8" hole thru concrete wall - how?

[Piper]

So I have to create an 8" diameter hole in a concrete wall for exhausting a natural gas tube heater. The tube is 4" in diameter and it needs 2" on either side of open space. I also require a 4" diameter hole at the opposite end for a fresh air intake. Anyway, the wall is ICF (insulated concrete form) in design, and the concrete is 6" thick. With my luck, where I need the hole there'll be rebar running thru. I"m looking at ways to cut this hole with the best finish, easiest etc. Of concern is the fact that this hole will be ~10 feet off the ground so I'll be on a ladder or scaffolding.

Does anyone know of an effective way to do this short of a big drill, cold chisel/hammer and a lot of sweat equity??

Piper

 

[nate379]

Core drill, though an 8" one is not cheap.. few hundred $$s

Can rent them at the rental place here, maybe check that out.

 

[65Stang]

Core drill companies can go through rebar if need be. They can also xray the wall for rebar position to miss it, but the price isn't going to be less that $500 I would think.

Up high like that and doing it by yourself off a ladder... not so sure.

 

[PurdueSD]

Buy or rent you a good hammer drill and drill a series of small (5/16" ish) holes in a circular pattern about an inch apart. Then grab a small sledge and knock out the hole and clean it up. Not more than a hour job at most.... I would think you could rent a drill for 40 to 50 bucks. You get a lot better results than the the ol' chisel method.

Never used a bore drill myself, so can't comment on that.

Goodluck!

 

[buening]

How tall is the wall overall?

I'd also recommend getting an epoxy paint to paint the rebar that you may cut through, to prevent them from rusting.

 

[rwhite692]

To add to what Nate already said....Go to your local equipment rental place and rent a core drill. A good rental place will have core drills probably up to around 6" diameter, what you could do (since you need an 8" dia hole) is to rent like a 2" core drill and just drill out an overlapping series of holes to get your rough 8" opening.

It shouldn't cost you more than 60-70 bucks to rent the drill and a couple of core drills, for an hour. definitely get the insurance/damage waiver, so that if you break one of the core drills you won't be responsible for it.

Seriously, once you use a core drill setup you will never want to use anything else to make a (large) hole in concrete. You will be astonished at how these plow through concrete, it's like boring holes in wood.

The thing will barely slow down going through rebar, if there is any in the way. In a case such as yours, to make those two holes with a core drill rig should take about a half hour give or take...

Rent the right tool and git er done

 

[buddyboy]

just an idea

you need 2" clearance from flamiable materials?

cut 8" hole in the styrofoam and then 4" hole thru the concrete with rented borer

would that work?

 

[pcmeiners]

Agree with PerdusSD, but I would use a 3/8, with the drill holes closer, say 3/8-1/2" apart. Once the circle perimeter is drilled, I would mark a cross hair in the circle, again drill holes along the cross hair, using a larger drill bit, if possible (3/4")... approx 30 minutes to drill the holes. Once you have all the holes drilled, change to hammer mode, use point bit to break the hole out, takes about an hour if crete is fairly new, less if crete is old.
In my area if you rent a core drill it costs a fortune, as they charge a ridiculous amount for the tiny wear of the diamond bits.

 

[viper522]

canon. bowling ball.

 

[Kevin54]

Coring companies MIGHT be less than $500. They have cut doorways in foundations in our area for around $250. I'd at least give them a call and check on the price. You may be surprised. And if a concrete coring company does it, at least it would be a nice clean hole.

 

[Buckled]

Most core rigs have a slot in the base so you can anchor them to the wall. If you rent one your biggest challenge will be anchoring through the foam. What most coring companies use is a 5/8" drop in anchor (female threads) in concrete, then they put a 5/8" bolt with a washer through the slot in the base of the core rig stand. This bolts it to the wall so they can drill the hole. Setting a drop in might be a little tough because of the foam forms. I'm not familiar with the thickness of the forms.

If you go that route you'd more than likely have to cut the forms away where the core base would sit on the wall anyway, in order for it to sit firmly on the wall.

After that the core rig should have a water hook up and will cut through rebar very easily. You'll know when you hit the rebar because the water will go from tan to grey with little metal shavings in it. An 8" hole through solid concrete with no rebar should take about 10 minutes to cut, if you hit rebar it will take a few minutes longer.

 

[glider]

I would pay the $500 , been there. Please post the results and how long it took and what a pain in the *** it was.

 

[mrjsl]

Buy or rent you a good hammer drill and drill a series of small (5/16" ish) holes in a circular pattern about an inch apart. Then grab a small sledge and knock out the hole and clean it up. Not more than a hour job at most.... I would think you could rent a drill for 40 to 50 bucks. You get a lot better results than the the ol' chisel method.

Never used a bore drill myself, so can't comment on that.

Goodluck!

I have done 10"-12" holes this way several times through some pretty serious concrete, but we used a 55# air hammer drill with a 1" bit and knocked out the middle with a small jackhammer. All at the bottom of a 30 foot deep hole in the ground.

 

[Mike83]

Choose the side you start on carefully. The opposite side will blow out when the core bit comes through.

 

[nate379]

It doesn't usually if you let the drill do it's job and don't force it.

 

[walrus]

Use a concrete saw, won't make a round hole but the unit I rented would make that hole in less than 5 minutes. Had a diamond blade and you could plunge it right into the wall like it was a knife in hard butter. I cut a mandoor into my basement in a half an hour once I was set up to go. Make sure you cut the bottom cut first, then the sides, then the top. Piece of cake

 

[MikeD74T]

Think about it, a core drill is made to make large round clean holes. Why would you consider anything else unless no core drill was availible???? MikeD74T

 

[Daniel Dudley]

I had a coring company drill a 12" hole thru an 80 year old 6" slab that was harder than any concrete I had ever seen before. It took them less than 3 hours to be in and out. They cleaned up the mess and the results were perfect. I don't remember the exact price but it was much less than I thought. IMHO this is a job best left to a professional.

I just cored two five inch holes in my slab in less than four hours with a rented coring drill, and the rental was almost two hundred bucks. It would have been very difficult for me to get the machine up on a wall though. They weigh a ton for one man to lift. The cores were through over 14 inches of concrete with one core going right through three sticks of rebar. Amazing tool. I guess I did save some money, but the rental wasn't cheap.

I have done the multi hole breakout before, and it does work. I couldn't do it in an hour , but a drill rental for a Hilti or Bosch to do that job would be about sixty bucks. You could sleeve the hole with some flue liner, and or metal, and use hydraulic cement to make it pretty.

Let us know how you make out.

 

[Motown 454]

If you use the multi hole method when you get the small hole around the edge drilled,use a chisle to connect the holes it will help to keep the outer edge cleaner. Sort of like drilling the back side of a piece of wood to prevent breakout. The deeper you chisle in the less chance of breakout.

 

[krooser]

Don't do what I did... in '75 I needed to bore an 8" hole thru my basement wall (8" concrete). I used a hand chisel cuz all this fancy stuff wasn't around back then... took hours and hours.

the worst part was I got concrete dust in one eye and darn near went blind due to burns from the lime... got lucky but be sure you wear a respirator/dust mask and safety glasses...

 

[NUTTSGT]

I'd compare the price to rent the coring machine vs having somebody come and do it.

 

[metal1313]

id just drill a series of holes, the core drills are a pain to posistion and move around, and most places will charge for wear on the bits. it really shouldnt take too long and i assume your gonna have flanges around the vent pipes inside and out to make everything look good.