foundation style, slab mesh positioning... need some quick feedback

[tff]

My garage started yesterday and I already have some concerns based on what I'm seeing. Would welcome any feedback/advice from folks (before it's too late & concrete gets poured).

Foundation 'style'
-My contract says 'concrete footings' and 'block foundation', but what I think i'm getting (based on looking at the excavation) is a monolithic foundation.
...Is a monolithic 'worse'?
...Is a monolithic cheaper?
...A book I have states that the monolithic slab needs to be 6" above surrounding soil, which frankly I don't want it that high. I presume with a footing + block foundation the foundation can run up higher than the slab and therefore the slab can be, say, 2" above the surrounding soil - correct?

I'm getting a wire mesh in the slab. I presume that that mesh needs to be raised near the middle of the slab vertically... it does no good to rest it on the vapor barrier - correct?

And finally... what kind of change in elevation over 15 ft (how many inches) would be reasonable from the front edge of the slab outward into the driveway (for reasonable drainage?).

Many thanks!

 

[The Cobbler]

monolithic is fine in the right conditions & circumstances and considerably cheaper than footing and foundation walls . you should confirm with your contractor asap
wire mesh should be on stools to keep it off the stone ,otherwise it has little or no value

 

[papp101]

Stem walls and footing are much more expensive depending upon the depth. I would confirm that.

They may be planning to lift the mesh as they pour, or just add the chairs right before they pour. Did they tell you it would lay on the vapor barrier?

Yank the brakes on this project until your questions are answered!

Sent from my Pixel 2 using The Garage Journal mobile app

 

[papp101]

Also, 1/8" per foot seems to be acceptable for drainage. 15ft is 1.875 inches drop total.

Sent from my Pixel 2 using The Garage Journal mobile app

 

[ard]

Your contractor will claim 'oh, we will pull it up into the middle of the slab as we pour'

I prefer placing it on chairs. I am not sure, but I believe 'promises to pull it up' will not meet code.

Is this job being inspected????????

IMO a monolithic slab- so slab and footings all in one- is far different than footings, block walls to support the walls, and then an independent slab poured at a later date.

Telling us what you GUESS, and then having people give you advice based on guesses may lead you astray....

How deep is your footing? Dimensions? How tall is the 'block foundation wall'? Is this stick built? Where were the walls to be placed? On the slab? or on the wall?

 

[Radix2]

Any floor should be at least 6 in above grade - it doesn't matter the style. Its a basic measure to make sure it remains nice and dry.

And from that point the surface should slope down away from the building....

 

[matt_i]

99% of every contractor will "hook" the mesh with rakes during the pour to pull it up.

I like the chairs/dobies because of the reliable placement and the vapor barrier isn't swiss-cheesed, but you have to make sure it can be walked on *all over* by people who aren't walking on eggshells, during the pour. They have heavy boots, the work is hard and there is no time to mess around.

Also the mix truck can't be driven on the chairs/dobies at that point so you might need to pump if the mix truck can't distribute it all from the chute.

I personally think monolithic is better than block, because its easier to get consistent strength. Block can be made strong with adding vertical and perimeter bar and core-filling but it adds to the time involved considerably. In monolith, the rebar can be set, forms set, and the concrete flows in all over. You see the common denominator of having rebar in the foundation, perimeter style, to keep cracks tightly knitted.

 

[ConCretin]

M
-My contract says 'concrete footings' and 'block foundation', but what I think i'm getting (based on looking at the excavation) is a monolithic foundation.
...Is a monolithic 'worse'?
...Is a monolithic cheaper?

... I presume with a footing + block foundation the foundation can run up higher than the slab and therefore the slab can be, say, 2" above the surrounding soil - correct?

I'm getting a wire mesh in the slab. I presume that that mesh needs to be raised near the middle of the slab vertically... it does no good to rest it on the vapor barrier - correct?

And finally... what kind of change in elevation over 15 ft (how many inches) would be reasonable from the front edge of the slab outward into the driveway (for reasonable drainage?).

First off, you need the slow the roll on this thing and have this conversation with your contractor. These are all things that should be addressed in some plans i.e. your contract. You'll be back on here with another 'what the hell do I do now?" thread if you don't get these issues resolved before he places concrete.

With regard to your questions;

Nothing wrong with a properly constructed mono slab but I wouldn't say that's what described in your contract. It's possible he intends to build a block curb wall on top of the slab to lift the framing up and keep your slab at the elevation you desire. And yes, a monolithic slab is less expensive to build.

Wire mesh definitely needs to be supported in the middle third of the slab before placement

With regard to drainage, 1/4" per foot is the minimum pitch you want to ensure decent drainage. For exterior areas, more would be better.

Assert yourself soon. It's your garage and your money. Good luck with the rest of your build.

 

[tff]

Thanks everyone for your feedback. A few responses.
-First, I have left a message with my contractor to talk first thing this morning.
-It's possible that they will do the mesh correctly but just haven't gotten to it. Will confirm.
-The county is inspecting the project at certain stages
-Probably the grayest area to me is the elevation of the slab top. I wanted it a bit lower (to blend into the surroundings better and to match the existing garage slab). Looks like i need about 2 to 4" of elevation change in front of the garage over 15" (this area is concrete driveway). Not clear to me is a separate foundation (vs monolith) would allow the slab to be lowered some.

Thanks all.

