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  1. #1
    Join Date
    Jul 2008
    Posts
    33

    Default old dirt basement

    Hi.
    I have a house built in 1830 which still has a dirt floor in the basement. I have it coverd up with heavy plastic sheeting, but, I wish to concrete it over to make some good storage space. I don't want to bother digging it out. It's not in the budget, and it's too much work for me to do. It's a full basement (15x40) and about 5' high. I could put a tiny workshop down there for the occassional project, but, mostly for hoiliday decorations and tools and stuff.
    I guess I wanna do a "rat slab". About 2" thick with fiber mesh brought in from a pumper truck. The bulkhead door is tiny.
    Anything special that I have to do?
    Plastic sheeting is already down...........do I use gravel or could I use sand or do I use both?
    Thanks.

  2. #2
    Join Date
    Jul 2010
    Location
    SoCal
    Posts
    6,302

    Default Re: old dirt basement

    If you want to pour a slab in your basement, why only 2" deep?

    And at 5' tall it will be difficult to walk around, don't you think so?

    Generally speaking, a 3.5" thick slab of concrete this large has to sit on the following: 6mm thick plastic, 2" sand, 2" crushed rock and rebars. Less than that will result in a lousy job.

    Remember that once you pour concrete it will be almost impossible to make any changes.

  3. #3
    Join Date
    Jul 2009
    Posts
    157

    Default Re: old dirt basement

    I agree with dj1-----you've got to figure on 7' so you'll have enough headroom for a person of average height & for incidentals such as overhead lighting, overhead plumbing, HVAC & electrical lines, as well as at the base for a few inches of crushed stone/sand and 3 to 4" of concrete.

    There's usually no need to think about excavating the entire 15' X 40'---from your post, it sounds like with your current need for storage/work space you could get by in the foreseeable future with, say a 10' X 15' or 10' X 20', as examples---but as you note, excavating part of your cellar down to 2' raises a number of issues that have to be dealt with:

    1) It DOES require a lot of hard work---dirt cellar floors have been sitting there for years, and require pick & shovel or power tool to loosen the packed soil before it can be removed.

    2) Some way of excavating the soil out of the basement has to be found--either by a motorized conveyer belt thru a cellar window, or some other way.

    3) Depending on how far down the existing foundation walls go down, you will probably have to put in either a bench concrete footing, or a concrete underpinning under the existing wall, if the new room will butt up against the existing foundation.

    4) You would have to get a building permit from the town hall, and sometimes the town requires you to hire a civil engineer to draw up a structural plan for the new wall ($500-$1000.)
    Last edited by Pelton; 07-09-2011 at 08:37 AM.

  4. #4
    Join Date
    Jul 2010
    Location
    SoCal
    Posts
    6,302

    Default Re: old dirt basement

    Pelton said: "3) Depending on how far down the existing foundation walls go down, you will probably have to put in either a bench concrete footing, or a concrete underpinning under the existing wall, if the new room will butt up against the existing foundation".

    Pelton said it correctly, there will be issues with digging. You don't want to mess with the integrity of the existing footing/founadation.

    Also, doing all these for storage purposes, may not pencil out and be so uneconomical.

  5. #5
    Join Date
    Jul 2008
    Posts
    33

    Default Re: old dirt basement

    yeah...............um............thanks.........bu t.........the whole idea is to AVOID digging anything out.
    I just wanna deal with what I have.
    An architect that I know said that a RAT SLAB (about 2") is the minimum amount needed to do the job, and that I could use fiber mesh-small fiberglass particles mixed into the concrete to get around having to use rebar or steel wire mesh.
    I now that it's only high enough for Cousin It to fit into, but thats what I have to live with. It's only for storage and maybe a tiny work area to do the occassional annual project or something.
    I was just seeking some advice rether than shelling out a few hundred for an architect to draw up some plans.

  6. #6
    Join Date
    Jan 2011
    Posts
    93

    Default Re: old dirt basement

    Build a work/storage shed out back

  7. #7
    Join Date
    May 2008
    Location
    Pacific Northwet
    Posts
    1,564

    Default Re: old dirt basement

    For what you're proposing, I don't think there's anything special to do. You're just trying to slightly improve a poor existing space so your boxes don't sit on the dirt. As long as you don't make any structural changes, or attempt to make it livable space, or do any plumbing or electrical work, or change the way that a fire would propagate through the space, you might not even need a permit (think of it as "floor covering") as long as you don't have tattletale neighbors.

    I really think that the idea of using this space as a work area is a poor one. After working on a project down there for an hour your back and neck will be complaining.
    The "Senior Member" designation under my name doesn't mean I know a lot, it just means I talk a lot.I've been a DIYer since I was 12 (thanks, Dad!). I have read several books on various home improvement topics. I do not have any current code books I can refer to. I was an apprentice plumber for two years.

  8. #8
    Join Date
    Jul 2008
    Posts
    33

    Default Re: old dirt basement

    Quote Originally Posted by Fencepost View Post
    For what you're proposing, I don't think there's anything special to do. You're just trying to slightly improve a poor existing space so your boxes don't sit on the dirt. As long as you don't make any structural changes, or attempt to make it livable space, or do any plumbing or electrical work, or change the way that a fire would propagate through the space, you might not even need a permit (think of it as "floor covering") as long as you don't have tattletale neighbors.

    I really think that the idea of using this space as a work area is a poor one. After working on a project down there for an hour your back and neck will be complaining.
    I was thinking of setting up a little table and chair to sit at while doing some small DIY thing. I don't make any big stuff, but, I do like to tinker a bit in the Winter with some small project or two.
    I was just wondering what a rat slab would consist of.
    Plastic sheeting (6 mil)
    sand?
    sand & gravel?
    A couple of inches of concrete.
    I was just wondering what goes under the concrete.
    Thanks.

  9. #9
    Join Date
    Jan 2008
    Posts
    1,897

    Default Re: old dirt basement

    I've converted a few basements this way, but there's no point in it unless you're going to end up with adequate headroom. I'd rather see you spend half the concrete money on a neighbor's kid to dig out half the area for you, then cover the rest with plastic sheeting with pallets for storage space. That way you get what you need, don't break a sweat (which seems to be an issue here- odd that on a DIY forum but whatever), and you won't be patching your head where you forgot to duck. Oh, and with adequate headroom it will be an asset upon sale whereas without it you may be seen as being a couple letters short of that- especially if the next owner wanted the headroom but now had to break up concrete to get it!

  10. #10
    Join Date
    Jun 2014
    Posts
    1

    Default Re: old dirt basement

    We are moving into a house built in 1883 with dirt still in the basement. The precious owners said to keep a bulb burning 24/7 to keep mold from growing. True or false? I'd rather save the electricity. Thanks for your help.

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