Old brick buildings across the country have a tendency to get painted over the years by owners looking to “improve” their look. Whether its just a chimney or the whole building that’s been painted, a lot of us want to go back to that original brick look.
So how do you strip paint from century old brick? Well, the first thought a lot of folks have is sandblasting old brick. There are countless videos and well meaning bloggers who will tell you that sandblasting is the answer, but what they won’t show you is what happens after sandblasted brick is exposed to the elements for a few months.
In this post I’ll show you the dangers of sandblasting old brick and how that can take what would have been a relatively low maintenance brick building and turn it into a crumbling maintenance disaster.
How Old Bricks Were Made
In their simplest form brick are just clumps of clay mixed with varying degrees of shale and sand. Until the mid 1800s, most bricks were formed by hand and set out in a brick yard or in tunnels to dry for a couple weeks until they were ready for the kiln.
The kiln was often built using just these “green” bricks as the walls so as to act as their own kiln. The bricks were cooked at a lower initial temperature slowly to remove any remaining water and then once they were dry enough, the fires were stoked to bring the temps up to around 1800°F before letting them slowly cool down.
Once the bricks had cooled enough, the kiln was disassembled and the bricks were sorted. If only raw bricks were used to build the kiln, the bricks from the outermost walls were kept to be burned again in the next kiln. Some bricks that were closest to the fire received a glaze from the sand that fell into the fires and became vaporized and deposited on the bricks. These less attractive bricks were used in the interior courses of the walls. Bricks that became severely over-burned and cracked or warped were called clinkers and were used less for structural purposes and more for decorative uses like gardens.
This early process of making bricks resulted in much softer and less consistent bricks than what we have today. Today, the bricks are fired evenly and under controlled high temperatures where every brick gets the same amount of heat resulting in much harder bricks.
What Sandblasting Does to Old Brick
Imagine that bricks (especially old bricks) are a loaf of bread, after all they were baked much the same way! Just like how a loaf of bread develops a crust as it is baked in the oven, bricks also develop a protective skin on them from the firing process. That skin keeps them protected from the elements and just like bread, without a crust, they won’t last long without it.
Sandblasting old brick removes paint, yes, but it also removes the outer skin, leaving the brick exposed to the elements and susceptible to an early death. Here are some of the biggest problems sandblasting old brick causes.
Spalling occurs when the brick slowly self-destructs, turning into a powder and falling apart. Spalling can also occur from repointing with a mortar that is too hard which causes the face of the brick to break off exposing the softer interior. Sandblasting causes this en masse as ALL the sandblasted brick is now exposed and weakened. I’ve seen whole walls turned to powder within months of sandblasting depending on the climate.
It’s a big word and it’s as frightening to spell as it is to see. This is not a direct cause of sandblasting, but still an issue because it seems that a lot of people like to sandblast old brick and then apply a sealer to the face to prevent spalling or other damage to the weakened brick. That’s where the problem starts.
Old brick and lime mortar are very breathable building materials that are constantly taking in and expelling water through both sides of the wall. If you seal up one side of the wall, then you prevent that natural breathability from happening.
Moisture builds up within the brick on the underside of the sealer and minerals are deposited just below the surface of the sealer. Eventually this build up can cause the exterior 1/4″ or more of the brick to be forced off the wall and fall to the ground.
Not only does it damage the structural integrity of the brick, but the appearance of sandblasted brick is destroyed too. Any decorative tuckpointing or tooled mortar joints are blasted away along with the face of the bricks, leaving a uniformly rough scarified surface that doesn’t have the same attractive appearance as the original.
An Alternative to Sandblasting
So, what are you to do if you need to remove paint from old brick? Usually the best solution is chemical paint stripping. Using a product like PeelAway1, I have had great success removing decades of old paint from brick.
You brush the paste onto the brick, cover it in a special paper that comes with it, and come back the next day to peel the paper (along with most of the paint) off the wall.
I’ve written an earlier post about some testing I did with this product. It was tested on wood in the post, but works much the same on brick and other masonry.
I’m hoping that by now I have convinced you to skip sandblasting as a method of paint removal. It works well for stripping some metals and concrete, but other than that it usually creates more problems than it solves.
Protect that old brick and keep the sandblaster away.
Founder & Editor-in-Chief
I love old houses, working with my hands, and teaching others the excitment of doing it yourself! Everything is teachable if you only give it the chance.
43 thoughts on “The Dangers of Sandblasting Old Brick”
I have sand blasted the front of my property taking the glaze of the brick at the same time is there anything I can now do to protect the brick?
I have this same issue did you find a solution?
I have this same issue did you find a solution?
What is your take on dry ice blasting of bricks?
P.s. My proposed solution was to strip the brick with an abrasive grinder head (not metal) & coat with a breathable sealant. However, this will probably damage the surface of the brick. Any comments?
Alternatively, maybe it doesn’t need to be removed!
Your professional opinion would be appreciated.
I have a conundrum with an old house I’m restoring. I have insulated the house thoroughly with breathable materials in the walls in order to install an air source heat pump. To ensure good ventilation the walls need to be breathable. However, the exterior walls have been covered in some kind of thin render which I assume is not breathable. I therefore would like to remove it to restore the bare bricks to visibility. However, this thin render is difficult to remove and impervious to easy-peel! What would you do in this situation? 🙏🏼Thanks
I was disappointed by Peel Away. It did not remove all the paint, was expensive, laborious, and took the sheen off my slate porch and spotted some of the bricks on my walkway even though I hosed off the way per instructions after removing the chemical. If there is nothing near the brick you want the paint removed from, good. Otherwise, think twice, even if you cover everything. I will like re-paint the brick, much to my chagrin.
Any companies you would recommend in Orlando that will remove paint from an exterior brick chimney?
Have just come across your website – the front of my house is almost finished, ive had the paint removed and repointed. The paint removal method was sanding and now I’m worried it’s weakened the bricks and will cause long term damage?! Any advice or suggestions would be greatly appreciated.
I have a thin render coat 2mm mixed with aggregate bits of 3-4mm then painted.
After reading about sandblasting, would you reccomend “peelaway” , chemical paint stripping ? Thank you, Adrian
Freind of mine just cleaned and sealed a brick wall in a building dating back to the early 30’s. After sealing a white color has appeared on areas of the bricks mortar joints?? Do you have an idea why this has happened? Would you have a remedy for it as well? Thank you
Sounds like efflorescence caused by the sealing. Brick does not need to be sealed and it often leads to problems when it is.
We have a red/orange brick farmhouse 1897. The wooden porch post are original as well as the top rail around the porch. The corbels were removed before we bought it. Anyway, My question is, I would like to paint the wooden porch post and the whole-round wood trim around the windows. Would a dark slate blue look good as trim around the white windows, and possibly detail the porch post where they have some curvy details? I’m wondering if it will look quaint or trashy. The windows have a wood round arched above the windows.