A friend of mine is adding a concrete slab patio to the back of his house.
He has enough experience in pouring and finishing concrete that he is
comfortable doing the patio. But, he has a question about where the patio
meets the house. The house has a brick exterior where the patio will meet
the house, and he is wondering if he should just pour the concrete right up
to the house, or place an expansion joint along the back of the house and
pour up to that. I don't know the answer but I said I would try posting the
question here. His house is in New Jersey in case that matters in terms of
Risk of a close-up patio is, that if the patio frost-heaves (and most
do, since foundation under house stays warmer), you can get ponding
against house after heavy rains, which ends up running into basement,
and can sometimes ever build up enough hydrostatic pressure to bow the
basement wall, if it has nowhere else to go. Seen it several times as a
kid working in the business, and again a few years ago when house-shopping.
But yeah, I always see an expansion joint used. Your friend should make
sure their foundation drains work, and make sure patio has enough slope
and a good set of footings under it. Maybe even add a sideways drainage
slot near the house, headed to a drain tile or dry well under a bush or
something. That far north, I would do deep actual footings, not just a
'thick edge' monolithic pour. If there is a chance in hell he will ever
want to make it into a 3-seasons room, actual footings below frost line
I'd think that anyone with experience would know an expansion joint should
be there. He should probably check his knowledge of base prep and
reinforcement too. All of NJ is in freezing zone and that patio will move.
Thanks for the feedback.
I don't know what is correct, but in doing an Internet search it does seem
that more often than not people do recommend putting in the expansion joint.
I was surprised to also see a number of other options also posted on the
Internet that involved tying the patio into the foundation with rebar etc.
I don't know if that is a good idea, but it seems a little strange to me.
Also, some of the videos I see of professional contractors pouring and
finishing a patio do not show either an expansion joint at the house
interface or rebar tying the patio into the house foundation.
I do know that my friend is using stone underneath and compacting the base,
plus wire mesh, plus rebar, and will be sloping the patio 1/4 inch per foot
away from the house. And, he said that when ordering the concrete, he is
getting concrete that is called something like "fiber reinforced" (I forget
the term) and a higher strength concrete (I forget the "pounds" or whatever
it is called).
For those who may be interested, here are some of the links I found when
doing an Internet search:
I am not sure if the fibre-reinforced concrete is really any better.
Our condo association in CO used the reinforced concrete for a patio,
and the new concrete cracked within 2 years even though the base was
properly compacted, etc. It may just be a selling $$ point.
On 6/22/2011 12:44 PM, hr(bob) firstname.lastname@example.org wrote:
Issue isn't the slab cracking- patio is light-duty, and nobody is
driving on it. Issue is the side of patio away from house lifting when
ground freezes. That 1/4 per foot slope can quickly be pointing the
other way, and you have a pond by the house. Gravel layer is good, but
make sure the water under there has somewhere to go. If it is trapped
under there and freezes, it'll lift the slab right up. I still think
footers are a good idea.
A new install should have a joint but be aware that the joint must be
maintained or water *will* get into your basement. Not to mention
sloping it away from the house. If its possible to slope the patio
toward a drain your results will be even better. We were able to connect
up to a buried 4" drain intended to catch down spout water that runs
along the end of the house. Its carried about 60' away from the house
along a good down slope.
In snow zones, melting snow is more of a problem than rain. Get the snow
off the patio or at least away from the foundation or it will very
quickly seep into the joint when it melts.
We poured a third layer (probably close to a foot thick by now) over an
existing 40' patio four or five years ago due to repeated moisture
problems in the basement. Unlike the other two layers it was poured
directly against the brick this time. Since then the moisture problem
has gone away and there is no sign of bowed walls. Brick over concrete
block is pretty sturdy but only a really-really thick sub base made this
From SW Pennsylvania,
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