pouring a basement floor

topic posted Mon, December 18, 2006 - 12:59 PM by  Sassy Bastard
I have a 14x11 foot area in my basement which has a dirt floor. There used to be coldrooms there, but I just finished pulling them out. Where the walls used to be there are concrete footings which are 3inches above the main floor height.

What I want to do is pull those footings out and pour a floor into this space, but i have 2 main concerns.
1. One of the reasons I'm doing this is to lower the humidity level in the house, so I want to make sure I have a good vapour barrier under the new slab. I'm not sure how to tie the poly sheeting into the existing slab. I am thinking about digging under the existing slab about 4 - 5 inches and then using some sort of industrial adhesive to stick the poly to the underside of the slab.

2. I am planning to put rebar in my new slab, but it won't be tied into the existing foundation. is this a real problem?

the only thing i have ever done with concete is fenceposts, so any advice or tips are very welcome.
posted by:
Sassy Bastard
  • I can't imagen a reason for either of these. covering the dirt will lower the humidity in the house, no point in additional vapour barrier. If you have moistur problems in your basement, you have drainage problems. Nor is there any point in re-bar. Unless you intend to be moving heavy equpment down there ! 3-4" of gravel rolled reinforcment ( looks like cow pasture fence ) and 3-4'' of cement. You do need to put a expansion filler between the old and new slabs. they will move independntly of each other.
  • Unsu...
    book stores have some great concrete books. taunton press has a great on on concrete "for pros" it will teach you all the mistakes as well so you dont make em.
  • Unsu...
    Humidity is going to penetrate the concrete no matter what you do unless you seal it with an epoxy or something like Dry Lok.

    You can lay some perf pipe under your new pour in the gravel inclined to run out and down from the house but that means you'll have to dig outside the building to hook to it and drain it off. That much excavation could open up more water problems than it might solve.

    I am looking at that very problem right now. My daughter just did an addition to her house. The excavation played havoc with the water table necessitating more digging to get the main foundation sealed up and to evacuate the water.

    Once you pour the concrete you will notice a dramatic drop in humidity. Adding a sealer will increase the benefit.
    I'd just stick with that.

  • Unsu...
    ahh lot's of people trying to help you but obviously without experience. I wouldnt take my word either. Go to a professional. But here you go

    You should slant the floor I'd say about 8 inches but it has to be perfect no flat spots. put a french drain in on the low side the whole floor should slant down and to one corner.

    Cover with gravel. you will have to ask for help as to what size gravel to use and how much gravel. probably four to six inches. the gravel will allow moisture to drain.

    you need to pour the slab with control joints and you MUST use rebar. unless of course you want a floor that had to be torn out and re-poured a couple years later.

    you need to find out what size rebar you need and what type of concrete you need. Probably a lower PSI concrete so it wont crack as much.

    And the floor should be sealed with a waterproof barrier that you brush or roll or spray on or I do believe that there are add ins for the concrete itself.

    you absolutely do not need a vapor barrier under the slab. this wont work and will create problems.

    I would also make sure that the majority of the moisture is coming in through the floor and not somewhere else. This way you wont waste thousands of dollars.

    This is a big project which will take a long time so make sure you get some help from someone who has experience. and make sure that you have a permit so jsut in case something happens your insurance may cover it.

    thats all the advice I can give from my experience with concrete. I can't give you exact details since I would have to see what exactly is going on.
    • Unsu...
      woops sorry if i offended anyone by saying people without experience. I have a bit but am just like everyone else commenting. I am probably completely wrong.
      • You should slant the floor I'd say about 8 inches but it has to be perfect no flat spots. put a french drain in on the low side the whole floor should slant down and to one corner. <<
        8 inches ?? he wants a 11 x 14' section of floor, not a "Pine wood derby" race course ! And french drains go around the outside of the house, not under it. That would cause a much bigger moisture problem. Since the drain has no place to drain to, it would become a catchment, NOT good under the house.
        Rule of thumb ----- the bigger the job, the more you need pro. advice.

Recent topics in "DIY - do it yourself"

Topic Author Replies Last Post
Hot Water Heater Azeeza 9 September 11, 2015
Controlling humidity in house? Brad 24 June 7, 2015
Kindle and Tablet Azeeza 3 March 29, 2015
DIY political party,...? offlinerik 1 December 30, 2014