To get mold, you don't necessarily have to have water intrusion from the exterior.

A few years ago, I had a couple of sheets of styrofoam temporarily stored behind my headboard. Headboard was on an exterior wall--winter, cold climate. When I moved them, I found some mold on the wall. What almost certainly happened was moisture condensed from vapor on the cold wall and was trapped by the styrofoam. Enough for mold to start to grow.

So, if this corner is on an exterior wall, possibly cold air is infiltrating and moisture vapor inside the dwelling has condensed and, if you had stuff piled in the corner blocking air movement, that could account for the mold.

The bottom of a wall can be a source of cold air seeping in underneath the wall plate. Anytime that I have baseboards removed on an exterior wall, I get out the caulk gun and caulk that seam/ gap where the wall plate sits on the subfloor.

Or, like Winter said, the moisture may be intruding from the outside.

You can't clean it up with out pulling the baseboards. Follow to the source.

Here after the flood we had to use contran20. We got it at Lowes. I think that was the name. We also used a lot of Odorban. They were not recommending bleach.

Vinegar was also a good option.

Bleach will kill mold on the surface of such things as counter tops, tiles, tubs, walls, but cannot penetrate below the surfaces of items to kill the roots of the mold. Vinegar, undiluted, sprayed on mold will penetrate into the interior of what the mold is growing on, thus killing the roots of the mold. Sometimes you will need to repeat the treatment for 2 or even possibly 3 times if the mold has been on the item for any length of timel Ravencajun has been to this rodeo a time or two!

I agree that the source of the moisture needs to be found.

I believe the OP (always) lives in Southern California so the weather isn't cold, rainy, or even damp. It's been a pretty dry winter with mild weather.

I would check a few things:

Outside- on the other side of the wall where the mold is, is there a planting strip with bushes or whatever that's watered with sprinklers every few days? Does the wall or the dirt there get quite wet and take awhile to drain?

Or, does water puddle on a walkway or dirt against the building on the other side of the mold spot?

Inside source - how's the ventilation in the room? Are there things under the bed to block airflow? If there's an adjacent bathroom, does it have an exhaust fan to remove humidity from showering/bathing? Do you keep it running long enough with the bathroom door closed?

Is the door to this room left open or closed when you leave your home after bathing? (Should be open)

You need to find the moisture source first. The mold is the consequence of a problem, not the cause or an isolated problem. If you do nothing but apply something to treat the mold, it will grow back.

Good luck.

Property mgmt company is sending someone out Thursday morning to try to determine where the moisture is coming from. My feeling is it has something to do with drainage around the condo. It's only that back bedroom that I've seen mold. The guy that called was careful to NOT call it mold...he called it "organic matter or growth"...something like that!!

ETA: the room does have a bathroom next to it, but the wall is opposite the bathroom. It the back side/corner of the bedroom. There's no walkway by the wall, not even a lot of plants where there would be sprinklers. That back room does get a lot colder than the rest of my condo though.

"organic matter or growth"

😏I've found that property management companies have a descriptive language all their own.

From what you've posted, always...I think you're probably right in your conjecture. The fact that the room is colder than the other rooms also tends to support that theory. There's an opening somewhere in that wall area that's letting the outside elements enter that room and the fact that it starts in a corner...strengthens that assumption for me. Perhaps the corner framing isn't as it should be....or it comes in contact with the actual soil where it shouldn't. Or there's a slight crack in the foundation where water/moisture is pooling. There are a myriad of possibilities.

I'm as interested as you are in what the inspecting agent has to offer. Please keep us posted. I hope he appreciates how observant you've been. It's always the little things that turn into big problems if they're not caught in their initial stages. As my young neighbors would say..."You done good!"

This morning I met with the guys the property mgmt company sent out. They seem to think its moisture the bathroom. Didn't find any moisture readings in the floors, walls. Baseboards and laminate flooring not swollen as if there was moisture building up in them. Everything they said, made sense to me. Although I would love a complete redo in my bathroom, a new fan will be the first thing on my to do list!!

That is good news, always. Plus it sounds like you have a responsible management company. That's a BIG plus these days. My bathroom fan gives minimal moisture protection, too. It's a difficult chore, at best. These days I leave the bathroom door open when I know it's going to get steamy. That works far better than the fan. Air circulation at any level is best.

I'm glad you have a starting point. If you're having a new exhaust fan put in, I have three suggestions for you:

1) Make sure the installer confirms the duct vents to the outside

2) Have the installer put the exhaust fan on a timer switch so that it will turn itself off. Run the exhaust fan while bathing/showering and then another 30 minutes after you're done. Keep the bathroom door closed when it's running.

3. Crack open a window in another room when the fan is on. The exhaust fan won't do much unless there's "make-up air" available in your home from an open window.

I just saw winter's post.

The humidity problem in homes from showering isn't just moisture in the bathroom, it's moisture in the home if the exhaust fans don't function properly. As with always' problem, it wasn't moisture in the bathroom but rather the adjoining room.

Keeping the bathroom door open isn't a good idea when the problem is something else. Not having a window cracked in another room of the house is often a cause of poor bathroom exhaust fan performance.

We bought a second home and it had moisture damage from window condensation throughout the upstairs where the showers are that the seller had to have repaired. The bathrooms had 20 year old exhaust fans that I suspected were not functioning well. We replaced them and the result is night and day different from before.

