Mold inside exterior walls, WTF!!!

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  #1  
Old 02-27-13, 03:06 PM
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Angry Mold inside exterior walls, WTF!!!

This is quite a shocker to me and my wife. We have been working on our house for a while and finally got to doing some interior finish. Opted out of drywall and went with 3/4" TG wide pine flooring. We found mold growing on the inside of exterior sheating, as we pulled fiberglass insulation to run some CAT5 before installing wood finish. We now checked several areas and mold is in almost every stud bay.

Profile of the wall looks like this (all new materials, foundation up):
- no siding yet
- windows not taped yet
- 1" polyiso foam, foil side to the house, not taped yet (I am debating this as the cause of a problem here)
- housewrap
- 1/2" OSB
- 2x6 studs
- R-19 unfaced batts between studs
- at some areas we had 4mil plastic, to avoid contact with fiberglass (but mold is also in spaces without plastic)

Mold is growing from the sill plate up, about 4ft high. It's also present under insulation between floor trusses (above the space we are talking about) and in the walkout basement wall, where we actually used 1" pink foam (taped at the seams) - which has damaged my theory that it happens because we haven't taped polyiso.

I am literally speechless and devastated... what do I do next?
Pull insulation, spray with borax/peroxide mix? Spray with PermaGuard?
Tape seams outside, tape windows?

Help!
 
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  #2  
Old 02-27-13, 03:40 PM
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Sorry, but I'm not able to sort out your explanation as to what is where. However, from the sound of it, there are some general rules that need to be followed to avoid condensation, which is what feeds the mold.

First, mold is everywhere at all times, it just doesn't grow until it has moisture and food (wood, paper, yada). Second, inside warm air contains a lot of moisture and when that air moves into cooler places, like filtering into the fiberglass insulation, it can deposit that moisture. You didn't mention that I saw whether the inside was covered with drywall. If it was just insulation, ecen with a plastic vapor barrier, air easily moves in behind the plastic.

I'm not sure where the foam insulation is placed, but depending upon your climate (WI is rather cold) the foam needs to be thick enough to keep the inside above the dew point. The dew point is the temperature where the air cannot hold any more moisture, 100% RH.

Let's see if others can sort out your description.

Bud
 
  #3  
Old 02-27-13, 04:08 PM
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It reads as if you have been living in a partially constructed home, or have partially de-constructed areas of your home to add on or do a major rehab. It reads as if you have left the walls open to the rest of the house with fiberglass insulation and no vapor barrier. It also reads as if you have made some major mistakes on how you have constructed some new walls.

Please detail EXACTLY the "sandwich" of your walls from the inside going to the outside. If I read your ambiguous description correctly you have a vapor barrier (the foil-faced insulation) on the wrong side. This will trap moisture inside the walls and mold growth is almost guaranteed to happen.
 
  #4  
Old 02-27-13, 04:38 PM
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IMO, the problem that caused the mold is that there was no air barrier (drywall) to keep moist heated air from passing through the fiberglass and condensing on the cold surface (the back of the OSB) during the winter months. (since it sounds like its been open / semi-open this way all winter long) Even where you had the poly vapor barrier, if it was not completely sealed (taped) to the floor/sill plate, moist warm air would migrate from the floor up and could get trapped in there, so you would see problems.

I don't feel that the "sandwich" of double vapor barrier is necessarily a problem, but it sure would be amplified when there is no drywall on the wall.

If you wanted to snap a picture and post it, then we could see how much mold we are talking about.
 
  #5  
Old 02-27-13, 06:00 PM
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Wall sandwich, from outside in:
- 1" polyiso foam, foil side to the house, not taped
- typar housewrap
- 1/2" OSB
- 2x6 studs
- R-19 unfaced batts between studs
- started installing 3/4" TG pine flooring and stopped upon discovery of this problem (this house will have no drywall)

Mold happened where there was additional vapor barrier inside (4 mil plastic) AND where there was no vapor barrier.

