[Strawbale] cracks in the plaster

[gary dorn]

>I know, I have to expect some cracking...but...
>
>We've built a two story modified post and beam strawbale house.  We 
>are finally plastering the inside of the house, on the exterior bale 
>walls, and on the interior partition walls, some of which are dry 
>wall, and some are plywood.  We've put on probably three coats of 
>lime plaster, and got the typical cracks in the plaster as it dried. 
>We rubbed all of these out.  Now that we are on the final coat, 
>every room is cracking along the bottom of the box beam.  As time 
>goes on, these cracks are getting worse.  One room we've put on a 
>lime wash, and the cracks really show here!  I'm trying to figure 
>out why this is happening, and what to do about it.
>  snip>


this sounds like a very good opportunity to do a case study.

Write down the conditions, make observations. If you can post some 
drawings and photos of you construction and current status that would 
help.

Googles Picassa photo sharing may  work http://picasaweb.google.com

now is the cracking  at the top of the ground floor or 2nd floor, is 
it localised around the roof bearing /floor bearing points, or 
equally cracking along the top of the wall.

What was the time between each coat of plaster, and what ratio of mix 
did you use ie 3s:1l,  5s:1l ?
how well did you float the lime plaster.

Was the timber used for your posts, box beams etc green or  dried - 
you could be having a little shrinkage there

Lime dried initially by evaporation then slowly by carbonation ( 
reaction with the air) a slow drying is better than a fast drying. 
Cracking is first coat is expected because of the massive sucking and 
absorption of the water into the dry bales. After allowing for a good 
deal of time to dry say 4-6 weeks, the second coat is applied and 
almost no cracking ought to show up, particular if it is occasionally 
misted with water. floating this coat 2-3 times makes it harder, more 
compact and more stable.

Having cracking along the top under the top plate would suggest extra 
compression along the top probably by some extra load or massive 
movement of the frame.

I am curious about the top plate design, and where it is positioned 
on the top .
please advise

-- 
Gary Dorn
Permaculture architect
<gary.dorn at eepo.com.au>
Perth, Western Australia, Australia
integrating Permaculture , Organic Solar architecture,
Straw bale construction & Solar and wind power systems
http://web.mac.com/dornworks/iWeb/HOME/Dornworks.html