[GSBN] URGENT! Drying moisture out of SB walls

Chris Magwood chris at endeavourcentre.org
Fri Apr 7 07:54:21 CDT 2017

It's not a cure-all by any means, but the silicate paints from 
Canadian-based Perma-Tint (used to be Eco-House) have worked extremely 
well for us: http://permatint.com/brick-staining-products/.

However, it's important to note that even a well-painted (or 
rainscreened) bale wall is still susceptible to rain penetration at the 
top of the wall and around all window/door framing. In every moisture 
issue I've ever been asked to inspect, the bulk of the water entering 
the wall is coming from a junction where plaster simply bumps into wood 
or a window frame. It's astounding how much water can enter a 1/16 
reveal-crack in a driving rainstorm...


On 2017-04-07 5:05 AM, Feile Butler wrote:
> Hi All
> Throwing my tuppence into the mix from the Emerald Isle - famously 
> green due to our impressive levels of rain.
> While you may succeed in drying out the walls, the weather will keep 
> on doing what it does ... and with climate change, it will only get 
> worse. We are definitely noticing an increase in frequency/intensity 
> of winter storms and in wetter summers here (oh joy!). In our 
> practice, we never specify lime applied directly on to bales. It just 
> cannot cope with the external moisture loads inflicted on it. There 
> are too many stories of rotting bale walls in Ireland.
> While there has been some discussion that the moisture levels recorded 
> in these bales are not over concerning (yet), the fact that there is 
> an appalling smell is a pretty good indicator that all is not well (as 
> long as other sources have been ruled out).
> Martin mentioned the building paper and that we don't know what it is. 
> We have heard reports of buildings where the construction moisture 
> levels were so high, that micro-porous breather membranes were 
> overwhelmed by the amount of water vapour trying to pass through as 
> the building dried out and basically self-sealed .... thereby creating 
> a situation where moisture became trapped in the building - not good. 
> This has been reported a few times for roof construction, not for 
> walls. But there is no reason why it might not be happening in walls - 
> it is just much more obvious when you are sitting in an attic space 
> and drips are rolling off the membrane. So when we can, we specify 
> cellular membranes like Intello - which act by osmosis (and can 
> reverse direction of vapour flow depending on vapour pressure loadings 
> internally and externally), rather than the micro-porous membranes.
> I would recommend adding a rain screen, as advised by John and others. 
> In Ireland, we design to keep the rain out and then we design another 
> line of defence for when the rain breaches the first detail ..... and 
> we have to design for horizontal and even upward driving rain.
> If this building was in Ireland, I would recommend drying it out by 
> whatever means necessary. If it means pulling off the lime render, 
> then so be it and I would then wrap the bales externally with a 
> cellular-based membrane (if the clients can afford it). If they can 
> dry out the bales without removing the lime, then this should be 
> adequate as the second line of defence and the addition of the 
> cellular membrane would not be necessary.
> If they want the appearance of a solid render, rather than timber 
> boards, then I would fix 50mm vertical battens to the dried-out bales 
> (covered with lime or with an appropriate membrane) to form a drainage 
> channel and ventilation space. Then apply render carrier boards. 
> Ensure that ventilation is retained at the top and bottom of these 
> boards. To save money, as there is a ventilated cavity behind, these 
> can be cement based (i.e.they don't need to be breathable). Or the 
> client can go full eco if they can afford it. Install anti-vermin 
> steel mesh at the bottom, but ensure that the cavity is still 
> ventilated and can drain out. Then apply lime render to the boards. 
> Use a good multi-direction mesh where the render boards connect back 
> into the other elevations.
> If the clients are happy to have vertical timber boards, I would still 
> install 50mm vertical battens behind the horizontal battens (fixings 
> for the vertical boards). Having a clear flowing drainage cavity 
> (uninhibited by horizontal battens) is key to keeping the rest of the 
> building dry.
