Pour Stop or No Pour Stop 2

[marinaman]

I've been thinking about a mechanical slab that I am designing atop a building. The slab is 3 1/4" concrete on 2" metal deck for a total of 5 1/4" thickness.

The mechanical units require openings thru the slab to run ductwork thru.

I've provided beams around every opening.....but I've been thinking....do I really need pour stops to form these openings in the slab? Would I be better off just pouring the entire slab and then allowing the GC to come back and cut-in the holes he needs for ductwork? If he cuts-in the holes, there will not be a bent plate finish to the openings (obviously!).

 

[GerryBertier]

On a side note:

I always have them core drill the corners of the opening before they saw cut to make sure they are not over cutting the corners.

I can't think of any reasons why you need a pour stop, but maybe others will.

 

[racookpe1978]

5-1/4 total concrete slab inch thickness, when you include the 3 to 4 inch diameter of the cener of the concrete saw, will require a very large diameter concrete saw (18 + inches diameter. This gives you a very radius "edge" cut, so a simple core drill at each corner is not enough to end up with "square corners" on your finished hole.

The more expensive "band saw" type devices are available, but fewer people have and they charge more for that ability to make square corners. Need scaffolding and access udnerneath also = more costs when cutting. Add it up, and building the pour stops sometimes becomes less expensive overall.

Also, adding pour stops puts the expense (profit ) n the concrete form and carpenter people, not on the HVAC installer. But a pre-poured HVAC "hole" requires the HVAC contractor to be more careful about where he puts the topside unit, where the duct has to go, etc. If the HVAC company cuts the hole, they don't care (may not lok) at where the rebar and joist and framing is underneath the roof. SO there are motives on both sides.

 

[steellion]

Pourstops are not required if they are going to cut openings after the fact. If the openings locations and sizes are known, I don't know why you would fill a slab just to cut it out, but in my opinion that's a means and methods thing for the contractor. The results of either construction method should be equivalent from a structural perspective.

 

[cvg]

agree with RA Cook, the HVAC contractor will not have either the equipment or experience to sawcut concrete. core drilling is not a bad idea, but who will do that? drilling and sawing will require a specialty sub contractor or a really motivated general contractor. getting a clean, square hole will be difficult and avoiding cutting into the framing around the proposed hole will be difficult to do. I'm not convinced that you will be saving money and quality will almost certainly suffer

 

[JLNJ]

Really, it comes down to whether or not you think the slab guy can coordinate with the mechanical guy and get it right.

If the design team and contractors work together to set the final size and location, then it makes sense to get it formed and poured in place.

If the timing doesn't work out, then maybe saw cutting is the way to go. I specify no oversawing with the use of hand tools in the corners. Expensive, yes, but less expensive than filling in a wrong hole AND cutting a proper one.

 

[LECT12]

Just block the flutes with styrofoam and box out the opening with 2x4's. Then have the GC bandsaw the metal deck after the concrete has been poured. You get your flat concrete finish and you're not dropping a 150# piece of newly constructed slab.

 

[Ron]

Agree with LECT12...but in either case they'll be in the wrong place!

 

[hokie66]

Murphy at work, Ron?

 

[XR250]

Do you have enough capacity in your system to deal with all random the penetrations?