Advice for cutting concrete?

[thestrangebrew1]

I'm going to be building a patio cover but need to put three posts in my existing patio. CA Building Code requires my footings to be 12"-18" deep, so I'll need to cut my concrete up about 1 square foot each (prob a little more). I've never cut concrete before and was going to rent a saw. Just need some advice as I'm not very handy. Is the saw heavy? Should I expect the saw to be jerky/kick back? I know I should be wearing safety goggles and some sort of respirator, and I'll be wet cutting, but anything else I need to be aware of? I think my existing concrete is ~4". Thanks!

 

[Greenman]

You'll most likely use a 14" gas cut off saw. They aren't all that heavy, under 25 pounds. Don't use too much water as it just makes a mess, use just enough to keep the blade from producing dust. Wear eye and ear protection. Mark your lines with a board and spray paint against the edge so it won't wash away. You'll have to over cut at the corners so the blade goes all the way through the slab. Don't force the saw, let the blade cut at it's own speed, you'll be able to tell if you're pushing it to hard, the engine will slow down a lot.
Keep the kids and dog away from where you're cutting.

Next you're going to need a way of breaking up the concrete you cut, it isn't going to lift out of the hole. When you return the saw get a small demolition hammer and a point. Break a hole in the piece you're removing to give the concrete a place to move to as you break the rest up. A few hours, some sore muscles, a blister or two, and a little blood later, you'll be all done.
Good luck.

 

[Moonbeam]

What about your existing patio. Does it have posts? Do they rest on the existing concrete, if so? That law seems quite burdensome to me. I could see it if there were no pre-existing concrete and you were on bare ground.

 

[echo4747]

You might also be able to rent a core drill if a round hole could work for you. I had a friend do a similar project to what you describe, a few years ago. I think he drilled 10inch holes thru concrete. I was surprised at how nice and clean the cut was.

 

[edro]

You might also be able to rent a core drill if a round hole could work for you. I had a friend do a similar project to what you describe, a few years ago. I think he drilled 10inch holes thru concrete. I was surprised at how nice and clean the cut was.

That sounds much nicer and easier. I would love to see this "core drill" in action.

 

[thestrangebrew1]

What about your existing patio. Does it have posts? Do they rest on the existing concrete, if so? That law seems quite burdensome to me. I could see it if there were no pre-existing concrete and you were on bare ground.

The cement area is what I call a patio without an awning. I'll be building an awning in that area, so no posts at the moment. I asked the guys at the building department (I work in the planning dept.) if I could just drill some holes into the concrete and anchor the posts that way with some bolts etc., but they said the building code doesn't allow that. I have to have a footing of at least 1 square foot and 12-18" deep. I think the bracket(?) for the post needs to be 1" off the footing too.

Here is the detail they gave me:

 

[thestrangebrew1]

You might also be able to rent a core drill if a round hole could work for you. I had a friend do a similar project to what you describe, a few years ago. I think he drilled 10inch holes thru concrete. I was surprised at how nice and clean the cut was.

I'll have to ask if I can do a round hole. I think they said I could as long as it's 12" diameter and 12-18" deep.

 

[NutBucket]

You could also do the brute force method....hammer drill and a series of small holes. Follow up with a nice sledge hammer!

 

[cabri]

Cut the 12" round hole
Get a post hole digger and excavate
Plant the pole
Align it
Pour in concrete footing
Attach bracket

Less of a mess and headache for you than cutting a square opening. Otherwise to look nice; you would need to cover over the extra cuts caused by the saw.

 

[echo4747]

That sounds much nicer and easier. I would love to see this "core drill" in action.

The one my friend used was very similar to this:


https://www.youtube.com/watch?v=TMCSG-gMv_Q

At work we had a section of fence installed that was partly over an area with concrete. The folks from the fence company "core drilled" several 4 inch dia holes with with a big handheld unit.

 

[thestrangebrew1]

Would this core drill be able to cut through rebar in the process of drilling? I'm not 100% sure rebar was used, but just in case.

