Bubbling Painted Pointing of External Wall

[MonsterMonster]

Part of our property was built in 1860. The whole of the external brick work was painted about three years ago by the previous owner. I have noticed that that there is a small section of exterior wall under an upstairs window (about 1 square metre) where the pointing appears to be bubbling under the masonry paint. The bubbles vary in size up to about 3mm in diameter, seem fairly solid but crumble when pressed revealing the mortar as crumbling. Some bubbles have evidence of very slight fungal\moss growth. The bubbling is isolated only to the pointing and not the brick face. I cannot see any obvious evidence of water leaks and internally all seems okay with no signs of damp.

I know I will have to rake out and repoint but does anyone know what this could be and the cause and any special considerations? By the way I have no idea how old the pointing is what type. Pictures are attached.

Thanks

Untitled

• MonsterMonster
• 11 Oct 2009
• 1

Untitled

• MonsterMonster
• 11 Oct 2009
• 1

Untitled

• MonsterMonster
• 11 Oct 2009
• 1

 

[hotrod]

How often does that window get cleaned, with what, and by whom?

There's no overflow blowoff pipe in that area is there?

 

[MonsterMonster]

I cannot say how often or how the window was last cleaned as we moved in back in June (I like mucky windows ). There is no overflow pipe on that wall. There is a soil pipe outlet over a metre to the left of the patch but pointing between there and the affected area is fine. The only thing I can think of is rain water hitting the window and running down the wall but if that was the case rain hitting the whole wall would have an effect.

I suspect this is something that has been going on for a while and could be related to the replacement window that was installed several years ago.

 

[hotrod]

I cannot say how often or how the window was last cleaned as we moved in back in June (I like mucky windows ).

That rules out my first theory then, although it was always going to be a long shot - a window cleaner with OCD

I suspect this is something that has been going on for a while and could be related to the replacement window that was installed several years ago.

You're probably right, but for life of me I can't think why a replacement window would cause those symptoms. I mean you won't even have a cavity wall, will you? It will be a 9" solid wall due to the age of the property I'm guessing? Best thing to do would be to get a stiff brush (not a wire one) and scrub the affected areas, then re-coat with a quality masonry paint such as Sandtex. Maybe look at applying a stabilising solution first as well, although this isn't my area, so a decorator would be better placed to advise once you've got the wall stripped back.

hth

 

[jeds]

Old brick pointing was generally made of lime mortar which is soft and breathable. This is a sacrificial system that allows moisture to evaporate through the joints but over time causes the pointing to deteriorate. Of course it's much easier to replace pointing than brickwork.

Usually this is a fairly invisible process but in your case the paint is blocking the evaporation and indicating where moisture is trying to escape. All solid walls breath moisture all the time but if what you have there is a concentreted area you probably have an excessive build up for some reason.

 

[MonsterMonster]

I suspect that there may well have been a past problem elsewhere that has been fixed and what I am seeing is another sympton left untreated.

Looking at other parts of the same wall there seems to be new'ish (i.e. neat looking) repointing. Maybe what I am seeing has been repointed with a dodgy batch of mortar.

I do not know if the existing mortar is lime mortar or ordinary sand and cement mortar. Is there any way to tell easily bearing in mind it has been painted? Would there be any problems if I used the wrong type of mortar alongside the present?

You might guess this is all new to me!

Thanks for your help.

 

[jeds]

Dig a bit out and have a look. Lime mortar will be soft and white or yellowish - most likely with gritty sand. If it's grey and hard it is cement.

 

[MonsterMonster]

Just been looking at my old threads and thought I'd update six years on!

It turns out that the area in question used to be where an internal chimney stack used to be. In effect the window is where the fireplace was located. The bubbling lime mortar is a reaction to the various sooty chemicals that have built up over the years and is reacting with the soft mortar.

What out for the next update in 2021!

 

[theprinceofdarkness]

The sooty residue is acidic and it "rots" lime mortar, or to be more specific it turns it into sand which can be brushed out. So has zero water protection. Best thing to do is to clean out the pointing in the effected area, repoint with lime mortar and repaint. It could occur again until all the acid is used up.
Frank

 

[ree]

shmac50,

Thanks for coming back with that info.

1. what, if anything, was done about the old sooty flue line inside the wall?

2. There's a frame in an opening below the dodgy brick panel with a "bit" of lintel showing - did this opening have any bearing on your investigation results?

3. Was the bubbling pointing raked out and repointed?

4. its hard to tell what kind of paint was used in the 2009 pic - was it masonry paint or what's called a plastic paint (plastic paints form skins).