# How to properly (effectively) flash a field stone chimney?



## aribert (Apr 7, 2012)

So how does one flash against an irregular surface such as a field stone chimney?

I ask this question because I was not overly successful in flashing one side of the chimney 24 years ago. THe fireplace /chimney projects outside of the house but has soffits on both sides of the chimney. When I did the previous tear-off and reroof I built a cricket and built up the mortar between the stones so that I had a flat surface for the step flashing and a way to secure the down-standing leg of the cap that covered the step flashing. On the sides of the chimney, I did not want to see so much mortar protruding past the stones so I copied what was done previously - **short** step flashing (contour cut) up to the underside of the stones with an application of roofing cement to cover the upper edge of the step flashing (no cap over the step flashing). Both rafter tails adjacent (technically inside of the chimney) were water damaged 24 yrs ago. On one side the repaired rafter tail looks as good as when I did the repair in '94. The other side the rafter tail has rotted an additional 8 or so inches closer to the outside wall.

I am guessing that water leakage from ice damming caused the rafter tail decay - no visible damage inside the house. Many nails low on the roof in this region were very rusted, some with heads that disintegrated while tearing off the shingles and I saw a few nails that were rusted thru the shank about 3/16 below the "head".


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## Nealtw (Jun 22, 2017)

Something like this.


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## aribert (Apr 7, 2012)

Nealtw: Thanks for the link. 

My field stone chimney is a bit "lumpier" than the chimney in the link. Back in '94 when I replaced the roof, I built up the backside with mortar and was able to snake in a counter flashing without trying to modify any of the field stones. The downside to what I did was that the upstanding flashing leg was only about 2 inches tall and I was not able to do the same on either side. I am thinking of raising the counter flashing up to about where the dotted line is - this would require both mortar build up and a bit of a groove in several of the stones. I plan to try creating a groove on the backside tomorrow. I used an air chisel to carve clearance on a stone on the front side for the face-board(I shortened the rafter tails 2.5 inches).






. I hope that with an air chisel, diamond blade in a 4.5 inch grinder and an abrasive blade in a 7 inch grinder that I can get a slot thru the stones that are in the way - I do not want to have a bunch of counter flashing pieces jogging around each stone.


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## roofermann (Nov 18, 2013)

Counter over the step, set into a reglet is likely your best option. Make the reglet deep enough so the counter will fit over any projecting stone without kinking.


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## aribert (Apr 7, 2012)

roofermann said:


> Counter over the step, set into a reglet is likely your best option. Make the reglet deep enough so the counter will fit over any projecting stone without kinking.


I learned a new word - reglet; I have ground them into mortar and bricks on a couple of brick chimneys (just did not know what the groove was called). 

I was dreading cutting into the stones. Turned out it was the easiest part of the project. I used a 4.5 inch grinder with two diamond blades with a washer as a spacer between the blades. The groove is about 5/16 wide. The blades cut the stone relatively easily. Wished I had built up the mortar joints before cutting the reglet. It would have been a lot faster than building up the mortar to form a slot. I laid out my slot to cut thru the least amount of stones - in hind sight it would have been better to lay out the slot so that the greatest amount of stones were to get a slot and less mortar work between the stones. I'll still have some contouring to do on the flange of the counter flashing to get a reasonable amount of depth into the chimney.

What appears to be black painted mortar joints is in fact **tar** painted on the mortar joints. Someone's misguided and I presume quick and dirty form of "tuck pointing" at some point in the past. I spent a serious amount of time chipping at the tar (and the mortar under neath) to get a clean surface that I could add more mortar onto to build up the surfaces between the stones.


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