Spalling is the deterioration of the brick, spalling is when portions of the bricks are falling off the chimney structure. Most spalling is caused from water/moister intrusion into the capillary pours of the masonry materials.
If your chimney has a old flue liner, chances are the seals between the tiles are structurally compromised. A terra-cotta flue liner has a joint seam every two feet as the line rises up the chimney structure. With cracks or gapes in the joints between the flue tiles the venting system is compromised, with out a proper seal the combustion byproducts traveling through the tiles have multiple seepage points. As this vapor seeps out of the tiles it continues its journey up the inside of the cavity, once resting in the top area of the chimney is starts the seeping or freezing process depending on the season seen in the photo fallowing this one.
One theory is in the frost in the picture shown here. It starts with moisture in the brick and or moisture getting trapped in the chimney chase. As the moisture slowly tries to escape from the brick as it reaches frozen elements, the molecules of water trapped in the brick freeze, they expand and that results in many fracture points threw-out the brick. Over time they deteriorate more and more through the seasons, the loose pieces will starts to break off and fall away from the chimney structure, you will start noticing pieces in the gutter some on the roof.
When water penetrates the chimney from common entry point such as a crack or chipping to the chimney crown. Once this water has pooled in the core area of the bricks it drains from brick course to brick course, at some point the water will start the seeping process. During the colder seasons its not uncommon for snow to melt during the day and freeze at night. During this freezing process the moister trapped in the brick from the seeping moister will expand and cause damage to the masonry materials.
Grind Out Damaged Area: After locating the damaged areas and marking bricks to be fixed, we use a 5" diamond blade grinder to grind roughly half way through the bricks to their core area."As seen in photo" By getting in so deep, it ensures the bonding agent gets a strong bite into the core of the brick structure.
High PSI Air Blower: This is the second step in our Spalling Brick Refurbishment process. As you can imagine after cutting through mortar with a diamond blade grinder, it leaves a drastic amount of fluffy textured mortar dust. After this process roughly 70% of the dust debris is removed, theirs still a good amount of dust clinging to the open pours created by the diamond blade. So we move on to our next step in the prepping process.
Water Treatment : This final step in the prepping process is key, for the fact that neither a brush nor high PSI air will completely remove all leftover dust molecules from the grinding process. This step is commonly missed with many masons. Our outlook on this is every step matters for proper adhesion. When water pressure is applied it completely clears the surface area of the brick joints, by opening up all the surface pours to ensure proper adhesion. A great analogy of skipping this step is like sticking a piece of tape on a dusty floor before using it.
Brick Face Cutting: After selecting a good match to the bricks in question: by comparing color,tint,width,length and texture, we mark the brick out for face cutting. Brick face cutting is the process of cutting 3/4" sliver off of a full-size brick. After the brick is cut it undergoes basically the same process as step 2 and 3 to ensure the opening of pours for adhesion.
Polymer Modified Mortar: In this step we apply Quikrete Polymer Modified Stone Mortar generously to the back of the brick, this mortar is designed for veneer and real stone application. This mortar contains ASTM C 270 approved cementitious materials properly graded masonry sand, dry polymer resin. Polymer Modified Veneer Stone Mortar has excellent adhesion characteristics which allows it to be used on both horizontal and vertical applications.
Application Of Face Cut Brick: After applying the polymer modified mortar to the back side of the brick, slowly install it into the empty cavity we have created from the grinding process. By moving the brick slowly back and fourth it will become still as it begins the suction process. Once the brick has set up its time to move to tuck pointing around the affected area with grout bag, then strike the mortar joints with a tuck point tool. Last step after proper dry stage, brush over area with mason brush.