Cement Pigment for External Plaster in Hot, Sunny Climate (Greece)


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Old 09-07-09, 01:12 AM
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Cement Pigment for External Plaster in Hot, Sunny Climate (Greece)

We need to decide whether to follow a suggestion by a friend, to use pigments to colour the external plaster of our house. We want to achieve a rustic look, with thick, rough external plaster in an earthy, light-brown colour. Most people in our village use ordinary plaster and paint it. Our builder thinks any colour added to the plaster will make it less strong and will also bleach in the sun, but maybe he only has knowledge of local pigments. I have been doing some searching around and it seems synthetic iron oxide pigments are strong and last - are they the right thing for the job ?
If we could achieve a lasting colour for the plaster, that would be good (one that does not fade over time and will not need re-painting after some years).
If pigments are recommended, what's the best brand (we can shop in Greece or in UK).
Thanks for any help.
Michael
 
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Old 09-07-09, 05:24 PM
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Is the external plaster going to be Portland or lime based? If it's going to be Portland based, I don't see how the pigment would weaken it. I can't comment on the sun bleaching it, since I don't live in a hot climate but I tend to doubt it.
 
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Old 09-07-09, 06:00 PM
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Synthetic iron oxide is without a doubt the purest, strongest and most durable pigment that there there is for tinting cement-based product that there is. The natural oxides are cheaper, have less strength and more impurities. the only downfall with the synthetic oxides is that they are very strong and care must be taking to be uniform in a small batch.

The major brands are Bayer Chemical, etc, and other international suppliers that frequently sell to others that package into smaller packages. The raw ores come from different countries before they are refined from natural to synthetic oxides. Many go into paint pigments and magnetic striping for cards and tapes.

There is a limit to the maximum dose in a concrete mix that is set at 10% of cement, but most used in the concrete products manufacturing being in the 1/2% to 4 % range. This is in a 6000# batch, so the uniformity variation is not a big problem in a large batch.

Dick
 

Last edited by Concretemasonry; 09-07-09 at 06:05 PM. Reason: spelling
 

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