How To Remove Black Stains On Brickwork

[Guderian]

The concrete walls around my garden are finished off with small sandy-coloured decorative bricks. During the rainy season the north-facing wall has developed quite a lot of dirty looking black stains. This wall doesn't get much if any direct sunlight. The south-facing wall gets a lot of sun and does not have a similar problem.

I assume that these black stains are either fungal or bacterial - does anybody know which it is, and how best to remove them? Is there a fungicide or anti-bacterial agent sold for this purpose? I was thinking of using a solution of washing powder. A friend suggested bleach, but I'm afraid of that discolouring either the bricks or the coloured stone murals set into the brickwork. Do the big home stores sell anything suitable to clean these black stains off the wall?

Thanks for any advice.

[TS79]

It looks like algae so something with Chlorine in it. You can buy granulated chlorine at a pool shop, mix some with water and spray it on.

[sezze]

Easier and cheaper ( probably ) is standard toilet cleaner or something with acid in it . The toilet cleaner certainly does the job since it's got plenty of hydrochloric acid in it . This is a routine job on sandstone since it will develop everytime again . I got some sandstone in my bathroom and it needs to be treated regular with this .

[Riley'sLife]

I would first try a small area scrubbed with bleach -wear gloves and goggles- as that is the cheapest. But, look out for the bleach staining it pink.

If that works, or if you try the helpful suggestions others have given, I would- once it is clean- apply 2 or 3 coats of PVA (Polyvinylacetate) as the stain is a mold which will find a porous surface easy to re-inhabit. PVA will seal the surface without leaving a sheen and would make it easy to clean again if necessary.

PVA is a white liquid which can be diluted with water up to 1:1 ratio. clean brushes with water.

Good luck!

[Guderian]

Thanks for the replies. I guess I'll have to test the bleach on a small inconspicuous area first to check for staining.

A friend suggested sealing the bricks, but he didn't mention PVA. Is that something you can buy easily in the home wares stores here?

[kamalabob2]

In 2008 we had sandstone facing installed on columns and exterior parts of our home which are exposed to rain. The builder gave us two choices in what to apply to the sandstone facing and we selected a product that would "soak into the sandstone, but not make the sandstone glossy". The lowest cost product of "Masonry Water Repellent" from where I shopped at that time, was "Dulux Silicone R 221". As I have expanded my shopping horizons I have seen similar "Masonry Water Repellent" at most every building materials store in Thailand, but you would have to rely on someone who can read Thai to see if what you buy keeps the sandstone the same color, OR if the particular product will give it a glossy sheen. When the OP is able to rid the sandstone facing of that black "efflorescence" (funny google ad pops up on this page) he should look into spraying some sort of "Masonry Water Repellent" onto that nice sandstone. Some of the cans in the store by MANY brands, show sandstone and /or bricks on the front of the metal container. It was NOT imported, it was not outrageous in price. We had a nephew "clean" the new sandstone in 2008 with a Makita blower, and then use a small hand held plastic spray bottle to apply the Dulux R 221 to every piece of sandstone. Of course , our written builders contract included the sandstone facing, but NOT the protection of the sandstone. Silly me to assume that was included in a building contract.

[Guderian]

Thanks. I'll take some photos to the local home stores and see what they suggest.

[Mooner]

Do you live in Thailand? In the UK there is a product called brick acid. If you do live in Thailand im sure there is something similar. Alternatively anything acidic should work especially if you use a wire brush to clean it. As mentioned always test a small patch first.

[colinneil]

Yes you can buy brick acid in thailand most builders merchants have it . I bought some before in my local merchants.Good idea about p.v.a. stops it happening for 3/4 years.

[Guderian]

Thanks, I'll also look out for brick acid.

[WilliaminBKK]

I think brick acid is muriatic acid ? but BE VERY CAREFUL you need to neutralise it once applied otherwise it will eat away at your brick work and that will change the brick colour.

I'd try a mixture of water/bleach as your bricks are coloured, I use regular strength bleach on concrete and works like a charm. Should do the trick in 10 minutes and rinse .

[wayned]

It looks like mold, similar to what my house and outside walls looked like after the flood last year in Bangkok. Weas did everybody else, used the toilet cleaner in the purple bottle. Did a good job claenib=ng and stopped the mold from growing, mold is a livce fungus.

[Guderian]

Thanks for the replies folks. Once the rains have stopped (and they seem to be very late finishing here in Pattaya this year) I'll experiment to see what works best.

[Pib]

A pressure washer will take it off in a heart beat....and I've got some brick on my house just like in the OP's picture. I have a pressure washer I use around the house all the time...it takes algae/mold/black stains off bricks/rocks fast, easy, and without damage as it's just water under high pressure...no acids...no detergents....dangerous chemicals...etc. I fact most of my usage of the pressure washer is to remove stains off brick/concrete walls & sidewalks around my Bangkok house. I bought a Zinsana Andaman 120bar model for around B5,000 at Big C (they are sold at many locations like HomePro, Makro, Lotus, etc) after the major flooding last year as I had a lot of cleaning up to do...should have bought it a lot sooner based on how well it works in cleaning algae/mold/black stains. It's even fun to use.

Edited November 29, 2012 by Pib

[jbrain]

As Pib says, a pressure cleaner is the way to go.Be careful with any products since sandstone is very porous and absorbs easy.

