Concrete to replace asphalt

[brownsmustang]

Hey guys, I'm looking at buying a home with a 30x40 shop, the driveway and shop are both asphalt. I will want to replace the asphalt in the shop with concrete, so I can put in a lift and just all around better flooring.

My questions are, can I just peel up the asphalt and put concrete diwn or do I need to redo the substrate as well? If so what substrate would you recommend?

Also, the rebar, will the mesh be strong enough or should I go with larger rebar?

There seems to be some controversy over moisture barrier under the concrete, but is there really any negatives, besides cost to use it? Thanks for your help.

 

[ConCretin]

Give my Guide to Floor Slabs in the link below a read for some additional thoughts but if the asphalt is in good shape, the base material is probably adequate for a concrete slab. Asphalt has less inherent strength than concrete so if the base provided enough support for the asphalt to remain intact, it's probably fine for concrete.

The only negative to a vapor barrier, other than cost, is increased bleed water, which can cause a number of surface problems if not managed properly. A qualified finisher shouldn't have too much trouble managing this but it is a potential issue. A vapor barrier is really only necessary if you intend to apply an adhered floor covering such as epoxy so you'll need to weigh the risk vs benefit.

Rebar really isn't necessary and larger bars don't make any difference at all. Steel reinforcing doesn't make a slab stronger or prevent cracks, it just hold cracks together. Properly supported wire mesh is less expensive and provides the same function.

Good luck with your project!

 

[The Cobbler]

I would do a few test holes to see how deep the stone is as you will probably want to remove some , asphalt is usually 2 or 3 " where the concrete you'll probably want at least 5"

 

[brownsmustang]

Thanks guys!

 

[Jking24]

The main problem you will have is peeling up the asphalt without damaging the sub layer. Theirs probably 4"or less of whatever is their. As you rip up the asphalt and traverse around with what ever machine you use the base will certainly be disturbed and contaminated with dirt and other debri. Other than the obvious structural reasons the second most important reason for a good base is to provide a capillary break and give area for moisture to drain away from the pad. if their is dirt and other things mixed in it may not function correctly. The proper way to do it is just plan from the beginning to excavate down to at least 4"below the bottom of the slab and put fresh clean stone in compact it and move on. I also think this approach will be faster and more efficient in the long run

 

[brownsmustang]

The main problem you will have is peeling up the asphalt without damaging the sub layer. Theirs probably 4"or less of whatever is their. As you rip up the asphalt and traverse around with what ever machine you use the base will certainly be disturbed and contaminated with dirt and other debri. Other than the obvious structural reasons the second most important reason for a good base is to provide a capillary break and give area for moisture to drain away from the pad. if their is dirt and other things mixed in it may not function correctly. The proper way to do it is just plan from the beginning to excavate down to at least 4"below the bottom of the slab and put fresh clean stone in compact it and move on. I also think this approach will be faster and more efficient in the long run

Definitely something to be said about this.... I'd rather plan for this in advance, have the material on hand and give myself the peace of mind.

 

[nadogail]

IMHO, You will have a better shop with a concrete floor rather than asphalt. Concrete was the pavement of choice until someone realized that asphalt was cheaper and quicker. For politicians, the advantage of asphalt is they can pave more miles with less money; nobody seemed to consider the life cycle cost differences between the two.

 

[brownsmustang]

IMHO, You will have a better shop with a concrete floor rather than asphalt. Concrete was the pavement of choice until someone realized that asphalt was cheaper and quicker. For politicians, the advantage of asphalt is they can pave more miles with less money; nobody seemed to consider the life cycle cost differences between the two.

Oh, without a doubt it is getting replaced by concrete. I am rebuilding a 68 mustang and want a nice, clean, well lit shop with a lift to do it in.

 

[machsnell]

The main problem you will have is peeling up the asphalt without damaging the sub layer. Theirs probably 4"or less of whatever is their. As you rip up the asphalt and traverse around with what ever machine you use the base will certainly be disturbed and contaminated with dirt and other debri. Other than the obvious structural reasons the second most important reason for a good base is to provide a capillary break and give area for moisture to drain away from the pad. if their is dirt and other things mixed in it may not function correctly. The proper way to do it is just plan from the beginning to excavate down to at least 4"below the bottom of the slab and put fresh clean stone in compact it and move on. I also think this approach will be faster and more efficient in the long run

Any decent operator won't have an issue getting asphalt up with minimal overdigging keeping subgrade intact.

Also there is no such thing as fresh stone. All stone is old. If its there and of sufficient depth and as LLwillys pointed out has supported the asphalt decently you should be fine. Stone, as long as it hasn't become contaminated doesnt go bad.

Dig a few test pits and see what you have. If you have good weight supporting soils and adequate stone I wouldn't plan on removing the stone other than to get desired section of concrete.

