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by Home User, Aug 1, 2012

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Q: What would be the best way to construct an exterior step for outside the back door?

I have recently had a back door installed in the house I am renovating? What would be the best way to install a step? I would like a concrete step and was thinking of making a wooden cast and pouring in concrete and then leaving it to set. What would you suggest?

Matt Long profile image

by Matt Long, Aug 2, 2012

A: Building a wooden former, or shuttering, and then pouring in concrete is exactly the way to make a concrete step. But there are things you have to watch our for, as it is not as simple a job as you would think.

Design: Make the step the right height, width and length. The step should be about 150mm longer than the width of your door. Its tread (the bit you stand on) should be at least 300mm wide, and you should make the step of a height so that it is exactly half way between the height of the inside floor, and the ground - that way a person has two equal steps from the floor inside to the ground outside.

Foundation: There is no point in building the most perfect step if you just build it on soil, which will let the step move and sink. Make sure the step has adequate foundations... dig out soil to a depth of 150mm and add 75mm of hardcore, then lay your step on top of that, so that 75mm of your concrete step will be in the ground.

Building the wooden former: Concrete is heavy, so use at least 19mm ply to form mould. You should make sure the plywood is supported by wooden stakes all the way around, too, at the corners and along its length. This will stop the former moving when you put in the concrete - that's a disaster! Better to have a former over-supported, rather than under.

Pouring the concrete: Use a normal concrete mix, shovel it into the mould. Don't put it all in at once. Fill about half way, and then with a shovel or metal bar, 'stab' the concrete mix over and over to remove all air bubbles and any voids around the former. Then, with a hammer, repeatedly tap the outside of the wooden former all the way around to further remove voids or any stones touching the wood. Pour the rest of the concrete and repeat the procedure. Then flatten off the top.

Next with a length of flat smooth timber (say 75mm x 25mm), agitate the top of the step by tapping the batten edge over and over onto the concrete, slowly moving the timber along the concrete, to bring all the liquid to the top of the concrete. Then with a float, smooth off the surface.

Finishing the surface: Once you've got a flat surface on top, then leave the concrete to harden off a fraction. Then, with your float, you need to create a 45 degree bevel about 7mm deep all the way around the top edge of the steps. Never leave a sharp edge on concrete steps. It will break off, and is dangerous if someone falls.

Next you need to make the surface non-slip. An easy way to do this is to draw a stiff brush across the surface to create tiny ripples in one direction.

Removing the former: The time to remove the former is when the concrete has dried off enough to be stable, but still wet enough so that you can work up the concrete if you use a float on the surface after applying a little water. This can be hard to judge because concrete sets at different speeds in different conditions. But wait a few hours.

Then use your float, and water in a sprayer, to work the sides of the step to the same flatness you achieved on the top of the step. If there are any voids, fill these with concrete and then float over the top. Use this time to correct any defects in your chamfer, too.

Curing the concrete: Concrete needs moisture to cure properly... one way you can do this is to cover it with plastic sheeting to keep the moisture in while it sets (and keep the rain off it), or lightly spray it with water a couple of times a day for a few days.

You should now have step that looks great and will last. After a couple weeks you can apply a concrete sealer to protect the step and make it easier to clean.

Here's a great article about building a flight of steps, which will help illustrate some of the points I've made above.

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