Bricks, Masonry, Asphalt and Concrete - Expansion Joints

:wall:
I am building a picnic shelter with a covered 16X24 foot 4 inch thick concrete slab. I plan on using a trowel to cut in expansion joints every 8 feet. My past concrete projects have been limited to sidewalks and driveway aprons, but never anything this large.

Since it is near a pool, I plan to screed the concrete and then use a broom to create a slightly rough texture. I don't plan on using a float.

In the past, I have always been able to reach at least 1/2 way across when using the expansion joint trowel. In this project, I can't do that. I have a 2"X10"X10' that I plan on using as a straight edge that I can also walk on.

My question is: When can I make the joints? If the concrete is hard enough to walk on (even using a 2X10), won't it be too hard to use the trowel? How do I tell when the time is right?

If you have a long aluminum or fiberglass extension ladder, you might be able to elevate it and lay it flat- use it as a platform to set your plank on. I've often used a short handsaw to cut through the cement- I like the control that the handle of the handsaw gives me. Wait until the cement has no water on top. It needs to be dry enough that it won't "seal" back together behind the saw, but wet enough that you don't have difficulty pulling the saw through. You can snap a chalk line or use a board as a straightedge so that you get a nice straight joint. Once you've cut it all the way through, then you can use your joint trowel to finish the joint.

BTW, hope you're using some rebar or wire in this slab.

As another alternative, you might think about doing it in 2 pours. It would be much easier (esp if you have little experience in such a big pour) if you would form up and pour 8x24... then a few days later, pour the other 8x24. It would be a lot easier to screed and bullfloat across a 8' pad vs a 16' pad, esp if you are like me and don't do cement work every day for a living.

I poured 30 yards one day and about died. ;) lol

Often contractors saw the control joints the next day to get a better appearance. If you have access to a saw you may want to try it.

If you saw as soon as you can walk on the slab, the concrete will be soft and cut much easier.

Dick