Mold on balcony ceiling

[zzffnn]

Sorry, this is not close up nor photography. But rather I am asking for identification help.

A biologist friend and home owner told me those could be mold.



They are located high up on my balcony ceiling. House location is close to Houston, Texas, USA. Warm and humid weather, even in winter.

They seem to grow over the 9 months I live in my house.

I looked at them under phase contrast at 100x objective. They don't look like spider webs. Rather tiny irregular granules about 1/4 -1/8 the size of my cheek cells. I could see one or two that looks like mold spores, but 99.9% of them have very irregular shape (so irregular under phase contrast microscopy, that I decided not to take a photo, but rather show that ceiling photo). I am a bacteriologist by trade so I know what pure old spores look like from culture; they don't really look that way.

Could that be mold? They do wipe off easily with wet cloth (as you may see in the photo, I already wiped off some).

[ChrisR]

What's the ceiling substrate; painted wood, plastic...?

Could it be that a liquid, eg a paste/glue, was spread thinly on the surface, now has absorbed moisture and recrystallized?

It also sounds like efflorescence (nothing to do with light!) but that happens to brick, typically, where salts in the brick come to the surface. You wash them off and they keep coming back.

You'd better show us a picture quick !

[zzffnn]

I am guessing ceiling substrate is plastic. I scratched off the brown paint and saw white stuff under the paint (not yellow like wood).

The ceiling does look like recrystallization.

And under macroscope and microscope, they do look like inorganic material (kind of like super tiny beach sand particles), rather than typical mold.

Sorry no photo, I already ran out of scope time for today.

[Sharnbrook]

On the vertical course of stretchers where the wall adjoins the ceiling, it looks as if there could be some efflorescence there, patchy creamy coloured effect. ChrisR made the comment that if you wash the salts off with water, that they keep coming back. This is because the salts dissolve in the water, and are drawn back into the brickwork by capillary action, only to return when they have dried out. If they are salts (efflorescence) brush them off when it is dry, or even better vacuum them off, and the cause (salts) will be removed. You might have to do this a few times, but each time it will lessen the amount of dissolved salt, and by definition, efflorescence.

It would also appear to me that the ceiling material might be Fibro-cement sheeting that has been painted. If this is the case, there is a very good chance that there is efflorescence on the sheeting too, as there will probably be salts in that as well.

Short of making an inspection, it is difficult to determine the problem, but I'm afraid it is too far from Australia to come across for half an hour's work, so it would pay to ask a local building materials engineer if you are really keen.

[zzffnn]

Thank you very much, Mike.

My builder's engineer checked it and said they look at salt more than mold. Since house is still under builder warranty, they will come over and clean it.

He mentioned material of the ceiling, which sounds like the one you mentioned, but I cannot remember exactly. What you said makes sense. Under 100x phase contrast microscopy, those do look more like salt than mold.

[ChrisR]

Expect him to say that whether you wash it off or brush it off, it still comes back!
Obviously you'd dry-remove what you can.
The salts have a supply from deep inside, where there is also always moisture present.

I've come across the issue to some extent and have just looked a bit more.

Washing will remove some that the brush can't reach, from the surface. Salts from near the surface will dissolve of course, and can be washed away. You'd do it on a "dry day" hoping that your new clean water will evaporate. Atmospheric humidity will mean more moisture goes into the substrate than you'd have on a dry day, sooner or later.
Eventually you hope to deplete the substrate of salts near the surface, such that the rate of salt production at the surface is insignificant.

If the salt is alkaline then weak acids may help, if it's just NaCl then HCl will push the solid out of solution. Carbonates(lime) will react better, but seem to be more persistent. (Stalactites in multi-storey car parks). You could see if yours reacts in vinegar.
Some advocate sealing the surface on a dry day, gambling that moisture won't ever get to remaining salts and push the coating off. Silicones retard the rate of diffusion of water, potentially to zero, but some claim to "breathe"! YMMV!

Urea hydrochloride is packaged and sold as a wonder soluton in many products. It has claims of replacing salts with non-troublesome ones (dubous??), but mostly of being less nasty than hydrochloric or phosphoric acids. It doesn't for example, dissolve rust, which sounds useful.

No single answer, it seems.