> As the overhang is reasonable, you should not need to extend the roof, 
> as this detail can take a whole heap of rain. Only the window reveals 
> and cills will increase. I recommend a min. 50mm overhang for cills to 
> throw rain off the wall below.
> Cheers
> Feile
> Feile Butler
> feile at mudandwood.com <mailto:feile at mudandwood.com>
> www.mudandwood.com <http://www.mudandwood.com>
>     ----- Original Message -----
>     *From:* Martin Hammer <mailto:mfhammer at pacbell.net>
>     *To:* GSBN <mailto:GSBN at SustainableSources.com>
>     *Sent:* Friday, April 07, 2017 4:58 AM
>     *Subject:* Re: [GSBN] URGENT! Drying moisture out of SB walls
>     Hi all,
>     I agree with Derek that the straw close to the exterior could have
>     a moisture content significantly higher than the readings
>     provided. Especially near the bottom of the wall. I suggest the
>     owners obtain a longer probe or drill holes in at least a few
>     places in the exterior plaster in the bottom third of the wall to
>     take readings for the first few inches of straw. Enough to get a
>     clue about the highest moisture content of the straw in the walls.
>     One fact about the wall assembly that hasn’t been mentioned by the
>     GSBN moisture sleuths is that it has two layers of building paper
>     between the plaster and the bales. This could be a benefit
>     (allowing less water that has penetrated the plaster to reach the
>     straw) or a detriment (inhibiting the release of moisture in the
>     straw to the outside air, depending on its vapor permeability).
>     And we don’t know exactly what the “building paper” is. I imagine
>     that if water penetrated the plaster, and if the paper was
>     installed properly, almost all of that water would be stopped by
>     the two layers of paper, except maybe at fastener penetrations or
>     tears in the paper. Gravity should then pull the water down and
>     out, but only if there is sufficient means of safe escape at the
>     bottom of the paper/plaster.
>     A four foot overhang is substantial, but apparently not enough for
>     this exposure/climate. David’s idea of a 10’ porch overhang
>     certainly is one way to solve the problem. Or an exterior cladding
>     suggest by Derek and John. Or regarding water repellent,
>     colleagues in northern California have claimed success using
>     siloxane over lime or cement-lime plaster on straw bale walls. It
>     repels water but maintains good vapor permeability (I don’t know a
>     perm rating). I’m not sure if has been used successfully over clay
>     paster.
>     One other thought is regarding the use of heat on the interior to
>     drive moisture to the exterior. Wouldn’t that pull the moisture to
>     the drier/warmer interior instead, or do I have my moisture
>     mechanics backward.
>     Cheers,
>     Martin
>     */Martin Hammer, Architect
>     /*1348 Hopkins St.
>     Berkeley, CA  94702
>     510-525-0525 (office)
>     510-684-4488 (cell)
>     From: Gsbn <gsbn-bounces at sustainablesources.com
>     <mailto:gsbn-bounces at sustainablesources.com>> on behalf of Derek
>     Roff <derek at unm.edu <mailto:derek at unm.edu>>
>     Reply-To: GSBN <GSBN at SustainableSources.com
>     <mailto:GSBN at SustainableSources.com>>
>     Date: Thursday, April 6, 2017 at 6:18 PM
>     To: GSBN <GSBN at SustainableSources.com
>     <mailto:GSBN at SustainableSources.com>>
>     Subject: Re: [GSBN] URGENT! Drying moisture out of SB walls
>     I’m concerned that we don’t have enough data on current moisture
>     levels near the exterior of the wall.  If rain has entered the
>     straw through the exterior plaster, because of the extreme wind
>     and rain, the straw might be several percentage points wetter in
>     the first few inches under the exterior plaster skin.  As I
>     understand the moisture testing done so far, the readings have
>     been taken from the inside, and the probe probably never got
>     closer than 6” or further from the outside plaster.  I’m sure that
>     there is a desire to avoid adding visible holes/patches to the
>     outside plaster, but if this hesitation leads to severe decay in
>     the straw, that is obviously a poor trade-off.
