Expansion joint for 8x4 concrete walkout slab?

Posted by Fr@nk on July 16, 2005, 1:07 pm

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

Posted by Edwin Pawlowski on July 16, 2005, 5:49 pm

> 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
heaved slab.

Posted by Fr@nk on July 16, 2005, 2:00 pm

> 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.

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:
------
| <<< Basement door threshold (overhang)
------
X |
X | <<< Basement concrete wall
X |

AFTER INSTALLING STRIP:
------
| <<< Basement door threshold (overhang)
------
X | |X|
X | |X| <<< Expansion joint strip outside basement concrete wall
X | |X|

My basement sliding door's threshold overhangs the basement slab slightly.
Is that the way it should be?

Fr@nk

Posted by Edwin Pawlowski on July 16, 2005, 9:07 pm

> 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:
> ------
> | <<< Basement door threshold (overhang)
> ------
> X |
> X | <<< Basement concrete wall
> X |
> AFTER INSTALLING STRIP:
> ------
> | <<< Basement door threshold (overhang)
> ------
> X | |X|
> X | |X| <<< Expansion joint strip outside basement concrete wall
> X | |X|
> My basement sliding door's threshold overhangs the basement slab slightly.
> Is that the way it should be?

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.

Posted by Norminn on July 16, 2005, 9:25 pm

Fr@nk wrote:

> 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
>
>

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.

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