Capping a garage floor

[Fred LeBail]

I am going to add an additional 4" of concrete to my existing garage / lumber storage/and furnace room . They are on the ground floor of my work shop , so this makes it into this forum , I guess.
When I talked to a contractor about this , he suggested the 4" and said that because there was rebar in the original floor it would not be required in the recap. Also he is going to acid wash existing cement and apply an adhesive/bonding agent between the two. He is also going to put in a floor drain that isn't there now . Does this all sound about right ?

The reason for the recap is the existing floor is just on grade and I am getting ice build-up at the man-door and water coming in. Not a lot, but enough to make it dangerous for walking and freezing the door closed.

[Lee Koepke]

That sounds about right.

At 4" thickness, I would add some wire mesh or use fibermesh concrete. Concrete is going to crack and move, regardless of what you do, and the mesh helps contain the cracking ( keeping the concrete from seperating ). My entire basement slab is done with fiber mesh, and I dont have any floor cracks in over 1600 sqft. They didnt even cut control joints, so I would say I am lucky.

Adding the bonding agent is not really necessary as a 4" slab is considered structural and will have enough strength on its own, but bonding the slabs shouldnt be a detriment.

Add an expansion joint around the perimeter ( if you have poured walls or masonry ) because that structural element is already settled, and your new slab will move a bit, so the expasion joint will help. after the concrete cures, you can come back with a good structural caulk and fill the gap.

[NICK BARBOZA]

definitely add some 6"x6" wire mesh to that slab. and i also agree with what Lee said before me.

good luck,
Nick

[Thom Sturgill]

The purpose of the rebar or mesh is because concrete has great compressive strength but no tensile (stretching) strength. When a concrete slab slab flexes under pressure, it fails because the bottom is put under tension and cracks form at the bottom and spread to the surface. Since your existing slab has rebar in it, that problem is cured and the upper slab does not need it. Using the fiber additive can prevent or limit shrinkage cracks, but make sure that it cures properly. It sounds like your contractor knows what he's about, but as was mentioned above, I would want to make sure there is an expansion joint around the perimeter.

[Tom Godley]

I was always told that the over pour does not require any rebar or mesh -- I would look into this before I spent the money on it.

I have had the fiber cement installed, but that was because some of the pour was on the thin side -- it is an expensive concrete and requires more labor to finish.

With four inches -- I see no reason to acid or use a bonding agent especially since you will want to put down a vapor barrier as well as some perimeter insulation. If the original slab is not insulated - now is the time to fix all the problems.