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.
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
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.
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.
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.
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.
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.
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