PaulAmaranth
10-16-2006, 08:27 PM
I'm looking for any experience on this one. None of my contractors have had experience with this and I'm getting a little tired of being the experiment.
I have a large (8 ft x 3 ft) CMU chimney that comes up through the central section of the roof. The idea being that it will be covered in cultured stone to match the exterior walls which are cultured stone and cedar.
The first time we did it, the masons put a bunch of nails through the flashing and the chimney leaked. That roofing contractor left the state. The cultured stone specs say to leave a 2 inch gap above the roof. The looked fairly ugly.
We ripped off half the stone, redid the flashing, redid the stone and mortared the joints. The chimney leaked. That roofing contractor ended up in jail. The chimney appeared to leak when water was directed against the middle of one of the side walls, but not when flooding the flashing. The stone was not applied on a 1/2 inch scratch coat as specified by the manufacturer, but varied to as little as 1/16. When the stone was reapplied, the roof gap was not constant, angling up on one side looking even uglier than before.
We ripped off ALL the stone and mortar this time down to the bare block. Any suspect joints were tuck pointed. It appeared that the last flashing job was bad, there were gaps in the original mortar joints in the CMU and there may have been possible leakage paths through the scratch coat.
The cultured stone manufacturer says that a 1/2 inch scratch coat over CMU is sufficient to provide a waterproof surface. There has also been a run of stone recently that allowed water penetration, according to some of my local sources. I'm not willing to depend on a sealer as the primary water barrier.
When I say the chimney leaks, the block is unfinished in the interior with a couple of open areas near the ceiling. Water drips from the block cores at the open areas. If I had finished the interior, I never would have seen it until the roof rotted out. Apparently, the water was able to get behind the flashing and into the block cores.
I'm tired of leaks and I'm really tired of tearing this thing apart. My current roofing contract came highly recommended, although I'm beginning to wonder, and I think we're closer, but not there yet. Here's what we've done this time:
Grace ice and water shield was used as a flashing membrane between the roof and about 6" up the CMU chimney. A curb was constructed around the chimney out of 2x material and fastened to the roof sheathing. A copper Z flashing was installed over the curb on the long sides, nailed to the roof and sealed to the chimney with more Grace. On the sides, step flashing is attached to the roof and a Z flashing is set over that , fastened to the curb and sealed to the chimney with Grace. My contractor then covered all exposed block with more Grace. The next step would be to apply metal lath on top of the Grace and then apply the cultured stone to that. The curb provides a nice transition for the stone and allows the copper flashing to be seen. That idea I like.
I have a number of problems with this.
1) Grace I&W seals the flashing to the chimney. There is no provision for independant movement of the roof and chimney structure. Now because of the roof/chimney construction details, there shouldn't be much movement, but still... When questioned, my contractor said the Grace will give. Because of the previous leaks, he was trying to avoid cutting into the block and opening potential leakage paths.
2) Because I had some concerns that the Grace was not specified as a mortar underlayment, I was going to either replace or overlay it with a CMU waterproofing membrane which has a PVC layer specified for mortar underlayment. It's been about a week, the weather turned a little cold and the Grace has already separated from the block in some areas. Clearly this is not a good solution and I would not want to apply the membrane over either the Grace or the current Z flashing. The contractor is offering to come out, cut out the stuff that has pulled away and put more Grace on it. This does not sound like a good solution. Since the Grace is not bonding to the block, the top joint where the Grace ends could serve to funnel water down behind the whole mess. That joint was sealed with Silicone, which I wouldn't trust to hold for more than a week.
I am not a roofing expert, but it seems the way this should be done is to use normal flashing/counterflashing over the curb with the counterflashing cut into the block about 6" above the curb and mortared (not caulked) in place, then apply the masonry membrane over the exposed block and over the top of the counterflashing, tapcon the lath in place and then apply the scratch coat and cultured stone. That way the chimney and roof can move and there are no leakage paths to or through the block.
However this is built better last for 50 years since the stone would have to be torn off to fix it and a leak would result in water damage to a structural insulating panel that would cost $$$ to replace (not to mention ripping the center of the house apart).
