DIY building an inspection pit

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    • #893

      I have a garage that I seem to spend a lot of time in sliding around on my back under the car. It’s a pain and I regularly wish I had a pit or a lift. A lift isn’t possible (money and roof height), but a pit is, but I don’t know how to make one. Nuts and bolts is one thing, building/construction is new to me.

      Unusually, the garage floor is a really solid suspended wooden floor (no idea why, but it is nice and warm in the winter!). Under this is a layer of concrete (don’t know how thick), and presumably rubble/mud under that. I suspect this rubble/mud isn’t all that stable as it’s on ‘made ground’ in an ex-mining region and there is on-going movement in a lot of buildings in the area.

      Cutting out timbers to make a space for a pit is easy, and I’d do it in such a way that the removed section/s could be placed back on top to cover it up. Cutting through the concrete and removing it in chunks is also ok, as is digging a hole with a spade. But what then? How do I stop the walls collapsing as I dig? How do I line the walls after I’ve made the hole? Is it something I could do in a weekend, or is it a significantly bigger project that I realize?

    • #894

      I might be over cautious here, but personally I wouldn’t want to start digging about under the floor near my house in an ex mining area.

      Do you know anyone near you that worked for the coal board in a technical stopping buildings from falling down kind of job? Local knowledge may be a good idea.

    • #895

      I’ve given some thought to this for a new build we are planning. Digging the hole would be easy if there’s only a layer of concrete with soil underneath, as long as you’re sure you’re not going to fall into a capped mineshaft! If you do it, loose soil will require shuttering to prevent collapse and I suppose you might be able to copy the Brunels of the world, who would add to the weight of the shuttering so that it slid down as the floor was dug out. In building brick-lined shafts I believe it was common to sink an iron ring into the hole, lay bricks on top of it and allow it to sink under its own weight providing an instant brick liner.

      If I was to build one I would provide a sump in the middle for pumping out water, possibly leaving a sump pump installed and piped to an outside drain. LED lighting around the edge. Some recesses in the wall for tools. A ladder. Wood boards on top. Having seen the consequence of a petrol vapour explosion in a pit I would also pay attention to ventilation.

    • #896

      One of the few DIY things where I’d want an expert opinion. Serious point – for the cost of a pit done well, how much more could you pay a garage to do?

      Look into tanking to keep water out – most likely Soverign Chemicals Hey’Di K11. It’s not cheap.

      A pair of drive-on steel ramps has made my under-car scrabbling much nicer.

    • #897

      Thanks all, some useful comments there.

      Should have said earlier, but the garage is distant from the house, but yes the mining history is a valid concern. It’s actually possible to search the Coal Authority online and see where old shafts etc were located. None on my property, but some under the houses on the other side of the street!

      Also well aware of ventilation issues and these would be addressed. Water is a valid point as well. Any ideas how I could estimate the depth of the water table in a particular area?

      Ladder, yes that would be in there for sure! As would forced ventilation and lighting and a gas monitor. Luckily I’m quite short, so could probably get away with a less deep pit than most folk would need.

      Regarding paying a garage to do it, where’s the fun in that!? I’ve got drive on ramps for easy jobs, but they’re still a pain a crawler would help slightly, but it’s the working height that’s the issue. Dropping the gear box on drive on ramps would not be an enjoyable job! So that one is going to the garage. I’ve always wanted a pit though, and perhaps a project car one day if funds ever allow it.

      I might lift a few boards and drill a few pilot holes to see how thick the concrete is, maybe cut out a square and see what’s underneath. If I could estimate the water table depth that would be great.

    • #898

      Unless you do the job right, you’ll have an indoor pond.

    • #899

      Apart from exhausts and oil changes what’s a pit actually good for? Most jobs in the corners of the car you need access from both under and outside the car. A pit isn’t really much of a substitute for a ramp. For similar effort could you make some more headroom in the garage?

    • #900

      Have you seen the purpose made fibreglass liners for inspection pits?

      You may need planning permission to dig one by the way……

    • #901

      Could you look into (safely) modifying some drive on ramps to make going underneath easier by making them taller?

      Going through the concrete and then digging the inspection pit and dealing with any water/damp issues, not to mention what to do with the soil you remove, it sounds like the mother of all jobs.

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