Mold; if I can smell it, why can't I see evidence?

500 sq. ft. basement finished out about a year and a half ago. Reverse grade under the deck where the dog dug out a cool spot and sprinklers near another ext. wall. No sign of moisture intrusion at ceiling, wall (poured concrete) or floor (slab). A strong musty smell like long-term moisture damage w/mold present.

On this level, a bathroom with a shower has no ventilation. About three minutes of the shower running caused the humidity to rise from 24% to 31%. Long showers a possible source?
With a smell this strong I would expect to find visible moisture damage in materials that have been in place for a year and a half if the source were groundwater/ runoff.

I thought that the smell mold gave off was a gas excreted as mold fungus consume cellulose or lignen or whatever they’re eating. If they’re active and eating, where’s the evidence of moisture? If there is none and they’re inactive, where’s the smell coming from?

Recommending invasive investigation by mold mitigation co.

Inside wall, under carpeting…sometime owners place plastic down before pad…problem. Deep moisture scan flooring and walls also do an Thermal Image scan, the problem will be easily shown:)

i’ve always wonderd if one can rent a thermal image cam.? might be a good cash cow for the right co. to rent there’s out. i can’t afford 10-15 grand for one, but i’d rent one and just break even on the use to get the buisness.

Hi Jay, Yes you can rent thermal imaging. Flir is one company that comes to mind. Darren is right on the money as to where mold can hide. Doug

The advice to seek further invasive inspection is right on the money. Though thermal imaging may help, the EPA states quite clearly that if you see or smell mold, you have it. Thermal scans far exceed all SOPs, as far as I can tell, and are not a part of an inspection.

If the inspector chooses to go further, that’s fine. But be aware that once you (correctly) call for further investigation, the client or seller may want to engage a mold testing and remediation company. The path is to eliminate the source of the moisture first, amd then clean up the mold, or replace damaged components.

Flir does rent them, i checked out there site. I was kinda looking for something local. ya know like were you’d rent a carpet kicker, or a laithe, or enough chairs for 100 people at a b.b.q… not a long term rent, but a short term "just rent it job by job’’ kinda thing. Thanx for the info though.:smiley: :smiley:

Mr. Shepard –

One possibility is that probably 90% of the time, when someone tells me they can smell mould, what they are actually smelling is not mould at all, but soil borne Bacteria. Thus, it’s possible that the reason you can’t find the mould growing is because it isn’t.

Caoimhín P. Connell
Forensic Industrial Hygienist

[/size][/FONT] (The opinions expressed here are exclusively my personal opinions and do not necessarily reflect my professional opinion, opinion of my employer, agency, peers, or professional affiliates. The above post is for information only and does not reflect professional advice and is not intended to supercede the professional advice of others.)


Just throwing this in…cat pee?


Funny you mentioned cat piss.

I was called to a home that a realtor was listing. I also happened to know the homeowner quite well, so there was no way I would ever do an inspection on the property. I knew where the defects all were.

Anyway, I was called because, after having a Broker’s open house, the comments came back that the basement stunk of mold. I went to the home, starting walking down the basement stairs, and WHAM. I was hit with a funky odor that nearly knocked me down.

Problem was, it wasnt mold. It was a gigantic cat box, filled with cat feces and pee. The owner wouldnt get rid of it. She wouldnt disprient the cats. Too bad, because after 6 months, this house has never has an accepted offer on it.

By the way, there WAS mold in the basement, as well. She had several floods at one time or another.

Warm air and humidity make cat piss REEK! I know people who had to get new carpet AND put new sub floor down. I have even had to re-place all the corners in a hardwood floor being the people pulled the carpet up and then saw the hardwoods but all the corners were rotten and it smelled bad when the carpet was first pulled up.
I always told myself i would never have an indoor pet for those reasons…now married with a child, i have two cats!!! Varments! If i catch one take a piss in my home…BOOT! Really, i am not that mean.