>     One thing we can be certain of is that extreme, nearly horizontal
>     rain has been hitting these walls.  This year may have been worse
>     than average, but it is poor strategy to suppose that the same or
>     worse won’t happen again in other years.  That suggests that a
>     physical barrier is needed to protect these walls, along the lines
>     of the ventilated rain screen that John Straube described.  The
>     probability, and in my view, the certainty, that the exterior
>     plaster needs to be covered, ought to decrease the worries about
>     drilling a few holes in the exterior plaster, in order to take
>     additional moisture readings.
>     Derek
>     Derek Roff
>     derek at unm.edu <mailto:derek at unm.edu>
>>     On Apr 6, 2017, at 6:21 PM, Paula Baker-Laporte FAIA
>>     <paula at econest.com <mailto:paula at econest.com>> wrote:
>>     We have used Keim liquid silicate coatings over earth plasters in
>>     an area that was very susceptable to erosion from driving rain
>>     and had great success with it. They make many different products
>>     and do a lot of restorations with it in Europe and so I imagine
>>     they have a solution to use over lime. Coatings are clear or
>>     pigmented. They can also do very exact color matching if a sample
>>     is sent to them.
>>     http://www.keimpaints.co.uk/about_us/comparison_of_keim_mineral_paints_and_limewash/
>>     On Thu, Apr 6, 2017 at 2:19 PM, John Straube <jfstraube at gmail.com
>>     <mailto:jfstraube at gmail.com>> wrote:
>>         Hi all
>>         Interesting case because it looks like they did almost
>>         everything correctly. I am sorry to hear of their bad luck.
>>         The photo is quite telling, but I do wonder how the rain is
>>         getting in  at that angle (other than stupidly high levels of
>>         wind)
>>         I agree with you Dave that the numbers are not “run for the
>>         hills” but they are worrisome.
>>         Definitely worth checking for any of the obvious bulk water
>>         flaws and being more careful and complete in your MC
>>         measurements.
>>         I can be certain of one thing … there is definitely an amount
>>         of rain that will over whelm the lime plaster, and cause
>>         wetting of the straw.  That amount depends on the drying
>>         potential of the climate and the lime plaster thickness and
>>         properties.  Nothing magic about lime, it is just better than
>>         cement, and much better than unite.
>>         It is expensive and invasive to  dry the wall by drilling
>>         holes and blowing dry air. The hard part is the machine with
>>         dry air (desiccant driers are available from flood
>>         restoration companies).  One could simply blow heater air
>>         into holes… easier, still annoying.
>>         I would consider hanging a dark coloured (to collect solar
>>         heat) tarp or geotextile from the overhang edge/gutter to the
>>         grade to act as a highly ventilated (critical), rain screen. 
>>         This will stop further wetting and along drying.
>>         Also, adding heat to the inside will be helpful: increases
>>         the interior temperature where wetness is evident by even 5
>>         degrees will help, although a steady and spatially uniform 10
>>         or more will really make a difference in a matter of weeks. 
>>         I know people who have used arrays of heat lamps, plug in
>>         electric heaters with the door closed, and stoked up wood
>>         stoves to drive moisture out of walls.
>>         If the MC can get below 20% or so, then I think you have a
>>         lot of time to design an upgrade… almost all coatings have
>>         limits and are not as good as a real over clad.  Xypex is a
>>         pore blocker (hence reduces vapor permeance) that reacts with
>>         alkalinity to form calcium silicates.  Could work well with
>>         fresh lime, but probably wont work well with the exterior
>>         carbonated surface of the lime.  I would be quite skeptical
>>         of most coatings… products like Silanes certainly work and
>>         can make a pretty big difference, we just dont know if they
>>         make enough of a difference.
