I have a single story home with a floating slab (I believe it is
called) surrounded by an expansion joint (cardboardish material) which
is then surrounded by the stem wall. I have a musty odor which
appears to be coming from the expansion joint between the stem wall
and concrete base/slab of the home. I have removed the baseboards and
so I have a better view of the area. The odor is musty, someting
similar to an old basement I think. The expansion joint appears it
may have been torn up or decayed in some areas (possible from moisture
or poor construction?). There are also some gaps between the
expansion joint and slab, which are up to 1/4 inch wide. The odor is
only coming from one room in the house and it is difficult to pinpint
exactly where the smell is coming from (perhaps it is from all along
the wall). It appears most pronounced in the corner of the room where
there may be some missing expansion joint. There is about one foot of
stem wall showing outside the house and there are no apparent cracks
in the stem wall. Outside the all there is a drip irrigation system
which has been turned off for 2 weeks and I still get the odor (I
thought it might be seeping into the concrete stem wall, up the wall
and into the expansion area). However it is possible the odor is also
coming from an adjacent room (much less odor though) which has no
irriation system near it.
Can I use a silicone based caulk and to caulk around the expansion
joint as a test to see if the odor goes away? What are some other
Please do NOT email me as this is my spam email account. Thank you.
Different names, John . . .
. . . for different folks. If your slab is poured up to the
surrounding stem wall without actually bearing on the stem
wall, it is a floating slab. The joint may or may not
define a floating slab. The stem wall may be thicker below
the slab than above, with the slab bearing on the thicker
ledge. The important thing in your post is that there
actually is a stem wall (except in some areas, "stem wall"
is an unknown quantifier of a foundation wall).
Or, perhaps from being the "cardboard" you previously
mentioned. Have seen worse.
So, obviously the "expansion joint" did not expand. When
the concrete contracts from curing, etc., the joint material
is supposed to expand, and fill the void. It is also
supposed to survive the elements and aging. Yours hasn't
done either. Many don't. Especially in instances when the
builder believes the term "expansion" (vs "contraction,"
which is the more definitive term) applies to the slab only
expanding and compressing the joint material. That occurs
only after the slab has contracted. As you see in your
instance, the joint material has not been called upon to
expand beyond its original thickness.
the room where
one foot of
up the wall
This, John . . .
. . . was an appropriate place to start. And, you are
likely correct, whether or not this is the actual source of
your odor. However, two weeks isn't nearly sufficient
duration to dry-out a wet condition either without or within
your stem wall. Do make sure your irrigation system is
placed sufficiently away from your stem wall and there are
no opportunities for pooling, etc. The idea of a drip
system is to allow watering without saturating the soil or
penetrating your structureal components. Proper adjustment
and operation is crucial. Drip systems are wonderful . . .
but with potential dangers next to the house.
That is not a however. The system's conditions are not
Yes you can; however, you are sort of treating the symptom
here without actually knowing what is the problem.
A unique odor requires a unique source. Fresh water (only
kind you will get after only two weeks) will not smell the
way I understand from your description. However, that does
not remove the irrigation system from consideration, as the
water may well aggravate the actual source.
You may have a house built over a landfill . . . or over a
livestock carcass burial pit . . . or just plain-old
vegetation, trash, garbage or an unfortunate drug dealer in
a deal-gone-bad . . . or over any of many buried sources of
decomposition and off-gassing. Equally likely (and getting
a nod from me knowing what I do about fill practices),
especially as your odor source is apparantly isolated, is
some really nasty fill was placed within your stem wall
before the slab was poured.
If your slab is actually a floating slab, a continuous
moisture barrier, preferably turned down around the
perimeter to fully reach the top of the stem wall footing,
is required. I find a very high percentage of moisture
barrier film doesn't even quite reach the edge of the slab
and doesn't even come close to wrapping down the outer
edges. At best, a separate narrow strip is laid down on top
of the main film and abutting or nearly abutting the edge of
the stem wall. There is plenty of opportunity for odors as
well as moisture to react to the various pressures under the
slab and come up through the perimeter or "expansion" joint.
Don't know that I would recommend silicone, but that or a
similar, non hardening, elastic (withstanding constant
cycles of compressing and expanding) and sealing-binding
(adhesion to the adjacent surfaces) filler is desirable.
Not an end-all panacea, but certainly part of the solution,
if not the cure.
You can investigate the condition of the soil beneath your
slab and within your stemwall in the immediate vicinity of
some of the worst odor. Frankly, that investigation is
likely best left to professionals. I mean, would you know
what to do if you actually found something? Experience pays
in this case.
To prepare yourself, I suggest you research RADON GAS and
its investigative and curative solutions on the web. You
can employ similar techniques. You may even begin to
suspect you have a radon problem. Hope not, but at least
there are known, safe remedies for that.
I don't usually say this, but in your case it will help:
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