How to drill round hole into concrete roof for drain pipe?

[DIYpowered]

Hello,

I need to drill a round hole into a concrete roof (with rebar) to pass a PVC 75mm pipe as a water drain. I have done some research and it seems like the best option is to use a hole saw of the same pipe diameter.



But the problem is that since there is most probably rebar somewhere in that concrete spot where i need to drill, the cutting bits on the hole saw will get damaged and break off. That's what i was told at the hardware store and also based on my online research (there is auto audio translation from YouTube):

So, my question is how to go about this? Is there a better option? I have already spent money on that hole saw so i am really hoping that it will work. I just need it to last for one single hole drill. The thickness of the concrete is about 25cm. I also bought an SDS Plus flat chisel to cut the rebar if needed (or i need a pointed chisel instead?), and i will be using a Makita SDS Plus drill 800W HR2630T: https://makita.ae/product/combination-hammer-hr2630t/



I also found some additional information online about using a Diamond Core Drill Bit but i can't find it in the local hardware stores and i would rather not spend more money on this project, if possible, since i just need to drill a single hole - i don't care if the drill bit gets damaged as long as it can cut cleanly through the concrete for the PVC pipe to go through it.



Any advice is much appreciated! Thanks in advance.

 

[thomp1983]

Start your core, once your in 10 to 20mm take the core drill back out, get a masonry bit long enough to drill all the way through and drill holes all the way round inside the groove the core drill made.

The extra holes will making cutting the core hole alot easier and if there's rebar there you should hit it with the masonry bit, this should give you an idea of the depth and position, then core down to near the depth, break out the bit of core with a chisel and deal with the rebar, then carry on with the rest of the core.

 

[DIYpowered]

and deal with the rebar, then carry on with the rest of the core.

Thanks for your explanation, but how do you suggest that i cut the rebar? Is the SDS Plus flat chisel that i bought enough to cut through it without causing damage to the surrounding hole area or blow out below the hole where the drill is supposed to come out?

 

[stevie888]

I very much doubt you'll cut rebar with a chisel though if it's mild steel you might do it.

The best bet would obviously be to use a diamond core drill, but you've nothing to lose by trying with what you've got: you may get lucky and miss any bars. (One option might be to see if you can get hold of a cover meter and plot where the bars are and position the hole to suit.)

Steel should be within the first couple of inches and if you hit any then cutting down with an angle grinder and tidying up afterwards will probably be the easiest approach.

 

[ree]

OP,
There are various Diamond bits that will go straight through the concrete & rebar.
Core drilling is simple enough but problems can occur when you attempt to seal whatever is going through the core hole?
Why do you propose to core through a concrete roof?
Can you post a pic of the roof?

 

[DIYpowered]

I very much doubt you'll cut rebar with a chisel though if it's mild steel you might do it.

The best bet would obviously be to use a diamond core drill, but you've nothing to lose by trying with what you've got: you may get lucky and miss any bars. (One option might be to see if you can get hold of a cover meter and plot where the bars are and position the hole to suit.)

Steel should be within the first couple of inches and if you hit any then cutting down with an angle grinder and tidying up afterwards will probably be the easiest approach.

A cover meter would be nice but i do not have access to one and i'm not buying it just for this one project but thanks for the suggestion.
The hole needs to be 75 mm for the PVC drain pipe and i only have a 115 mm cutting disc on the grinder, so it will be a problem to go deeper.

I will probably go ahead with the first solution from thomp1983. But i am wondering...
1. If a 6.5 mm concrete drill bit will work to drill along the groove made from the hole saw? or do i need a smaller 5 mm drill bit? or bigger 10 mm?
2. Is it safe to use the SDS drill i mentioned in my original post (Makita SDS Plus drill 800W HR2630T) or should i switch to a normal hammer drill (the same SDS drill has an extra chuck that converts it into a normal hammer drill that accepts plain drill bits)? The concrete roof has a fine crack in it and when it rains, it drips along that crack on the inside of the house. So, i am quite concerned that the SDS will do more damage to the concrete roof as it pounds the concrete to drill the hole. The crack is not at the place where i will be drilling - it's about 1 metre away.

 

[noseall]

A cover meter would be nice but i do not have access to one and i'm not buying it just for this one project but thanks for the suggestion.
The hole needs to be 75 mm for the PVC drain pipe and i only have a 115 mm cutting disc on the grinder, so it will be a problem to go deeper.

I will probably go ahead with the first solution from thomp1983. But i am wondering...
1. If a 6.5 mm concrete drill bit will work to drill along the groove made from the hole saw? or do i need a smaller 5 mm drill bit? or bigger 10 mm?
2. Is it safe to use the SDS drill i mentioned in my original post (Makita SDS Plus drill 800W HR2630T) or should i switch to a normal hammer drill (the same SDS drill has an extra chuck that converts it into a normal hammer drill that accepts plain drill bits)? The concrete roof has a fine crack in it and when it rains, it drips along that crack on the inside of the house. So, i am quite concerned that the SDS will do more damage to the concrete roof as it pounds the concrete to drill the hole. The crack is not at the place where i will be drilling - it's about 1 metre away.

We'd just punch a crude hole through and then do a careful repair. Any rebar in the way gets recipped off.

 

[stevie888]

A cover meter would be nice but i do not have access to one and i'm not buying it just for this one project but thanks for the suggestion.
The hole needs to be 75 mm for the PVC drain pipe and i only have a 115 mm cutting disc on the grinder, so it will be a problem to go deeper.

I will probably go ahead with the first solution from thomp1983. But i am wondering...
1. If a 6.5 mm concrete drill bit will work to drill along the groove made from the hole saw? or do i need a smaller 5 mm drill bit? or bigger 10 mm?
2. Is it safe to use the SDS drill i mentioned in my original post (Makita SDS Plus drill 800W HR2630T) or should i switch to a normal hammer drill (the same SDS drill has an extra chuck that converts it into a normal hammer drill that accepts plain drill bits)? The concrete roof has a fine crack in it and when it rains, it drips along that crack on the inside of the house. So, i am quite concerned that the SDS will do more damage to the concrete roof as it pounds the concrete to drill the hole. The crack is not at the place where i will be drilling - it's about 1 metre away.

The chuck and "normal" masonry bit will still be in the same drill so no difference, but many SDS drills have adjustable speeds so if you're worried just dial it down.

I suspect a 6.5 will be fine as your core drill will bounce about and cut a reasonably wide groove. I would start with a normal length and work up to one that will go right through: a long bit will whip about if not supported by the hole;