Oct 16, 2014

Building Concepts I Course CMCC- Concrete Slab Foundation Placement Week 4

This short week of class was at no shortage of hard work. The concrete truck was due to arrive with our slab on Wednesday October 14th and we were the students arranged to place the slab inside of the foundation we had been preparing concrete for. We wore rubber boots while we worked the concrete into the corners where we then troweled the mix to our grade (chalk) line that we snapped.   

Here I am working the concrete into the cracks of the corner next to the plastic and foam we have against the wall with a special rake made for moving wet concrete.

In this photo you can see us screeding the concrete. Screeding is the process of using a long piece of metal (usually aluminium or magnesium)  or wood to make back and forth motions across concrete. One or two of us worked the mix behind the screed team to be sure the concrete was at the proper height while its being leveled. Without the man behind the screed you can create pockets where you will then have to go back, fill and re-screed. The people behind the screed are also there to remove what concrete is catching up behind the screed as it can pile up. 











Towards the end of our manual screed job, our instructor for the afternoon showed us the took he was using in the photo below. Its called a power screed, it operates doing the same screeding-job we did, in a fraction of the time with half the manpower necessary.




This tool here is called a Bull Float. What this does is give the surface a clean smooth finished after it has been screeded and still has some ripples from the screed left on its surface. It goes a long pole and is made of magnesium or aluminium so it wont fall into the fresh concrete, it just glides right over it.  





Here we are hand troweling the slab. For this process the concrete had to cure or hydrate for a half hour to forty-five minutes. Hydration is the process that wet concrete goes through while it is hardening up. It does not take long to harden enough to put something to stand on and walk on it. Also here the surface is still malleable enough that we can work with it. Going over the top with trowels like this will gave the surface a clean finish without any large rocks protruding from the top.

Like the screeding exercise, we were shown first how to do it by hand, then by way of a machine that can do it in half the time and with less manpower. The tool that Dave was using in the photo below is a power trowel. It have 4 blades that spin and work the large rock either down or out of the surface face of the concrete slab.









The finished product! It wont be fully cured for another 25 to 30 days but it becomes increasingly  harder every day. By the next day you could walk on it but it wont fully cured for an estimated 25 to 30 days from the day it was placed. 

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