Cutting holes in a concrete floor

arrowman · 10-02-2021 6:22pm #1

I have a lad making up a steel post and rail fence in sections which will be used to divide a concrete yard.
The steel posts will be buried about 15 inches below floor level into the concrete and re-concreted around.
While the guy making up the steel will do the welding and fitting of the final sections I have to get the holes dug out for him to bury the posts

So I have seven holes to break into an existing concrete yard/ floor. I am not sure of the depth of the concrete as it was pored before my time here. I would think the depth is hardly more than 75 - 100mm

The holes will need to be about 15 inches square. I would like to keep the holes as neat as possible.

I am wondering on the best way to tackle this. I'll have to hire the gear to do it from the local plant hire
Would a con saw to cut the concrete and then a kango hammer do the job?
Would I get a 15" X 15" hole cut easily with a con saw?

Is there a better way?

listermint · 10-02-2021 6:46pm

arrowman wrote: »

I have a lad making up a steel post and rail fence in sections which will be used to divide a concrete yard.
The steel posts will be buried about 15 inches below floor level into the concrete and re-concreted around.
While the guy making up the steel will do the welding and fitting of the final sections I have to get the holes dug out for him to bury the posts

So I have seven holes to break into an existing concrete yard/ floor. I am not sure of the depth of the concrete as it was pored before my time here. I would think the depth is hardly more than 75 - 100mm

The holes will need to be about 15 inches square. I would like to keep the holes as neat as possible.

I am wondering on the best way to tackle this. I'll have to hire the gear to do it from the local plant hire
Would a con saw to cut the concrete and then a kango hammer do the job?
Would I get a 15" X 15" hole cut easily with a con saw?

Is there a better way?

Hire a consaw with hose attachment and have access to a water hose. Keeps the dust down. Don't to it with no water.

Hire a decent kango I rented a Hilti unit with built in vibration damping in the handles it was an absolute dream machine for getting through a concrete accessibility ramp which I literally had ridiculous Hastle with a breaker and 4 ton digger . The Hilti ripped through it . I think it was a te3000 .

Wanted to keep it afterwards

arrowman · 10-02-2021 6:52pm

Cheers listermint.

Ya I'd say that Hilti gear is the business - I had a lad tiling at the house last year and he had all the Hilti stuff- mini grinder, impact driver etc. - he said he wouldn't use anything else.
I might have to take what's available from my local Plant Hire but I will ask for one.

Good tip about the water for the dust.

I was worried the con saw would be too big for a 15 inch square hole

11-02-2021 8:56am

If you really want to keep it them square you can drill the corners with a long 10,12mm bit and that will make them crack nicely .
If I was just doing 1/2 holes I'd just drill mark them and drill a line of holes and then kango them out.

GreeBo · 11-02-2021 10:22am

Did you get engineers advice on burying the posts 15" down?
Just wondering if you looked at bolting them directly to the existing floor instead?

arrowman · 11-02-2021 10:35am

The lad that is fitting the fence and myself did talk about bolting them but where this fence is going it will also be acting as a sort of crash barrier so we decided that fixing the posts in concrete would be a better lifetime job.

GreeBo · 11-02-2021 11:13am

arrowman wrote: »

The lad that is fitting the fence and myself did talk about bolting them but where this fence is going it will also be acting as a sort of crash barrier so we decided that fixing the posts in concrete would be a better lifetime job.

It might be cheaper and faster to buy a large concrete percussion hole saw such as below and drill out the 4 corners of each hole and kango off the leftovers?
You can then just lift out the middle

arrowman · 11-02-2021 12:51pm

Thanks GeeBo - if using that hole cutter would I not still need something to give me clean lines around the edges of the hole for the kangoo to break off??

GreeBo · 11-02-2021 1:17pm

arrowman wrote: »

Thanks GeeBo - if using that hole cutter would I not still need something to give me clean lines around the edges of the hole for the kangoo to break off??

It depends on how exact you want to be really, you are going to be reconcreting so it will be uniform afterwards anyway.

You could use any anglegrinder/consaw to create straight lines on top, but they dont need to be 100mm depth since its only the top you will see afterwards.

The other option is that you drill 5 touching holes (or as many as you need to create a 15" hole in the middle) the edges don't need to be square, you just need a hole that's at least 15" with neat edges it seems?

arrowman · 12-02-2021 4:30pm

Thanks for that. I might just fire up my DeWalt angle grinder with a stone disk to do the marking so- as you say I only need to mark the top lines. I might drill the holes at the corners as was suggested above.

I am a bit OCD about neat lines when I get the holes broken out even though as you say they will be concreted in around the post.

arrowman · 24-02-2021 1:51am

Thanks for all the comments. Did the job last Saturday.
Drilled the corners with a 1/2 inch bit then marked / cut the lines with a diamond disk on my DeWalt grinder.
Hired a Bosch kangoo hammer for 3 hours and broke them out. 3 to 4 inch thick concrete so not too bad
Job done and as neat as you'd ever want.
Just have to wait for yer man to come with the steel now

Calahonda52 · 24-02-2021 10:07am

arrowman wrote: »

Thanks for all the comments. Did the job last Saturday.
Drilled the corners with a 1/2 inch bit then marked / cut the lines with a diamond disk on my DeWalt grinder.
Hired a Bosch kangoo hammer for 3 hours and broke them out. 3 to 4 inch thick concrete so not too bad
Job done and as neat as you'd ever want.
Just have to wait for yer man to come with the steel now

Lets have some pictures?

ted1 · 24-02-2021 11:43am

GreeBo wrote: »

It might be cheaper and faster to buy a large concrete percussion hole saw such as below and drill out the 4 corners of each hole and kango off the leftovers?
You can then just lift out the middle

Is their rebar in the concrete? Would that cut through it ?

Cutting holes in a concrete floor

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