3 May 2016
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United Kingdom
I'm building a new doorstep. I've smashed out the existing one which was bedded on loose rubble filled with sand, contained by an outer edge of mortared bricks.

Current goal is to get a solid foundation on which I can mortar some new bricks and top with paving slabs. The new doorstep is going to have a larger footprint so I've dug out a hole the correct size and backfilled it with the rubble again.

I am now feeling completely out of my depth (no pun intended).

  • The soil is clay.
  • I found the house's original doorstep foundation of a concrete slab which seems sound. I was going to bring the rest of the area up to that level before buidling the step on top.
  • I've never made concrete, laid bricks or slabs. I have done tons of research though.

  • I discovered that the gas pipe from the house runs down the wall and then out at a diagonal angle through the ground where I was digging. I also discovered another thicker, rusty pipe which I think is also gas, running through the same area. Both encroach on where I want to concrete a foundation for the doorstep. These pipes were originally just sitting in the earth. I can't tell what they are made of or if they are insulated with anything.

    I have read that concreting in these pipes would be a big no-no due to risk of damage and no ability for maintenance. If I have to reduce the width of the doorstep to avoid those pipes, that's just what I'll have to do unless there is a safe suggestion of how to manage it with them being directly through the step foundation.

  • I don't know how to fill the hole to create a solid, flat foundation. Someone told me to fill the hole with rubble (which I've done) then pour in a soupy cement mix to fill all the gaps. I'm having doubts about the strength of that (I have never made cement but have researched enough to learn) because the cement would have to be really watery to fill all the gaps.

  • How do I ensure the foundation doesn't sink or move? I've read that clay soil moves a lot with moisture changes.

  • Could I do something like chuck in a mix of dry sand and cement to fill all the gaps in the rubble and let it cure naturally over time?

  • How on earth do I calculate how much sand/cement I need?

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First off, loosely wrap the pipes in two layers of corrugated cardboard, then finish off with a layer or two plastic (from supermarket bags), which should be taped tightly on. Make sure that the protection extends beyond the concrete. The plastic is to stop the concrete leaking right through to the pipes. The cardboard is to provide a a little give so the old pipes can be pulled out.
Throwing rubble into the hole is not doing much good other then leaving a lot of air voids. The rubble needs to be broken down into smaller bits and pounded down hard. That a huge hole, where did all the other muck go? A wooden frame work should be built (planks on edge) with top edge providing the level of the concrete. Make sure it is really strong by hammering in stakes down the outside edges of the planks and use external blocks in the corners, this is so you can keep a nice rectangular shape to the concrete. Fill the whole void with well thumped down rubble just leaving a 4" gap all round from the finished edges and top. Fill wiith concrete, making sure that the concrete next to the formwork is well tamped down, else you will get air bubble, spoiling the edges of your concrete block. When the concrete is up to the top of the formwork, use a long piece of wood and use it to scrape excess concrete off (put it on a piece of news[paper to go off). After a couple of hours go over the surface with a steel float to polish the concrete, could be better to leave it a little rough, or it will be slippery in the rain or ice.
Thanks Frank.

Yep, hole is big - was mostly filled with that rubble and sand/clay. The soil/sand is separated and I still have it round the back if need be. I had planned to make the doorstep area that big, with pot plants either side of the door, rather than just a small functional step up to the door.

Just to clarify, the concrete itself will not be the doorstep. I just want a flat base of concrete up to that existing slab, on which I will then build a doorstep using bricks and paving slabs.

Like this:


That would be phase 2. Right now, I need to learn how to actually turn that ground into a level base for the step build.
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There are two beds which suggest a DPC, the bed above the air brick looks most likely. Can you point out which bed the DPC is in?

The gas pipe should be covered and protected by lightly tamped soil. Jagged brick rubble isn't the best way to cover it.

So far, your excavation only shows top soil: no clay?

Removing the flag and under packed soil to give a single level starting surface might be best.
Do you then want a concrete slab finished level with the man hole cover or slightly higher? A slab surface that would cover the excavated footprint?
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  • Yes, the DPC is on top of the air brick.
  • The whole area of my property is pockets of clay, the bottom of that hole is clay and soil. The first 20cm of that hole was rubble and sand from previous owner's doorstep foundation.
To be honest, since the gas pipes mess up my entire plan I will have to change the design of the paved area. Rather than it being symmetrical I think instead I will just fill the gas pipe side in again with soil as you suggested Vinn. Then I could do something like pave a little area to one side for pot plants, or just forego that entirely.

I have a recessed manhole cover which I will redo the manhole with and put the paving slabs into so they are seamless with the path, but this also requires that I have the path 3 slabs wide (1350mm) and the door is approx. 900mm wide so the step would have to be 2 steps but I think it will look alright. I've drawn up a new plan quickly.


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