[GSBN] latex paint on lime or cement plastered straw bale walls

john rehorn rehorn at frontier.net
Fri Jun 23 17:10:23 CDT 2017


It would be cool if you could get to the bales and inspect them, even in a 4 inch by 4 inch region.  Also, interviewing the residents to gain insight as to the impact they have had regarding moisture.  This would help us all. I have a friend who did an addition to an sb after 20 or so years.  They used cementatious stucco on the outside, and I do believe they put up felt and then stucco wire.  The removed bales looked as fresh as when they were put in.  Southwest Colorado is a dry climate with monsoonal moisture in the late summer and sometimes heavy snow and even winter rain.  This observation goes against (non)conventional wisdom.

Seems like the best method would be to score the plaster aggressively and skim a nice color coat over everything.  Where clay meets clay, there would be moisture migration.

I have another friend who procured a bale from a remodel of a 150 year old Nebraska sb.  The bale was yellow prairie grass and there was even a moulted snake skin in the bale.  All looked like it could have been pulled out of a barn having been stored a year or two.  The stucco looked like a lime render, and I wouldn’t have been surprised if at some point in the life of the house, someone took latex to the walls.

This is all just anecdotal, but I hope useful.

John Rehorn 
> On Jun 23, 2017, at 1:53 PM, Jim Reiland <jim at manyhandsbuilders.com> wrote:
> 
> Hi everyone, 
> 
> I'm fortunate to have over forty permitted straw bale residences here in my
> S. Oregon county; as these homes resell and second owners decide to make
> changes I sometimes have an opportunity to see how the walls--some of them
> twenty years old--have held up.   
> 
> Something I occasionally see is latex paint on the interior of plastered
> straw bale walls.  I'm recalling that a few coats of latex paint may be
> fairly permeable, but that many more layers could effectively seal the wall
> surface, preventing moisture vapor from moving through the wall.  
> 
> So far I have run into latex paint at only three coats--a primer and two
> cover coats--over a lime or cement-lime plaster.   
> 
> Is the straw bale wall in any danger with three coats of latex paint?  I
> understand that latex paints have different characteristics--some may be
> more permeable than others--but in my experience the new owners don't have
> access to that information.   
> 
> If the paint needs to be removed so a more permeable color alternative can
> be used, e.g. pigmented lime wash or plaster, etc., does anyone have
> experience with removing it?   I imagine that may depend on the texture of
> the plaster.  Yesterday I saw a painted finish plaster with the texture of
> popcorn--it may have been sprayed on--sure didn't look troweled!   A few
> weeks ago I saw a painted wall that was much smoother.    Sandpaper, a
> scraper, and possibly paint remover might work on the smoother finish...but
> not on the more textured surface. 
> 
> If the straw bale wall is OK at two or three coats, is there a tipping point
> where additional latex paint layers effectively seal the wall?  
> 
> The climate here in S. Oregon is similar to most of N. California--hot dry
> summers, relatively mild, wet winters characterized by regular rainy spells
> alternating with dry periods.   Most of the straw bale homes I have seen do
> not have mechanical air conditioning, so while they may be naturally cool
> inside when it's hot outside, it could be a different challenge than is
> faced by people who use mechanical air conditioning in regions with hot,
> humid summers and cold, wet winters.  
> 
> Thanks for any experiences, insights, and explanations you can offer on this
> subject.   I apologize if this topic has come up before and answers are
> already somewhere in the archives.
> 
> Jim
> 
> Jim Reiland
> Many Hands Builders
> 541-899-1166
> 541-200-9546 cell
> jim at manyhandsbuilders.com
> www.manyhandsbuilders.com
> 
> 
> 
> -----Original Message-----
> From: Gsbn [mailto:gsbn-bounces at sustainablesources.com] On Behalf Of
> gsbn-request at sustainablesources.com
> Sent: Friday, June 23, 2017 10:23 AM
> To: gsbn at sustainablesources.com
> Subject: Gsbn Digest, Vol 71, Issue 3
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> Today's Topics:
> 
>   1. Re: Load-bearing straw bale idea (Derek Stearns Roff)
>   2. Re: Load-bearing straw bale idea (Derek Stearns Roff)
> 
> 
> ----------------------------------------------------------------------
> 
> Message: 1
> Date: Fri, 23 Jun 2017 17:09:02 +0000
> From: Derek Stearns Roff <derek at unm.edu>
> To: Global Straw Building Network <gsbn at sustainablesources.com>
> Subject: Re: [GSBN] Load-bearing straw bale idea
> Message-ID: <AA7E4B63-7ABD-4DDD-9181-887DB4E2B7FF at unm.edu>
> Content-Type: text/plain; charset="utf-8"
> 
> Hi, Rikki,
> 
> It sounds like your architect plans what we call a ?gable roof? in the US.
> I don?t know if anyone has tried the design shown in your architect?s
> drawing, but I would advise against it.  It asks bales to do what they are
> least good at- resisting point loads/forces.  A ridge beam in this kind of
> roof framing will bear about half the weight of the roof.  That isn?t too
> bad for a lightweight metal roof on a sunny day in summer.  When the roof is
> covered by two feet of snow, or clay tiles, or a couple of layers of asphalt
> shingles, a large amount of weight is concentrated on one spot in the top
> bale, and on the gap between two bales on the second row.
> 
> The thin wooden panels shown will help a little bit, but they, too, will