Sent from my SM-G960U using Tapatalk

 

[brownsmustang]

Any decent operator won't have an issue getting asphalt up with minimal overdigging keeping subgrade intact.

Also there is no such thing as fresh stone. All stone is old. If its there and of sufficient depth and as LLwillys pointed out has supported the asphalt decently you should be fine. Stone, as long as it hasn't become contaminated doesnt go bad.

Dig a few test pits and see what you have. If you have good weight supporting soils and adequate stone I wouldn't plan on removing the stone other than to get desired section of concrete.

Sent from my SM-G960U using Tapatalk

Something to consider. My "contractor" aka my cousin, says it shouldn't be an issue if they laid the asphalt correctly and since they park their rather large motorhome on it without sinking, it looks pretty stable. Although my "contractor" says running a power tamper over the substrate would not be a bad idea.

 

[BombShelter]

I'm not a concrete expert but I used to sell jobs similar to yours. It would help to know where you live, there's different climate conditions that change the specs. I doubt the asphalt is more than 2" thick, you're going to want 4"-6" of concrete so most of the base will probably be removed. We used recycled class 5 gravel and tamped it down, 4" minimum under the concrete. Use rebar, not mesh, here in Minnesota it's very common to see garage floor heaving where the crack gaps are 1/4"-1" and there's no reinforcement or, if there is, it's rusted mesh.

I'm also not a fan of fiberglass filiments, the fiberglass will wick water and after 2-3 years you'll see thousands of micro-cracks on your surface. I've been told they've went to something like polyethylene so that might have changed but rebar is the product that works the best.

You might want to consider something like CETCO Voltex under the floor, it's a bentonite-based waterproofing membrane with a vapor barrior. It's rolled over the class 5 and concrete is poured right on top of it. The benotonite will stop any moisture from moving up through the floor. Here we see very small cracks that tend to be moist and nobody wants a humid garage.

 

[brownsmustang]

I'm not a concrete expert but I used to sell jobs similar to yours. It would help to know where you live, there's different climate conditions that change the specs. I doubt the asphalt is more than 2" thick, you're going to want 4"-6" of concrete so most of the base will probably be removed. We used recycled class 5 gravel and tamped it down, 4" minimum under the concrete. Use rebar, not mesh, here in Minnesota it's very common to see garage floor heaving where the crack gaps are 1/4"-1" and there's no reinforcement or, if there is, it's rusted mesh.

I'm also not a fan of fiberglass filiments, the fiberglass will wick water and after 2-3 years you'll see thousands of micro-cracks on your surface. I've been told they've went to something like polyethylene so that might have changed but rebar is the product that works the best.

You might want to consider something like CETCO Voltex under the floor, it's a bentonite-based waterproofing membrane with a vapor barrior. It's rolled over the class 5 and concrete is poured right on top of it. The benotonite will stop any moisture from moving up through the floor. Here we see very small cracks that tend to be moist and nobody wants a humid garage.

The new place is in SW Missouri, near Springfield. Rebar it is... Ill look into the underlayment, we was planning on putting down something, I want to paint the floor after cure. I am currently in Central MN and my parking garage floor has a 1" heave right in the middle, no rebar in sight.

 

[ConCretin]

The new place is in SW Missouri, near Springfield. Rebar it is... Ill look into the underlayment, we was planning on putting down something, I want to paint the floor after cure. I am currently in Central MN and my parking garage floor has a 1" heave right in the middle, no rebar in sight.

Give my Guide to Floor Slabs a read before you spend too much time and money on rebar or bentonite membranes in an effort to stop heaving and humidity.

 

[spudley]

There seems to be some controversy over moisture barrier under the concrete, but is there really any negatives, besides cost to use it? Thanks for your help.

When poured, it definitely will have more surface bleed water but a good finisher should know how to handle that.

My neighbors garage has no vapor barrier and his floor is "wet" for several months as temps increase. I put vapor barrier under mine and it's dry.

Bldgs are 50' apart.

I did lots of stone base over very sandy soil, not sure how much base on neighbors.

If you're doing radiant floor heat, your floor should be dry either way.

 

[brownsmustang]

Give my Guide to Floor Slabs a read before you spend too much time and money on rebar or bentonite membranes in an effort to stop heaving and humidity.

Thanks.

 

[brownsmustang]

When poured, it definitely will have more surface bleed water but a good finisher should know how to handle that.

My neighbors garage has no vapor barrier and his floor is "wet" for several months as temps increase. I put vapor barrier under mine and it's dry.

Bldgs are 50' apart.

I did lots of stone base over very sandy soil, not sure how much base on neighbors.

If you're doing radiant floor heat, your floor should be dry either way.

No in floor heat, I like to bolt things down and I don't want to run the risk of hitting a line.

 

[arindom]

Very informative post...!!!!