It makes me believe that the biggest error was not taping the foam. Polyiso, when taped is the only required and effective vapor barrier. Doubling it down makes no good and can cause worse problems than described.

It looks like the dew point is right on the inside of the OSB. I am doubting that one layer of vapor barrier inside the house would fix the problem. It probably would make it way worse, as wall would have no way of drying, inside or out.

Question - without removing foam (cos removing it would invite rain and moisture to the sheeting) and just taping it, then removing the mold and mold-proofing the inside of the OSB, what are chances of wall sandwich drying out and mold problem not coming back?

I am only guessing, but I bet I am not the only one with this problem. It's just most construction sites, once insulation is applied, it's not removed and such problems remain hidden in the wall... or they go away, structure dries out.
 
  #6  
Old 02-27-13, 06:23 PM
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I'm not sure you are understanding the problem.

First off, in cold climates like Wisconsin, the vapor barrier ALWAYS goes on the interior warm side of the building envelope. That's the interior side of your walls, not on the outside of the sheathing. That's problem number one. You have the whole concept of a vapor barrier backwards. Not taping your foam is probably a good thing.

Second, it's likely that mold happened in your walls (regardless of whether or not there was a poly vb installed) because a). the poly was not sealed and b). there was no barrier up to prevent heat and moisture from easily getting to the cold wall on the other side of the insulation. I've seen this many times in houses that are under construction during winter months. You fire up a propane heater to keep the building warm inside and if there is unfaced fiberglass in the walls, you get frost and ice behind the fiberglass. When the wind blows, air pressure carries your moist, conditioned air to the opposite side of the house where it exits any place it can.

Third, your plan to omit a poly vapor barrier, omit drywall and put up tongue and groove planks is a bad one. The tongue and groove planks will allow warm air to pass into the fiberglass insulation, carrying moist air into the wall and this condensation and mold in the wall will just continue for ever after.

So is this happening on all sides of the house, or just one- the shady side or the side opposite the prevailing wind?
 
  #7  
Old 02-27-13, 06:35 PM
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I concur with X. You should never have added that polyiso on the outside of the sheathing. The lack of a vapor retarder inside compounded the problem.
 
  #8  
Old 02-27-13, 07:08 PM
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Hi again,
Your question is where to go from here, difficult. I'm going to just list some issues you are going to need to deal with.
1. Vapor barriers can cause more problems than they help. Air sealing is the fix that prevents the majority of the moisture. This link and the links they reference will help: Do I Need a Vapor Retarder? | GreenBuildingAdvisor.com

2. Even though you often see the foil faced polyisocyanurate being applied to the outside of a home, there are guidelines which are often not followed. The ratio of r-value needs to be such that the inside surface of the rigid foam never drops below the dew point. In your climate that should be about 2.5" when combined with r-19 on the inside. 2" would probably get you by.

3. Using T&G wood will still require an air barrier behind it. With the foil faced material already on the outside, drywall would be my choice. One coat of tape and mud and air seal it as it goes up. seal wood at top and bottom and around electrical boxes and penetrations. They make special boxes for air seal applications.

4. What are you currently heating with

5. If you removed all of the fiberglass and left just the osb and exterior foam, the inside would be warm enough (at a cost) to prevent moisture.

6. Depending upon how bad the mold is, you may be able to just clean it up and seal the wood. I'm not a mold pro, so do some reading.

Here's another article on vapor barriers and why they are not always needed: Should the Paper Facing of Batt Insulation Face the Inside or Outside? | GreenBuildingAdvisor.com

Bud
 
  #9  
Old 02-28-13, 11:49 AM
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I really don't see how drywall is a fix here. We don't plan on using it at all.

I see where you are going with dewpoint here. I know it had to happen few times over past 5 months, where that dewpoint fell exactly on the inside of the OSB and hence the condensation and mold growth.

Again, mold also happened on the wall where we used just a regular pink foamular (1in). Part of that wall had plastic inside, part didn't. It's moldy without a specific reason or formula to it.

