New concrete pad, thickness with hoist

[quick86]

I've been reading threads for a couple days on this. But here goes ---

New 30x40 construction to break ground next month. My concrete contractor and I have been talking about what to do and I sent him BendPak's concrete specs.

He suggested we can do what they say "New" concrete should have which is 12" deep and 48"xMin OA Width+12". Then do a 6" slab with 16x8 on the outsides and an 8" tall wall.

In their other specs it says that 4.5" thickness is fine with rebar.

He and I are still not set in stone on what to do as there is plenty of time to figure out the plan.

I'm doing a 2 post hoist, probably the XPR 9 or 10 series from Bendpak. I am going to epoxy the floor as well.

Now, what little I know about concrete is not much. But I heard that keeping the pad the same thickness across is definitely better than having varying areas of thickness. So should I even both with that 12" deep section? Would I be better off going 6" thick across with rebar? The minimum thickness for "existing concrete" on Bendpak's website is 4.25" with rebar.

Sorry for sounding like an absolute idiot. I am trying to make sure this floor lasts for the rest of my life.

 

[Buckgnarly]

Go a true 5" (6 even better) with rebar and be done. Does Bendpak really say 12" for new?....that's NUTS. I have 5" for my 10k assymetrical Bendpak.

 

[ace10]

The XPR10 book

https://www.bendpak.com/XPR-10-Series-Two-Post-Lift-Manual-5900951-BendPak.pdf

"Q: How thick does my Concrete have to be? A: 4.25 inches thick, 3,000 PSI, cured for a minimum of 28 days. Do not install the Lift on cracked or defective Concrete. Do not install on asphalt or any surface other than Concrete"

"• Concrete specifications. Make sure the concrete is at least 4.25 inches thick, 3,000 PSI, and cured for a minimum of 28 days. Do not install the Lift on cracked or defective concrete. Anchor Bolts must be more than 6 inches from cracks and expansion joints in the concrete or from a wall"

"Concrete specifications are: • Depth: 4.25 inches / 108 mm thick, minimum • PSI: 3,000 PSI, minimum • Cured: 28 days, minimum Anchor Bolt specifications are: • Length: 6.3 inches / 160 mm • Diameter: .75 inch / 19 mm • Anchor torque: 85 – 95 pound feet (never less than 80 or more than 110) • Effective embedment: 3.25 inches / 82.5 mm or more"



This reads very clear and consistent to me.

 

[grant00]

Bendpak's guidlines can be a bit confusing. The specs for "new" is for when your existing slab is unknown OR does not meet the 4.25", 3000 psi, and rebar specifications they have and you need to cut out your floor and put is new "pads" just under where the posts will go.

If you are putting in a new slab and can meet those requirements then you do not need to follow the 12" thickness.

 

[Yankee2bbq]

Go a true 5" (6 even better) with rebar and be done. Does Bendpak really say 12" for new?....that's NUTS. I have 5" for my 10k assymetrical Bendpak.

I agree with the above statement. Go with 3/8th rebar.

Sounds like your going to do a monolithic pour? (Basically a footer around the perimeter of the slab) If true, 1 foot deep, 1 ft wide, with 3/8 rebar uprights and horizontal rebar to hold that slab nice and tight.

 

[quick86]

The XPR10 book

https://www.bendpak.com/XPR-10-Series-Two-Post-Lift-Manual-5900951-BendPak.pdf

"Q: How thick does my Concrete have to be? A: 4.25 inches thick, 3,000 PSI, cured for a minimum of 28 days. Do not install the Lift on cracked or defective Concrete. Do not install on asphalt or any surface other than Concrete"

"• Concrete specifications. Make sure the concrete is at least 4.25 inches thick, 3,000 PSI, and cured for a minimum of 28 days. Do not install the Lift on cracked or defective concrete. Anchor Bolts must be more than 6 inches from cracks and expansion joints in the concrete or from a wall"

"Concrete specifications are: • Depth: 4.25 inches / 108 mm thick, minimum • PSI: 3,000 PSI, minimum • Cured: 28 days, minimum Anchor Bolt specifications are: • Length: 6.3 inches / 160 mm • Diameter: .75 inch / 19 mm • Anchor torque: 85 – 95 pound feet (never less than 80 or more than 110) • Effective embedment: 3.25 inches / 82.5 mm or more"



This reads very clear and consistent to me.

Yeah their 800 number guy said "If you're doing new concrete we recommend 12 inch depth" and I think he just defaulted to their "if you are cutting in to pre existing that doesn't meet the specs"

 

[ace10]

Yeah their 800 number guy said "If you're doing new concrete we recommend 12 inch depth" and I think he just defaulted to their "if you are cutting in to pre existing that doesn't meet the specs"

The installation manual, which has presumably been reviewed by engineers and lawyers, states exactly what their specs are.

I don't understand why you're wanting to make this more complicated than it needs to be.

 

[ConCretin]

Now, what little I know about concrete is not much. But I heard that keeping the pad the same thickness across is definitely better than having varying areas of thickness. So should I even both with that 12" deep section? Would I be better off going 6" thick across with rebar? The minimum thickness for "existing concrete" on Bendpak's website is 4.25" with rebar.

Sorry for sounding like an absolute idiot. I am trying to make sure this floor lasts for the rest of my life.

I think subsequent posters have cleared up the confusion about concrete thickness. I'd go with a 5" slab to account for normal variations in sub grade and top of slab elevations and ensure you have the minimum 4.25" depth.

There is nothing wrong with varying depths within a slab. The only consideration is that the thickened sections, particularly around the perimeter will restrain the slab from contracting and increase the likelihood of shrinkage cracks. This is easily mitigated with the use of control joints.

Making sure your new slab lasts the rest of your life is actually pretty challenging. Ask all the guys who post on here with slab issues. Take a look at my Guide to Floor Slabs in the link below for some additional things to consider. Good luck and congrats on the new project.

 

[salguod]

I just built a 30x40 and am planning a 2 post lift, although not likely a BendPak. Almost every lift manufacturer recommends 4.25" / 3,000 psi, but BendPak is the only one I looked at that recommended rebar (the other outlier was Apluslift who said 6" / 3,500 psi). Since I wasn't going BendPak, I just went with the 4.25" / 3,000 psi, but my builder had the concrete guy clear some gravel in the area the lift will be before the pour so I should have around 5" there, 4.25" everywhere else.

 

[BillK]

If you think about the cost of your entire build, the difference to put in a thicker section in the slab for the lift is almost nothing. I would rather have it thicker than not thick enough

 

[danho]

I just had the slab poured for my new 32x40 build and went with full 5" concrete with 3/8' rebar, 2' OC so that I could have options in the future to put the lift wherever I wanted. The added cost was $750.