New exhaust fans are inexpensive to buy, easy to replace, and are much quieter than older ones. But you need to let them run long enough after the shower to allow them to work.

off topic -- I read the topic as

mold on bast*rds !!!

if true, they deserve it!

Three things to add to Elmer's list.

1. Be sure the fan is properly sized for the room that's being ventilated.

Length X Width X Height X 0.13 equals volume of room. Be sure contractor is installing the proper size or your improvement is a disappointment. Size matters.

2. Some cheap fans and new construction fans eliminate the housing flange that seals the housing to the ceiling, leaving an air gap around the unit. Choose a fan with a flange (like Broan EZ Fit) or make sure the gap is sealed. If it's not sealed, the fan will pull air from space above ceiling, lowering its efficiency.

3. Since you're in a Condo, there may be a make-up-air duct inside the mechanical room. Usually a 6" diameter pipe extending below ceiling. Make sure the area is free of obstruction to allow make-up-air to flow to gas furnace, gas water heater and vent fans.

Example of make-up-air duct in mechanical room.

"Since you're in a Condo, there may be a make-up-air duct inside the mechanical room. "

Yes and no. In California, where I believe this person is located, typical construction puts gas appliances in garages or attics. Sometimes both, as in a Calif condo I have where the water heater is in the garage and the furnace and A/C coil are in the attic. If she's in a single story unit without an attached garage, you could be right.

For safety reasons, mechanical rooms and gas combustion appliances should be isolated in air sealed spaces (with weather stripping around the four sides of a door, including the threshold) so that combustion exhaust can't backdraft into the living space with negative pressure situations, as when an exhaust fan is operating. That would negate the availability of HVAC area fresh air ventilation for use inside the living area.

Neither basements nor "mechanical rooms" inside the building envelope are common in California. It happens that two of my three gas appliance locations at my primary home ARE inside the envelope but both are well ventilated at floor and ceiling to outside air and have tightly weather-stripped doors. Arguably, they're within the 4 walls but "outdoors" because of the ventillation. The third is in the garage, plenty of fresh air there.

I'd like to find a safe way to keep my window (bedroom) cracked a little to keep a little are flow in there. I don't know if the old stick in the track is safe enough. The bathroom is very small. I'm looking at a fans that have a moisture sensor...but they range from $85. to $300.+ so I'll ask the electrician why and what I'll need for my bathroom.

YOU are the best moisture sensor available. Turn on the fan when you turn on the light, extend the timer time after bathing and close the door. Done.

Exhaust fan rule of thumb sizing is not less than 1 cfm (cubic feet per minute) for each square foot. If your small bathroom is 5 x 10, that would be 50 square feet. So a 60 or 80 cfm fan would be fine. Home Depot has them at that size for $75 or less. A timer switch is $20. Under $100 out the door, you just need to pay for the install. Consider buying the same brand as you have to insure an easy fit, or measure it to be certain.

For sliding windows, a dowel or piece of wood can prevent sliding. But sliding windows can also be lifted up to be removed so you need a tab screwed on the end or smaller diameter dowel placed on the top of the frame to prevent that. I guess you don't have an upstairs. Keeping an upstairs window that's visible to others cracked is almost always safe to do.

If you combine the two, keeping an exhaust fan running at night (with the bathroom door left slightly open) when a window is cracked in another room is a good way to provide nighttime fresh air.

All sliding windows I've sold and installed over 40 years have a header bump to prevent lift out unless the sash is opened all the way. Some will permit removal when 3/4 open. Of course, since you're in California, you'll have to examine the header pocket to be sure that feature applies in California. :)

Sliding window

If your sliding window has a header bump, 99% do, simply cut the track block (wood or metal) to allow for the opening size of choice, as long as the sash maintains contact with the header bump it's relatively safe.

15 years ago, I replaced all the windows and glass doors in my house. Nearly 20 window frames (with side sliders) and 5 sliding doors. The new ones are double paned, mid-market models of various sizes but all of the same brand. I used new construction models that required each exterior hole to be cut out and reframed, not "replacement windows" that fit into an existing opening, partly because I changed sizes almost everywhere. I used a mid-market brand and they came with a lifetime warranty on the panes which I've used a few times for moisture intrusion.

I just checked - they don't have the internal plastic piece the video shows and the three I checked can be lifted out. Furthermore, if all that's needed is to move the slider to the middle to get clear overhead space in the frame, why can't a would-be intruder do the same thing?

For sliding windows, a dowel or piece of wood can prevent sliding.

Elmer, sliding it to the middle wouldn't be possible if you've installed the metal or wood bar in the bottom track, limiting the travel.

You have the ability to modify the units and install your own anti-lift lock. You can purchase the anti-lift lock and install it. Or, a piece of parting bead moulding strip/sash stop also works. Cut it to desired length and mount to header.

Or, visit the hardware store and get rubber bumpers to mount to headers.

Bumpers

Maybe the installers forgot to install the anti-lift device?

Okay, I see.

I don't need anything but maybe always will look into such alternatives.

Home burglaries are rare where I live. Anyone who wants to break in is welcome to do that, so long as I'm not home. I'll hope they'd look in the garage window first and have the sense to know that cars in the garage means the house is occupied. Heck- we don't even have an alarm here. At our other place, the one the prior owner installed is turned off. I can't be bothered. Don't tell anyone my secret!

We have no precious belongings and all the tangible things are replaceable.

I actually have the window people coming this week to fix that window I'm my room..I'm going to ask him if a stick in the track is safe enough or if he has another suggestion.