After cleaning apply a water reppelent which you can have from Dulux as anothet poster said already, but also from TOA, Silca and many other brands.Look for the thins with a picture of natural stone.

Keep in mind that sandstone absorbs a lot and that this can be a costly operation if it involves a lot of square meters.

[Guderian]

The pressure washer sounds like a good idea, and whoever built this place tiled it all around with off-white tiles which get marked so easily that it's daft. Actually they may have been white to start with and are now off-white due to discolouration. The pressure washer might help clean all the paths. What's the typical power rating (Watts or KW) of such a pressure washer?

[Pib]

The pressure washer sounds like a good idea, and whoever built this place tiled it all around with off-white tiles which get marked so easily that it's daft. Actually they may have been white to start with and are now off-white due to discolouration. The pressure washer might help clean all the paths. What's the typical power rating (Watts or KW) of such a pressure washer?

The Zinsano Andaman 120 Bar I mentioned draws 1600W or about 7 amps.

[Guderian]

The pressure washer sounds like a good idea, and whoever built this place tiled it all around with off-white tiles which get marked so easily that it's daft. Actually they may have been white to start with and are now off-white due to discolouration. The pressure washer might help clean all the paths. What's the typical power rating (Watts or KW) of such a pressure washer?

The Zinsano Andaman 120 Bar I mentioned draws 1600W or about 7 amps.

Thanks. Does it damage the mortar between the bricks at all? From what I've seen here, the Thais are extremely bad at mixing up good quality mortar, they try to save a few Baht and use too much sand, often leaving the end result a bit too soft and prone to erosion.

Any problems using it on the grout between the patio and pathway tiles?

[Pib]

The pressure washer sounds like a good idea, and whoever built this place tiled it all around with off-white tiles which get marked so easily that it's daft. Actually they may have been white to start with and are now off-white due to discolouration. The pressure washer might help clean all the paths. What's the typical power rating (Watts or KW) of such a pressure washer?

The Zinsano Andaman 120 Bar I mentioned draws 1600W or about 7 amps.

Thanks. Does it damage the mortar between the bricks at all? From what I've seen here, the Thais are extremely bad at mixing up good quality mortar, they try to save a few Baht and use too much sand, often leaving the end result a bit too soft and prone to erosion.

Any problems using it on the grout between the patio and pathway tiles?

No problems unless you put the wan nozzle close to paint in its pensil stream pattern---then it will cut the paint off. The washer comes with two wans. One is adjustable from a fan stream (which I mostly use for all cleaning) to a pensil stream (which you can use to remove paint from concrete). The other wan is a special purpose wan which I have rarely used. You could wash you dog or put holes into your dog--all depends on how you adjust the wan stream and how close you get to your work. But to damage something would take some real idiot effort and disregard for what they are doing.

[Guderian]

The pressure washer sounds like a good idea, and whoever built this place tiled it all around with off-white tiles which get marked so easily that it's daft. Actually they may have been white to start with and are now off-white due to discolouration. The pressure washer might help clean all the paths. What's the typical power rating (Watts or KW) of such a pressure washer?

The Zinsano Andaman 120 Bar I mentioned draws 1600W or about 7 amps.

Thanks. Does it damage the mortar between the bricks at all? From what I've seen here, the Thais are extremely bad at mixing up good quality mortar, they try to save a few Baht and use too much sand, often leaving the end result a bit too soft and prone to erosion.

Any problems using it on the grout between the patio and pathway tiles?

No problems unless you put the wan nozzle close to paint in its pensil stream pattern---then it will cut the paint off. The washer comes with two wans. One is adjustable from a fan stream (which I mostly use for all cleaning) to a pensil stream (which you can use to remove paint from concrete). The other wan is a special purpose wan which I have rarely used. You could wash you dog or put holes into your dog--all depends on how you adjust the wan stream and how close you get to your work. But to damage something would take some real idiot effort and disregard for what they are doing.

Cheers. I'll have a look for one, I can see quite a few uses here.

[Guderian]

I just thought I'd report back with my experiences. The pressure washer is the way to go, at least as far as I am concerned.

I looked at using the acrylic to paint the bricks but there's an awful lot of them and that stuff is expensive. Nonetheless I bought a gallon and gave it a try, but the surface of the bricks is so rough that it is a real pain trying to get good coverage with the acrylic. I reckoned that even using plenty of thinner it was still going to cost several thousand Baht in paint and take me weeks to complete the job.

A Thai friend has a pressure washer and he was happy to lend it to me for a week. It's not one of the famous brands like Karcher, but an Imperial Airman pressure washer, rated at 107/214 bar. Here's a picture:

As mentioned above, it's fun to use, takes the black marks off the bricks effortlessly, and the result is quite rewarding. I didn't want to overdo things, so I limited it to around an hour a day, and finished the whole place inside a week. That included cleaning the black stains off some large lumps of ornamental white coral that are scattered around the garden. Now it's all nice and clean I should apply the acrylic, but as mentioned it's too much work and expense. I'd far sooner spend the money buying myself a pressure washer and then once a year get it out and clean the brickwork as necessary. On a hot day it's a nice way to spend an hour, splashing water all over the place. Plus it has many other uses like cleaning the car and motorbikes, cleaning the patio and path tiles, and so on.

A great recommendation thanks, Pib, and thanks to all the other posters for your interest and help.