Anyone got any comments or ideas? Does my contractor's solution seem odd to anyone? Has anyone built one like this? I can't believe I'm the only one dumb enough to have built something like this.
I have a large (8 ft x 3 ft) CMU chimney that comes up through the central section of the roof. The idea being that it will be covered in cultured stone to match the exterior walls which are cultured stone and cedar.
The first time we did it, the masons put a bunch of nails through the flashing and the chimney leaked. That roofing contractor left the state. The cultured stone specs say to leave a 2 inch gap above the roof. The looked fairly ugly.
We ripped off half the stone, redid the flashing, redid the stone and mortared the joints. The chimney leaked. That roofing contractor ended up in jail. The chimney appeared to leak when water was directed against the middle of one of the side walls, but not when flooding the flashing. The stone was not applied on a 1/2 inch scratch coat as specified by the manufacturer, but varied to as little as 1/16. When the stone was reapplied, the roof gap was not constant, angling up on one side looking even uglier than before.
We ripped off ALL the stone and mortar this time down to the bare block. Any suspect joints were tuck pointed. It appeared that the last flashing job was bad, there were gaps in the original mortar joints in the CMU and there may have been possible leakage paths through the scratch coat.
The cultured stone manufacturer says that a 1/2 inch scratch coat over CMU is sufficient to provide a waterproof surface. There has also been a run of stone recently that allowed water penetration, according to some of my local sources. I'm not willing to depend on a sealer as the primary water barrier.
When I say the chimney leaks, the block is unfinished in the interior with a couple of open areas near the ceiling. Water drips from the block cores at the open areas. If I had finished the interior, I never would have seen it until the roof rotted out. Apparently, the water was able to get behind the flashing and into the block cores.
I'm tired of leaks and I'm really tired of tearing this thing apart. My current roofing contract came highly recommended, although I'm beginning to wonder, and I think we're closer, but not there yet. Here's what we've done this time:
Grace ice and water shield was used as a flashing membrane between the roof and about 6" up the CMU chimney. A curb was constructed around the chimney out of 2x material and fastened to the roof sheathing. A copper Z flashing was installed over the curb on the long sides, nailed to the roof and sealed to the chimney with more Grace. On the sides, step flashing is attached to the roof and a Z flashing is set over that , fastened to the curb and sealed to the chimney with Grace. My contractor then covered all exposed block with more Grace. The next step would be to apply metal lath on top of the Grace and then apply the cultured stone to that. The curb provides a nice transition for the stone and allows the copper flashing to be seen. That idea I like.
I have a number of problems with this.
1) Grace I&W seals the flashing to the chimney. There is no provision for independant movement of the roof and chimney structure. Now because of the roof/chimney construction details, there shouldn't be much movement, but still... When questioned, my contractor said the Grace will give. Because of the previous leaks, he was trying to avoid cutting into the block and opening potential leakage paths.
2) Because I had some concerns that the Grace was not specified as a mortar underlayment, I was going to either replace or overlay it with a CMU waterproofing membrane which has a PVC layer specified for mortar underlayment. It's been about a week, the weather turned a little cold and the Grace has already separated from the block in some areas. Clearly this is not a good solution and I would not want to apply the membrane over either the Grace or the current Z flashing. The contractor is offering to come out, cut out the stuff that has pulled away and put more Grace on it. This does not sound like a good solution. Since the Grace is not bonding to the block, the top joint where the Grace ends could serve to funnel water down behind the whole mess. That joint was sealed with Silicone, which I wouldn't trust to hold for more than a week.
I am not a roofing expert, but it seems the way this should be done is to use normal flashing/counterflashing over the curb with the counterflashing cut into the block about 6" above the curb and mortared (not caulked) in place, then apply the masonry membrane over the exposed block and over the top of the counterflashing, tapcon the lath in place and then apply the scratch coat and cultured stone. That way the chimney and roof can move and there are no leakage paths to or through the block.
However this is built better last for 50 years since the stone would have to be torn off to fix it and a leak would result in water damage to a structural insulating panel that would cost $$$ to replace (not to mention ripping the center of the house apart).
Anyone got any comments or ideas? Does my contractor's solution seem odd to anyone? Has anyone built one like this? I can't believe I'm the only one dumb enough to have built something like this.