Core drilling

[moonapprentice]

I had to core drill through pre-cast concrete the other day. First I cut out the bottom plates in a square pattern using a sawzall and then chiseling out the back end of it so it would pop out and still leave a little bit of meat on the backside of the bottom plate. The bottom plate wood was really dense, and went through about 10-15 sawzall blades (50 holes). Used a good one to cut all the way through except the last eight inch and switched to a junky blade when it were to hit the concrete. It took forever and was wondering if there is a better method to cutting the bottom plate?? (circ saw??) Anything will help!!!! Thanks!!!

 

[Cacher_Chick]

I'm trying to understand what you were doing.
What did you have to drill 50 holes through, and why?

 

[Sponsor]

 

[Dlarrivee]

If you used 15 blades you're doing something wrong.

Sawzall blades last plenty long unless you're dragging them on concrete or through a lot of nails or roofing material.

He is core drilling through concrete and needs to remove a chunk of bottom plate before setting up the core-drill.

Is this rough-in-stage, or a reno, or what?

 

[LLigetfa]

I assume the 50 holes was to play connect-the-dots. If I had made 50 holes, I would have used a hammer and chisel to connect the dots.

 

[Dlarrivee]

He said CORE holes, not 50 1/4" holes...

 

[moonapprentice]

50 separate core drill holes ..... 50 separate different bottom plate chunks cut out... core drilling down through precast concrete (units above parking garage)..... used good blades only on wood and worn blades to finish the cut by scraping the concrete.... rough stage of construction. was cutting at a downward angle so I wouldn't cut the backside of the plate, seemed to wear out blade quick with blade teeth in one spot constantly.

 

[Dlarrivee]

50 separate core drill holes ..... 50 seperate different bottom plate chunks cut out... core drilling down through precast concrete (units above parking garage)..... used good blades only on wood and worn blades to finsih the cut by scraping the concrete.... rough stage of comstruction.... was cutting at a downward angle so i wouldnt cut the backside of the plate, seemed to wear out blade quick with blade teeth in one spot constantly.

Comes with the territory there, sort of like cutting a stud with load on it, you're almost always pinching the blade.

 

[Ballvalve]

You cut the wood with an angle grinder using a small saw blade, set to not touch the cement - chisel the remainder. I see people on the home tv shows drilling cement and grantite often without any water. total stupidity. dangerous dust and compete ruin of the cutting tool. Americans do not seem to understand the miracles of lubricants, unless its in the bedroom.

 

[ckl111]

I hope you have the plans for the slabs you are coring through so you don't drill through a tendon in precast concrete.

 

[Dlarrivee]

It's likely a suspended slab, not pre-cast...

 

[Jadziedzic]

Look for "flush cut" reciprocating saw blades, such as the Milwaukee 48-00-1600 - these have small guard "teeth" that project slightly past the cutting teeth to keep the cutters from being damaged when cutting out bottom plates on concrete.

 

[ckl111]

It's likely a suspended slab, not pre-cast...

You obviously know the difference. I hope the OP does too.

 

[Ballvalve]

That's a LOTTA lube... Must have a busy nightlife...

Thats hilarious. I guess you just put your dipstick right inside. Might make a sale to a Saudi arabian harem.

 

[hj]

A "suspended slab" will have reinforcement, and maybe "post tensioned" cables, running in several directions, which must NOT be cut. Precast "T" bars will also have the cables, but they run longitudinally in the webs so they are less likely to be encountered. You will know when you hit a tension cable, because the entire floor will vibrate and you will lose about 1/2" from the end of the core drill bit.

 

[ckl111]

A "suspended slab" will have reinforcement, and maybe "post tensioned" cables, running in several directions, which must NOT be cut. Precast "T" bars will also have the cables, but they run longitudinally in the webs so they are less likely to be encountered. You will know when you hit a tension cable, because the entire floor will vibrate and you will lose about 1/2" from the end of the core drill bit.

Your wallet will be a lot lighter too....