Brick patios do best on concrete slabs
Q: We bought a house that requires an immediate patio repair. The brick patio in the backyard is warped and looks like a wave ran under it. We want to replace it but don't want it to end up like this again. We live in a mountain town that has freezing ground temperatures for a good portion of the winter and think this has been a contributor. Can you advise how to construct a lasting flat brick patio in our environment? — Evana S., Steamboat Springs, Colorado
A: Based on the photo you sent, your patio is useless. It's so bumpy you won't be able to put a table or chairs on it. The good news is the high-quality paving brick can be salvaged and reused when you rebuild the patio.
In my opinion, the best way to start the job is to install a 5-inch-thick poured concrete slab with half-inch steel reinforcing bars.
Set up the steel so it looks like an empty sheet of graph paper before the concrete is poured. The rods should be set 2 feet apart from their parallel neighbors, and be sure the rods end up in the middle of the slab. You need at least 2 inches of concrete under each bar.
The soil under the concrete should be compacted well before you pour the concrete.
Screed the top of the concrete so it's smooth, and be sure the concrete pitches away from your home at least ⅛ inch per foot for good drainage.
I use thin paving bricks that are 1.5 inches thick, but you can use full-sized brick if that is what you have. You can install the brick directly on the poured concrete if you like, but you'll get the best results if you mortar them to the fresh concrete.
Your existing patio has the bricks touching one another with no mortar joint. Dirt and debris can get in the cracks, and weeds will grow in short order. Setting the brick in mortar with a mortar joint between makes it nearly impossible for weeds to gain a foothold.
Make a strong mortar mix to resist freezing weather. I recommend a 1:1 mixture of Portland cement to fine sand. You may need to add additional cement to make the mixture flow with ease from the mortar bag. (You use a mortar bag to install the mortar mix between each brick to avoid smearing the face of the brick.)
I first used the above method in the late 1970s to rebuild my failed first attempt at a front sidewalk. You can drive by the house today in Cincinnati. It's the first house on the north side of Robison Road, just east of Montgomery Road.
It's 40 years later, and the walkway looks exactly like it did the day I finished rebuilding it. The same is true for all the other patios I built for my wife. You'll never regret installing your brick on top of a rigid concrete slab.