 

[echo4747]

Would this core drill be able to cut through rebar in the process of drilling? I'm not 100% sure rebar was used, but just in case.

should be able to go thru rebar... might be able to use a metal detector to see if rebar is in the spot you intend to drill/cut. (wire mesh if used may also set the metal detector off)

found this video of 12" core drilled to a depth of 10 feet ( multiple layers of rebar too:


https://www.youtube.com/watch?v=7j43xFaLrAg

 

[Greenman]

12" is a big core drill, I've never seen one that size at a rental yard. It would make a neater job though.

 

[skyking]

you're not going to get a core drill that big. The pros will bring one out like that but is a big honker and they would drill at least a couple of 1" holes to bolt the drill to the slab.
The handheld saw and the square hole will be the most cost effective.

 

[schmuckley]

k12 with small blade + sledge.

 

[thestrangebrew1]

you're not going to get a core drill that big. The pros will bring one out like that but is a big honker and they would drill at least a couple of 1" holes to bolt the drill to the slab.
The handheld saw and the square hole will be the most cost effective.

I called a local United Rentals and he said he had a 10" drill he could get delivered from another shop. He did say it'd be more expensive and I'd have to drill an hole to bolt the drill to the slab. I might just use a saw as it'd be cheaper also.

 

[skyking]

you need a pretty big rotohammer for that hold down hole.

 

[Greenman]

you're not going to get a core drill that big. The pros will bring one out like that but is a big honker and they would drill at least a couple of 1" holes to bolt the drill to the slab.
The handheld saw and the square hole will be the most cost effective.

Don't they make a suck down drill that will turn a 12" hole saw? I've used a 4", and it worked very well.

 

[DrPizza]

How close to the edge of the patio are your footers going to be? Is there a chance you couldn't simply dig down at the edge, then dig under the patio? From the patio, drill through the patio into where the footer will be; stick your anchor in, and then back fill with concrete (build a frame for it) under the patio; then after concrete hardens, remove boards, fill hole in front of patio with soil.

 

[Micrornd]

Don't they make a suck down drill that will turn a 12" hole saw? I've used a 4", and it worked very well.

You can vac down using a 12" bit but the surface needs to be real good and you have to advance the bit slower.

Normally on a horizontal surface a single 1/2" wedge anchor is all you need.
As long as the anchor bot is embedded good, you can't pull it out, and the drill just isn't powerful enough to break it.
You're trying to hold the core drill in place, uplift isn't an issue.

The leveling studs on the corners of the core drill base will keep it from rotating as long as you tighten down the anchor bolt.
Any cheap 1/2" wedge anchor will do, no need for an expensive one .
It will need to be about 6" long to go thru the base of the core drill and get a good bite (about 3"-4") into the concrete.

Drill the hole for the anchor at least 5" deep in the concrete, so that when you are done, you can cut the anchor bolt flush with the concrete with an angle grinder.
Then you can use a punch or steel rod to drive what remains of the anchor down well below the surface of the concrete, and fill the anchor hole with cement when you pour your footers and it will eventually blend in and you won't know there was an anchor hole there.

I asked the guys at the building department (I work in the planning dept.) if I could just drill some holes into the concrete and anchor the posts that way with some bolts etc., but they said the building code doesn't allow that. I have to have a footing of at least 1 square foot and 12-18" deep.

Actually that depends on the slab.
Dig down along side of the slab where you will be putting the posts, the builder may have put in a thickened edge in anticipating selling an upgrade (such as a "Florida" room or screened room) when the house was built.

If it is thickened and it is at least 12", you can normally get an engineer to "sign off" on it, allowing you to use a wedge anchor to fasten the connector the post sits in to the slab.
Most building depts. will accept a licensed engineer's recommendation for this.
Worth checking, it will save you money.

 

[thestrangebrew1]

How close to the edge of the patio are your footers going to be? Is there a chance you couldn't simply dig down at the edge, then dig under the patio? From the patio, drill through the patio into where the footer will be; stick your anchor in, and then back fill with concrete (build a frame for it) under the patio; then after concrete hardens, remove boards, fill hole in front of patio with soil.

So my cement goes about 18" from the fence. My footings have to be minimum 5' from the fence. If I want an overhang of about 18", my footings will have to be 6'6" from the fence, so footings will be approximately 5' from the edge of the cement.