>>         If acceptable, it is pretty cheap and simple to install
>>         horizontal 1x4’s with 45 degree sawn top edges over the lime
>>         plaster at, say 36” on centre or so, then add vertical boards
>>         with generous joints.  Or add vertical 1x4 and clapboard
>>         siding (much more effective at rain shedding).  This will
>>         reduce the wetting by a factor of 10 or more, and only slow
>>         drying by a bit (if well ventilated) so a pretty massive
>>         improvement and certain to solve driving rain problems (if
>>         that is what this is).
>>         Planting a hedge and some trees a dozen yards upwind would
>>         also be a good idea.
>>         More good pictures like that one sent would possibly help
>>         provide more ideas.
>>         John
>>         > On Apr 5, 2017, at 7:42 PM, David Arkin, AIA
>>         <david at arkintilt.com <mailto:david at arkintilt.com>> wrote:
>>         >
>>         > Hello Global Balers:
>>         >
>>         >  A CASBA member poses the questions outlined in the
>>         situation below.  I’ve attached my responses below the query
>>         and photo, and invite any of you to weigh in with further
>>         recommendations, follow-up questions or anecdotes that may be
>>         useful.
>>         >
>>         > Best,
>>         >
>>         > David Arkin, AIA, Director
>>         > California Straw Building Association
>>         >
>>         > ps: Joins us for CASBA’s 2017 Spring Conference, May 5-7 in
>>         the San Francisco Bay Area, featuring architect Craig White
>>         of the U.K.:  "Towards a Photosynthetic Architecture -
>>         Renewable Buildings for the Circular Carbon Economy”. 
>>          Registration is open:
>>         http://www.strawbuilding.org/event-2497515
>>         <http://www.strawbuilding.org/event-2497515>
>>         >
>>         > *  *  *  *  *
>>         >
>>         > I’m  hoping you can address some of my questions or direct
>>         me to anyone with experience dealing with this problem, or
>>         anyone who has any insights into causes and solutions.
>>         >
>>         > I was contacted this morning by a client just south of
>>         Portland who has measured high levels of moisture in their
>>         straw bale walls, and is asking for advice on how to deal
>>         with the problem.
>>         >
>>         > The core questions I have are these:
>>         >
>>         > 1.       Assuming there isn’t a bulk water leak from the
>>         roof, downspout, or window, can wind-driven rain account for
>>         high levels of moisture in a straw bale wall assembly?  In
>>         other words, what does it take for a properly installed lime
>>         plaster to be overwhelmed by wind-driven rain?
>>         >
>>         > 2.       What are the options for drying the wall out? 
>>          Waiting for dry weather (summer!) may not  be an option as
>>         wet straw bales may not survive that long.
>>         >
>>         > 3.       Once the wall is dried out, assuming there isn’t
>>         significant permanent damage to the bales, what surface
>>         treatments are available that would prevent liquid moisture
>>         from soaking into the walls, yet keep them vapor permeable. 
>>          I can imagine several landscaping and rain screen (siding)
>>         solutions, but am not familiar with surface treatments.
>>         >
>>         > Background Information.
>>         >
>>         > Details about the wall assembly.   The SB walls are on a
>>         raised floor.   The space between the sill plates was filled
>>         with rock wool insulation and capped with 1Ž2” plywood to
>>         handle the bale weight.  The wall assembly has 2-string rice
>>         straw bales laid flat, and is part of the building’s shear
>>         wall system, using 17 gauge lath and lime plaster (exterior
>>         and interior).   Instead of applying a finish coat of lime
>>         plaster the client chose to apply a lime based paint from
>>         BioShield.    I didn’t plaster the structure or apply the
>>         lime paint, but believe it was done by capable professionals
>>         in accordance with best practices.  The bales were stack in
>>         April-May of 2016.  Bale wall moisture readings just prior to
>>         plastering averaged 14.1%.   The wall was prepped to receive
>>         a lime plaster—2-layer building paper stapled to all wood
>>         framing, shingled to shed water, etc.  The windows have
>>         sills, the 4’ roof overhangs are guttered and the downspout
>>         installed properly.   The walls were plastered during late
>>         spring and early summer.   Three coats of exterior lime paint
>>         were applied in late summer-early fall.    When I visited in
>>         November, I saw vertical cracks at the corners only (where I
>>         always see them, regardless of how much corner-aid or exp.
