[Strawbale] possible additive for lime plaster

[Chris Green]

lgweaver wrote:
> seen this posted on another list. thought it would be useful here.
>
>  >>  http://www.nycon.com/default.htm <http://www.nycon.com/default.htm>
>   
The link connects to a company which markets the new Kuraray PVA fibers 
meant to be used in strengthening concrete and reducing the amount of 
cracking which may occur.

PVA stands for Polyvinyl Alcohol ( not to be confused with PVC, or 
polyvinyl chloride. ) The important point about  PVA fibres is that when 
they are added to concrete, at a rate of one to two pounds per cubic 
yard, and at a cost of less than $3 a yard, the fibers form a chemical 
bond on the molecular level with the stuff in concrete.

Unlike steel, which can rust, fiberglass, or other similar fibers.

With strengths up to 203,000 psi / 1400 MPa these fibers are very strong 
and help prevent microcracks from forming.  
They are being sold as an additive to reduce cracking in concrete, and 
there is some talk of being able to eliminate the use of steel 
reinforcement in some applications, such as floor slabs.

PVA fibers are said to reduce cracking by  40% and more when compared to 
controls in side by side tests.
No cracks, no water penetration, no spalling caused by ice formation.

If used in straw bale construction, the stucco finish may prove to be a 
lot stronger than an ordinary cement render with chicken wire/ stucco 
lathe in it.
One can imagine several  potential benefits to using these fibers:
1: With the fiber added, there should be fewer cracks to allow moisture 
penetration.
2: Since-- or rather if -- the stuccoed wall assembly is stronger, the 
wall can carry more of a load.  This opens up the possibility of sb 
buildings with load bearing walls taller than two stories. A Warning: 
Before anyone jumps up and starts building a three- or four story SB 
load-bearing wall, though, his notion should be tested by engineers.
3: If the additive does prove to add significant strength to the walls, 
it may be possible that the render can be applied as a thinner layer, 
thereby reducing the overall amount of portland cement used.
That means less CO2 produced.

In the post Lee quotes, I said:
> >>  I hope someone will test it in a lime plaster to see
>  >>  if it works as well with lime.
>   
I said that because I have no idea if the same chemical and molecular  
bonding that happens in concrete will also happen in lime plaster.
It sure would be nice if it did...
>  >>  The low price is astounding, too.
>   
About $2.85 US per pound, or $114US  for a 40 pound bag.  For a 20' x 
20' by 10" suspended concrete slab that adds about $35.18 to the cost of 
the slab.
Cheap added insurance if nothing else.
Charmaine Taylor of www.dirtcheapbuilders.com has been experimenting 
with it, and advises that the ferrocement/ thin shell concrete builders 
are quite excited about this new material.
> Yes I have used the fiber in plaster over a test 
> surface, it  seems 
> fine,  the wee fibers can be smoothed down with a 
> trowel if they stick 
> out, but that was not  often.    but I cant report on 
> any long term  
> use of it yet.
>
> SInce it -PVA fiber - is made for cement use, and lime 
> is the main 
> component of cement, then I am trusting it is fine in 
> lime plasters,  
> they are not load bearing, and also in a ,mortar for 
> stone or brickwork 
> are not in a critical load bearing use.
>
>   I am guessing the PVA  creators have tested it with 
> lime stright, but 
> not certain.
>
>
> check out the dicussion archives at 
> www.ferrocement,net, a lot of us at 
> the ITSA confrence  bought  sacks of it, and  it is 
> more pricey than 
> straight Nycon  fibers, but has much stronger use 
> specs.
>
>
> Charmaine Taylor Publishing
> www.dirtcheapbuilder.com
More links about PVA fibers:
http://www.findarticles.com/p/articles/mi_m0EIN/is_2005_Nov_9/ai_n15786264
http://concreteproducts.com/mag/concrete_bond_strength_improves/

The manufacturer:
http://www.kuraray-am.com/pvaf/overview.php
Note the photo here of the test sample being bent in a hydraulic press. 
Wow.

To close, PVA fibers seem to have a lot of possibilities beyond reducing 
cracks in floor slabs.

Cheers,

Chris Green.