Expansion joint for 8x4 concrete walkout slab?

[Fr]

Hello. I'm planning to pour a small 8' x 4' (4" thick) concrete slab for a walkout from my sliding basement door. I think I have just enough height from the bottom of the door threshold to slope the slab away from the house slightly. Anyway, while doing some reading about it on the quickrete.com website, I noticed their mention of fiber "expansion joints" that are recommended when pouring a slab that will butt up against a concrete foundation (which IS what I'll be doing). My slab will essentially go right up to the concrete wall foundation of my basement.

So, should I place one of these fiber strips down in my small "pit" (against the concrete foundation), extending down from the basement door threshold, so my newly-poured concrete doesn't bond directly to my concrete basement wall/foundation? This would make my new slab a separate structure from the basement wall. Is the gap that this strip would create a water seepage concern? Is there a recommended thickness for this joint strip? Thanks.

Fr@nk

[Fr]

Thanks. Now, do you see any problem if my basement door's threshold overhangs the location of the expansion strip (which would really prevent me from adding anything to the top of the expansion strip after installation)? Like this:

CURRENTLY:

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[Edwin Pawlowski]

Yes, it is apart from the foundation and should remain that way. Just put the strips against the wall and pour right up to it. If you think seepage is going to be a problem, use a caulk like material after the concrete is set up. With no expansion allowance, you could end up with a cracked or heaved slab.

[Fr]

Thanks for the tips, guys. I'm glad I didn't start this project without planning for the expansion strip.

Fr@nk

[Edwin Pawlowski]

That would be OK. The expansion joint is maybe half inch thick. You can place it so that the top of the material is the same as the top of the concrete when poured. If a little of the concrete gets on top of it, no problem, it may even help make a seal.

[Norminn]

There is caulk that can be used over expansion joints to keep water/ice out. Leaves them flexible, which is the whole idea so it doesn't crack or push against your basement wall.

[Don Young]

I am not sure of your situation but if you have a door at the same level as a weather exposed slab you will have trouble with rain water running under the door. Even the best of seals and a slope away from the door will not prevent wind driven water from entering. Unless you can tolerate this you need a step down from the door to the outside slab if at all possible. I am lowering a 6'x12' concrete porch because of this problem. Don Young

[Fr]

Hmm. How much of a step down are you talking about? If I bring this one down more than a couple of inches, the outer edge of the slab will be well below the ground; I'd need some sort of "curb" surrounding the slab.

What I'm looking at right now would put the top of the slab just below (1/2 inch or so) the bottom of the door threshold. Sounds like you're saying that's too close, and that wind-driven rain could still come in under the door.

Really, I'm mostly concerned with yard drainage/runoff coming down a slope and "wandering" toward the basement door (which I'm controlling effectively with simple diverters). I mean, right now, it's just dirt outside the door (again, coming up to within a half inch of the bottom of the door), and I'd like to "finish" it with a slab. If I'm not experiencing a problem with blown-in water now (with the dirt), are you saying the addition of concrete would increase the possibility?

Fr@nk

[Edwin Pawlowski]

I guess it may be a reasonf or concern, but how much rain and snow do you get? If the water level builds up that much you probably have other problems to dealw ith. As longs as the slab is pitched, it should not be a problem. Just like the curb cuts for wheelchar access at the curb. Water still stays in the street because the sidewalk is still higher than the street regardless of the sloped access it now has.

[Don Young]

Unless you have a lot of water 1/2 inch will probably be enough. The concrete will increase the possibility of water entry simply because it will catch and direct the water, just like a paved parking lot does as compared to an unpaved area. I don't think you will have a problem but wanted you to be aware of the potential. Don Young

[Norminn]

clipped

I would be squeamish about putting the patio smack-dab against the house. With so little space between patio and threshold, windblown water would be one issue. Snow/ice melt another. I'm in Fla., have two patios, but about four inch curb up to living space (on slab). Only an

8' storm surge or a busted pipe will flood us :o)

I don't know the likelihood, but settling could leave you with the low end next to the door, or pitching against the basement wall. Can your situation use a patio away from the basement wall, with soil border and a paver or walk between? My daughter has a driveway smack dab against her foundation, which is actually higher than her basement window sills. Problem with snow and water accumulation.

[Fr]

Yep, I'm still trying to find pre-fab concrete slabs (basically large stepping stones) to just lay in place here. The permanency of poured concrete freaks me out a bit, for the reasons you mention. At least with large rectangular concrete squares, I could always move them if necessary.

If I can find pre-fabs, I'll probably throw a couple of those down, and forget about pouring concrete. But mixing and pouring concrete would produce a nice walkout. We'll see...

Anyone know where you can get the nice big concrete slabs that (for example) you see placed under heat pumps or outside AC units? Something 3' x 3' would be fine, or 4' x 3' would be perfect. I definitely can't find these things at HD or Lowe's. Thanks.

Fr@nk