 

[GMCGarage]

My garage started yesterday and I already have some concerns based on what I'm seeing. Would welcome any feedback/advice from folks (before it's too late & concrete gets poured).

Foundation 'style'
-My contract says 'concrete footings' and 'block foundation', but what I think i'm getting (based on looking at the excavation) is a monolithic foundation.
...Is a monolithic 'worse'?
...Is a monolithic cheaper?
...A book I have states that the monolithic slab needs to be 6" above surrounding soil, which frankly I don't want it that high. I presume with a footing + block foundation the foundation can run up higher than the slab and therefore the slab can be, say, 2" above the surrounding soil - correct?

I'm getting a wire mesh in the slab. I presume that that mesh needs to be raised near the middle of the slab vertically... it does no good to rest it on the vapor barrier - correct?

And finally... what kind of change in elevation over 15 ft (how many inches) would be reasonable from the front edge of the slab outward into the driveway (for reasonable drainage?).

Many thanks!

I would want what my contract says if thats what you bought.

Also mesh in a slab should be down about 1.5"-2" from the top. Will do little in the bottom or middle, (depending on thickness)

 

[matt_i]

You might want to set a master grade pin (basically a piece of rebar hammered into the ground somewhere that's close enough to access with a laser level but not close enough to be disturbed by site-work. Use that as the reference for all drawings. Otherwise the dimensions are referenced to ???

 

[alexb2000]

Put this provision in your agreement: "The rebar will be in the top 1/3 of the slab as verified by scanning or the job is free". Watch the contractor pee their pants when you ask for that. I have cut a lot of concrete for demolition and 95%+ of the time the rebar is in the bottom mostly in the dirt, doing absolutely NOTHING.

Lifting the rebar during the pour is B.S.!

Put it on chairs (use a lot) or dobies, either that or don't even bother to put it in the pour, just use fiber.

 

[racer-john]

People are mixing up "re-bar and mesh". Concrete has has little strength in tension, therefore the re-bar handles this problem @ 1.5 to 2 inches in the bottom of the slab (on chairs and wired joints in a square pattern about 12", and wired to chairs).
Mesh is used to control shrinkage while curing and should be located about 1.5 inches below top of finished concrete hopefully. The mesh is usually 6 x 6 x 4 with an overlap of at least one square and wired.

From a C.E.T. in Canada.

 

[GMCGarage]

People are mixing up "re-bar and mesh". Concrete has has little strength in tension, therefore the re-bar handles this problem @ 1.5 to 2 inches in the bottom of the slab (on chairs and wired joints in a square pattern about 12", and wired to chairs).
Mesh is used to control shrinkage while curing and should be located about 1.5 inches below top of finished concrete hopefully. The mesh is usually 6 x 6 x 4 with an overlap of at least one square and wired.

From a C.E.T. in Canada.

A slab on grade for a garage should not need reinforcing in the bottom. If mix design and placement and finish are done correct, mesh is not really needed either.

We do use alot of 'Mesh' for structural reasons too. It does not have to be just rebar used.

 

[850xpeps]

Good advice here. Don’t let them lift the mesh when they pour. It never stays up. And they will step on it. Your slab make them do it right.


Mesh or rebar placement on a slab depends on use of a slab. With a garage and good compaction aim for the middle and will be fine. Don’t let rebar get within 1” of the top or your slab will look like junk.

Monolithic is fine if built properly and prep is done. I personally prefer this method and I would not install block for anything. I would opt for a cement wall. Your slab protrusion is the same regardless of type. I would be fine with 6” as it keeps water and dirt out. Don’t let them talk you into what “we’ve done for 20 years”. You have to live with it so you make sure your happy about it.

 

[ard]

Question guys....

OP states he needs a slope on 15 ft

1/4" per foot, is 15/4 or 3.75"

So the slab slopes 3.75 inches

In a monolithic 'slab plus foundation' will this not mean the wall of the garage also slopes 3.75 inches?????

Im used to a stem wall (or block wall) being level, and the garage floor slab INSIDE having a slope. Allows hosing the floor without soaking the sill plate, walls and framing members too....

Am I missing something?

 

[tff]

Question guys....

OP states he needs a slope on 15 ft

1/4" per foot, is 15/4 or 3.75"

So the slab slopes 3.75 inches

In a monolithic 'slab plus foundation' will this not mean the wall of the garage also slopes 3.75 inches?????

I was asking about the recommended slope OUTSIDE of the garage from the front edge of the slab to the existing driveway (for sufficient drainage). I understand that the monolith itself will have a small slope but probably not that much.

 

[ard]

I was asking about the recommended slope OUTSIDE of the garage from the front edge of the slab to the existing driveway (for sufficient drainage). I understand that the monolith itself will have a small slope but probably not that much.

Got it.

There was someone here recently that had this problem...walls sloped with floor.

 

[Pluribus]

The check's in the mail. I won't **** in your mouth. We'll pull the mesh up to the middle of the slab when we pour/place.

Notice a pattern above? Sounds like you already have a contract without this specified, so the contractor might balk, and you may have to pay extra to have it done correctly. I wouldn't want to trust that it will be pulled properly to the middle, so I'd want it on chairs, etc.

 

[850xpeps]

He shouldn’t have to pay for chairs because that’s the proper way to have it done. If contractor won’t do it then do it yourself and bill him for it.

 

[brownbagg]

after 24 hours mesh does nothing