hi,
i’m located on cape cod, massachusetts, where we have strong concerns with both freeze/thaw conditions and wind driven rain infiltration. accordingly, proper flashing details are essential, and require thorough, exacting, and even over-cautious workmanship to avoid future problems. i’m starting my first cultured stone project, an exterior chimney application over a 4″ solid concrete block base using el dorado stone. i’ve read the web instructions, watched their installation movie, and read literature provided by a local supplier. i’ve spoken with a few local tradesmen who have experience with such installation, and while most agree on the basics, i have had several conflicting ideas about flashing details.
considering the vertical flashing between the masonry and the gable-end plywood sheathing, some have suggested that the el dorado is waterproof, and thus i could use 4″ lead folded 90 degrees to flash the face of the tar-papered plywood and the face of the block. i would then apply the el dorado over the block and lead. this has the advantage that the flashing would remain unseen. it seems likely to me however, that any water blocked by the flashing could get behind the el dorado. freeze/thaw would then be free to force the el dorado from the block of the chimney to fall away. so it follows that the lead should be applied to the face of the ply and the face of the el dorado. now 1. the lead flashing is visible, 2. the lead must be tamped to fit around each stone, many of which are irregular, and all of which have varying thicknesses, 3. the joint between the lead and the stone must be caulked, diminishing (not preventing) water infiltration over its finite lifespan before inevitably failing. also, i plan to use white cedar shingles as siding. do i face a tedious week of scribing shingles to the stone (or lead fitted to the stone)? can i hold the stone an inch back from the plywood (increasing the width of the lead accordingly) and fasten a vertical 1x cedar trim board to the plywood, over the flashing, between the stone and plywood, to have a straight edge to shingle to? i would welcome the experiences of anyone having faced this situation and appreciate any suggestions for this area of concern. thanks.
Replies
You've described your situation very thoroughly, but a picture is worth 1000 words. Got any?
I invented olympic walking.
i'll see if i can get a couple of shots of what i mean.
I don't have personal experience with NE winters. I have some with cultured stone. To my mind, I start from the premise that you ought to flash it as if it were the "real thing." Partially that's aesthetic--it looks better because it "looks" right. Flashing is one of those things that done wrong will stand out to the eye. Do it right and it will look right.
But that's just my opinion.
Piffin needs to walk you through it. I've done some work with cultured stone but no chimneys yet. One thing to consider however, would be placing snow and ice shield down before any flashing. You might even want to cover the entire chimney with it before anything else. The L flash which extends up the chimney wall should run well up the wall behind the stone. You can apply 1/4" mesh over the flashing to give the mortar a skeleton of support. The 'waterproof' properties of the stone will be directly affected by how well you mix the mortar then apply the mortar.
Masons are a wonder to me with how deft they are with the stuff. I look like I dove into a bag of Portland anytime I get within ten feet of it. There's some serious talent on this board so hang in until they offer their experience and knowledge. Good luck.
thanks for the replies. i'm on to investigating real stone chimney flashing, for one. also, hw, you suggest ice/water shielding the chimney. when the chimney base is cement block? plus, if the water gets in to the point where the ice/water shield must repel it, it's already behind the stone and subject to freeze/thaw. i have seen other posts describing how to use the wire lath to cover the underlying L flashing. this means that the cultured stone is adhered over the lath and over the flashing. but now to prevent water infiltration behind the stone, aren't we relying on a mortar bond between the back of the cultured stone and the flashing? i know the lath is in the middle and will help with the support, but is it wise to trust a mortar/metal joint? i know it sticks to my shovels, but i also know i don't have much trouble cleaning off my trowels.
but is it wise to trust a mortar/metal joint?
Ah, not to answer for HW, but my recollection of the Coronado installation manual is that you need water or weather proffing on block before installation of the cultured stone. The wp would extend over the L flashing. That would create the plane against which moisture would travel.
I'm thinking I need to go dig up the Coronado literature and actually look at the recommendations for cold weather installations (not normally a large worry down here at 29º N latitude).