>>         metal lath is underneath!).
>>         >
>>         > Building site.  The house is located in an open field and
>>         has no barriers to wind driven rain.    The general
>>         contractor, who happens to live next-door, told me the field
>>         is like a wind tunnel.  He reported that since it began
>>         raining in the fall of 2016 he hasn’t seen the walls look dry
>>         more than a dozen times.
>>         >
>>         > The problem first came to my attention about a month ago
>>         when the client told me they smelled something awful in one
>>         of their rooms—the one with the most weather exposure (S. W.
>>         corner of building, labeled “office” on the plans).   I
>>         haven’t visited the site, but advised them to first
>>         investigate and rule out all the other likely possible causes
>>         for an odor (e.g. decomposing straw piled near the house,
>>         something else rotting in the crawl space, etc.), and if the
>>         odor persisted, to gather quantifiable information, including
>>         using a moisture meter probed into the wall near outlets,
>>         which they have now done, (see below).
>>         >
>>         > <image001.png>
>>         >
>>         >
>>         > <image002.png>
>>         >
>>         > The office is in the S. W. corner of the structure.  I’m
>>         not familiar with the probe they used, but it’s likely that
>>         the shaft is about 18” long, and if used as described to me,
>>         “poked in a 45 degree angle from the interior of the wall
>>         near the outlets”, probably penetrated about 5” into the wall
>>         when it reads 8”, and about 12” into the wall where the chart
>>         says “full in.”  From all the points they gathered data,
>>         moisture readings were higher towards the exterior of the wall.
>>         >
>>         > My understanding is that lime plasters will absorb and then
>>         release liquid moisture from wind driven rain, and are quite
>>         able to handle regular, frequent wettings without
>>         compromising the straw beneath.   If bulk water isn’t
>>         entering the wall through a breach in the flashing or another
>>         leak of some kind, is it possible that an unusually wet
>>         winter (I believe the Willamette Valley is experiencing a
>>         well-above average rainfall year like much of the west coast)
>>         could create the moisture levels seen below?   Is it possible
>>         that the  water is soaking in, and just keeps soaking in,
>>         unable to dry out because of the constant rains?
>>         > <wind driven rain on lime plastered SB wall, S exposure..jpg>
>>         >
>>         > *  *  *  *  *
>>         >
>>         > [Arkin comments in reply]
>>         >
>>         > The moisture readings aren’t as high as I would’ve guessed
>>         based on your description … that’s perhaps good news.  We had
>>         a wall at the Real Goods Solar Living Center that was an
>>         exterior site wall with very little overhang, and it would
>>         get pounded by the rain.  We had a moisture reading over 50%!
>>         However, in Hopland’s sunny hot climate it dried out between
>>         rains and now with a new broad overhang it is doing fine, 20+
>>         years later.  Similarly a small outbuilding on that same site
>>         was flooded to the middle of the second level of bales.  It
>>         was earth plastered and we advised to simply let it be and
>>         see what happens.  The building has no windows or doors (it’s
>>         a ‘welcome pavilion’) and once again it dried out promptly
>>         and has been fine.
>>         >
>>         > At the same time, I’m recalling an olive oil facility that
>>         was on top of a hill in San Luis Obispo County, that had
>>         wind-driven rain penetrate cracks in the Gunite finish on
>>         their bale walls, to the point of black goo oozing out the
>>         base. That’s when you know you have real trouble. They
>>         drilled holes and drove air into the bottom of the walls, and
>>         also put a layer of breathable waterproofing on the exterior
>>         of the walls.  Similar to your case here, it was the windward
>>         side that had the worst problems, but rain swirling around
>>         the building caused some issues on the leeward side too.
