When should I be worried about a crack

[old.mason]

I was doing some routine checks around my house and noticed a small crack running vertically on one of the bricks on the exterior wall. At first glance, it doesn't seem to be spreading rapidly, but it's definitely caught my eye.
This house is probably about 20 years old, and I've never had major issues with the brickwork. We've had some heavy rains recently, and I'm wondering if that could have contributed. I'm not sure if this is just normal settling or if it's a sign of something more serious with the foundation.
I've been thinking about whether I should patch it up myself with some mortar, or if it's worth getting a professional to take a look. How do you tell the difference between harmless surface cracks and structural concerns?

 

[BanditVarkas]

Don't overthink it. Mix a little mortar or use a sealant, patch the crack, and watch it. Costs you a couple bucks and a Saturday afternoon. If it keeps opening back up, that's when you spend money on a mason or foundation guy.

 

[TheStoneBuilder]

I was doing some routine checks around my house and noticed a small crack running vertically on one of the bricks on the exterior wall. At first glance, it doesn't seem to be spreading rapidly, but it's definitely caught my eye.
This house is probably about 20 years old, and I've never had major issues with the brickwork. We've had some heavy rains recently, and I'm wondering if that could have contributed. I'm not sure if this is just normal settling or if it's a sign of something more serious with the foundation.
I've been thinking about whether I should patch it up myself with some mortar, or if it's worth getting a professional to take a look. How do you tell the difference between harmless surface cracks and structural concerns?

Hey, good on you for checking and trying to catch things early! That's often just a cosmetic thermal stress crack, common for a 20-year-old house. The recent rain is just a reminder to seal it. So tell whether it's minor or a major concern is take a look at the pattern. Minor means it's on a single brick while major or structural means you see stair-step cracking in the mortar joints, a continuous crack across multiple bricks or anything wider than 1/8 inch.

I'd discourage you from using mortar and suggest to use a quality polyurethane caulk to seal the hairline crack and stop water intrusion. If it stays confined, you're done. If you notice it spreading or find more cracks in the mortar, stop work and call a structural engineer right away!