How To Clean A Neglected Stone Fireplace


When we moved into our Georgian Cottage, one of the things that struck me was the fireplace in the living room, for two reasons.

First of all, it’s a large and imposing stone fireplace, hand carved and solid – a great feature for the room.

Secondly, it was a blackened mess. There were horrendous soot stains all over it. This stone fireplace had certainly seen better days.

What Is Soot?

Soot is a black residue which builds up due to the incomplete combustion of wood, coal, paper and other carbon-based matter. Its deep black powdery consistency makes it a tough job to get rid of it, for a number of reasons:

  • The black carbon ash that is left behind after burning can easily stain anything that it comes into contact with. Back in the 1800s, when our cottage was first built, people used to disperse ash into liquid and use it as a writing material.
  • Tiny smoke particles can also intermingle with the black carbon ash and stick to your stone fireplace. These smoke particles are very difficult to remove
  • The carbon deposits that make up soot comprise of partially burnt hydrocarbons, coming from the same family as organic fuels like petrol and diesel. As a result, they are very oily and can cling to surfaces like grease.

Sealed Or Unsealed Stone?

Because natural stone is made up of many microscopic pores, ash, soot and other stains can get beneath the surface of the stone, making it much more difficult for the stains to be wiped away.

I think that’s what happened to our fireplace.

A good impregnating sealer will fill all those small holes to keep stains on the surface where they can be easily cleaned off. I haven’t used a stone sealer, so can’t comment on its suitability or performance.

How To Remove Those Black Soot Stains

I tried a variety of household cleaners to get the black marks off the stone. Everything from four-in-one sprays to vinegar and bleach-based cleaners and an abrasive cleaner. The week we first moved in, my parents came over to help unpack and my mum also spent a good few hours working on cleaning the fireplace.

I spent a whole bunch of hours and energy scrubbing at the stonework fireplace with a stiff brush soaked in boiling hot soapy water. Lots of time spent. Very little to show for it!

Although lots of black seemed to be coming out each time, once the stone had dried, it looked almost exactly the same, as if we’d not even put all those hours into cleaning it at all. These were hard, black, baked-on soot deposits. I’ve no idea when the stonework had last been given a thorough clean, but this stuff must have been baking on for years.

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The fireplace after many hours of scrubbing!

Enter Tri-Sodium Phosphate (TSP)

I decided to dive in and buy a pack of tri-sodium phosphate (TSP), going on eBay to make the purchase. I’d heard that it works very well for cleaning away organic compounds, but was a bit concerned about its aggressive nature. This stuff is supposed to be hardcore.

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It is highly alkaline and caustic, so make sure you use rubber gloves and protective goggles when using it.

Before starting, cover any surrounding carpet and fabrics. If you spill TSP onto anything, it’s going to destroy it.

Dilute half a cup of TSP into about 6 litres of warm water and then you’re good to go.

I soon discovered that TSP is so strong that it does most of the work for you. The black soot was coming off in spades. I used a sturdy kitchen sponge and a stiff bristle brush to work into the soot marks. The water was getting very black, very quickly. But unlike with the other cleaners that I’d used, the tri-sodium phosphate was also making the stonework look cleaner.

After a first pass with the TSP solution, I scrubbed down the fireplace with a few buckets of warm water to make sure all the TSP was washed away.

I then left the fireplace to dry overnight. Before I went to bed, I could already see that the fireplace was starting to look cleaner.

Coming downstairs the next day, I was amazed by the difference. TSP has worked!

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The results of just one scrubbing session with tri-sodium phosphate.

Using Oven Cleaner

One trick that I heard about after I’d already had success with the Tri-Sodium Phosphate, is the use of oven cleaner. This stuff is specifically designed to remove baked-on food deposits, so is supposed to work well on stone fireplaces too.

I haven’t tried this method, so I’ve no idea of its efficacy or whether it will damage your stonework at all.

If you go down this route, make sure you first do a spot test somewhere on a hidden area of the fireplace. Follow the instructions and break out those rubber gloves and eye protection.

All things considered, if you have thick, stubborn soot marks on your fireplace, I would definitely recommend you take the tri-sodium phosphate route. It certainly worked well for me!

How Did You Get On?

Did you find this post useful, what fireplace cleaning products have worked for you? Just how bad was the state of your fireplace? We’d love to hear from you, so please leave us as message below.

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