>>         >
>>         > Here are my opinions on your questions, but let me be the
>>         first to admit there are others who could answer these better
>>         than me:
>>         >
>>         > 1.  The photo sure makes it look like wind driven rain, and
>>         at quite an angle! Another 10’ of overhang (aka a porch)
>>         along that facade seems in order. Exactly how much moisture
>>         it takes to overwhelm a lime plaster wall is difficult to
>>         say.  I’m recalling studies done by the University of Bath
>>         that placed plastered wall samples in very exposed marine
>>         climates to determine this.  You might search for this,
>>         perhaps starting with EBNet’s BuildWell Library. Bruce King
>>         may be able to connect you with Pete Walker, or you could try
>>         to reach him directly.
>>         >
>>         > 2.  Again, the numbers aren’t so high that invasive
>>         measures need to be taken. I’d suggest putting some more
>>         powerful heaters on the interior, and aim to drive the
>>         moisture out toward the exterior.  At the same time they
>>         should deploy tarps or some other means of keeping wind
>>         driven rain off the walls going forward, but let the sun and
>>         warmth at them otherwise.
>>         >
>>         > 3.  Again, my first suggestion is a longer porch roof along
>>         that whole facade, perhaps with some landscaping or something
>>         to break up the laminar wind.  I suppose a deployable system
>>         of a rain screen of some sort could also be used.  Allowing
>>         the walls to see sun this spring and summer will be good
>>         though.  Xypex is a product that folks have applied to walls,
>>         but I’m more familiar with its application on cement stucco
>>         than lime, so research that a bit first.  David Easton
>>         suggests Glaze ’n’ Seal on his earth walls.  I believe both
>>         have that waterproofing effect while still remaining breathable.
>>         >
>>         > As you know, both the plaster and the straw have a
>>         significant capacity to store and release moisture, and it
>>         seems they are doing exactly that.  I can’t say for certain,
>>         but this being their first season they may not be damaged to
>>         the point of needing to be replaced, but the smell detected
>>         is concerning.  Getting them to dry and then keeping them dry
>>         going forward is key, and if necessary some replacement may
>>         be needed, but I’d advise trying to avoid that first.
>>         >
>>         > *  *  *  *  *
>>         > Arkin Tilt Architects
>>         > Ecological Planning & Design
>>         >
>>         > Please Support (or Join?!) my 2017 Climate Ride (bicycling
>>         300 miles from SF to SLO, June 9-13, with a fundraising goal
>>         of $5,000 to support Straw-Bale outreach)
>>         >
>>         http://support.climateride.org/index.cfm?fuseaction=donorDrive.participant&participantID=4497
>>         <http://support.climateride.org/index.cfm?fuseaction=donorDrive.participant&participantID=4497>
>>         > Thank you!
>>         >
>>         > David Arkin, AIA, Architect
>>         > LEED Accredited Professional
>>         > CA #C22459/NV #5030
>>         >
>>         > 1101 8th St. #180, Berkeley, CA  94710
>>         > 510/528-9830 ext. 2# <tel:510%2F528-9830%20ext.%202%23>
>>         > www.arkintilt.com <http://www.arkintilt.com/>
>>         >
>>         > "There is no way to peace. Peace is the way."
>>         > — A. J. Muste
>>         >
>>         >
>>         >
>>         > _______________________________________________
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>>     -- 
>>     Paula Baker-Laporte FAIA,BBEC
>>     Econest Architecture Inc.
>>     www.EcoNest.com <http://www.econest.com/>
>>     paula at econest.com <mailto:paula at econest.com>
>>     Phone: 541.488.9508
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Chris Magwood
Director, Endeavour Centre

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