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Old 01-28-2012, 10:48 PM   #1
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Proper way to flash a stone chimney


I'm getting bids to replace the asphalt shingles on my roof (4/12 pitch) which has a stone chimney in the middle of one side.
By stone chimney, I mean very hard flagstone mortared together around a tile flue.

The current flashing was put in when the chimney was built about 40 years ago and is stepped aluminum sections that were mortared in the joints.

One company said they would replace the flashing with the same stepped arrangement, but the guy they sent to give the estimate was vague on how they would accomplish that ( I do know that the flagstone is extremely hard to cut or drill).

Another company said their method was to cut off the existing flashing flush with the chimney and use a continuous piece rather than stepped flashing and to attach it by drilling holes in the mortar joints and driving in lead anchors, then filling the gap between flashing and stone with a silicone based sealant.

(Never flashed a chimney, but this method seems to depend on the sealant adhering well to the flashing and to the rough stone and mortar and staying that way for the life of the roof. )

I have seen flashing videos where a masonry blade in a circular saw was used to cut through brick and mortar for both a stepped flashing arrangement and for for a continuous flashing arrangement, the top edge of the flashing on both methods is folded into the cut/cuts and wedged in with lead and sealed with a sealant.
This method seems to make sense, but not sure if it would be viable with this hard, rough surface flagstone.

What say ye for the best method for my chimney.
(The flagstone surface is considerably more irregular than what a brick chimney would be, and the mortar joints are aged with some cracking.)

Edit: (Another question)

Is peel & stick ice & water membrane sufficient for valley flashing, or should metal flashing be used ?

Arky


Last edited by Arky217; 01-28-2012 at 11:19 PM. Reason: Another question
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Old 01-29-2012, 08:01 AM   #2
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Proper way to flash a stone chimney


Another company said their method was to cut off the existing flashing flush with the chimney and use a continuous piece rather than stepped flashing and to attach it by drilling holes in the mortar joints and driving in lead anchors, then filling the gap between flashing and stone with a silicone based sealant.

Don't let those guys on your roof.

The flashing needs to be let into the chimney, either at the mortar joints as it's done now or a straight line cut through both stone and mortar. A 7 1/4" grinder or saw is about the smallest dia machine that will work on stone if it's very irregular. A diamond blade is pretty much a necessity, as well.

Most of the time on stone, we prefer to use the straight line method. We set a 2x4 or 2x6, narrow side on the roof, and rest the grinder on it as we cut to produce a consistently straight cut. We use the same grinder if we're cutting into the mortar joints, but they're normally too irregular on stone. On brick, we almost never use the straight line method, preferring instead to use the mortar joints.

The counter flashing metal will have a 2"-3" flange bent on it to insert into the reglet. This will have to be scribed and cut to match the irregularity. The flashing gets held in place with flashing wedges and the the joint gets caulked with a high quality flashing caulk. We prefer Geocel 2300. There are other good products.

edit: I prefer Ice and water shield (there are numerous types of peel and stick products) for valley lining over metal if the metal is to be covered by the shingles. I actually prefer open metal valleys, but if the valley liner is covered, the I&WS will seal around any nails penetrating it, but valley metal will leak if it gets punctured.


Last edited by seeyou; 01-29-2012 at 08:06 AM.
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Old 01-29-2012, 11:21 AM   #3
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Proper way to flash a stone chimney


the previous post is how you should counterflash stone however stone should not be flashed on the exterior ... instead to be done properly you should rip out the stone and flash behind the stone then reinstall the stone ... this is alot more expensive and will be almost impossible to match to the 40 yr old stone so the whole area would probably need to be torn out and redone.

Chris Hendershot
Master roofer for the North Ga area
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Old 01-29-2012, 11:26 AM   #4
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Proper way to flash a stone chimney


Quote:
Originally Posted by chende9 View Post
the previous post is how you should counterflash stone however stone should not be flashed on the exterior ... instead to be done properly you should rip out the stone and flash behind the stone then reinstall the stone ... this is alot more expensive and will be almost impossible to match to the 40 yr old stone so the whole area would probably need to be torn out and redone.

Chris Hendershot
Master roofer for the North Ga area
The OP is talking about a stone chimney, or so I thought. You, I believe, are discussing a stone veneer chimney. Two different, but sometimes hard to differentiate, animals.
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Old 01-29-2012, 12:40 PM   #5
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Proper way to flash a stone chimney


I prefer flashing to the mortar joints but sometimes you need to cut the stone. We do not cut brick for flashing, and we use close matching mortar to seal the joints.

