The same history that makes a house charming can leave its exterior looking dull and neglected. Algae, mildew, mold and climbing plants like ivy, among other things, can leave their mark on classic masonry. Left untreated, bricks can become discolored, develop white spots and pull away from the mortar. Homeowners who want to improve the look of bricks on their old house should start by addressing any issues with the mortar (the paste that holds building blocks in place, like grout does for tile), which can corrode over time, then move on to the bricks' actual appearance.
Is It Safe to Clean Historic Brick?
First, identify what's causing the eyesore. If it's a build-up that's so embedded in the wall that cleaning it would damage the brick, as is the case with some mineral deposits, you may want to reconsider your options. Removing paint may cause similar problems. Keep in mind that centuries-old brick isn't nearly as strong as its modern, mass-produced equivalent.
If you're unsure what caused the brick's fading or dinginess, professionals like preservation architects and conservation scientists can offer analysis and advice on the best cleaning methods. Check with your local historic district commission or state's historic preservation office for more information.
Is Your Improvement Historically Accurate?
For historic houses, you may want to consider researching the evolution of its appearance. For example, if there's a layer of paint over the bricks that you'd rather not have, try to find out why it's there in the first place. Was it painted to cover imperfections or protect weak brick? (If so, you might be better off leaving it alone.) If the home was painted shortly after construction to match the style of the day, keeping that coat is the historically appropriate thing to do.
Fix the Mortar First
Before you can clean the walls, you should patch up any gaps in the mortar so water doesn't get behind or in between the bricks. This is most likely not a do-it-yourself project because removing too much of the mortar joint can cause structural damage.
A professional bricklayer starts by taking a sample of the interior mortar, which hasn't been exposed to nature's elements, and matches the new mortar to it. The new application may look brighter than the original at first but will eventually reach the same weathered color. Restoration contractors use the following techniques to restore mortar:
- Repointing, which involves methodically filing down the outside layer of mortar and filling in the joints with a layer of new mortar.
- Tuckpointing, which involves replacing the existing mortar with new mortar in two different contrasting colors to create the appearance of bricks that are very precisely and narrowly stacked.
Allow any mortar repairs to sit for at least a week before moving on to the next step of cleaning.
Start by rinsing the walls with a pressure washer on the lowest setting that's still effective at removing dirt. Experts recommend working from the bottom to the top to ensure soaking of surfaces.
Next, add a mild detergent that's suitable for cleaning brick homes—using the wrong kind can actually make the mortar dirtier—to the power washer and spray in a bottom-to-top motion again. Because bricks and mortar are porous, more detergent and less pressure is the most effective combo. Let the detergent soak into the brick and loosen dirt particles for about 10 minutes.
You can remove stains by scrubbing them with a nonmetallic brush or rotary brush attachment, which is gentler than using high-pressure water. Always do a trial run of your selected cleaning method on a small, hidden patch of the house and allow it to dry for at least 24 hours before tackling the rest of the exterior.
After the detergent has had ample time to do its job, switch the pressure washer to a delicate spray pattern; too much pressure will damage the brick. This time, work from top to bottom, being careful not to aim the water at one spot for very long. Use slow, consistent sweeping motions and spray in a circular pattern around problem areas.
Allow the brick to dry for at least 24 hours. Then, you can add a clear sealant to the brick and mortar, which acts as a barrier against water, oil, grease and other grime. This will help your home's improved appearance last longer. The sealant may need up to 72 hours to set and moisture can create spots in the surface. Be sure to cover walls with a plastic tarp if the forecast calls for rain.