Q&A / 

Brick Patio Mortar Repair

DEAR TIM: I have a lovely brick patio that has mortar between the brick. After pressure washing it this past weekend, I noticed several locations where the mortar has disintegrated. Most of the mortar is in excellent condition, but a few places need to be repaired. Some of the voids are 1 inch deep, while others only need perhaps one-eighth inch of mortar. How do I mix the new mortar, and what tools do I use so I don't make a mess of things? I have lots of free time, so what are the best weather conditions to work in so the repairs last a long time? Holleay P., Kitty Hawk, NC

DEAR HOLLEAY: Brick patio designs are as plentiful as blossoms in spring, but a traditional brick patio that has been mortared in place is one of my personal favorites. These patios are like a brick wall that is lying flat on the ground, and the mortar becomes an interesting design element because of its texture and color. I have two brick patios just like yours, and they get compliments each time a friend or neighbor sees them for the first time.

These deep joints can be filled with new mortar using the special grout-bag tool. Once the mortar is stiff, scrape off excess with the small trowel. PHOTO CREDIT: Tim Carter

These deep joints can be filled with new mortar using the special grout-bag tool. Once the mortar is stiff, scrape off excess with the small trowel. PHOTO CREDIT: Tim Carter

When I am building a brick patio like the one you and I have, I use a special mortar that will withstand years of Mother Nature's abuse. It sounds like your builder did the same thing, but the mortar in a few locations was defective. That has happened to me in a few spots on my own patio. I traced the defects to excessive water from a rainstorm that happened soon after one section of the new brick was grouted.

I suggest you repair the defective joints in your patio with the same type of mortar mix I used when I installed my patio. It is extremely durable, and will last for 40 - 50 years, if you cure the joints once they are installed. Your biggest challenge is going to be matching the color and texture of the existing mortar. You did the right thing by thoroughly cleaning the brick and mortar first. All too often, people try to match mortar colors and fail to clean the surrounding mortar first. Mortar on walls, and especially on flat patios, can get very dirty.

The first thing you need to do is look very closely at your existing mortar joints. Look at the color of the sand. Believe it or not, not all sand looks the same. Sand is simply a collection of very small rock particles, and the color of individual sand particles can be vastly different if the particles come from a variety of black, red, white and gray rocks. Visit different building supply businesses and/or sand and gravel pits, and try to find sand that matches both in color and particle size.

Once you have the correct sand, mix it one part of it to one part of pure Portland cement. This will make a very rich mixture that will be exceedingly strong. You need this strength, even though you do not get too many extremely cold days. The extra cement also helps make the mortar flow easily from the tip of the special grout bag you will use to fill the defective mortar joints. Mortar grout bags are just like icing bags used by professional cake decorators. They are larger than an icing bag, and have a metal cone tip that has a one-half-inch hole at the end.

I prefer to work on cloudy days when the temperature is in the 50 - 65 F range. Do not work on a hot, sunny windy day. The mortar will dry too rapidly, especially where you are filling slight depressions in the existing mortar joints.

Once you have the mortar mixed, lightly spritz the mortar joints you are going to fill. Do not get them too wet, just slightly damp. Fill the grout bag half way with the mortar mix, and apply slight pressure to make the mortar mix flow just as toothpaste oozes from its tube. If you can't get the mortar to flow, you need to add more cement and/or slightly more water. The mortar mix needs to be fairly wet so that it doesn't clog the grout bag tip.

Check out the different colored pieces of sand. Each grain is a small piece of solid rock. The sand for the repair job should match the existing sand as close as possible in grain size, shape and color. PHOTO CREDIT: Tim Carter

Check out the different colored pieces of sand. Each grain is a small piece of solid rock. The sand for the repair job should match the existing sand as close as possible in grain size, shape and color. PHOTO CREDIT: Tim Carter

Carefully guide the grout bag tip so that you apply new mortar only to the joint. Move the bag along and make sure you apply mortar so it rises above the level of the brick by about one-quarter inch. The fresh mortar needs to touch the top edges of all the brick. Let it set until you see it change from wet and glossy to a flat gray color. Use a small triangular trowel to gently scrape off the excess mortar so the top of the mortar is flush with the brick. Keep the fresh mortar damp for three days so it cures well.

If you scrape the excess mortar too soon, it will smear onto the brick. You do not want this to happen, especially if the brick has a rough texture or grooves created by the wire-cutting process as the brick is manufactured. If mortar gets in these grooves, it is a nightmare to remove.

You also have to be careful about waiting too long to scrape off the excess mortar. If the mortar gets too hard, you run the risk of breaking the bond between the new and old mortar. If this happens, your new mortar may fail in a few years.

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2 Responses to Brick Patio Mortar Repair

  1. Tim , is there a sand mix that hardens over time after being brushed into the joints between bricks? If so this might prove to be a solution to this problem.

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