I am about to start a fresco on a cement wall.
I had to clean the wall before from the paint, and i am wondering (before I put my first layer of lime plaster) if I should use an acrylic bonding agent between the concrete wall and my first layer of lime...
Could a product like this acrylic agent be dangerous for lime and eventually deteriorate the pigments?

Any ideas about adding cement in the lime putty to make it more resistant? The fresco painter Jean Charlot did it in the 50's, his work is in perfect shape today, it doesn't look like the cement damaged the pigments or the lime mortar.

LAST EDITED ON 28-Dec-01 AT 02:32 PM (PST)
 
<<Any ideas about adding cement in the lime putty to
<<make it more resistant? The fresco painter Jean
<<Charlot did it in the 50's, his work is in perfect
<<shape today, it doesn't look like the cement damaged
<<the pigments or the lime mortar.

Hi Mathieu,

The pigments are fine with cement, the problem is a setting time - more cement - the faster the plaster sets. If added to intonaco you will have only a couple or so hours of painting time. Unless you paint outdoors you should not add cement to arriccio (brown) coat and intonaco.

You should add cement to scratch coat and perhaps to rough coat.

Read the article on preparation:

http://www.truefresco.com/albuquerque/preparation_albuq.html

for your (prev. painted and cleaned) wall I would line it up with tar paper attach/fasten expanded metal mash (found in masonry yard) and use scratch/rough/brown(arriccio)intonaco. or take a hammer and a grinder with concrete disks and "wack" (score, dent, grove) the wall - that will be your scratch coat. You can use "concrete" glue from masonry yard but do not put it into the mix, just apply it to the wall before the first(rough) coat 2-3-8 (cement-lime-sand)

http://www.truefresco.com/workshop

ilia, thank you for those very valuable tips.
I've red with attention the albuquerque fresco workshop "report" on your site, you insist on angular sand as opposed to round sand, it seems that the only sand I can get here is round, ocean sand but washed and sterilized, guarantied without salt, I'm wondering if this sand would allow me to do a decent plaster.
I am also wondering if the cement can be incorporated in the putty many days in advance, if is has the same capacity as lime, to remain moist and workable after a week in a air proof bucket.
In other words, is it possible to mix all the ingredients in advance includind Portland cement?

Hi Mathieu,

No, cement can not be incorporated and be stored because it's process of setting is different from lime setting. In cement water activates the reaction (setting) in lime water prevents the reaction(setting).
In lime putty carbon monoxide in the air activates the lime. In lime plasters water prevents carbon monoxide from reaching the lime.

On the interior wall you need cement only in the scratch coat. You should use white portland cement and you can use hydrated (dry) lime for the mix type N

About sand: It is important for the sand in lime plasters to be angular not round since the layers must "have a tooth" to "stick" to each other. I believe that you can get volcanic "tuff" (i do not know if this is the right word) in Hawaii. You can use it instead of sand, in Italy it was often added to sand
for better "tooth" and at times sand was not used at all, for intonaco they used "marble dust".

About sand being "guaranteed" to be without salts - do you want to experiment to prove their guarantee?
I am skeptical about that - why do you wash sand?
To get read of organic particles and dust - solids that are lighter than water. When sand is being washed those particles float on top and you remove them (sand falls to the bottom). Salt dissolves in water and you need a river of it(water) to wash it away.

http://www.truefresco.com/workshop