How to Clean a Fireplace Firebox (Friday Five)

This might be the least glamorous, messiest project I’ve ever done! When I took off the brass insert from our fireplace, I was left with a nasty, dirty fireplace and firebox. Before I decided to use this repurposed window screen as a DIY fireplace screen, I knew that I would need to clean and paint the inside of the firebox.

I knew the basics of how to clean a fireplace firebox, but not the details of how to get nearly 100 years of soot off the brick. And I didn’t want to use any strong chemicals, because this is a 1929 firebox and it’s not in great shape. The mortar is crumbling in places, and no one has really taken care of it, maybe ever, but certainly not lately.

After a lot of research and trial and error, I figured out the best way to clean it. So, for today’s Friday Five, I’m sharing how to clean a fireplace firebox in five steps – the best way, all in one spot, so you don’t have to do all that legwork!! At the end of the post, I list the other cleaners people suggested that didn’t work.

Here’s what you’ll need:

A scoop or small shovel

Trash bag (a paper grocery bag works best here)

Dishwashing liquid

Baking Soda

Rubber or other protective, water-proof gloves

Scrub brush (I bought mine at the dollar store!)

Spray bottle with water

Bowl and a bucket

Mr. Clean Magic Eraser

Paper towels

Plastic dropcloth

How to clean a fireplace firebox in five steps:

(1) Clean out the big stuff.

If your fireplace is one that you use, make sure first and foremost that it is completely cool. Make sure any ash or pieces of wood in the fireplace are cool. You don’t want to start a fire or burn yourself!

Once you know that the fireplace is cool (or if it’s not a fireplace you use, like mine), remove any larger pieces or ash that may be in the firebox. Our fireplace had some logs (there for show only), a rusted grate, a pine cone (not sure how that got there?), and some chunks of soot that had fallen off over time. Remove all of that stuff first with a scoop or a shovel and put in the trash. I found that a paper grocery bag works best for this, because it stands up and stays open as you scoop the trash into it.  Any smaller bits can be picked up with a Shop-Vac (you can use a regular vacuum cleaner for this but make sure you clean it afterwards or you will smell fireplace/burnt wood for a while!).

(2) Make the cleaning slurry.

Grab the bowl – a medium-sized mixing bowl that will clean up well is best here – and mix up the cleaning slurry. First, add one cup of baking soda to the bowl. Then, add dishwashing liquid – just enough to wet the baking soda, about a quarter- to half-cup – and stir until you get something that’s about the thickness of pancake batter.

That’s what it should look like.

I ended up making about three batches of this stuff for the whole fireplace, but I’m telling you – that thing hadn’t been cleaned since 1929! It was so dirty!

(3) Put on the gloves and spread the slurry.

You are going to want rubber gloves for this part. Wearing gloves, take a handful of the slurry and smear it on the firebox walls. It will look like this:

Yum, right?!? Kidding.

Let the slurry sit on the surface for a bit. Like half an hour. Forty-five minutes to an hour is fine, too. If you let it go longer, no big whoop.

Then take the scrub brush – while still wearing gloves (trust me!) – and scrub the soot off the brick or stone. This takes some elbow grease, but let the brush do the majority of the work here. Otherwise, you will have sore arms (also, trust me).

But look!

Amazing, right? Wait! It gets better!

(4) Spray the soot away!

Take the paper towels and put a double layer of them down on the floor of the firebox. Then take the spray bottle with water and spray the slurry + dirt that came off from scrubbing. (If the spray bottle has two settings, choose the one that’s the stream spray.) The spray bottle acts like a mini-pressure washer and it rinses away the soot, dirt, and slurry!

Now, this is not a quick process. To get from the first picture of the soot-covered firebox to the last picture above took about three days of scrubbing. No, I’m not kidding. My arms assure you that we are not kidding. But it’s so worth it.

(5) Clean the Brick Surround.

Because of the ugly brass insert that was there before, there was a ring of soot around the firebox.

That had to go, too!

For this part, what worked best was a Mr. Clean Magic Eraser! Just dampen it and scrub the brick.

For some reason, the baking soda-dishwashing liquid slurry did not work as well on the painted brick. The Magic Eraser worked perfectly, though!

Instructions for Painting the Firebox

Once the firebox is as clean as you can get it, and the surface is as smooth as you can get it, it’s time to paint!

Tape off the brick surround first, to make sure you don’t get paint on it. Make sure the tape covers not only the brick, but the mortar lines in between, so the paint doesn’t seep through.

I used (affiliate link) Rust-Oleum High Heat black paint, for two reasons. First, if anyone ever wanted to fix up this fireplace and use it, then it would be fire-ready. Second, I wanted a true black in there, so that the firebox just receded away. I used a wide brush (3-inch) meant for uneven surfaces and any kind of paint.

Note: the paint is a little stinky. Make sure you’re using it in a well-ventilated area and/or open a window.

After two coats of the paint:

So. Much. Better!!

I then added my DIY fireplace screen and now my fireplace is back to being right for a 1929 home!

What didn’t work:

When I started cleaning the firebox, I checked the google to find out what other people had used to clean a fireplace firebox. Ideas and suggestions included:

• baking soda and vinegar;
• oven cleaner;
• commercially-made products just for this type of job, but warned that they contained harsh chemicals.

I will tell you that I did not try anything with harsh chemicals, because this is an old fireplace with crumbling mortar and I didn’t want to make it worse. I did try the baking soda and vinegar, and it didn’t really work at all. I also tried some all-purpose cleaners – Method spray and Krud Kutter – and neither worked to remove the soot, either inside the firebox or on the brick.

And I was surprised that the slurry didn’t really work on the painted brick. The Magic Eraser did the trick easily and cheaply (it only took one Magic Eraser!).

So, there you go – how to clean a fireplace firebox in five steps, with some bonus info, too!