[Strawbale] used to much sand to cement

[Rob Tom]

On Tue, 03 Jul 2007 06:31:46 -0400, Bruce Fraser  
<bruce_fraser at hc-sc.gc.ca> wrote:

>
> I just plastered much of my south interior wall and parts of the exterior
> south and north wall. Some of the batches I think had to high a sand  
> ratio (maybe 6 sand to 1 part cement) and I am worried it might not dry  
> hard.
> Does anyone have any suggestions for how to harden up the plaster? It was
> done between 8 am and 6 pm Sun July 2. Should it be done asap or after it
> dries?

Bruce;

While a 1 part cement (+ plasticiser presumably) to 6 parts sand mix is a  
bit on the lean side, it's not an overly poor mix and should yield good  
results.

The scratch coat should typically be a "poor" mix anyway.

What is probably more critical is:
   (1) the water to cement ratio in the mix
        and
   (2) retention of mixing water in the plaster during the curing period
        and
   (3) proper sand particle size and shape (ie coarse, sharp)

I don't know of any way to harden a poor quality plaster other than to  
speculate about the possibility of slathering on something like Acryl 60,  
a chemical goop that is typically used as an admixture during the mixing  
process to improve the mechanical properties of Portland cement plasters.  
(Google it, for further info).

I had thought about simply mixing up a slurry of Portland cement and water  
and painting it on but it (and quite likely, products like Acryl 60)  
probably wouldn't penetrate very deeply into the plaster and may just  
result in something like a glaze, which probably isn't a very good thing  
to have.

Although it's likely too late for you (Bruce) now, it would likely have  
just been best to implement a moist curing process whereby the mixing  
water was retained in the curing plaster for a week or more, to ensure  
that moisture was available to the cement in the mix so that full  
hydration of the cement could occur.


-- 
=== * ===
Rob Tom
Kanata, Ontario, Canada
< A r c h i L o g i c  at   C h a f f Y a h o o  dot  C a  >
(winnow the chaff from my edress in your reply)