Spalling brick is what happens when the face of a brick begins to crumble and fall away from the body of the brick. This eventually results in the softer portions of the brick being exposed to the elements and the eventual total destruction of the brick if not resolved.
In this post, I’ll teach you how to avoid spalling brick issues and how to repair spalling bricks on your property to avoid going through full scale brick replacement.
It may seem complicated but the repair and prevention of this is a doable DIY repair if you feel comfortable tackling it. Keep reading to find out how.
What Causes Spalling Brick?
Bricks may seem like a relatively bulletproof and maintenance free building element. After all, the big bad wolf couldn’t take that brick house down so it should be built to last, right?
Under the right conditions you shouldn’t have any issueS with your brickwork. It’s only very specific conditions, that are typically easy to resolve, that will cause spalling brick.
Cause #1 Improper Mortar
The number one cause of brick spalling is the use of the wrong mortar. This happens most often on historic buildings which have softer bricks than modern building. These softer bricks are incompatible with modern mortars which are much harder than the historic lime mortars. This article will tell you the difference between the two.
Brick and mortar must be carefully selected to be compatible. The bricks must be harder than the mortar that surrounds them. The mortar must also be more breathable than the bricks it surrounds.
Modern brick is perfectly suited to portland cement mortar which can have a psi strength of between 750 and 3000. Whereas historic clay bricks from before 1920 or so were designed for a lime mortar with a psi of between 70-250.
To avoid spalling brick you need to inspect for new mortar on old brick and where you find it remove it immediately. A quick test is if your house key can scratch the mortar and cause it to crumble out then it is likely lime mortar. If they key makes no marks then you likely have portland cement mortar.
As the wall expands and contracts with temperature swings the harder and less flexible portland cement mortar literally crushes the face of the brick until it falls off.
Cause #2 Moisture Issues
Brick and mortar walls are like a sponge. They constantly pull in and expel moisture. They are even transferring moisture from inside the building to the outside and vice versa. If the moisture drive is too strong or blocked with “brick sealers” then the moisture can literally push the face of the brick off.
This often shows itself early on in the form of efflorescence, which is a white or yellowish deposit on the face of the brick as the moisture moves through the brick and leaves mineral deposits on the brick as it evaporates.
Brick sealer only exacerbates the problem, trapping moisture just behind the face of the brick. Avoid them especially on historic bricks. A healthy option for protecting brick is a traditional whitewash which is a mixture of water and lime (not the fruit) that seals the surface but is breathable.
Moisture in the brick during a freeze thaw cycle can also cause issues when the moisture freezes in the brick face and expands so much that it breaks the brick apart.
How to Repair Spalling Brick
Spalling brick can be repaired if it hasn’t gotten so bad that there is very little brick left to repair. If you are missing most of the brick then it may be time to do a brick replacement like in the video below.
Before you repair any spalling bricks make sure you have resolved the moisture or mortar issue that is causing your problems or the spalling with continue. If you need help on repointing your brick work with a compatible lime mortar check out this post to walk you through the tools and steps for that process.
Once you have removed the cause of the spalling you can get down to repairing the damaged brick. I prefer a product called Lithomex to repair old brick. Lithomex Is a lime based product, so it is breathable like the other elements of a historic brick wall and can be worked while still in its flexible state, once it is set, or any time in between, making it user friendly for the artist, sculptors, plasterers, and stonemasons alike.
You can purchase Lithomex from Limeworks.us in a variety of colors to match almost any brick or stonework you need to patch or you can even get a custom color made by them for a perfect match.
Step 1 Clean Out Damage
Clean out any of the powder or loose pieces of the spalled brick using a chip brush and vacuum until you have a clean substrate.
Step 2 Mix Lithomex
Mix up your Lithomex thoroughly until you reach the right consistency. It’s best to start with small batches until you get the feel of it. Mix about 8 oz. water with 3 lbs of Lithomex to get the right consistency. It will cure faster in warm, dry weather so keep that mind as you work the product.
Step 3 Pre-wet the Wall
Pre-wetting the wall will prevent premature drying of the Lithomex. Using a hose sprayer on the mist setting is usually best and may take a few shots until the brick is saturated.
Avoid any pooling water on the surface. You want a damp brick surface but not fully saturated with pools of water. Wipe up any excess water if necessary.
Step 4 Apply Patch
Using a margin trowel or brick trowel, or any other trowel that will fit the area you are working on, apply the Lithomex into the old brick, pressing it back and packing it firmly to avoid any air pockets and ensure good contact on all sides.
Think of it like spackling a wall. You want to over fill the area and make sure every spot is filled. We can come back and tool the shape as needed to match the dimensions and texture as it cures.
The minimum depth of a patch is 3/16” and the maximum layer is 2” at a time. You can add multiple layers throughout the day in 2” thickness if necessary as the previous layer begins to cure. This will avoid sagging.
For patches deeper than 4” in total you may want to drill in dowels or rebar to secure the patch in place and increase its long term stability.
Step 5 Tool & Shape
As the patch cures and becomes firm to the pressure of a thumb you can begin tooling and shaping it to whatever shape and texture you need. Depending on the texture of your brick this may be easy or difficult and may require some unique tools.
I’ve used items like forks to striped bricks or chisels to add character marks to match old bricks. It’s just like sculpting in art class to match the surrounding brick.
The Lithomex can be sanded just like any epoxy wood filler to match rough surfaces or troweled smooth with a wet trowel for a slick surface.
Once your spalling brick is repaired make sure to protect the repair and the rest of the brick by avoiding improper mortar, excessive moisture, or self imposed damage by brick sealers.
Check your sprinklers to make sure they aren’t aimed directly at the house, install gutters to better manage the water issues around foundation brickwork, and consider a dehumidifier for muggy basements.
These are all simple solutions to help you keep your historic brickwork healthy and avoid the dreaded spalling brick.
Founder & Senior Editor
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.