mould on recently plastered wall

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stan the man

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i need a bit of advice please regarding mould.

i did a job a couple of years ago in a late 1800s house which had a small area of damp patches in one corner of the room. after hacking off the old plaster back to the stonework in the area {1.4m x 2.2m} i gave it three coats of synthaprufe and sharp sand to blind the last coat, followed by hardwall and multifinish feathered into the surrounding areas. the walls had dried out within a few days and it looked like the damp issue had been solved

yesterday i had a call from the customer to say there is now black mould on the area that i did but nowhere else in the room

i have arranged with the customer to pop round and have a look at the problem, but before i go i just wondered if anyone has come across this before and what the likely cause might be and the best way to rectify it, so that i have some answers for the customer.

many thanks for any advice
 
stan the man said:
i need a bit of advice please regarding mould.

i did a job a couple of years ago in a late 1800s house which had a small area of damp patches in one corner of the room. after hacking off the old plaster back to the stonework in the area {1.4m x 2.2m} i gave it three coats of synthaprufe and sharp sand to blind the last coat, followed by hardwall and multifinish feathered into the surrounding areas. the walls had dried out within a few days and it looked like the damp issue had been solved

yesterday i had a call from the customer to say there is now black mould on the area that i did but nowhere else in the room

i have arranged with the customer to pop round and have a look at the problem, but before i go i just wondered if anyone has come across this before and what the likely cause might be and the best way to rectify it, so that i have some answers for the customer.

many thanks for any advice
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If you could be more specific as to where the mold is on the wall? bottom / top / middle?
Is the wall external?
Bit more info and we'll be able to help :cool:
 
thank you for your reply timeservedspread, i have not seen it yet so i cant be specific at this stage but ill update the post once i have seen it
 
tell the property owner to clean the mould off using dettol mould spray. the problem is condensation, with water going to the coldest area of the room and turning to mould so turn the heat up in the room and open the window to give the room air movement.
i would not have used your method of plastering with hardwall or prep with bitument for this room.
 
Condensation tell them that they need to ventilate and try to keep the humidity down in the property.

Are they drying clothes etc ? is the bathroom & kitchen ventilated ?

Heating does help but the humidity is the problem.
 
Yes I too think that this is not due to plaster or paint, this is condensation problem. There might be plenty of moisture in place where mould occur. First ask them to clean up the mould with any best mould remover available in market and then use a ventilation system like ventis to reduce moisture level.
 
Black spot mould is caused by condensation as already said. Nothing to do with the type of plaster used.
 
(just a student but I am actively studying damp problems, still big pinch of salt anyway)

Was it penetrating damp? If a small amount of moisture was penetrating and you didn't fix it then it is going to come back. My introduction to plastering was not fixing a penetrating damp problem and inadequate backing allowing black mold to come through as a response to damp.

If it is an old house it is very unlikely to be condensation from simple air vapour accumulation as they are not glueable (airtight, sealed like a modern home, plenty of ventilation) but do suffer from the cold. Can't just assume it is condensation as mold will grow in any condition where there is water, cellulose and spores.

When you go around see if the plaster is blown. If it is condensation possible from a cold external wall then there is insulated boards or a heat recovery ventilator to prevent it coming back.


 
Black mould doesn't come through the plaster but grows on the surface. It's is more comon in old building due to lack of insulation thus giving more cold spots for it to form.


If it was penetrating damp the plaster would get salty and break down. Damp plaster is colder than dry so it would encourage mould growth but not be the root cause.
 
carlos said:
Black mould doesn't come through the plaster but grows on the surface. It's is more comon in old building due to lack of insulation thus giving more cold spots for it to form.


If it was penetrating damp the plaster would get salty and break down. Damp plaster is colder than dry so it would encourage mould growth but not be the root cause.
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Ah so its water thats come through then mold formed.
 
The humid air condensates on the cold surface and then mould forms.


Its just a case of the customer closing the door in the bathroom when having a shower or bath until the room has vented and the same for the kitchen.

Also no drying clothes in the house as that water has to go somewhere.
 
carlos said:
No mate ate as adapt said. It moisture collection on the cold surface.

Think ng of condensation on glass, it's not coming though from the other side.
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So it can NEVER be water coming through? This doesn't make any sense.

In my example it was definitely penetrating damp, the damp came through immediately in an area that has never suffered from condensation and it was black mold.

Doing the research on it, it doesn't have to be condensation. Mold will grow in the presence of water and cellulose.

But hey ho, I Tanked the wall and got rid of the damp and no more black mold, had it have been condensation then why has it not come back? When nothing except my treatment of the area has changed?
 
Yeah that is what I am getting, don't get me wrong I'm not ignoring what you say either as I am just a student. It just doesn't match with my own experience that is all.
 
A picture paints a thousand words cowen70

If we could physically see the area then we could have told you it was either condensation or ingress from external.

So a bit of advice to anyone on here wanting some advice is please post up a pic

I get it now and then, people ring you up for damp ingress or suspected rising damp and its condensation.
 
I can't today but I can post pics (and have hang on see if I can find em) of the external penetrations and where I've tanked (sandc) but unfortunately not the actual mold itself.
 
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