Cultured Stone Corp & Coronado are online, and I'm pretty sure the installation intructions are too, if you want to go browsing.Occupational hazard of my occupation not being around (sorry Bubba)
This story from my Mom in the Pennsylvania Poconos sems strangely appropriate right here:
"My friend rents here. Before they moved in some years ago, the Landlord had
a new roof built. But it has leaked into a bedroom every year since and he
refuses to pay for another roof, as he was told. Naturally.
So Dee's son is a contractor, living in Harrisburg. He climbed the roof and
found there was no flashing where the roof is on two levels at one section,
the place it leaks.
She told the owner who called the roofer who informed him that the Pocono
roofers do not use flashing at chimneys or that sort of roof. If one wants
flashing, one has to know before the job, tell the roofer and the "extra"
clause will be included in the contract at additional cost."
Jim, that is such a lame excuse! That guy is not a roofer. He is a shingle layer is all.
I'm gonna go do a drawing of jhow i think I would flash this chimney. Think only because there are a couple options opossible. Stone might be rated warter resistant, but mortar is not so the assembly would be able to take on moisture. regardeless of flashing method, regular treatment with a sealer is a good idea for any masonry chimney.
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Yeah, but just goes to show some of the hacks out there. And these are friends of my mom's and they wouldn't know to ask and they sure won't get up there and look. It tarnishes the entire profession.
p, i think i've figured out your sketches, thanks. the block chase as i'm describing is exterior, built adjacent to the gable end and exposed on three sides before punching through the rake and becoming fully exposed on all four sides. is your sketch of an interior chimney? in my case the step back with the block would cause an unacceptable corresponding step back with the stone. the flashing question that i have presented is on the vertical seam between the block chase and the gable end plywood, not the angled seam along the roof plane between the block chase and the roof ply. it was the sidewall shingles that i proposed scribing, and the vertical lead flashing that i proposed to tamp-fit to the stone, not the flashing between the chase and the roof plywood. i'm still concerned about this area, should you have any insights there. thanks.
Gottcha now - had to go back and pay attenshun to what I was reading.
I would probably just coat the block with Thorocrete for water resistance on that structure, and butter the stone to it, then tool the joints and apply a sealer for the masonry portion of the work. El Dorado might have a prescribed product in place of the Thorocrete.
For flashing, I think you are probably worrying too much. Vertical walls shed water pretty quickly so it tends to not find its way into joints as much as on a roof such as cloud's story.
See the picture attached here. Your chimney mass is probably spaced out 2" from framing. Make a bumper block by ripping a 2by and run it up the sheathing. Then have a leaded copper broke at the local sheet metal shop as shown. I don't know the sizing and thickness of the stone, but if you place the 2by and flashing so it is slightly shy of finished faces, then you create a pockeet for the shingles to fit behind the stone and have a smooth face to shingle onto. The stone protruding slightly wil keep 90% of the water from getting to it, and very little will ever wick its way up in behind to do damage.
I also would not expect it to do much freezing. After all, when the weather is that cold, this chimney will be in use, radiating heat - right?
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hi,
i wanted to say thanks for your suggestion. i used your flashing detail on my chimney. i'll send some pics if you're interested.
luther
cape cod
I would not try to fit shingles or lead to the stone.
If this were cultured srtone ove a wood framed chase, the answer would be a little simpler. I would run my flashing tight on the sheathing of the chase, lay tarpaper down over that, and then apply the expanded metal weave and butter the stone onto it, capping with a meetal top extending over the stone facade.
And if this were a true stone or brick chimney, the masions would build up with block to step above the roof. Then the flashing would fold on top of the block steps, and the stone or brick would be layed above it, with a lead cap flashing under the poured crown. You can see in this sketch something like that on the right. That might work well with cultured as well.
But another possible option here would be as shown on the left drawing, where flashing is let into the mortar joints on the block chimney and then the cultured stone is layed over it. Still use a full lead cap flashing under the poured crown.
Hope this helps.
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Edited 9/23/2004 3:27 pm ET by piffin