Bad odor coming from expansion joint around interior wall of home

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 options?
Please do NOT email me as this is my spam email account. Thank you.

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This may sound crazy,
Are you the original owner of the home, and if not, did the previous owner have cats? They love corners, and usually have a favorite one.

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it is

material) which

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).

stem wall

baseboards and

appears it

from moisture

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.

to pinpint

all along

the room where

one foot of

apparent cracks

irrigation system

odor (I

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.

has no

That is not a however. The system's conditions are not likely consistent.

some other

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:
Good Luck!

Thank you.
You're welcome, Jim

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