On vapor barrier inside the house. What about spaces between floors, where all you have is just fiberglass insulation? Noone puts vapor barrier in header space or between joists/trusses. That's where we have mold too and I am thinking that many people have that hidden problem as well (that they don't know about).

House is heated by the central air furnace and some supplemental wood burning stove heat. It's not humid inside. Just measured 38% RH.

As far the outside goes, all doors and windows are installed on the top of 1" polyiso. I don't see it being feasible to remove everything just to add another 1". What about taping seams and adding another layer of some non-permable housewrap? Again, I was told that 1" polyiso, taped is all vapor barrier we need and doubling down on vapor barrier is a big no-no. Put plastic inside and you create a sponge sandwich that will never dry.

Now, from my own experience, I have seen a house where licensed contractor installed faced fiberglass, then 4" poly, drywall over. Summer time there was water rushing down the baseboards like a waterfall. Drywall had to be taken down, plastic removed. That fixed the problem. Local inspector suggests slitting the paper on the batts, since plastic is required anyways and some people hate installing unfaced insulation.

In case that happens on the outside of the house though, that's fine (taped polyiso and plastic/wrap layer) since excess water would run down outside of the house.

Just can't believe that 1" taped polyiso isn't enough for vapor barrier...
 
  #10  
Old 02-28-13, 03:52 PM
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Your 38% RH concerns me. Assuming a room temperature of 68░, when you cool that air down, its dew point is 41░. Forced hot air and certainly a fireplace rarely warm the exterior walls very well so that 41░ is very likely, especially inside those walls.

Now, unless you are running a humidifier (not stated) forced hot air and a fireplace would typically result in a dry house. The possibilities are a very tight home (sounds unlikely) or a significant source of moisture. Any dirt floors in a crawl space or basement or other source of moisture. Some common sources are: dryer vented inside, storing firewood inside, wet basement, long showers with no exhaust fan, lots of plants or fish tanks.

Keep reading
Bud
 
  #11  
Old 02-28-13, 04:10 PM
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Like XSleeper said, your vapor barrier is on the wrong side of the wall. If anything, the polyiso will help prevent moisture infiltration from the outside but trap it on the inside.

At 70 degrees and a relative humidity of 38% the dewpoint is at roughly 43 degrees. Now your unfaced fiberglass helps keep the heat in your house, but allows the water vapor in the inside air to pass through where it condenses on the cold sheathing. The polyiso has minimal R-value and the fiberglass effectively keeps the heat getting to the sheathing, at least to the point that the sheathing temp drops to or below the dewpoint, causing condensation.

Your only solution is a barrier that prevents the inside air from infiltrating the wall. Faced batts with a vapor barrier and drywall must be used to prevent that from happening. It doesn't have to be finished perfect, just airtight and a good coat of latex paint, then put your wood planks over top.

Yes your wall is now 1/2" thicker which may mean adding wood trim around window and door frames to bring them out flush with your finished wall. Pain in the arse, but not many alternatives the way I see it.
 
  #12  
Old 02-28-13, 06:49 PM
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First, let me say that I appreciate all help.

Second, there is no drywall planned anywhere in the house. Can't take the dust, don't want added cost, labor, weight, etc. If it's meant for vapor barrier, wouldn't plastic do just the same? Really don't see a need of drywall anywhere.

Upon further inspection, I found that mold is quite fresh, not much black stuff. Insulation is dry on both sides and mold transfer is very minimal. I will re-measure humidity on Sunday when I get access to more accurate apparatus.

I do understand now that condensation in the winter is driven outside and in the summer inside the house. That would warrant 2 separate vapor barriers to stop it, outside layer in the summer and inside layer in the winter, right?

But then nowhere have I seen any manufacturer, scientist or professional advising using 2 vapor barriers. Quite opposite. Warm climates should have outside VB and cold climates inside VB. Problems start in mixed humid climates like WI. Cold winters and hot humid summers are not helping here.

