Maintenance: Tuckpointing A Brick Chimney

By Bruce W. Maki, Editor

	This chimney was ready to disintegrate. All of the bricks in the top 5 rows were loose.
	Much of the mortar was gone.

	Large pieces of mortar were loose.
	Some bricks had split completely.

I suppose that most masons would simply rebuild this chimney from the roofline up, but the homeowner needed a quick and simple fix to last a year or two. The chimney is no longer used for a furnace, and has a wood burning fireplace connected to it.

I am not an expert in masonry, but I do have enough knowledge to be dangerous. I cannot recommend that you follow the methods used here. Consider this article to be for entertainment value only.

I used a screwdriver to remove some of the loose crumbs of mortar.

	The materials, from left to right: Type N masonry cement, a bucket of sand, a small 1 pint pail for measuring, and a mortar mixing tub.
	I dumped some sand in the mixing tub.

	I estimated that 12 pints of sand would be enough.
	I added masonry cement to the sand, 6 pints. A 2:1 ratio of sand to cement has always worked for me.

	I used a hoe to mix the dry powdered ingredients.
	Then I added water and mixed until the mortar was the right consistency.

	The mortar was still too dry. I can tell by the lumpy appearance.
	The mortar slid off the trowel when tipped sideways.

One indicator of proper mortar consistency is it's ability to stick to the trowel. Some general rules that I am aware of:

• The mortar must stick to the trowel when the trowel is held upside down.
• The mortar should, ideally, stick to the trowel when it is held sideways.
• When held sideways and given a little flinging motion, the mortar should slide off the trowel.

	I dumped the mortar into a plastic pail
	Up on the roof, I laid out the tools and materials near the work area.

I trimmed the small end of the pastry bag to enlarge the opening, making it about 3/8" in diameter.

	I sprayed water on a small area, about 1 foot square.
	I loaded the pastry bag with a little mortar.

The Fun Part:

	I was completely inexperienced at this. I had never even used a pastry bag for applying cake icing. I simply stuck the nozzle in a hole and squeezed.
	I stuck the nozzle in deep and withdrew it as I squeezed out the mortar.

I found that it helped if I occasionally gave the bag a downward jerk, to make the mortar settle into the bottom. I also had to temper (add a little water to) the mortar in the plastic pail, to keep it creamy enough to flow out of the pastry bag.

The tuckpointing took about an hour. I had to re-wet the brick often. The dampness of the masonry is critical. It needs to be almost saturated on the surface, but not shiny-wet. If the surface is too dry, you'll know it, because the mortar will not stick.

Also, if the masonry is too dry, it will absorb water from the mortar, causing it too bond poorly, fall off, or develop tiny cracks from excess shrinkage.

When the mortar joints were all filled, I used my finger to press in the joints and smooth out the mortar. This is called "tooling the joints".

There are many different ways to tool the joints. Some techniques use a little rake-like device to scrape excess mortar out and leave a uniform depth recess. This homeowner only wanted the chimney to stay together for another year, so I did the simplest thing, a flush, finger-tooled joint.

Tooling the joints causes the mortar to compress and be bonded better to the masonry. I kept wetting my finger to help this bonding process.

There is an inexpensive spoon-like device for tooling masonry joints, but I didn't have it with me.

	A few minutes of joint tooling and I was done.
	After the mortar had dried for an hour, I came back. Using a small whisk broom with a pail of water, I carefully cleaned the excess mortar from the faces of the brick.

Then I used a garden hose to clean all the spilled mortar from the roof.  Mortar comes off easily with water and a little scrubbing, for an hour or two after being mixed.

I think the best way to deal with old crumbling masonry chimneys is to simply destroy them. Demolishing a chimney like this takes a couple of hours with a small sledge hammer. There are many metal chimney flue products on the market that will perform better and longer than masonry.

Suggested Reading:

The Homeowner's Guide To Building With Concrete, Brick & Stone

Author: The Portland Cement Association

Publisher: Rodale Press, 1988

ISBN 0-87857-795-5  Hardcover

ISBN 0-87857-795-3  Paperback

Copyright © 1999, 2005 HammerZone.com

Written December 28, 1999
Revised January 12, 2005