Carpet and drywall looked new and were spotless. I think I could identify cat piss by smell but you never know… and it wasn’t localized to one part of the basement as you’d expect with cat piss.

Soil-borne bacteria? 90% of the time? This was a concrete basement, so obviously soil-borne bacteria aren’t limited to dirt-floor basements or you wouldn’t be suggesting this, Caoimhin. Is a mold remediation company going to find a bacterial problem? If not, who?

Hey, Kent, you’re really digging up some good stuff!
I never had much mold problem in Colo whole inspecting, but, man, in the Inland Northwest, there’s gobs!
Say hi to the gang for me . .


It should be possible to pick up a reading using moisture meter pins down through carpet and pad (and plastic if any) if that’s the case. Remote probes on the meter might pick up moisture on the wall. Should be possible to remove a cover plate and insert them beside the box at a cable connection or electrical outlet.

I guess that’s actually a little beyond the scope, but if you’re going to fork out good money for electronics you might as well get all you can out of them.

Hi Russ, good to hear from you.
Are you seeing a lot of wood decay, people feeling ill, bad smell, mushrooms in the carpet? What are they doing for remediation?


Hello Mr. Shepard –

As you know, concrete is not exactly the impervious material the casual homeowner would envision. The ordours associated with microbial activity are volatile gases, and not surprising, behave like gases. In much the same way that radon (a gas) enters a structure, all other soil gases will similarly enter the structure – there is no filter mechanism that selectively permits some gases but excludes others.

In one particular case, I was called in to find a strong and offensive “musty” odour in an hospital. The hospital administration had spent THOUSANDS of dollars trying to solve their “mould problem.” I arrived on site and using only my nose as my scientific detector quickly tracked the odour down to a main air supply line and thence to the handler. The supply fan was housed in the basement at the corner of the exterior foundation wall and drew air from the outside intake mounted on the roof. The pressure drop in the upstream side of the fan was something on the order of 1in WC. The concrete walls of the of the basement had normal hairline cracks. The negative pressure induced in the fan housing was sufficient to draw soil gas from the surrounding soils through the cracks. I identified the odour coming through the cracks … so that begged the question, what was the source of the odours in the soils?

I inspected the outside and found that approximately two meters from the foundation wall was a leaking steam line buried perhaps 90 cm. The soils surrounding the steam leak were awash with a prolific and impressive collection of microfauna and microflora all producing a soup of volatile compounds that were traveling through the porous soils into the fan housing, where the odours were being efficiently throughout the building.

Recommendation: Fix the steam leak.

My bill to fix the “mould problem:” About $275

Samples collected: Zero

Instruments needed: None

Time on scene: About 90 minutes

Lesson: Stick to the established: A source, a pathway, a susceptible recipient.

Caoimhín P. Connell
Forensic Industrial Hygienist

(The opinions expressed here are exclusively my personal opinions and do not necessarily reflect my professional opinion, opinion of my employer, agency, peers, or professional affiliates. The above post is for information only and does not reflect professional advice and is not intended to supercede the professional advice of others.)


Cardboard, fabrics, clothing etcetera can give off mildew smells and pick them up, particularly damp basments, poor air circulation, cluttered basements, hockey equipment, et ceteras. Moisture will migrate through concrete floors in the form of water vapour.

Hello Mr. Connell,

I guess the long and short of it is, does it matter whether the source is mold fungus or soil-borne bacteria? Is the typical recommendation for both, not sampling, but to correct the source of moisture?

They still have a bad smell and I still can’t find a source of active moisture intrusion, but since the smell is there there must be moisture present which is encouraging the growth of either fungus or bacteria. Right?

So if I can’t find it, it must be time to take invasive measures. Would I recommend this be undertaken by an Industrial Hygienist or might a mold remediation company be capable of dealing with it at a lower cost?

Should I recommend sealing penetrations and cold joints in the slab as is typical with Radon mitigation?

Is there a difference in recommendations depending on whether the source of the smell is mold fungus or soil-borne bacteria?

Would this house happen to have a sump pump or any floor drains?