I know that my problems come also because we live in unfinished house. I have no choice here. For the first 4 months we had plastic just on part of the walls (all insulated though) and as said before, mold appeared in various spots, no rule or logic.

Now, I have went through countless articles, literature, and forum threads.
Here are some solutions I found and please don't take it as a to-do list. Some of them are quite conflicting.

0. Mold has to be cleaned and OSB sprayed with some kind of mold retardant (question would be, should that retardant form a vapor barrier itself, or be permeable)
1. Polyiso seams taped (which should have been done on day one; this creates something that acts almost as vapor barrier; 0.3 perm rating, where 0.1 is VB)
2. Another layer of polyiso added (1" should be doable and economic because of added insulation; this creates 100% VB and shifts temperature profile of the wall; transition to window and door openings might be problematic)
3. Layer of house wrap added on top of polyiso (vapor barrier without extra thickness, easy to transition to window and door openings)
4. Some kind of wicking/breathable wrap (so the back of future siding can dry up)
5. Perimeter of each stud bay sprayed with foam (to prevent major air intrusion)
6. Entire surface of each stud bay sprayed with foam (vapor barrier, added insulation)
7. Entire surface of each stud bay painted (something that will create vapor barrier, possibly more mold protection)
8. 4 mil plastic added on the inside of wall assembly (vapor barrier, but then it creates a sandwich that will never dry; more potential problems)
99. 3/4" TG pine installed as wall finish.

This a major 1 vs 2 vapor barriers discussion, especially that polyiso should be taped (effectively creating VB) - then the wall sandwich can dry to the inside only.

Not taping polyiso won't improve drying to the outside much (if any) and invite weather related problems (rainwater, humidity) from the outside.
 
  #13  
Old 02-28-13, 07:21 PM
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In the first post you said the iso was not taped, so there were gaps and the primary moisture barrier (Tyvec, etc.) apparently was not on the exterior and any exterior water could easily find its in and be held by fiberglass (it does not dry without significant movement and air flow through it) so there is a source of moisture for the mold to grow on a feeding surface (wood framing or the back of the drywall).

Dick
 
  #14  
Old 02-28-13, 07:45 PM
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Entire house was wrapped, overlapped and taped with Typar (Menards' own Tyvek brand) before installing polyiso. Direct water intrusion or injection shouldn't be the culprit here right now. I know polyiso shouldn't stay untaped, in case of more severe rainfall/wind driven rain depositing behind it in the future.

There is nothing on top of polyiso, if that's what you meant.
 
  #15  
Old 03-01-13, 03:07 AM
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Unless you keep the inside of your house like a meat locker with the a/c in the summer, air infiltration from the outside into the wall is not really a big issue. Here's why.

Relative humidity is the amount of water vapor in the air relative to the total potential the air could hold at a given temperature. Fire up your furnace and watch what happens to your hygrometer as the air temp rises. The relative humidity drops, even though there is little if any change in the actual amount of water vapor in the air.

Dewpoint is the temp the air must be colled to for condensation to form and conversly, if you allow the temp to drop in the house, you will see the relative humidity rise on your hygrometer.

The dewpoint temperature is always lower than the air temp. It is impossible for the temperature in side your wall to be lower than the outside, aside from the meatlocker scenario. Thus outside air of 60% relative humidity at 40 degrees would need to be cooled to 27 degrees for condensation to occur.

So your outside wall can look like swiss cheese and it can be foggy outside and yes the air inside the wall will have a relative high amount of water vapor in it, but as long as it remains in the vapor (gas technically) form and does not condense into liquid water, it hurts nothing.

Tyvek and similar products are not vapor barriers, they are actually full of very tiny holes designed to allow water vapor to escape and are meant to be a wind break to slow cold air infiltration.

You must find a way to prevent the inside air and water vapor from getting into the wall. Even plastic will allow some water vapor to pass through it, so if your outside wall is also impermeable to vapor, what does get past the plastic will be trapped.