> flex under load.  When roofing loads are distributed evenly, I don?t think
> that ?creep?, the slow deformation of bales under prolonged load, is a
> severe problem in most strawbale houses.  In this design, creep would
> probably be a factor, and the ridge beam could get a little lower each year.
> 
> If the pyramid of bales shown in the drawing was faced with plywood on the
> inner and outer faces, it would increase the resistance to deflection by
> about 1000 times, I?m guessing.  This would be a much more reliable method
> of transferring the roof loads to the wall, and then to the foundation.  It
> might be necessary to shave those bales down by the thickness of the
> plywood, to get the dimensions that you want from the bale and plywood
> composite.
> 
> Other architects and engineers on this list may have better ideas.  This is
> the best approach that I have thought of, which remains very similar to the
> architect?s drawing.
> 
> Best wishes,
> Derek
> 
> Derek Roff
> derek at unm.edu<mailto:derek at unm.edu>
> 
> 
> 
> 
> On Jun 23, 2017, at 9:06 AM, Rikki Nitzkin
> <rikkinitzkin at gmail.com<mailto:rikkinitzkin at gmail.com>> wrote:
> 
> Hi all,
> 
> I forward a petition from a Spanish architect who wants to know if his idea
> has been tried, and if it worked.
> 
> He is planning to build a Load-bearing SB home. The roof will have two
> ?waters? (what is that called in english?)- creating a triangular gap on
> both sides of the roof.
> 
> He wants to try to put the main beam (Spanish architecture doesn?t use
> triangular rafters, but a main roof beam, with the other beams resting on
> it) directly on the bales. His idea is to put a wooden panel on top of each
> row that is above the roof-plate, until reaching the main beam- using very
> well compressed bales.
> 
> Has anyone tried this?
> 
> Here is a drawing of the idea:
> 
> <hastial Alejandro.jpeg>
> _______________________________________________
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> Message: 2
> Date: Fri, 23 Jun 2017 17:17:18 +0000
> From: Derek Stearns Roff <derek at unm.edu>
> To: Global Straw Building Network <gsbn at sustainablesources.com>
> Subject: Re: [GSBN] Load-bearing straw bale idea
> Message-ID: <C2BE6169-431E-4E22-B21B-EB00F61FDBF9 at unm.edu>
> Content-Type: text/plain; charset="utf-8"
> 
> I was wrong in my last message, saying the weight on a gable roof ridge beam
> is 1/2 the total weight of the roof.  I should have said the roof beam takes
> 2/3 of the weight.  (This is in a roof using simple rafters, as Rikki
> indicated, rather than trusses.)
> 
> Derek
> 
> Derek Roff
> derek at unm.edu<mailto:derek at unm.edu>
> 
> 
> 
> 
> On Jun 23, 2017, at 11:09 AM, Derek UNM
> <derek at unm.edu<mailto:derek at unm.edu>> wrote:
> 
> Hi, Rikki,
> 
> It sounds like your architect plans what we call a ?gable roof? in the US.
> I don?t know if anyone has tried the design shown in your architect?s
> drawing, but I would advise against it.  It asks bales to do what they are
> least good at- resisting point loads/forces.  A ridge beam in this kind of
> roof framing will bear about half the weight of the roof.  That isn?t too
> bad for a lightweight metal roof on a sunny day in summer.  When the roof is
> covered by two feet of snow, or clay tiles, or a couple of layers of asphalt
> shingles, a large amount of weight is concentrated on one spot in the top
> bale, and on the gap between two bales on the second row.
> 
> The thin wooden panels shown will help a little bit, but they, too, will
> flex under load.  When roofing loads are distributed evenly, I don?t think
> that ?creep?, the slow deformation of bales under prolonged load, is a
> severe problem in most strawbale houses.  In this design, creep would
> probably be a factor, and the ridge beam could get a little lower each year.
> 
> If the pyramid of bales shown in the drawing was faced with plywood on the
> inner and outer faces, it would increase the resistance to deflection by
> about 1000 times, I?m guessing.  This would be a much more reliable method
> of transferring the roof loads to the wall, and then to the foundation.  It
> might be necessary to shave those bales down by the thickness of the
> plywood, to get the dimensions that you want from the bale and plywood
> composite.
> 
> Other architects and engineers on this list may have better ideas.  This is
> the best approach that I have thought of, which remains very similar to the
> architect?s drawing.
> 
> Best wishes,
> Derek
> 
> Derek Roff
> derek at unm.edu<mailto:derek at unm.edu>
> 
> 
> 
> 
> On Jun 23, 2017, at 9:06 AM, Rikki Nitzkin
> <rikkinitzkin at gmail.com<mailto:rikkinitzkin at gmail.com>> wrote:
> 
> Hi all,
> 
> I forward a petition from a Spanish architect who wants to know if his idea
> has been tried, and if it worked.
> 
> He is planning to build a Load-bearing SB home. The roof will have two
> ?waters? (what is that called in english?)- creating a triangular gap on
> both sides of the roof.
> 
> He wants to try to put the main beam (Spanish architecture doesn?t use
> triangular rafters, but a main roof beam, with the other beams resting on
> it) directly on the bales. His idea is to put a wooden panel on top of each
> row that is above the roof-plate, until reaching the main beam- using very
> well compressed bales.
> 
> Has anyone tried this?
> 
> Here is a drawing of the idea:
> 
> <hastial Alejandro.jpeg>
> _______________________________________________
> Gsbn mailing list
> Gsbn at sustainablesources.com<mailto:Gsbn at sustainablesources.com>
> http://sustainablesources.com/mailman/listinfo.cgi/gsbn
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