External Brick Stain

[Bobo]

Hi,

I've got a flat roof garage. The little grid on top which allows rain water to pass through into the downspout played up recently and I've since sorted the problem. However, prior to me fixing the damn thing water was ' missing ' the downspout and catching the garage wall making it...well.....wet. This left a wet patch. Now given it is no longer being subject to moisture I've noticed the edges turning white but when you stand back and look at were it was leaking there is a dis-colouration so how can I clean my bricks ? Hope that made sense by the way. Incidentally the stain isn't spreading. It just looks unsightly and is getting on my wick as I was hoping it would just dry and bugger off.

Thanks.

[Anna Kettle]

The white stuff is salt. You will be pleased to hear that the best thing to do is almost nothing. Wait until the patch has dried out and so has the salt. Then on the last dry day of the summer, dust it down to remove the dry salt. Should be sorted

Anna

~~ Anna Kettle, Suffolk, England |""""| ~ Lime plaster repair and conservation / ^^ \ // Freehand modelling in lime: overmantels, pargeting etc |____|

01359 230642

[The Natural Philosopher]

It may be other things than Sodium Chloride. Some insoluble salts get very soluble after treating with brick acid - you can get this at any builders merchant. Its just 30% hydrochloric acid.

First try hosing it off. Or pressure washing if you have access to one.

If that doesn't work, try a washing up brush in brick acid. Wear rubber gloves and goggles or something. Its not deadly dangerous but it STINGS especially in eyes. Wash out with lots of water if you get splash anywhere.

Keep clear of the mortar cos it dissolves that too..

Then hose down and keep hosing - especially if plants around. Want to dilute any acid to a low concentration.

[somebody]

In message , Bobo writes

Hi,

Google for "efflorescence brickwork".

Pressure washer without doubt. I have previously tried a yard brush, wire brush and brick acid to no avail.

On new, very "salty" brickwork it took three attempts with a month or two in between to truly be rid of it. I'd imagine one attempt should clear yours.

Hth Someone

[Stuart Noble]

Difficult to imagine how sodium chloride would get into the masonry in the first place. What else is it likely to be? Whatever was in the original water used to mix the mortar?

[The Natural Philosopher]

Oh..its never sodium chloride. I was being slightly ironic. Its various other *salts*, as in the *chemical meaning* rather then the common meaning of SALT.

Carbonates and some sulphates respond well to hydrochloric acid, becoming chlorides..most of which are more soluble..I always get a slight whiff of rotten eggs cleaning brickwork with hydrochloric, which suggest reduction of sulphates to chlorides and hydrogen sulphide.

The predominant effusion though is bubbles of CO2 from the cement.

Google 'efflorescence' for loads of in depth bollocks. Bricks themselves may carry salts that get carried out by water and crystallize on the surface. MOST of these dissolve in water, but some become solid carbonates (by reaction with air/CO2 IIRC) that don't. Brick acid gets rid of most of em. I think there are some other things that oxidise and stop being soluble as well. Key is to reduce them with acid and pull the oxygen out, then they get soluble again.

However when my brickwork went up, there was orrible efflorescence on it..4 years later its all washed off in the rain.

[Guy King]

The message from The Natural Philosopher contains these words:

While we're on the subject of brick acid...

What does it do to slate? I don't want to go and buy a jug then find it's going to make a dreadful mess of it. I've some smears of cement on a slate wall.