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

Jim Reiland jim at manyhandsbuilders.com
Fri Jun 23 14:53:06 CDT 2017


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



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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>
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http://sustainablesources.com/mailman/listinfo.cgi/gsbn


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