Expansion joints - yes or no

[5wndwcpe]

Hello all - I'm finalizing plans for my garage build and have a question about expansion joints. The slab will be 28 x 56, 4500# 6" thick fiber reinforced, 6 ga. wire on chairs, with hydronic heat. Do I need expansion joints and if so, how many and saw cut or full depth ?

Thanks

 

[elsensei]

yes definitely, every 10 feet, saw cut then caulk later.

 

[bmwpower]

To be clear, you're looking for "control" joints, not expansion joints. Control joints are inside the perimeter of the slab and are used to "control" cracking. Cracks will tend to form hidden within the joint versus in the rest of the slab.

Joint should be 1/4 the depth of the slab. So in your case 1-1/2" deep.

As elsenei said, they can be saw cut shortly after the slab has initially cured (up to 1 day). Or they can be hand formed with a tool. Saw cut joints tend to leave a nicer edge better for caulking to make it virtually invisible.

Are they necessary? No...but you may get some cracking overtime. I chose to not cut any joints in my 30x30 slab. I have some minor cracking in a couple spots, but they're hidden by epoxy. I wanted a smooth floor without joints so I could roll stands, jacks, etc. around without trouble. The big reason I didn't want any joints was due to my lift install requirements which required the joints to be at least 2-3 feet (can't remember exact spec) away from the lift post....not possible in my layout.

 

[5wndwcpe]

Thanks for the replies. My only concern with a saw cut joint is the possibility of nicking the PEX tubing. No, it shouldn't be that high in the slab, but you never know.

 

[JohnZ]

My slab is 44' x 58', control joints saw-cut in 8' squares and 8' x 12' rectangles; poured seven years ago and epoxied, not a single crack anywhere; joints were filled with the poured epoxy to about 1/8" below normal surface.

 

[boiler7904]

You have to sawcut the slab or tool expansion joints into the concrete as it sets up. The latter may be the best for you since you have the tubing in the slab.

Rules of thumb:

Joints should be 1/4 the depth of the slab.

Take the slab thickness in inches and multiply by 3. This gives a pretty good maximum spacing for the control joints in feet. Ideal spacing is in the 10' to 15' range.

Joint pattern should be squares (1x1) or rectangles up to 1.5x1.


To keep the piping from getting nicked, set you mesh on chairs and tie the piping to it (works best with a heavy gauge mesh). Fill the piping with pressurized water and keep a pressure guage on it. Have the contractor installing the piping on site during the pour and ready to fix any tubing that gets damaged.

If possible lay out permanent locations for items like lifts, floor anchors, etc. and avoid those areas with the piping.

 

[john56h]

I have a new 28' x 28' garage with a 5" thick concrete floor inside a full "frostwall" foundation. The floor slab was poured in October with no expansion or control joints whatsoever. I'm in New York, so it does get cold over the winter months.

This Spring, I've already noticed a sizeable crack. It is not opening up or anything, but is is about 8' long. I can't say that I'm surprised. At the time it was being poured, I asked the concrete contractor and he said "it'll crack no matter what you do...we can put joints in, but it still might just crack elsewhere anyway". I took his advice, but I'm hoping I don't regret it.

 

[bmwpower]

He's right....sort of. All concrete cracks, you just want it to crack in the joint. I went without any joints, too. The way I look at it as long as the crack doesn't start heaving, it gives the floor character.

 

[john56h]

Yeah, the cracks developing in mine are not from differential settlement...they are simply from expansion/contraction/shrinkage.

My floor was poured an extra inch thick (5" vs. the normal 4"), reinforced with wire mesh and had the fiber reinforcement mixed in, plus the concrete contractor drilled and pinned it to the frost walls prior to pouring. And the entire excavation within the building was backfilled with compacted crusher-run gravel.

I think a few cracks are just a fact of life. If you put in "enough" control joints, it might not crack elswhere...but then the floor will look like a waffle iron.

I've heard that proper curing has a big effect on future cracking too. The guys I know in the business say that if you can keep the concrete wet for a week or more after pouring...the strength will be a lot better. It would require covering it up and constantly adding water for an extended time.

 

[PAToyota]

My (roughly) 24'x40' main floor is divided into two slabs with an expansion joint between due to a level change. But the two slabs have no further control joints - roughly 24'x20' each. The slabs are 3500 psi, four inch thick, mat style wire mesh (not roll), no fiber reinforcing, four inch PennDOT 2B modified crushed stone over geotextile fabric and compacted, and kept wet with burlap for a week. Over ten years later not a single crack in either slab.

 

[5wndwcpe]

If I can manage to get them to do the pour on a Friday, cover it up and keep it wet, how long before work can resume ?

 

[ron in sc]

My geoteck report recomended saw joint spacing of 15 ft. or less for the garage slab. Not sure exactly what that is. Expansion joint?

 

[bmwpower]

My geoteck report recomended saw joint spacing of 15 ft. or less for the garage slab. Not sure exactly what that is. Expansion joint?

Saw cut control joints. No expansion material in the joint, just a saw cut to control the location of cracking.

 

[ron in sc]

just a saw cut to control the location of cracking.

How deep do the cuts go? All the way thru the concrete slab?

 

[bmwpower]

How deep do the cuts go? All the way thru the concrete slab?

Saw cuts should be 1/4 of the way through the slab, ie. 4" slab = 1" deep cut.