laying a concrete floor in 100yo house

june6294November 8, 2007

I have a 120yo house with an unfinished basement, dirt floor/stone walls etc. The floor is dirt mixed with stone that they used when they built the house. There is no drain and it is relatively dry. I want to have a floor poured but I've heard 2 ways

1 : to use a laser to level and just pour concrete 3-4 inches.

and

2 : to excavate the floor down 6 inches or so, then a layer of gravel- followed by waterproof barrier - then steele grid followed by concrete 4inches.

Can I get away with the first option? Should I worry about moisture problems and cracking with the first option?

thank you for any info.

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formula1

The general desire is to pour concrete on 'undisturbed soil', which typically means non-excavated soil. I would think soil/stone that has been trodden on for 120 years would qualify as that. I don't see why you can't go with pouring on the current floor, taking note of the added comments below.

Basement floors typically don't have metal reinforcing in them. At post or lally column pads the pour would be thicker and may require reinforcement. Evan a one inch layer of pea gravel would establish a drainage plane if things do get wet underneath, so I would recommend that and installing a drainage field with perforated pipe and sump pit (better safe than sorry). And by all means place a 6 mil visqueen vapor barrier over the floor before the concrete is poured; even though the floor appears dry to you now, most every basement foundation/floor is constantly releasing moisture into the home via water vapor. Also plan on sawing control joints to allow for controlled cracking.

    Bookmark   November 8, 2007 at 12:07PM
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Brewbeer

How much headroom do you have? Now would be a good time to improve the situation if it is lacking, as you will be losing 3-4 inches if you go with option 1.

    Bookmark   November 8, 2007 at 7:59PM
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worthy

Without knowing what the soil in the basement is composed of, any recommendations are being made blind. In general, the best practice in a new home is at least 3 inches crushed gravel followed by 5" of concrete, with 6x6 6/6 wire grid reinforcement. Vapour barriers are commonly recommended but my own engineer advises against them as he cites research showing that they weaken the slab.

Excavation in your case may be a very bad idea; the footings may be close to the surface and you will only undermine them by excavating. (I once bought a home where, unbeknownst to me, the previous owner had done exactly that.) Providing for drainage can't hurt.

Your best investment would be to get the advice of a local professional engineer on how best to procede.

    Bookmark   November 10, 2007 at 9:32PM
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