chimney mortar repair

[eiremed]

first-time homeowner with cinder block chimneys that need minor repair to mortar. some of the mortar is cracked and needs repair. chimneys are for oil furnace exhaust and wood-burning stove.

what is the best materials to use for repair? chimneys are not painted. what is the best paint for this?

live in upstate NY with cold winters and moderate amount snow.

cheers,

craig

[LazyPup]

You really should have the chimney inspected by a mason who builds chimneys. While you can point the exterior of the bricks with common mortar mix, the chimney liner is a greater concern, especially if the chimney is used on a woodburning fireplace. Burning wood creates high levels of creosote and carbon in the flue gases that are extremely combustable. If the liner has serious cracks the creosote, flyash and soot (pure carbon) will collect in the gaps and potentialy become a serious fire hazard.

Flue gasees also contain Sulphur Dioxide (SO 2) and when sulphur dioxide combines with water (H2O), be it condensate vapor or rain water entering from the top, the sulphur dioxide and water combine to form Sulphuric Acid (H2SO4)which can rapidly deteriate the flue lining if it can collect in cracks.

In a severe case the resultant sulphuric acid washers down to the bottom section of the chimney, collects on the metal flue pipe and will corrode the pipe away causing flue gas (carbonMonoxide and Sulphur dioxide) leaks into the structure.

[HayZee518]

I was told by an oil burner tech that combined exhausts into a common flue was illegal. Wood burners and coal should be in a seperate flue from the oil burner flue.

[imeduc]

Thats for sure. Dont put them both in the same flue. Call code and check it out for there. You cant set the barometic damper on the oil burner with a wood stove in the same flue.

ED

My mistakes dont define me they inform me.

[eiremed]

thanks for the replies guys! just to clarify, i have two separate chimneys. one is for the oil furnace and is located in the middle of the roof. the other as it the south end of the roof and is for the wood-burning stove.

really appreciate the tip on fire hazard. i'll definitely get it inspected. but, the pointing you say i can do myself? do i just go to home depot and get a bucket of mortar and slap the stuff on? also, what about painting the outside of the chimney? is this a good idea for a cinder-block chimney?

craig

[LazyPup]

Eiremed,
This is one of those areas that I have had rather limited experience at,so I am sure someone will correct me if I am wrong. I begin by using a narrow chisel to clean as much of the loose mortar as I can out of the joint, but not so much as to cause the brick to come out. Mortar does not adhere well to a dry surface so I wet the bricks with a brush and plain water. I use a bricklayers brush but I am sure a 3 or 4 inch paint brush would work. I then use a pointing trowel or common brick trowel to hold the mortar even with the bottom of the joint and i work the mortar into the joint with a 1/2 inch x 6 inch margin trowel. I continue to work the mortar into the joint until it is flush with the brickface or perhaps a little bit further out. Finish with a bricklayers convex striking tool. You simply hold the tool in the joint line and draw it along the joint to finish the mortar leaving a nice concave finish. In the past I have seen bricklayers simply use a short lenght of 1/2 inch PVC tubing as a finish striking tool. Allow the joint to set up a few minutes then smooth the rough edges by lightly rubbing with a small piece of carpet. I use the dry ready mixed mortar mix and mix it in small batches as it is a very time consuming process and you dont want to mix more than what you anticipate you will use in 30 to 40 minutes.

[eiremed]

lazypup,

thanks! i'll let you know how it turns out. plan to give it a try this sunday/monday.

cheers,

craig

[HayZee518]

Painting the concrete block? Try a mortar based paint like "Thoroseal" I believe it will seal the porousity of the block.