how best form for final slab in barn/shed

[Backwaterdogs]

Not sure if this is the right place for this question or not, but pouring a final ~10x40 slab in my shed (long over due)...this is going in a metal quanset style metal building.

My concern is, there is already a footer/foundation there, but too high that I can't use it as a strike off. so, not sure how to word, this other than I need to maintain a slope from existing slab to the existing foundation...so need the concrete line to land about 3/4 inches below top of that existing foundation.

Was wondering if anyone has encountered where it's not clear/easy to strike off the concrete. Do you just eyeball it?

 

[joes169]

We deal with this on an almost daily basis, it's referred to as "wet screeding". It's definitely more complicated than screeding directly off of the top of a form, but once you've done it over a few thousand yards, it's nothing to worry about........

You may want to mount 1/2" felt/ripped insulation to the foundation to run a mag off of before the pour, it will simplify the entire pour. Plus, it's ideal to have the separation between the two concrete elements.

 

[ConCretin]

As joes169 indicates, an experienced crew won't have a problem establishing grade without forms using a laser and wet screeding. I like his suggestion of installing expansion material to the existing footing. It will provide a reference for grade similar to a form board for striking off the concrete and isolate the slab from the footing. I usually use a closed cell foam material with a removable top strip that can be pulled out to leave a space for sealant. We call it zip strip but that term has multiple meanings.

 

[bigjon]

I’d use a chalk line for this situation. I’d still use the expansion foam also.

 

[Backwaterdogs]

thank you all for the advice, this is very helpful!