Formwork for Simple Slabs – Perimeter

Formwork for Simple Slabs – Perimeter
May 1, 2020 Marmelade-GF974

Welcome back out to the jobsite and what I wanted to do today was go through or start a series of videos.

Three I think will end up being on. The materials we need to pour this concrete footpath, so I’m going to break it up into three videos. One will be perimeter for our formwork Second one will be area for our reinforcement and the third one will be on volume for our to work out the actual concrete. So this will be the first one which is going to be primeter so In order to form our mould for our concrete footpath we need to have some formwork. Generally timber although you can use steel a lot of professionals use a steel product, but for the average builder, handyman timber is cheaper and we readily more readily available, so we generally use that and obviously it goes around the perimeter of our slab so the best method of calculation is to use perimeter.

There’s a formwork by itself So the best way to start a job will start working out something as always make a sketch so Sketch it out, it doesn’t have to be the scale put your dimensions on it, so this slabs 5.678. long 800mm wide it’s 75mm thick for a little footpath So the first thing we need to do is work out the distance around the outside which is perimeter and the formula for perimeter. Is just a sum of all the sides, so we’ll work our way around 5678 + 800+5678+500 add them all together gives us a total length of 12.956m for our formwork around the outside of our slab but If you go back and have a look at our formwork.

You’ll actually notice the formwork is longer then just that exact measurement of the slab advance past and not only does it run past by the thickness of the the formwork itself so that the thickness of this piece here and the same here on on all sides you can see I’ve set the form lookup in these pictures so that it runs past on each end so I don’t actually have to cut my formwork to an exact length I can let it run past and the less you have to cut formwork the more reusable it is later on so we always try and set it up so we can reuse our formwork so. Yep, even though I have worked out the exact perimeter of my slab then it’s not going to be really enough for my formwork so I have to allow a little bit more now.

The other thing is over here in Australia timber comes in standard lengths and usually increments of 0.3 or 300 millimetres and depending on the timber they might start at about 1.8 although generally you know 2.4 about the shortest length of timber a would stock and run up to anywhere up to about 6m for natural timber.

So we need to make our lenghts of timber that we’re gonna buy work into these sizes, so what I’m gonna do I’m going to take my 5.678 and I could go up to 5.7 but You know that’s really only another 22mm long, and they are timber Yeah It’s going to be a minimum 35mm thick so I’m going to round that up to 6m from our two long pieces on the edges.

They’ll let them run past a little bit And my two ends I can add 800 and 800 gives me 1.6 so I can round that up to my shortest length there 1.8 to allow for my ends so what I’m going to order from the timber yard would be 2 / 6m lengths and 1 /1.8m length so that gives me a total of 13.8 lineal meters of timber and that’s how they’re going to charge me they can only give me a price per lineal meter of timber.

So that’s my timber workout. That’s my formwork for around the perimeter and you’ll notice in the picture that we have a few pegs to hold that into place. Now have the number of pegs who put in does differ depending on how thick your actual edge board is a thicker the edge board the less pegs are going to need to have but as a general rule.

I like to put one in every 800 to 1000 and obviously you need to have a couple extra ones in your corners to hold both sides of the corner just so the slab doesn’t want or the formwork doesn’t want to separate in the corners, so to work at our pegs what we need is the length of our slab or the length of our form work, which we were working on 13.8.

A peg spacing which I’m going to say is 800 and then we need to add a couple one one extra peg for each corner so I’m going to say there’s an extra four four pegs for the corners so 13.8 divided by 0.8 gives us 17.25 so let’s say 18 pegs plus 4 for the corners and that gives us a total of 22 pegs for our job.

So that’s what we need to do in order to work out the formwork for our simple concrete footpath and the pegs that we need for.

So in the next video what I’m going to do. I’m going to look at how we work out how much Reinforcement we actually need to put the mesh or the reinforcement into this slab