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Chimney Q's & A's

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Building a cricket (or saddle) on a chimney

When building a cricket on a chimney, do the edges of the cricket go all the way to the edge of the chimney or are they set back from the edge to allow for flashing? If set back, how far?

The cricket may be built either way I run mine out to the edge of the chimney to ensure that when the flashing is added the water is run well away. You should remember to maintain your 1" clearance from combustible material for fire protection. The flashing will serve as the fire stop.

Masonry Chimney repairs

The chimney on my 30 year old house has crumbling mortar on the top 6 rows.  It appears to be stable from this point down.  What type of mortar can I use to repair this?  Are there any hints I can get? Can I just run up with a trowel, straight edge and some mortar?  Are the liner bricks likely to need remortaring?

What usually happens is the mortar will breakdown from where the chimney leaves the attic. This is caused by the temperature difference creating moisture and chemical breakdown from the burned fuel. I recommend taking the chimney down to the flashing and replacing it inside and out. You can use either a type S mortar (1 part portland 1/2 part lime 4 1/2 sand)or a type N ( 1 part portland 1 part lime 6 parts sand). You can buy this in bags by type and just add sand. Check the rest of the chimney for cracks inside and out but it will most likely be just the top and should be simple to replace.


Chimney chipping

My Chimney is being chipped away little by little in various spots, it seems as if the outside face of the red brick is just being shaved off by the elements of weather. How can I re-patch the faces of these bricks around the chimney, and with what? it almost looks as if birds are pecking at different bricks along the top and base of chimney.

Your right the brick are being broken down by the elements. The problems you are describing happen most often from water penetration. As far as patching the brick the only thing to do is replace them. Check the chimney cap for cracks and seal the new brick with a quality sealer and the problem should not come back.


Masonry block chimney

I would like to put up masonry block chimney with a clay liner. Any information on installation from footings to cap.

A check of local fire and building codes in your area should be your first stop. In most areas code requires that masonry chimneys have a minimum cross-sectional area of 50 square inches. Have a minimum clearance of 1 inch from any combustible material. This 1 inch air space must be filled at each penetration of floors or ceiling with a non-combustible material like fiberglass insulation or plaster.

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If your chimney is to be built outside of the house your footing also must be placed below the frost line in your area (normally where frost is a problem this is between 4 and 6 feet down). Your footing should be twice the width of the block you are laying and I recommend 12" thick. Measure 8" or one block from ground or floor level put in a cleanout door next determine what height to place your thimble (where your stove pipe enters the chimney)local codes vary on this also rule of thumb says 18" below ceiling to top of pipe.Once this is determined measure down from the ceiling 18" plus diameter of the stove pipe plus 12" this is where you start your flue liner. The best way to do this is to get some cement brick cut them so when laid they project into the chimney to the inside of the flue liner without leaving too much of a ledge inside. Laying the next chimney block will keep them in place and support the flue.

A second course of brick will offset the joints in the flues and block. Cutting the flue liner is complicated if a pre cut one is available take it. Fire clay for your flues should be an air set type because normal chimney temps won't be high enough to set heat set material. Your flashing should be in two parts one L shape under the shingles and up the sides of the chimney one out of the chimney and down to within 1/2 to 1" of the sub flashing or shingle. The chimney should terminate 2' above the highest point within 10' of the chimney(unless local code says different).There should not be more than 8" of flue exposed above the cap.

When pouring the cap wrap the flue with fiberglass to leave about 1/2" expansion (caulk later with fire proof caulking)and mix the concrete as dry as possible to prevent cracking.

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