What’s the best way to remove soot stains from painted white brick?

Q: We painted our brick fireplace white. But after some use, smoke has stained the brick. What’s the best way to clean it?

A: Soot is mostly carbon particles, but it often has a greasy nature that makes it difficult to remove. If you search online, you’ll find numerous solutions, including vinegar, dish soap, TSP (trisodium phosphate), Scrubbing Bubbles, and the Smoke Soot Eraser Sponge and similar products.

Before deciding how to clean, make sure you understand the risks and limits of each solution. It’s also worth testing a small area first because soot varies: Sometimes it’s a dry powder; sometimes it’s clingy and greasy, which usually happens when the soot starts from burning candles. Cleaning a fireplace surround poses the additional challenge of getting into all the little divots in the bricks and mortar. But because your fireplace is painted, the surface is smoother, which gives you an advantage.

Start with what you probably already have on hand. Try sponging off a brick or two with warm, soapy water. If that doesn’t work, add a splash of vinegar, but be aware that vinegar left on too long or in too high a concentration can make glossy paint look dull. So test on a small area and stop if it isn’t working. If it does work, an old toothbrush can help you get into crevices. Dip the wet toothbrush into baking soda to boost its scrub power, but be aware that baking soda, too, can dull paint. Follow up promptly by wiping the brick several times with a sponge rinsed with clean water. Wait for the test area to dry, then evaluate how it looks. If you’re satisfied, clean the whole fireplace surround, including bricks that aren’t stained with soot, to help ensure an even sheen.

If you need a cleaner with more muscle, one option is TSP, which stands for trisodium phosphate. It used to be a common ingredient in dishwasher detergents and laundry soaps because it effectively removes greasy deposits. But the high phosphate content led to algae blooms that depleted the oxygen in lakes, rivers and other waterways, so many states banned it as an ingredient in cleaners marketed to consumers. It’s still sold online, though, and in home centers and hardware stores in many areas. It’s frequently used to prepare surfaces before painting, especially if the paint is so glossy that new paint would have a tough time gripping.

That ability to de-gloss slick paint is one reason it’s not a great solution for removing soot from a fireplace with painted brick - unless you plan to repaint. Sure, you’ll probably get the soot off, but the paint will look dull. Also, if you have wood floors, drips can leave permanent dots of dullness. TSP dissolved in enough water to make it just 1 percent of the ingredients has a pH of 12 - very alkaline.

Scrubbing Bubbles, a brand of S.C. Johnson & Son, has a variety of spray-on cleaners. Some, like Scrubbing Bubbles Bathroom Grime Fighter, are alkaline; it has a pH of 12, the same as TSP. Others are acidic: Scrubbing Bubbles Multi Surface Bathroom Cleaner has a pH of 2.4, slightly more acidic than the 5 percent distilled white vinegar mixed with water that’s sold in grocery stores. But whatever the formula, Scrubbing Bubbles cleaners aren’t recommended for use on painted surfaces, said a woman who answers customer service calls for S.C. Johnson & Son.

That leaves soot erasers. ServiceMaster Restore, a branch of the ServiceMaster company with franchises across the country, lists sponge erasers first among the methods it uses to remove soot from walls, which are typically painted, just as your fireplace is.

These erasers go by different names, including soot removers, dry-cleaning sponges and chemical sponges. Absorene makes its soot-removing sponge from natural rubber that’s been treated to make it more elastic and durable. Ace Hardware’s Medium-Duty Dry Cleaning Sponge is made from cellular latex foam.

Both generally get good online reviews, although one person who bought the Ace version reported that it didn’t remove soot in areas where the person had first tried vinegar and Magic Eraser (a different type of cleaning sponge, made of melamine foam). So be forewarned - you might want to try a soot eraser first.

Melamine erasers clean by scraping off some of the surface, so they can affect paint. The rubber type actually absorbs the soot, said a woman who answers calls to Absorene. To get into divots in the brick, she suggested cutting little wedges from the eraser.

Customer reviews note that you might go through several sponges if you are tackling a large area, because each face of the sponge is useless once it is full of soot. But a tip sheet from Absorene says that a soot sponge that looks dirty can still work, and it offers two ways to extend the life of the sponge, which can also be used to remove dust from surfaces like wallpaper and lampshades and to pick up pet hairs. First, it says, “Sponge may look dirty, but particles are working their way into the unique cell structure. You may remove a layer of the sponge with a razor blade knife to expose a new surface if you wish.” The company says it’s also possible to wash a dirt-encrusted sponge in warm, soapy water as long as you don’t reuse it until it has air-dried completely, away from direct sun and air vents. But the company says customers usually do this only when they’ve tackled dirt and dust, not soot.