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Mushrooms in hardiplank


Chris Bernhardt
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I have never seen fungus growing out of fiber cement siding. From what I can determine the mfg.'s say it can't except from post manufacturing comtamination.

If so, what is the recommendation? replace the siding? There's no way that the fungus can break it down in this century. Should I recommend removing a board and inspecting the WRB? From inside the attic the OSB sheathing backing the affected area was clean as a whistle.

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Originally posted by Chris Bernhardt

I have never seen fungus growing out of fiber cement siding. From what I can determine the mfg.'s say it can't except from post manufacturing comtamination.

It's coming out between the siding pieces. I suspect it's growing on something that's behind the siding -- could be the OSB sheathing or maybe a wooden shim. I find it interesting that, in both pictures, there's a bit of this stuff growing right at the top of the headlap. Isn't that curious?

If so, what is the recommendation? replace the siding? There's no way that the fungus can break it down in this century. Should I recommend removing a board and inspecting the WRB? From inside the attic the OSB sheathing backing the affected area was clean as a whistle.

I'd describe the problem, speculate as to the cause and recommend removing a piece of the Hardi to find out what's actually going on.

- Jim Katen, Oregon

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Was there building paper behind it or did they apply it directly over OSB sheathing without a WRB?

The siding was on the front of the garage over the door. I was thinking the same thing and had concluded that removing a board was in order like Jim recommended.

When I was mining for info on JLC I ran into some not so nice performance traits of fiber cement siding. They were mostly due to mishandling the siding after it left the factory mostly letting it get wet but the one that concerns me is that it's being reported that the stuff loves moisture and that solar drive sends the vapor right thru the WRB to condense on the sheathing behind it.

Chris, Oregon

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Another thing I found was that if you're are going to caulk the butt joints then they should be gapped and dressed per the caulking mfg.'s recommendations.

What I usually see is gap widths all over the place. I know the mfg. installation instructions say no more then 1/8" but what it really means is per caulking mfg. recommendations but gap it no more then 1/8".

I hate the way the caulked joints look. Always looks like hell in front entries on southern exposures.

Concerning solar drive, William B. Rose wrote an excellent book which has become my bible on moisture. I have read it many times. I highly recommend this book. "Water in Buildings: An Architect's Guide to Moisture and Mold"

Chris, Oregon

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Y'know, looking at a close-up I'm not convinced that is caulk. It looks more like they tried to fill the gaps with a wood(?) filler. It has cracked or failed in a fashion that would suggest no flexibility at all. I wonder if that is what the fungus is growing on...especially if it wasn't an exterior grade filler.

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Originally posted by Richard Moore

Y'know, looking at a close-up I'm not convinced that is caulk. It looks more like they tried to fill the gaps with a wood(?) filler. It has cracked or failed in a fashion that would suggest no flexibility at all. I wonder if that is what the fungus is growing on...especially if it wasn't an exterior grade filler.

Nope. That's the characteristic look of Vulkem. It always looks like it contains sawdust or something.

- Jim Katen, Oregon

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Concerning solar drive, William B. Rose wrote an excellent book which has become my bible on moisture. I have read it many times. I highly recommend this book. "Water in Buildings: An Architect's Guide to Moisture and Mold"

Chris, Oregon

Thanks, but at $90 I can get by without buying a book to learn what solar drive is.

From what I have been able to find and read on solar drive, this is when moisture is heated under siding or roofing and the resulting vapor is forced into the structure past the moisture barrier. I found a few articles that call it "thermal vapor transmission" .

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Originally posted by Richard Moore

Not doubting you Jim, but I had to look up Vulkem. Is that the norm down there? I've never seen anything like that applied to Hardiplank butt-joints around here...just what I have to assume is regular caulk, and applied a whole lot neater than Chris's photos.

I'm amazed. Vulkem was the defacto exterior caulk used around here up until a few years ago. Now it seems that everyone is using DAP's Sidewinder. The only people I've seen using Big Stretch are homeowners.

I've used all three and, for Hardiplank butt joints, I don't like any of them. I prefer to see a tin shingle behind the joint and no caulk at all.

- Jim Katen, Oregon

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I should point out that I don't do phase inspections, just the finished product, so I only get to see the joints after painting and have no clue what they actually used. But, I do see a lot of hardiplank and I've never seen gunk smeared on like those photos.

I've only installed the stuff once myself (on my garage rebuild) and used DAP Alex Plus (35 year). I'm pretty sure the builder who did my upstairs remodel used the same. No good?

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Hi Richard,

Look at the tube. All the manufacturer says is:

Caulking

For best results use an Elastomeric Joint Sealant complying with ASTM C920 Grade NS, Class 25 or higher or a Latex Joint Sealant complying with ASTM C834. Caulking/Sealant must be applied in accordance with the caulking/sealant manufacturer’s written instructions or ASTM C1193.

ONE TEAM - ONE FIGHT!!!

Mike

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Originally posted by Richard Moore

I should point out that I don't do phase inspections, just the finished product, so I only get to see the joints after painting and have no clue what they actually used. But, I do see a lot of hardiplank and I've never seen gunk smeared on like those photos.

I've only installed the stuff once myself (on my garage rebuild) and used DAP Alex Plus (35 year). I'm pretty sure the builder who did my upstairs remodel used the same. No good?

I use Alex Plus indoors all over the place. I've never though to use it outdoors. How's it holding up?

- Jim Katen, Oregon

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I just grabbed a tube from the workshop. It says "Exceeds ASTM C-834" so must be OK although I'm getting the feeling from the posts there is "much more betterer" stuff out there.

Jim...this is indoor/outdoor caulk. I've used it for years in other places and it seems to do just fine. The garage and remodel are just over a year old, so too early to tell. I'm sure there is a "lesser" indoor only version, but I've never tried it.

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