Re­pair cracks and main­tain your chim­ney

The Palm Beach Post - Residences - - News -

Ques­tion: My wood-burn­ing fire­place has cracks in the brick and mor­tar out­doors. Is this some­thing that needs im­me­di­ate at­ten­tion?

An­swer: Gen­er­ally some mi­nor cracks in a chim­ney mor­tar be­tween bricks are com­mon, but the long cracks you de­scribed might in­di­cate a se­ri­ous prob­lem. The fact that the cracks con­tinue through the mor­tar and the bricks is what you should be con­cerned about.

It would be wise to have your chim­ney pro­fes­sion­ally in­spected. Your first step might be to call a chim­ney sweep to have the chim­ney cleaned. Al­though they are not struc­tural en­gi­neers, an ex­pe­ri­enced chim­ney sweep has seen most of the prob­lems that can oc­cur with a chim­ney. He/she may rec­om­mend you con­tact a li­censed struc­tural en­gi­neer to eval­u­ate it.

Bricks and mor­tar cre­ate an ex­tremely strong struct ure be­cause t hey have tremen­dous com­pres­sive strength of thou­sands of pounds per square inch. To the con­trary, they are rel­a­tively weak when they are stretched in ten­sion. If the chim­ney be­gins to tilt at all from be­ing un­evenly sup­ported, this puts some of the bricks and mor­tar into the weaker state of ten­sion in­stead of com­pres­sion as it was de­signed to be.

There are sev­eral pos­si­ble causes of the chim­ney crack­ing prob­lems you are ex­pe­ri­enc­ing. A chim­ney, due to its ex­treme weight, should have a large con­crete footer be­neath it to sup­port it. Code usu­ally re­quires a chim­ney footer to be at least one foot thick and ex­tend out a foot or more fur­ther out than the chim­ney. Check your build­ing plans for the size of the footer.

The footer should have been re­in­forced with steel rods (called re­bar) when it was poured. Even if it is large enough, if the con­crete was not ad­e­quately re­in­forced or there was a prob­lem with the strength of the con­crete mix­ture, the footer may be dis­in­te­grat­ing from the weight of the chim­ney.

Set­tling of the ground be­neath the chim­ney footer is an­other pos­si­bil­ity. If your house was built on fill, then the footer, even though it was prop­erly sized, may be rock­ing or sink­ing deeper. If it moves, even a small amount, the stresses in the heavy chim- ney can be tremen­dous.

An­other less likely pos­si­bil­ity is faulty bricks. If sev­eral weak bricks were placed on top of one an­other, un­usual stresses could have caused them to break. Once sev­eral of them break, it may cre­ate ad­di­tional stresses on the other bricks. The struc­tural en­gi­neer will be able to test this for you.

Whether you are able to re­pair the chim­ney or you have to to­tally re­build it, con­sider in­stalling a chim­ney cap and a metal flue liner. The cap will keep de­bris, rain and an­i­mals from get­ting into the top of the chim­ney. The liner will min­i­mize the pos­si­bil­ity of fu­ture chim­ney fires from cre­osote buildup. The liner will also make it eas­ier for a chim­ney sweep to keep it clean.

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