I hope I have explained this in a way you can see that it's all about the inside and not the outside. The facing on fiberglass insulation is paper, but the side facing the fiberglass is black, coated with a compound that is designed to stop water vapor from passing through.

Adding another layer of polyiso on the outside will only compound your problem. Take the advise everyone here is offering. If you don't, I guarantee you will have mold at best, and at worst your house will rot from the inside out.
 
  #16  
Old 03-01-13, 04:16 AM
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Let's back up a bit and make this work, because exterior rigid insulation has been approved for cold climates as long as it is thick enough and there is a minimal interior vapor barrier, class III.
Here's a quote from the link below:

"Install thick foam and no interior poly

To sum up, there are two important points to remember about foam-sheathed walls:

Make sure the foam is thick enough to prevent moisture acculmulation (´┐Żcondensation´┐Ż) in your sheathing or framing; and
Avoid low-permeance layers like polyethylene or vinyl wallpaper on the interior so the wall can dry inward.

Of course, foam-sheathed walls must comply with existing building codes. Until recently, that was difficult, because some building inspectors insisted on the need for interior polyethylene ´┐Ż even on foam-sheathed walls, where poly definitely does not belong.

Fortunately, the 2007 Supplement to the International Residential Code (IRC) came to the rescue. Since that Supplement was adopted, the IRC has allowed certain cold-climate walls to dry to the interior. The code now includes a table, Table N1102.5.1, listing which types of wall assemblies have minimal requirements for an interior vapor retarder. (In the 2009 IRC, these provisions can be found in section R601.3; the new designation for the table is Table R601.3.1.)

Table N1102.5.1 (also known as Table R601.3.1) serves two purposes:

It gives permission to builders of foam-sheathed walls to use a minimal interior vapor retarder ´┐Ż one with the highest permeance values, known as a Class III vapor retarder. (Ordinary latex paint is all you need.)
It spells out the minimum R-values for exterior foam to be sure that moisture won´┐Żt accumulate in a wall."

Calculating the Minimum Thickness of Rigid Foam Sheathing | GreenBuildingAdvisor.com

The problem in this home is you are caught half way through the process and you will need to get through the cold weather and sort things out in the spring. Drop your inside humidity to as low as you can tolerate. I find 20% about my lowest level. Your 1" rigid is near the minimum but probably ok.

I'll let everyone read and if more technical info is needed he provides a link to that. Let's pick it up from here, as exterior foam is good, it just has to be done right and the assembly allowed to dry to the interior, as the poster is stating.

Bud
 
  #17  
Old 03-01-13, 10:21 AM
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@OP,
Go back & re-read some of the insulation articles as you are still confused about the differences between vapor barrier vs. air barrier vs. vapor retarder.
Your exterior polyiso is not a vapor barrier unless it's foil-faced--it's a vapor retarder and an air barrier. Taping it won't help make it a vapor barrier but Will make it a better air barrier. Your Tyvek likewise is an air barrier and a vapor retarder. The combination of Tyvek + polyiso "doubles down" on air barrier while still allowing some permeance to vapor. Thus adding a true vapor barrier on the inside (paint or poly sheet) still allows vapor to dry to the outside. It does not create a "sponge sandwich" because you presently do not have a vapor barrier on the exterior.

You're not planning paint & I'm personally unclear whether poly film or faced batts would be a good idea in your situation. I'll let the pros hash that out. I just would like to see the correct terminology used to prevent further confusion.
 
  #18  
Old 03-01-13, 05:14 PM
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Taping the foam would make it a WRB (weather resistive barrier) which is also what the Typar is. So if he tapes it he will have 2 WRB's. Nothing wrong with that in itself, other than it's redundant. Leaving the foam untaped will not hurt anything since there is a WRB (the Typar) behind it. But he said he installed the windows on top of the foam. If that's the case, then the foam HAS to be taped to make it a WRB. Otherwise water behind the foam would leak into the rough openings around windows and doors.

