hey mates ,
My name is hesam and I live in Iran . I don't have any experience as a plasterer ,but , It's been a while that I've been trying to recreate and make my own lime plaster(marmorino) ,needless to say that haven't had any luck so far .
I joined this forum to see if I can find help.
here is what I know ,
the traditional recipe for venetian plaster is aged putty + granulated marble powder and probably some additives .
as you know , slaked lime is calcium hydroxide . I bought 2 samples
form Italy and sent off to lab . the composition was :
32 percent water, 58.5 percent calcium carbonate , 8.84 percent
calcium oxide , 0.68 some kind of polymer .
you can see here that there is no trace of calcium hydroxide .
all of it has turned to calcium carbonate .
( to avoid confusion ,I must add that samples were packed air tight
and during the whole procedure of analyzing the exposure to
calcium carbonate was minimal ).
and as you can see , there is about 8 percent cao present in the
composition , meaning that lime hasn't undergone aging otherwise
it would have hydrated entirely .
given that the amount of polymer is less than one percent , this
material can't be considered synthetic marmorino .
these samples were very plastic and workable , and could be
polished to a high sheen .
so , how does it work ?
i presume that the shiny surface of the venetian plaster is because
of formation of minute calcite crystals on the surface which will be
oriented under the trowel during polishing .
and the illusion of depth is also because if calcite crystal ,
given that calcite is a birefringent crystal .
well , according to my experiments portlandite (calcium hydroxide)
doesn't carbonate that fast .you may say that aged putty is different . lets reviwe what aging does to lime :
1.nearly all the calcium oxide content will be hydrated .
2.lime loses free water , hydrogen bond between lime particles
and water becomes shorter and stronger .therefore , lime
particles will be surrounded by a water membrane .
3.prismatic crystals break down to smaller plate like crystals,
giving higher surface area to putty .
these things can help accelerate carbonation , but still not as much
as the speed that i have observed in commercially made marmorinos.
I'm guessing , maybe they carbonate the lime but using an inhibitor
prevent calcite formation in the aqueous phase .
in other words , the calcium carbonate in the putty may be in
some other phase like : vaterite , amorphous calcium carbonate,
monohydrocalcite . and finally when the putty is applied on the
wall , it transforms to calcite in a solid - solid phase transformation.
this theory is also in accordance with thixotropic quality of lime putty .
so , any ideas ?
here is my email : hsm_379@yahoo
My name is hesam and I live in Iran . I don't have any experience as a plasterer ,but , It's been a while that I've been trying to recreate and make my own lime plaster(marmorino) ,needless to say that haven't had any luck so far .
I joined this forum to see if I can find help.
here is what I know ,
the traditional recipe for venetian plaster is aged putty + granulated marble powder and probably some additives .
as you know , slaked lime is calcium hydroxide . I bought 2 samples
form Italy and sent off to lab . the composition was :
32 percent water, 58.5 percent calcium carbonate , 8.84 percent
calcium oxide , 0.68 some kind of polymer .
you can see here that there is no trace of calcium hydroxide .
all of it has turned to calcium carbonate .
( to avoid confusion ,I must add that samples were packed air tight
and during the whole procedure of analyzing the exposure to
calcium carbonate was minimal ).
and as you can see , there is about 8 percent cao present in the
composition , meaning that lime hasn't undergone aging otherwise
it would have hydrated entirely .
given that the amount of polymer is less than one percent , this
material can't be considered synthetic marmorino .
these samples were very plastic and workable , and could be
polished to a high sheen .
so , how does it work ?
i presume that the shiny surface of the venetian plaster is because
of formation of minute calcite crystals on the surface which will be
oriented under the trowel during polishing .
and the illusion of depth is also because if calcite crystal ,
given that calcite is a birefringent crystal .
well , according to my experiments portlandite (calcium hydroxide)
doesn't carbonate that fast .you may say that aged putty is different . lets reviwe what aging does to lime :
1.nearly all the calcium oxide content will be hydrated .
2.lime loses free water , hydrogen bond between lime particles
and water becomes shorter and stronger .therefore , lime
particles will be surrounded by a water membrane .
3.prismatic crystals break down to smaller plate like crystals,
giving higher surface area to putty .
these things can help accelerate carbonation , but still not as much
as the speed that i have observed in commercially made marmorinos.
I'm guessing , maybe they carbonate the lime but using an inhibitor
prevent calcite formation in the aqueous phase .
in other words , the calcium carbonate in the putty may be in
some other phase like : vaterite , amorphous calcium carbonate,
monohydrocalcite . and finally when the putty is applied on the
wall , it transforms to calcite in a solid - solid phase transformation.
this theory is also in accordance with thixotropic quality of lime putty .
so , any ideas ?
here is my email : hsm_379@yahoo
