Cutting expansion joints

[kengoff]

My concrete guy stiffed me on coming back to cut the new floor I had them put in. Plan to do it myself now, but needing advice on how to.
Can I rent a saw for doing this? The shop is 30 by 80. Hope to be able to rent a saw I can operate while standing. Get old and have back trouble, but still try to do things myself.
How deep should the cut be? Concrete is 5 inches with wire in it.
My plan is to seal the concrete after expansion joints are cut .
Thanks for any help. Ken

 

[Wanna Ride]

I'm no concrete pro, but I don't believe those are true "expansion" joints. It's my understanding that expansion joints are actual separate sections of concrete pours. If I'm correct, the saw-cuts are just to stop possible future cracks from spreading. But I could be entirely wrong. When I poured my driveway and under advisement from a concrete contractor, I saw cut about every ten or twelve feet, just down maybe 3/8ths of an inch. All I know is that I poured my driveway (approx. 36' x 24') about fifteen years ago, and it's not cracked anywhere. I poured my garage floor (30' x 40') about twenty-four years ago, and fortunately, it's not cracked anywhere either. However, I poured all my sidewalks (approx. 60' and it's all 36" wide) about ten years ago, and there's only one crack (it formed about eight years ago) in them, but it hasn't separated.

 

[LegacyIndustrial]

1/4 of the slab thickness is your depth, has to be done within 48 hours. Green blade on the saw.

I am pretty sure once you pass 48 hours it’s a waste of time, it has already decided where it will crack.

Hopefully our concrete Guru , LLWillysfan, will chime in!! [emoji4]



Sent from my iPhone using Garage Journal

 

[ConCretin]

There are situations as Wanna Ride describes where a slab is placed in sections separated by construction joints, which are also referred to as expansion joints but you are referring to saw cut contraction or control joints.

Since the concrete is already a day or two old, any walk behind floor saw will work. It doesn’t have to very powerful because you are only cutting 1/4 the slab depth but a saw with a little more mass will be easier to control and keep straight. I’d call a local rental yard and tell them what you are doing. Don’t however let them give you an early entry or soffcut saw. They are designed for cutting very green concrete.

There is some more info in my Guide to Floor Slabs in the link below.

One final thought. I hate to be negative but the time for cutting contraction joints is likely past and depending on variables such as temp, mix and slump you probably already have random shrinkage cracks in your floor.

Concrete shrinks the most in the hours immediately after it is placed creating tension. Making matters worse, the concrete hasn't yet developed much inherent tensile strength. If you don't cut contraction joints to relieve the tension with a crack you can't see, the concrete will crack somewhere else where you can.

Random visible cracks aren’t a structural issue. Intentional cracks in the bottom of saw cuts aren't really any different than random cracks. They are however ugly and can pose some maintenance issues. If you haven’t paid the guy who was supposed to cut them, you may want to take this into account.

 

[kengoff]

Thank you all for the help. The saw and correct blade was of great help. Wish I would have used air to blow out the cuts when first cut. But hay the saw pulled me around for a few hours so I needed a nap.
So I'm down on the floor digging out the cuts so I can apply some kind of flexible something.
And again thanks for the advice. Ken