Q: I was on a tour of the Gamble House in Pasadena, Calif., and saw the most unusual deformed brick in a garden wall. The brick was twisted and looked more like random rocks than brick. I want some for my own house! How are these bricks formed, and where can I buy them? Are they durable, and will they last a long time? — Cindy H., Tucson

A: These bricks are called clinkers, and I saw them too when I toured the stunning Gamble House about 10 years ago. I don’t know if it was the architect or the clients who specified the use of this unique building material, but it was genius. If you ever have the chance to tour this mansion, be sure to wander through the outdoor gardens to see the walls built with this strange brick.

Clinker bricks are made just like any other bricks. They start out as clay and are put into a kiln, where the temperature of the clay is raised significantly. It’s important to realize that not all clay has the same chemical composition. As the temperature rises in the kiln, the clay softens and melts. This changes the internal structure of the clay such that it comes out of the kiln more like a rock than a soft material you can form with your hands.

Some bricks in the kiln melt and deform. These become clinker bricks. Keep in mind that the odd colors you sometimes see in bricks, and especially clinkers, result from the small amount of oxygen in the kiln as the bricks are heated.

The absence of oxygen almost always produces darker colors such as black and even blue. You can create all sorts of colors depending on when you reintroduce oxygen as the bricks start to cool. It’s all very complex, but the key point is that clinkers can be the most colorful and unusual brick you’ve ever seen.

Clinker bricks, depending on the minerals in the clay, can be extremely durable. There are many factors, but realize that some clinkers transform to a material much like glass if the clay happens to have a high silica content. The odds are clinker bricks will perform quite well in just about all outdoor applications, including garden walls and outdoor pillars.

You purchase clinker bricks at businesses that sell brick. Not all brick suppliers stock them, but you should have great luck ordering them, as the brick manufacturers would rather sell clinkers than throw them away.

No matter where you use clinker bricks, I recommend you spend time thinking about the mortar that will be used between each brick. I recommend creating a mortar blend that contains three parts Portland cement and one part hydrated lime. If you can source a special volcanic sand that’s high in silica, that would be ideal. Otherwise, use medium or loamy sand that’s very clean.

Q: Tim, my husband and I can’t agree on the best way to repair some cracks in our concrete. We have some long random cracks about one-sixteenth of an inch wide in our garage and basement floors. This concrete has a smooth finish. My husband wants to squirt caulk into the cracks. I feel this will look like a scar on someone’s face. How would you repair these so they look good and the repair is durable? — Monica M., Waterloo, Iowa

A: Concrete crack repair is a very common problem. I receive questions like this each week.

The first thing to realize is any repair you attempt may be temporary if the concrete is still moving or moves seasonally. I live in central New Hampshire, and each winter the ground freezes. The frost in the ground causes concrete sidewalks, driveways and patios to lift. If the lift is uneven, the cracks will reopen.

Interior concrete slabs such as those you find in a garage and basement are the easiest to repair, and the concrete rarely moves. It’s important to realize if the concrete is brand new, you’ll get shrinkage cracks as the concrete loses the extra water that was used when it was mixed. This shrinkage can take up to a year, so don’t try to fix a new crack, as it will most likely continue to widen as the months pass.

Interior crack repair on smooth slabs can be done using regular unsanded ceramic tile grout. This works best for cracks one-eighth of an inch or narrower. Unsanded grout can be bought in different shades of gray to match your existing concrete color. Match the grout color by pouring a little bit of the dry powdered grout on the concrete. The grout gets much darker once you add water, but it will dry the color it is straight from the bag.

I have four videos at my askthebuilder.com website that show the process of grouting floor tile. These videos show you how to achieve a perfect match when patching a crack in concrete. I recommend you watch them. The biggest mistake you can make is using the wrong tools to make the repair and pressing too hard when you wipe away the excess grout.

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