FormulaR Board...help!

[Overhaulin63]

Okay guys I need some expert advice. I am doing radiant floor heat but I understand the FormulaR250 will not be strong enough to support a 5" to 6" pour with a two post 10K lift....not sure if true.

If true I was planning on not routing the Pex tubing and 250 board in the area that will be supporting the post. Does this sound like a viable solution vs. running the FormulaR400 board though out the garage?

The garage is going to be 32x60.

Thanks in advance for any help!

 

[Rookie2]

R250 is 25# sq.in. = 3600# sq.ft.

some engineer will chime in and explain how the load (lift post) on the 5" concrete spreads the weight outward .

 

[Chris705]

I just let a 4'x4' area at each proposed post location be free from pex and insulation. I then wired 36" lengths of 1/2" re-bar @ 12"oc.

 

[wssix99]

I understand the FormulaR250 will not be strong enough to support a 5" to 6" pour with a two post 10K lift....not sure if true.

It's not true. Where did you hear that?

In a nutshell, a car on the two post lift doesn't put any significantly greater force on the base of the slab than when a car is parked directly on the slab.

If you are still uncomfortable and would like, we can walk you through the math. The 250 board is 25 psi and the forces at the base of your slab won't be anything close to that. (lift, or no lift) The thicker the slab, the less the compressive force at the base of the slab, as well.



The best thing you can do to help yourself out is to invest in thicker insulation vs. higher compressive strength.

If true I was planning on not routing the Pex tubing and 250 board in the area that will be supporting the post.

You should do this, regardless. The last thing you want is one of the tubes right where you need to drill an anchor bolt.

 

[wssix99]

I just let a 4'x4' area at each proposed post location be free from pex and insulation. I then wired 36" lengths of 1/2" re-bar @ 12"oc.

This will greatly increase the likelihood of cracking in the slab around the post and isn't something that should be done.


For a brand new slab:
Having a slab with a consistent cross section/thickness and consistent reinforcing will yield the strongest slab with the least chance of cracking.

For a renovation: (cutting out a pad and re-pouring it)
Having a different cross section and reinforcing profile is fine (and usually recommended) but the two sections need to be pinned or keyed together.

 

[Chris705]

Just to follow up, I can report no cracks at all in my slab...pour took place in the fall so the cure was slow and I used a top coating of a cure-in-seal. No mesh or rebar was used except to tie my pex to and in these two pads. Base was VERY well compacted and there was lots of fill in my case as one corner of my build was 6' of internal fill. Once I get my lift installed we'll see if she cracks then.....

 

[wssix99]

I just let a 4'x4' area at each proposed post location be free from pex and insulation. I then wired 36" lengths of 1/2" re-bar @ 12"oc.

What led you to believe this was a good thing to do?

 

[Jon_E]

Okay guys I need some expert advice. I am doing radiant floor heat but I understand the FormulaR250 will not be strong enough to support a 5" to 6" pour with a two post 10K lift....not sure if true.

If true I was planning on not routing the Pex tubing and 250 board in the area that will be supporting the post. Does this sound like a viable solution vs. running the FormulaR400 board though out the garage?

I built a timber-frame home, in which the design of the frame has the majority of the weight of the house resting on four interior posts, which transfer the load down to the basement floor. Based on rough calculations, there is probably 20k on each post. I do know that when I had to adjust a post after the house was built, I needed a 20 ton bottle jack to raise the frame just 1/4".

Anyway, at each post location, I poured a 6" concrete pad, 30" square, so that the top of the pad was flush with the bottom of the slab. The pad is unreinforced and sitting on compacted native soil. At each pad location, I placed a mat of #4 bar, 48" x 48" and 12" o.c. in the slab above the pad. There was no insulation under the pad, no insulation between the pad and the slab, and no PEX tubing within 18" of the post location. The slab is 5" thick and does not vary in thickness at the pad/post location.

It's been 10 years and there is no cracking anywhere in the vicinity of any of those posts. I'm sure there is a little bit of heat loss at each pad location, but probably not enough to notice. Each pad is at least 12' from an exterior wall.

 

[Chris705]

To be honest I never gave the difference in thickness a second thought....I mean aren't slabs hauched down all the time to get down to a foundation or to add rebar... or even in some cases there is no foundation only hauched slab edges? I only thought about the lift going in a specific area and since I was only able to pour a 5" slab I thought making the slab thicker there and adding reinforcing bar as the right thing to do.

 

[wssix99]

I mean aren't slabs hauched down all the time to get down to a foundation or to add rebar... or even in some cases there is no foundation only hauched slab edges?

Thickend edges aren't a problem because as the slab shrinks, (and the edges pull inwards) they are free to move. (That also assumes that the shape of the slab is a rectangle/square or a triangle. If the shape is compound or has a re-entrant corner, the edges will pull in ways that will cause cracks and methods need to be used to prevent that.)

When there are differences in the middle of a slab, (foundation, penetration, differing slab design, etc.) things start getting more uncertain as no one knows how the slab will move when it shrinks. Penetrations and differences create weaknesses in the slab where the slab is more likely to pull apart. However; if these things move with the slab or the shrinking happens exactly around them (pulling inwards towards them) no cracking would happen.