Brick Salting

[Gandalf]

Hi everyone,

I have a cottage dating back to 1800 it seems as though I have got bad salting on internal brick work starting from the chimney stack in the loft running all the way down to the front room fire place. Can anyone give me possible reasons for this, is it damp? or just the building material.
Any suggestions on how it can be cured would be great
Regards G

 

[Matt Green]

Is the brickwork on the chimneys exposed? Has it been recently exposed? If it's rendered with something, what is it and is it painted? Have you recently moved in, refurbished or changed the heating in any way? Is the chimney capped? Have the roof flashings been checked?

It's a hygroscopic salt problem, but a bit more information is needed for diagnosis.

Cheers,

Matt

 

[chuckey]

When you say "salting" do you mean those white stains you some times see on new brickwork? i.e. effloresence (Sp?). I believe these are caused by soluble salts caught in the bricks at manufacturing. So you see them on the outside until the rain washes them away. Now you say that you can see them in the inside. Is this because you have taken the plaster off? Or have they worked themselves through the plaster? Or was it never plastered?
I think its fair to say that the salts are carried by moisture and can be washed off. The presence of these salts on the face of bricks is an indication that there is(was) dampness about and plaster will not adhere very well to this "salty" surface.
Frank

 

[MdB]

Above is the salt produced in block work that was exposed when I removed the bath. It wasn't well installed and water leaked down the back when we had a shower. The wall is solid construction 1970's block with a high ground level outside so it was basically as damp as you can get for concrete. Now the bath has been removed, the wall has started to dry out and this has brought salts in the cement / concrete to the surface. The two pence piece gives you a sense of scale. There was no salt there when we removed the bath a month ago.

Salt is left behind as water saturated with salt evaporates from the surface. It is seems to be a sign that you are doing the right thing as the wall is having a chance to dry.

 

[arthurw3]

The salts that you can see are hygroscopic, i.e. they will absorb moisture from the air and make the wall damp, even if you brush the visible white efflorescence off. You will need to get rid of the reason for the damp in the first place and then seal the wall with a barrier, something like BPB drikote will be needed, before finally finishing the wall and decorating

 

[Nemesis]

I'd wait and see what Matt recommends.

He does this for a living...

 

[MdB]

... then seal the wall with a barrier, something like BPB drikote will be needed, ...

I assume that is some sort of waterproof(??) sealant. Google can't find it. If so, it will just trap water behind it until it fails and then you get a damp patch. I'm going to sort out the reasons for the damp and then just let it dry out. I won't be touching that wall for at least 6 months and I doubt there will be much additional salt growth.

 

[Ian Bond]

http://www.british-gypsum.com/produ...stle_undercoat_plasters/thistle_dri-coat.aspx

Just what you (don't) need for your Period Property.

 

[Gandalf]

Hi thanks all,
No Matt I have not checked the flashing yet but I have checked it through binoculars and it seems ok! The house is rendered but the stack is not.
The amount is only small down stairs, only a couple of tennis ball size areas. It appears more abundant upstairs in the loft.
looks as though I will have to get some roof ladders.

Regards G

 

[Matt Green]

The amount is only small down stairs, only a couple of tennis ball size areas. It appears more abundant upstairs in the loft.

Right, we're getting there then. Presumably the chimneybreast isn't plastered in the loft, what about downstairs? Is the internal side bare brick or covered with plaster?

The loft: is it insulated and has it been for long?

Still need to know if you've change the heating arrangements in the house in recent times. Sorry for the hassle, it's important to know if it's drying out or a longer term problem.


Matt

 

[Gandalf]

Hi Matt,
The loft isn't plastered and I have just taken off the plaster and render from down stairs. I have uncovered a beautiful brick fireplace which someone has tried to cover with new bricks and an out of period surround. I have reinsulated the loft some time ago. I have not changed the heating arrangement since we moved in so what do you think it may be? Bearing in mind I think the exposed chimney stacke may need repointing.
Regards G

 

[Matt Green]

The loft isn't plastered and I have just taken off the plaster and render from down stairs

Ok, that's useful.

The loft: brush the salts off and see if they return. Now the loft is insulated the relative humidity in the roof void should be low (because the air is colder now that the heat is trapped below), and that should reduce water evaporation from the internal face of the chimney. Which means less salt on the brickwork.

Downstairs rooms: if you have just removed inappropriate plaster from the chimneybreast the brickwork is likely to be drying and leaving a salt residue behind. Nothing to worry about, probably, but the bricks may well be hygroscopic. What you do about it depends on the finish you want. If you want the brickwork exposed you will be brushing off salts for a while before the chimney stabilises with the new bare brick environment, or you apply some irreversible gunk to block their movement through the surface.

If you want a platsered finish, then you could poultice the salts out with some sort of sacrificial lime plaster (time consuming, and the room will look rough for ages), or use a plaster with a salt-retardant additive (which might damage the face of the bricks on its eventual removal, depending on what you use. Pick one with as big a percentage of lime as possible).

It depends on how mush salt is in the brickwork and what finish you want. Brush the salts off for a few months and see what happens if you can.

Hope that helps


Matt

 

[Gandalf]

Thanks Matt,

Have bought some lime already for repointing hopefully I can use the exposed brick work but some bricks down one side have been smashed up and I need to ask a builder if they can be replaced without collapsing the stack.

Cheers G.

 

[Lime]

Effluorescence is always a better sign than damp IME.
It demonstrates that evaporation has taken place and in small amounts just gives character.
Don't seal the wall, that will just cause trouble in the future.