Four Causes of Chimney Crown Cracks

What is the Crown? 

I know I said that your chimney has a crown and to think of it like the king’s crown.

But actually, think of your chimney crown as a rain cap. Whereas your chimney cap covers the flue, the crown actually covers the entire top of the chimney.

The primary purpose of a chimney crown is to protect your chimney from deterioration from time or weather exposure.

When a chimney crown is properly built, you’ll have a slab of concrete or mortar about 2-3 inches thick, extending over the chimney about 2-3 inches.

This design helps direct the water away from your chimney and onto the roof without damaging the bricks and mortar of the chimney structure.

#1 – Natural Wear & Tear

Overtime, the waterproofing sealant on your crown will become less effective. Bricks and mortar are porous materials.

That means they absorb water fairly easily.

If the chimney crown is not retreated with sealant, water can seep into the concrete.

When the water freezes, it expands inside of the brick and mortar. As it expands, it chips away at the brick and mortar.

Then, with extra space from the cracks, more water is able to penetrate, freeze, and create larger cracks.

This creates pathways for moisture to seep into the masonry.

#2 – Improper Construction

We’ve seen a lot of newer homes, built within the last 5-10 years that have cracked chimney crowns.

The main issue from this is that the builder didn’t build the chimney crown properly.

That means that the builder didn’t put a steep enough slope on the crown to help push away the water.

Or the builder didn’t use the right materials.

Both of these options help contribute to quicker deterioration.

#3 – Shifting & Settling

Older chimneys that were built properly with the right materials can still have cracked chimneys.

After several years you could have some cracks, both inside and out of your house.

A general rule of thumb is that it takes about 2 years for your house to settle enough where cracks in the plaster inside are minimal.

It’s safe to assume that the same time frame and rule of thumb apply to the outside of your house, including your chimney’s crown.

After a few years, if you don’t have annual inspections (which you should), you ought to get on top of your roof (bring a step ladder up too) and take a look.

If you’re lucky, you won’t have to worry about any cracks!

#4 – Concrete Shrinkage

Many crowns are made of concrete. That’s what we use to build the crown. 

Some chimney companies use mortar. This is usually okay. But we opt for concrete because it’s stronger and able to withstand weather better. 

But the problem with concrete is that as the moisture content evaporates, it dries and ages. This can cause concrete shrinkage. 

Severe concrete shrinkage is known to cause the crown to crack. 

At Patriot Chimney, we implement a few tactics to help minimize shrinkage with our concrete including: 

• Limiting water quantity in our mixture
• Using additives to help decrease shrinkage
• Using adequate contraction joints and steel detailing. This not only helps to reduce shrinkage but also, just in case, helps with controlling potential cracks in the concrete. 

But we should always be aware that, despite all the steps taken, sometimes no one can fully eliminate the chances of concrete shrinkage.

What Can You Do to Prevent Cracking

Most of the time, there’s nothing you can do to totally prevent cracking. Mother nature is going to do as she pleases.

You can fight it as hard as you can and can help drastically minimize the effects of cracks in your chimney crown.

The best way to ensure your chimney crown is in good condition is to take a look at it. And you can’t do this from the ground.

The safest way to do this is to hire a chimney company to take a look with a level 1 inspection. This will allow the chimney technician to run a camera inside your flue to look for potential water intrusion.

And he or she will be able to look at the crown closely to make sure there are no premature signs of cracking.