Today, we're back out on the footpath job and in the previous video
we went through and I showed you how to work out how much
Formwork you're gonna need for the job
So today this video is going to concentrate on doing the area calculations to work out how much
Reinforcing mesh we need and the number of bar chairs that we need to reinforce our footpath
So as you can see our reinforcement is there
and to start our calculations always always start with a sketch
Just giving you the basic dimensions of the slab to say you've got a visual in your mind
Now the thing with our reinforcements is
we have a thing called Concrete Cover or the gap between the edge of the formwork and
our actual
Reinforcement, so this is so that water can't penetrate into the concrete get into the mesh start to rust the mesh and cause what they
Call Concrete Cancer
So we need you know depending on now your personal preferences you can allow
or you can take that distance off generally for an external
exposed slab it's 40 to 50mm of
Concrete cover so I'm going to use 50mm just for ease of calculation
So you can reduce the length and the width of your slab by that 50mm on each side or 100 mm overall
and work that out, or if you're not worried about that little bit on such a small job. you can
don't need to worry about it
you can just work out, but you know you didn't cut it off for now if you get it to the job site
so we go back to the job the plan and what I've done here is I've reduced my
dimensions by 50mm on both sides or 100mm overall so 800 comes down to
700 meters 678 comes down to 578 so they're going to be the
dimensions I work with for my reinforcement calculations
So to work out the amount of mesh that we need I'm going to use area calculation
So area is length x width and I'm going to use my new length and my new widths
so 5.678 and 0.700
times them together and you get 3.905 square meters of
area in this slab
That's nice and easy now when you go to Bunnings you're not going to be able to buy or Bunnings or your local hardware store
Whoever you got around at the time
you're not gonna be able to buy
You know point or three point something square metres of mesh, you're gonna get a sheet and your standard sized
Sheet for sort of normal building work is 6m long and 2.4m wide you can get
Smaller sheets, there called Ute sheets because they made to fit on the back of the ute. They're normally about 2.4m
sort of long and or you know 1.8 long or something like that this smaller anyway
So you're going to get a standard size sheet and you need to know the dimensions of the sheet obviously
So to work out how many square meters are in a full sheet in this case 6m by 2.4
that gives you a 14.4square meters of
reinforcement mesh in a full sheet so we only need
3.905 square meters, so obviously we're gonna need less than a sheet
If you need it more you might actually work it out, and how many sheet you need
so
3.09 sorry 3.905 divided by14.4
tells you you only need point two of a sheet
Okay, so you might go and buy a smaller sheet or you might just have an off cut
rr if the job is bigger it might end up that you actually needed more than one sheet
you might have had to buy two sheets, so that's how you look at how many sheets you actually need for this footpath
Okay, so in this case. We've got to buy one if we don't have any around
the next thing is bar chairs, so
in a previous
Picture here we go
Let's see I've got bar chairs here
Roughly every third
third Square
Okay, and each of these squares are genuinely 200mm so it's about every 600
millimeters apart
and while it works out is on a big
slab it's 4bar chairs
in every square metre of slab
Okay, so if we go 3.905 times 4 it gives us 15.620 so there's 16 bar chairs now
again if we go back to the picture and
do a quick count you'll find there's actually
20 bar chairs in that picture
Okay, and that's because this slabs less than a metre wide
so it's gonna give us that formulas going to give us a bit of a false a false answer
so what you could do to come to say that is just take the length of the slab?
Which is yeah 5.578 or you can say 6 meters
So that means you could have you could Say 6
square meters if it was a meter wide times out by four that will give you 24 bar chairs and
You'd be you'd have heaps you'd have it more than you need if this is a larger slab obviously wider than a meter
Then your formula will come out, and you'll have enough bar chairs, but just because this is under a metre that formula doesn't
Quite work, so you have to make a bit of an allowance for that
So there we go now we know how much
Reinforcement we need for our slab we also need how many know how many bar chairs that we need if you're doing a shed you
might also want to put a waterproof membrane
in underneath your reinforcement and again you can use square-meter each to work out how much
Waterproof Membrane you need but because this is a concrete slab it's going to be outside, I'm sorry, It's a footpath It's Gonna be outside
we're not too worried about the moisture coming through the concrete and sitting on top, but if you're doing a garden shed or a
patio or something you might be worried about that moisture coming through so you'd have to put in a
Waterproof Membrane underneath just a a 200 Micron plastic like Foricon would be fine
So there you go. There's our reinforcement worked out using area for our Footpath