Chimney and Flue Inspection and Repair

In another article (here) we have discussed fireplaces 150 - 250 years old, long before the invention of flue tile liners. What does it take to make these great old fireplaces safe for use? Why not use them the way they are, as long as there can be a careful inspection of the flue?

First, Why not just use them as they are? In our 34 years of fireplace and chimney restoration we have seen many unsafe building practices from that era. We have seen bricks turned on their side in the chimney, in order to create a shelf for a floor joist on the outside of the chimney. After years go by and the floor joist has moved, it has actually kicked the brick right out, leaving the end of the joist exposed to the sparks of the flue. This unsafe method of fireplace building exposes the entire house to the good chance of being burned down by fire.

In our rebuilding of fireplaces and chimneys another dangerous building method that we have seen takes place inside the actual fireplace. Often, the thickness of fireproof material (stone or brick) is inadequate. In other words the distance from the inside of the firebox to combustible material behind is not enough. Again, over time the mortar between the stone or brick on the back wall of fireplace has failed , thus leaving gaps or openings where heat and sparks can escape. The old wooden studs which form the wall members are highly flammable especially around the fireplace where the heat has dried them out considerably. Certainly, a visual inspection alone would not be adequate for true measure of the integrity of the fireplace.

In some instances old chimneys and fireplaces are inspected by means of lowering video devices down from the top. Although this method is certainly more thorough than looking up with a flashlight from the floor of the fireplace it still leaves an uncertainty as far as future continued use. How so? Remember, we are still speaking about old chimneys which contain no flue tile liners. Say for instance that a video camera reveals no openings whatsoever down the chimney and therefore the report is made that the fireplace is safe for use. Who can be certain that even the next week or next month this flue will be in the same condition as it was when the video device was used. Cracks or openings can develop at any time. A brick tipped on it's side blocking the end of a joist, as mentioned above can kick out of his original spot at any time and leave this area exposed to danger.

Modern Chimney Liners

Being that an unlined flue is obviously risky and unsafe, let us talk about types of liners for chimneys that are being used these days.

First, some companies install metal pipes or metal sleeves down the flue. One problem connected with this is that the size of the flue is reduced in the process. The flue needs to remain one tenth the size of the fireplace opening. Suppose that the fireplace opening is 40" wide and 34" high, this would make the opening size 1,360". One tenth that size would be 136". Also suppose that the brick flue that we are wanting to install a liner in is 11" x 15 or 165". This chimney flue was certainly built with adequate dimensions for a good draft. (We will discuss fireplace building in other articles.) The largest metal sleeve or pipe that could be lowered down would be 10" round. This would only be approx. 78" or about one half the size needed for a proper draft! Also, we have taken chimneys down that have had metal liners installed that have actually had decayed portions, even stainless pipe. So, this method of lining a chimney is not the best and invites problems.

Another method of lining chimneys was introduced to us about 25 years ago. The company was looking for someone to use their product and be an installer. An inflatable sack would be lowered down a chimney. Once the sack was in place it would then be inflated . Following that, a wet mixture of special cement was poured around the sack. The optimum theory is that the wet cement would flow into all cracks and seal them and then also provide a cement liner that would harden and remain permanent. We asked the salesman if there were any guarantee that the cement would flow and not have any gaps left. In other words if the cement was suppose to be 1 ½" thick could they guarantee that it would all be a uniform thickness? We asked this because of the bends older chimneys are known for. Their answer? There could be no guarantee that it would all be the same thickness. So some might be 2" - 3" thick and some areas may be 1/4" thick. This sounded like a weak link in a chain and very uncertain on many levels. Also, the extreme pressure from the inflatable sack that would be exerted on bricks laid up with soft lime mortar may have the tendency to bow a wall of the chimney out. So this method also seemed fraught with problems.

What then is the right material to use inside a chimney for a liner? Well, clay flue tiles are made with fire and so are designed to withstand heat from a fireplace or woodstove. Flue tiles come in all sorts of sizes and can fit nearly any flue. Their thickness is consistent. And if properly installed, will outlast any other product currently on the market. However, there are right and wrong ways to install these. We will speak in greater detail about this when we outline ‘building a proper fireplace’ in another article.

At Luft Construction Co. Inc. we strive to seek out and utilize the best and safest methods for fireplace and chimney building and repair. We would like to invite any comments on this subject and will be happy to use our years of experience to answer any questions you may have. You can contact us by clicking here.