Here is a short video of a recent stone chimney flashing; http://youtu.be/J3z089v323Y

More details here; Chimney Flashing

If the stone is very irregular, you may want to use lead for the flashing as shown here; Stone Chimney Flashing

Most chimney flashing videos on the web are garbage, but I have found some good ones and posted links to them here: http://www.chimneyflashing.info/Chim...7C-Videos.html

Good luck
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Old 01-29-2012, 08:03 PM   #6
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Proper way to flash a stone chimney


Quote:
Originally Posted by seeyou View Post
Another company said their method was to cut off the existing flashing flush with the chimney and use a continuous piece rather than stepped flashing and to attach it by drilling holes in the mortar joints and driving in lead anchors, then filling the gap between flashing and stone with a silicone based sealant.

Don't let those guys on your roof.

The flashing needs to be let into the chimney, either at the mortar joints as it's done now or a straight line cut through both stone and mortar. A 7 1/4" grinder or saw is about the smallest dia machine that will work on stone if it's very irregular. A diamond blade is pretty much a necessity, as well.

Most of the time on stone, we prefer to use the straight line method. We set a 2x4 or 2x6, narrow side on the roof, and rest the grinder on it as we cut to produce a consistently straight cut. We use the same grinder if we're cutting into the mortar joints, but they're normally too irregular on stone. On brick, we almost never use the straight line method, preferring instead to use the mortar joints.

The counter flashing metal will have a 2"-3" flange bent on it to insert into the reglet. This will have to be scribed and cut to match the irregularity. The flashing gets held in place with flashing wedges and the the joint gets caulked with a high quality flashing caulk. We prefer Geocel 2300. There are other good products.

edit: I prefer Ice and water shield (there are numerous types of peel and stick products) for valley lining over metal if the metal is to be covered by the shingles. I actually prefer open metal valleys, but if the valley liner is covered, the I&WS will seal around any nails penetrating it, but valley metal will leak if it gets punctured.

Still not clear on the valley lining.
Are you saying that if I&WS is used, that it should be over metal flashing or by itself ?
If just metal flashing is used in the valley, how far away from the center should any shingle nails be ?

I think my chimney would benefit from one of those 'chase covers' (I think that's what it's called) because the mortared top has quite a few cracks. ( I tried to seal them in the past with a roofing tar but don't know if it completely did the job.

Here's probably a weird idea that came to mind.
If I did get a chase cover, I wondered about the following:
The appearance would probably leave a lot to be desired, but instead of counter flashing at the base of the chimney, I wondered about painted roofing metal (completely flat, no ridges) completely covering the entire exposed chimney going from under the lip of the chase cover all the way down over the chimney roof flashing. (Two vertical 'U' shaped pieces, overlapped and riveted at the vertical seams and riveted to the overlap of the chase cover)

( I know, a weird idea, but for a badly cracked chimney, I wonder if it would
actually work.) (just thinking)

Arky
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Old 01-29-2012, 08:24 PM   #7
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Proper way to flash a stone chimney


Still not clear on the valley lining.
Are you saying that if I&WS is used, that it should be over metal flashing or by itself ?


By itself.

If just metal flashing is used in the valley, how far away from the center should any shingle nails be ?

I never put nails thru metal valley. There should be a hem on each side to lock in metal clips that are nailed down.

I think my chimney would benefit from one of those 'chase covers' (I think that's what it's called) because the mortared top has quite a few cracks.

I agree.

( I tried to seal them in the past with a roofing tar but don't know if it completely did the job.

Here's probably a weird idea that came to mind.
If I did get a chase cover, I wondered about the following:
The appearance would probably leave a lot to be desired, but instead of counter flashing at the base of the chimney, I wondered about painted roofing metal (completely flat, no ridges) completely covering the entire exposed chimney going from under the lip of the chase cover all the way down over the chimney roof flashing. (Two vertical 'U' shaped pieces, overlapped and riveted at the vertical seams and riveted to the overlap of the chase cover)

( I know, a weird idea, but for a badly cracked chimney, I wonder if it would
actually work.) (just thinking)

I've seen similar done. Shouldn't be necessary if no water can enter the top and it's flashed right.
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Old 01-30-2012, 06:21 AM   #8
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Proper way to flash a stone chimney


Step flashing and lead counter-flashing contoured to follow the rook outline is the correct way to do it. Not dependant on caulk, and maintains the stone look.
I can't find any of my pix to post at this time though. Sorry.
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Old 01-30-2012, 06:57 AM   #9
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Proper way to flash a stone chimney


The only one I have is too large to upload and BMP so I'm having trouble resizing and have to get to work anyway. E-mail me for the pic.

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