Witom said, "Polyiso, when taped is the only required and effective vapor barrier." This makes me think that he may be confusing "vapor barrier" with WRB.

Because Polyiso, when taped, is the only required WRB.

And again, Witom said, "3. Layer of house wrap added on top of polyiso (vapor barrier without extra thickness...)"

Which again shows that Witom is a little confused as to what the housewrap's purpose actually is. Housewrap is NOT a vapor barrier. It is just the opposite- it is vapor permeable. Its purpose is to serve as a WRB, protecting everything behind it from rain. If all the seams and edges on the housewrap are taped and sealed, it can also be a semi air-barrier. (I believe it's been commented on in the past that with all the staples and holes in the housewrap compromise it as a true air barrier, which I don't dispute.)

Hopefully the links and the advice given by others in the thread will help clear up these points.

@guy45068, Witom said in the first post that the polyiso was foil faced, and so when he tapes it, it will be both a VB and a WRB. (and as you pointed out, a better air barrier.)
 

Last edited by XSleeper; 03-01-13 at 05:44 PM.
  #19  
Old 03-03-13, 12:19 PM
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As far as interior plastic goes, from what I know, GBA and BS advise against it in all new construction, air conditioned homes and homes in zone 6. It's also a big no-no, when exterior vapor barrier is installed and in my case ISO or PIR is already there and not being removed. Actually added on, if anything. Taped it's air barrier and vapor barrier.

Interior plastic has to be installed and sealed perfectly to do it's work. Pretty much impossible, if you ask me and has to be done on entire room. So since my ceilings will be open for now and there is no way to put plastic on rim joist area, I will pass. Also, since outside has one air barrier, 2nd one inside will make the wall sandwich impossible to dry, both in and out.

I still think that the wall assembly needs a way to breathe to the inside. Also, makes me believe that houses with massive air (drywall) and vapor (plastic) barriers inside are healthy just because of lack of any insulation outside (so outward drying is possible).

I am positive my issue comes from either of 2 sources:
- cold sheeting itself (not enough R value outside)
- outward vapor drive (no vapor barrier inside)
- or both

Presence of mold in areas with 4" plastic make me think vapor drive wasn't a main problem (but then no 4" plastic install is perfect, especially with electrical boxes and lack of wall finish that would compress it to studs - unless of course no staples are used and everything is glued, taped and caulked in)

Since I can't consciously use plastic inside, because of reasons listed in the beginning of my post and just common-sense lack of any drying, I have to mainly deal with this problem on the outside of the house.

Using IRC FAQ: Insulating Sheathing Vapor Retarder Requirements — Building Science Information information, it looks like 1 more layer of 1" ISO should do. 1" ISO is R-6.5 aged and about R-8 to R-9 new. 2 layers of aged 1" ISO will add to R-13, probably little more because of air film between. That R-13 will have to counter-act R-19 between studs. Effectively less, of course, because of framing members, but it is probably little more than R-19 right on the OSB in stud bays because of OSB itself, air films and typar.

That's why, if I can get enough arguments for it, I would consider 2 additional 1" layers for the total of about R-20 outside. Trimming out openings outside would be just as much PITA as with 1 layer, I think. I plan on taping both layers, but then haven't found much info on adhesives vs fastening. Obviously you would want to limit the number of punctures to minimum, especially with strapping and siding coming on the top.

This still leaves a question on what to do inside, besides cleaning the mold. Additional mold-proofing? Picture framing stud bays with foam? Foaming entire stud bays? Or just nothing. I am leaning towards a thought that any vapor/air film on the inside of the OSB will not be a good or necessary, but "batt and flash" (1" foam in entire stud bay) is somewhat appealing.

After all said and done, if interior of my sheeting is above dew point and above freezing, even in the event of outward driven vapor in the winter, everything should balance out in the summer, or pose minimal risk in the winter, with controlled RH level.

House will be air conditioned. Heated in the winter using hydronic infloor and humidity balanced with forced air/humidifier to whatever RH I need. AC in the summer, as needed.
 
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