wear layer over that? How thick of a wear layer? 1"? I then have to re-engineer my joists for the additional load, yes?

 

[Anonymous Poster]

Or, you could simply derate the total avaialble floor load capacity by the weight of the additional 1" wear surphace.
Engineers generally underrate the load carrying capacity of floors and overbuild them, so it shouldn't be a problem. They consider that over the life of the floor additional layers of covering will be added.

 

[yooperdave]

I would use at least 2" to 3" of concrete topping (wearing course) for a lightly loaded structure.

Remember that each inch of thickness of normal weight concrete weighs 12.5 psf. The structural slab will have to support this additional weight.

I would get the EOR (engineer of record) involved in this process at this time.

He should have a similar design process in mind. He can then provide a design, details, and specifications for both slabs.

You deserve to have it done right the first (and only) time.

Good Luck

Yooper Dave

 

[ELMO67]

I still like my wood floor and i- beam combination.

 

[bebster]

I've got a drive out basement on a grade with garage door and concrete slab, and above the ground level floor of a barn with a very strong floor made from manufactured wood I-joists. You can get these readily, and if you space them 12" on center they can support a good sized load, depending on the span. I've engineered my floor to support heavy woodshop tools, but I bet it could be engineered to support a truck as well.