I have a concrete front stoop that drains some water into the basement, so I am going to knock it out and pour a new slab with better grading. The slab will be about 4 feet square, and fits into a corner so that two sides abut the house and two do not.

How do I frame this slab, knowing that it will be up against the house on two sides?

This poster had a similar problem, but he accepted an answer that calls for leaving a few inches of gravel between the house and the slab. I can't do that - below the slab is basement!

There are references (here and here) to using "pre-formed joint material" to separate the house from the slab. What kind of material is this, and is it used instead of a wooden form on the sides that touch the house?

  • Are you talking about how to secure the frame to the house - or pouring the concrete against the house?
    – Jeff
    Feb 18 '12 at 23:57
  • I'm asking whether to use a wooden frame at all, or to use some sort of "joint material" instead on the two sides that touch the house. It seems like a bad idea to pour the concrete directly against the house - but maybe I'm wrong about that. Am I?
    – Wesley
    Feb 19 '12 at 4:21
  • Are you having trouble with water getting into your basement? Joint material is not the solution! Jul 10 '12 at 0:58
  • The improved grade should remedy the water issues. If i were doing this project... I would consider a tar based sticky back type flashing applied to the homes sheathing between the concrete and joint material. After the slab has cured caulk the joint and use bent metal flashing neatly done so minimal will show and your siding covers flashing that is nailed to the wall. Its not bullet proof but any attempt to shed water away should be made.
    – user55421
    Jun 19 '16 at 20:33

The expansion joint compound you are referring to is a material placed between two concrete slabs to prevent cracking when they expand and contract. Unlike wood, this material will resist rotting.

Compound image

You'd still build a wood frame for pouring the slab, but you'd fill the joint touching your house with this material after it has set and the form is removed.

  • Steven, do you concur with @mcktimo that I can pour directly against the joint material, rather than pour against a frame, remove the frame, and then slide the joint compound into place?
    – Wesley
    Feb 20 '12 at 23:08
  • 1
    I'm not 100%. I think it should be OK, but I also think you'll get a cleaner edge with a wood frame. Maybe use a thinner piece of wood (as close to 1/2" as possible) on this side.
    – Steven
    Feb 20 '12 at 23:15
  • You'll probably also want to caulk the edge between your house and the new slab, in order to better guide water away from the house. Feb 20 '12 at 23:26

You don't need to frame against the house. Be sure that any wood of your house doesn't end up in contact with the fill under the slab or the bare concrete. Just tack a strip of that expansion material right against the house and pour right to it.

  • If you have brick exterior,There is no need for the expansion gap next to the house as the slab will expand away from the house as it needs to. If you were putting a slab in where there were 3 walls then an expansion gap product as suggested above is recommended. Be sure to caulk at all the walls where the slab meets.
    – user68386
    Feb 4 '19 at 20:14

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