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

Lance Kairl sabale at bigpond.com
Sun Jun 25 21:55:26 UTC 2017


HI Jim,
You seam to have similar weather conditions to us here in areas of South Australia ,
I have removed straw from  cement rendered ( stucco) wall just a few days ago,  straw as fresh as  it was 17 years ago when it was put in.
And a few years ago  in repairing  a 50 year old straw panel ( strammit panel  , 50mm thick straw bound by wire ) home.( all sorts of plaint coatings), only had damage to the straw where water had got in.
Always  check the straw in the wall  ( behind electrical wall sockets  ,  a small hole  the can be sealed afterwards).

Where low Relative humidity , and liveable outside  temperatures  do not (often) get extreme it appears to me the risk to straw is mostly from direct ingress of free moisture ( water).
Maintenance and repair to surface cracks that allow moisture in is the main concern, especially if the straw is getting wet at every rain event.  

I have long held the opinion  that I have the best climate to build straw bale houses in, that is  warm, dry , and low relative humidity.
I am glad there may be others , low risk ( places in the world) .
 I respect the wisdom, skill and work of those building in   the high risk areas, being snow covered areas ,  below zero degrees outside and  a warm  , high humidity , inside , its got to be concerning
having a dew point  within the width of the wall.

While the thought of sealing up the surface of a bale wall still makes me nervous , my  experience  makes me more concerned about free moisture ingress,
Especially in areas similar to my  local climate . (  50km away  the rainfall can be 3 x  my rain fall and sustained lower temperatures  over winter and  higher Relative humidity in summer)

IN CONCLUSION
Breathable  surface  coatings would always be recommended.
And caution should be  high on the list when  retro work is undertaken, or consulting on an existing property.
Is there a small grain dryer or  building dehumidifier  that could ( cost effectively) be  installed to  give some confidence  about  the integrity of the straw.
And only with caution and some local wisdom  would I have the confidence say  " it will be ok"
It all needs careful consideration.

Cheers lance 
House of Bales



-----Original Message-----
From: Gsbn [mailto:gsbn-bounces at sustainablesources.com] On Behalf Of john rehorn
Sent: Saturday, 24 June 2017 7:40 AM
To: Global Straw Building Network <gsbn at sustainablesources.com>
Subject: Re: [GSBN] latex paint on lime or cement plastered straw bale walls

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>
> _______________________________________________
> Gsbn mailing list
> Gsbn at sustainablesources.com<mailto:Gsbn at sustainablesources.com>
> http://sustainablesources.com/mailman/listinfo.cgi/gsbn
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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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