Exterior Chimney Staining? Cause and Remedy?

Hi,

I'm living temporarily in a friend's house and am looking for some help to solve an issue. As you can see from the photos, there is significant staining on the outside of his chimney. He just redid the top of it taking care of the brickwork and cap which is bluestone. He just replaced the 50 or so year old oil furnace with a new efficient oil furnace and he rarely if ever uses the fireplace. There are two flues in the chimney. From the photos, the right side is used by the oil furnace and the left side is for the fireplace.

Just wondering what people's opinions are about what caused the staining on the outside of the chimney and what is the best way to clean off the brickwork without damaging the chimney?

Thanks ahead of time for your responses.

Just to be clear, the staining is in-line with the oil furnace flue, and not the fireplace. Correct?

Yes.. it appears to be from the oil furnace flue. Not sure if it's a result of an inefficient burn or the degrading of the oil furnace over the years or something else... thanks.

I suspect that the old oil burner was creating some soot. The soot deposits on the cap/ top of chimney were then washed down the outside of the chimney every time it rained.

Also, he should really probably have that chimney lined if he is now using a higher efficiency oil furnace. There will likely be a fair amount of condensation forming in the masonry chimney and there is the potential for draft problems.

Thanks Rovert. I believe he did have a new stainless steel liner put in with the new furnace but will have to confirm with him. Now for the sixty-four thousand dollar question, how do I clean that crap off of the chimney?

I'm still working on him to get either a wood or pellet burner in the house... that will be a slow process.

I've never had to do this. I would probably start with something simple like a soap or vinegar solution or a pressure washer. If that doesn't do it, there is always muriatic acid... but use it with caution.

I've used muriatic on concrete, but never any type of brick. Don't fail to distinguish between clay brick and concrete brick when you do your searching on whether or not this is safe.

I spent a spring/summer working for bricklayers in NZ. The pair I worked with were very careful about leaving any mortar behind on the faces. Actually, they were very careful to make sure I didn't allow any mortar to be left behind. Anyway, we occasionally had to clean up after less careful bricklayers. We used hydrochloric acid on clay bricks. YMMV.

I tried straight water and vinegar solution in a small test area yesterday and didn't have a great effect but it did take some of the stain off. Will try soap and vinegar next and I guess I can move my way up from there or maybe just let the solution sit on the brick longer.. The bricks on this chimney seem to have a smooth finish. I've seen this kind of brick lose its face (say maybe 1/8 inch thick) in some other applications and I certainly don't want that to happen. Perhaps I could consult with the people who remove graffiti from buildings in NYC to see what they use.. haha..

Thanks for your replies.

Sounds like clay brick, based on your description. Concrete brick is usually rougher and more porous looking. Clay bricks often pop a face. The town I just moved from, where almost all the houses were built between 1880 - 1890 and all were brick, was full of houses with bricks whose exposed faces were popping off.

This house was built in 1950. I agree that it seems to be clay brick. Just found this by doing a search and adding "clay" to my search in google.. Looks to have some good information.

http://www.ibstock.com/pdfs/technical-support/cleaning-of-clay-brickwork.pdf

Bob. Good advise. Thanks. Looks like a good way to avoid damaging the brick is to pre-soak the brick.

I don't know if this is a hearth.com first, but I'm sitting in labor and delivery with the wife waiting for #3 to arrive. They have wifi here.. What a deal.

Now there's a guy who has his priorities straight!

I spent most of the time texting a buddy, who's wife went into labor within 30 minutes of mine. It was a race! His wife won.

In any case, congratulations!

Thanks Joful. I did put down my computer long enough for the birth of my second son. Time to buy the boy his own chainsaw and maul and put him to work..

You don't give a chainsaw to a newborn! He can't even lift it. Wait until he's 3.

Congratulations on what sounds like a safe and healthy delivery.