Understanding the Throat

I receive lots of calls for Massachusetts Chimney Repairs. When a chimney has suffered extensive damage such as pulling away from the house, cracking on the lower portion brick work or horizontal mortar joints that appear to have been a result of some sort of heaving of the masonry, the majority of the time it is caused by an improperly build throat system.

The following photos are of a throat system that was not built properly. The throat spans over the damper of the firebox and needs to support all of the flue tiles that are inside of the chimney. This throat was not able to protect the masonry from the expansion of the masonry from the heat of a fire in the fireplace.


The method use to build this throat did not allow for protection on the back wall of the chimney, nor did it support the flue. Furthermore it used metal to hold the masonry, which in this situation is a horrible idea.


The slanted portion of the throat was held in place by more of the metal pipes, in place, on the 4″ exterior side wall. Built like this it offered no bearing on masonry and it did not offer the required 8″ of masonry protection either. This is a serious design flaw only done for the speed in construction.

To build a throat system like this; unsupported and no inner walls to protect the brick shell, the chimney suffered structural cracking, and pulling away from the house at the top.

To remedy this a fully supported throat system needed to be built. It is not enough to simply remove the damaged portion of the chimney. It needed the inner guts rebuilt.

It is important to always use a professional chimney builder to do major work on your chimney. Extensive chimney repairs might be out of range of your local chimney sweeping company.

As you can this this throat is design to be supported on the left, right, back and front. It will be carried by masonry and no metal is used where it can expand and damage the chimney.

Top down view.

To complete the throat pieces of flue slabs are used. The taper is reinforced by building on top of it with solid masonry. This method protects the pieces from cracking and absorbs the heat into the masonry mass around it.

Inside view

Inside a throat should be fairly smooth.

Thank for reading my blog on masonry.

If you are looking for a Massachusetts Chimney & Fireplace contractor then please call 978-365-6800 or complete our online request form.


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