Removing soot from bricks in a fireplace that is 100 years old

[Rake722]

Hi everybody I am trying to remove black suit after having opened up the builders opening in a chimney breast in our house. I have tried using hydrochloric acid to no avail and I’ve also tried oven cleaner which also didn’t really work.

I was told that a mixture of caustic soda water and wallpaper paste applied to the bricks and then covered with clingfilm and left for 24 hours would have a good effect.

I’ve mixed approximately 7 L of water with two 250 g bottle bottles of caustic soda and added a packet of wallpaper paste to the mix mixed it up until it was semi gel like I think it was a bit too thin to be honest, applied it to the bricks and covered it with clingfilm to stop the wallpaper paste from drying. I don’t care if it doesn’t work. I’m now absolutely paranoid that the wallpaper paste will dry and I won’t be able to get that off now.

Does anybody have any experience of such things with the paste dry? Will the solution remove the soot ?

Thank you

 

[Kearn]

Nope. All a waste of time, the tar and various nasties have become one with the bricks, they leach in when wet and then dry out within the fabric, just look at the external walls of old buildings and you can track the flue up the wall from the dark staining.

Why are you trying to remove the markings showing the historic fireplace use?
If you’re leaving them as bare brick within the fireplace only, embrace the fires that have gone before, obviously lime plastering the jambs and breast.
Or, go get some fresh cow and do a few coats of the old recipe to stop the stains coming through your plaster, and plaster working the firebox as well as around.

At the moment, you’re wasting your time and probably doing damage to the brick faces.

 

[Rake722]

Oh balls - it’s gonna be interesting getting the damn stuff off

 

[Jonty1234]

We have been using trisodium phosphate with warm water to try and remove soot stains from the back of a chimney breast that has since been removed. I probably applied the stuff and scrubbed it on 6 or 7 separate occasions but I eventually gave up as it didn't seem to have much effect.

As above, the bricks will never be returned to their original condition so it's easier to appreciate their history and move on to the next challenge.

If you are going as far as repointing the wall you will find that the colour of the mortar lessens the impact of seeing all the black soot.

 

[Rake722]

I’ve spoken to a historic building restoration expert who advises to use hydrofluoric acid as it is the only chemical that will break the bond between tje soot and the brick.

It’s extremely expensive at £100 for 5 L and I don’t even know if it will work on a fireplace

 

[a twig]

It’s also pretty nasty stuff… I personally wouldn’t even dream of using it in a DIY situation.

Hydrofluoric acid, a solution of hydrogen fluoride gas (HF) in water, is one of the most corrosive and dangerous chemicals encountered in the laboratory. Exposure to HF can cause severe tissue damage and even death. The fluoride ions in HF readily bind calcium and magnesium, reducing their levels in the blood, resulting in hypotension and cardiac effects.1 Deaths have been reported from concentrated acid burns (involving ≥ 50% HF solutions) to as little as 2.5% of body surface area, which is equivalent to approximately one hand and forearm.2 In lower concentrations, symptoms may be delayed, which can lead to delayed recognition of exposure and a more severe burn. The following special safety precautions are necessary when using this chemical, regardless if using dilute or concentrated HF.

What are the hazards?​

Hydrofluoric acid (HF) exposure is very toxic and can be fatal if not treated immediately. HF is absorbed quickly; however, damage/symptoms can occur hours to days later.

Information on Hydrofluoric Acid – Stanford Environmental Health & Safety

ehs.stanford.edu

 

[Cubist]

Dumb question perhaps but; what exactly are you trying to achieve and why?

 

[Rake722]

Dumb question perhaps but; what exactly are you trying to achieve and why?

I’m just trying to get the bricks back to their original red colour for aesthetic purposes

 

[Cubist]

I'm sorry to tell you but that is about as likely as a snowball not melting in that fireplace when it was in use. The tars, oils, fine sooty deposits, salts and other chemicals resulting from the combustion of coal will have been absorbed or penetrated to considerable depths into the bricks and depending solely on how soft the bricks are. Frankly even aggressive sand blasting will not remove the staining and would inevitably destroy the bricks. Your best options are therefore either to remove the bricks, not an easy job, and replace them or simply accept the inevitable and re-consider your goal.

 

[Rake722]

I'm sorry to tell you but that is about as likely as a snowball not melting in that fireplace when it was in use. The tars, oils, fine sooty deposits, salts and other chemicals resulting from the combustion of coal will have been absorbed or penetrated to considerable depths into the bricks and depending solely on how soft the bricks are. Frankly even aggressive sand blasting will not remove the staining and would inevitably destroy the bricks. Your best options are therefore either to remove the bricks, not an easy job, and replace them or simply accept the inevitable and re-consider your goal.

I have resigned myself to this conclusion. The only challenge remaining is to remove the wallpaper paste and caustic soda mixture that I made yesterday.

 

[Cubist]

Citric acid dissolved in water carefully brushed over the residue left behind after you remove the cling film then washed off with water. Repeat as needed to clear all the residue away.

Please wear eye protection while brushing the solution over the remaining caustic soda and paste coating the brickwork - I still carry a small caustic soda burn scar in the corner of one eye courtesy of my own youthful carelessness.

 

[Rake722]

By jove it’s working

 

[Rake722]

Just look at the difference

 

[Rake722]

Done - pointing next

 

[Cubist]

Coo and wow. Thats much better than I would have expected. I'll make a note not to be so sceptical in the future.

 

[Rake722]

Coo and wow. Thats much better than I would have expected. I'll make a note not to be so sceptical in the future.

Caustic soda and wallpaper paste does the trick