DEAR TIM: Brick mortar and me don’t get along. At my house, the brick and mortar are falling apart. It’s happening on the walls and in a brick patio in my rear yard. I desperately need a brick mortar how-to course so I don’t end up with a huge mess. What are some of the important steps in brick mortar repair? Are there special tools that make the job go faster and look more professional? Steve T., Morris Chapel, TN
DEAR STEVE: Bricklaying mortar is a fantastic product when you stop and think about it. For all intents and purposes, it’s just a glue. You use it to stick two or more things together into one object. You may not believe it, but there’s an enormous amount of science that’s involved in mortar for brick. I can’t begin to scratch the surface in this column.
There are many different types of brick mortar, many with different strength properties. A standard mortar used with bricks in a wall often is a mixture of Portland cement, hydrated lime and some form of clean, washed sand. Note that the sand can have a significant impact on both the strength and final color of the weathered mortar joints. Not all sand looks the same, because the small rock particles that make up the sand are different colors.
Many old masonry buildings were made with a mortar that had abundant quantities of hydrated lime or just lime and sand. Typically the more lime that’s in a mortar, the weaker the mortar is. You may think you want a strong mortar, but the lime in the mortar offers a unique self-healing property that may be of great interest to you. If tiny cracks develop in a mortar joint, the hydrated lime can actually grow crystals that seal the crack.
In my opinion, one of the most important steps is to match the mortar to the job. You don’t use the same mortar for your brick walls as you would to patch the mortar joints in your brick patio. The patio mortar needs to be far stronger than the wall mortar as the patio is subjected to more wear and tear, and if you get freezing weather, the mortar must be able to withstand countless freeze-thaw cycles.
To make a strong mortar for your brick patio, you just use pure Portland cement, sand and water. I would make the mixture very rich meaning that there is lots of cement in the mix. Try a mixture of two parts sand to one part cement.
Be sure you have all loose mortar out of the joint, and that it’s dust free. Spritz the joint to be repaired with a little water and add the mortar. Make the mortar stand up a little higher than the brick. Wait until the mortar gets a little stiff and then scrape off the excess with a small pointed trowel. If the mortar smears onto the brick, you’re not waiting long enough.
To repair the mortar in your brick walls, look very carefully at the existing mortar joints. Pay attention to the small colored grains of sand that are visible. When mortar is first installed and it dries, it’s a uniform gray color. This happens because all of the sand is coated with the mortar-cement paste. But over time, Mother Nature erodes the mortar-cement paste from the sand exposing the different pieces of small rock that make up the sand. You may see brown, red, gray, white and even green pieces of sand!
The trick is to visit a local sand pit and look at the different sands. Note that there can be a difference in both grain size and color. You want to match both as closely as possible. This will be well worth the effort if you intend to restore your brick walls so the repairs match the original work.
You can purchase bags of premixed brick mortar from a business that sells building supplies. Avoid the home centers as they usually will not have a selection of different mortars. You want to match the color of the mortar as well as the strength. The older your home remember that you want a mortar that is weaker.
You don’t need too many special tools when working with brick mortar. I find that a medium pointed trowel, a small pointed trowel, a narrow pointing trowel that’s only as wide as the width of the mortar joint, and possibly a mortar grouting bag will commonly allow you to do most repairs. You may need a mortar chisel to help you remove crumbling mortar from between brick.
It’s really important to make sure the brick joints are clean, dust-free and damp before you add the new mortar. The water that you spritz on the brick and old mortar helps make your new mortar that much stronger. Without the spritz water, the dry brick and old mortar will suck out the water from the mortar too quickly. If this happens, the new mortar will never get as strong as it could be.
Take your time to avoid smearing the mortar on the brick face. If you do make mistakes, try to scrape off as much excess mortar as you can that day. Then wait 30 days before you attempt to clean the mortar paste from the brick. Use a solution of muriatic acid and water mixing one part acid to ten parts water. Dampen the brick to be cleaned with water and add the acid solution. Wear rubber gloves, goggles and old clothes. The acid is very toxic. Allow it to sit and fizzle on the mortar pastes, then scrub the area with a scrub brush after ten minutes. Rinse with plenty of water. Repeat if necessary until all mortar paste is removed from the brick.
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