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I bought 2 Kg of plaster, and i have some rubber templates for the plaster. now i added 2 cups of the plaster with one cup of pure water. i mixed the combination , then i applied the mixture to the template. but after around one hour, when the mixture get dried, i found that the plaster is actually light grey (creamy white) color and not pure white, as follow (where the plaster vase is not pure white compared for example to the wall behind the vase ):-

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so is the issue with the way i mixed the plaster and the water? or the issue is with the plaster itself? or there is not an issue and the plaster will not have a pure white color? and if there is not any issue, then how i can build a pure white plaster?

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Probably just the particular plaster you bought. Plaster intended for uses where it will be painted or covered with other plaster is not too particular as to color.

There certainly is pure white plaster available, don't know what your local sources might or might not have, or how far from local you might have to go to find it.

The white wall appears to be painted, which is another way to get there.

Art supply store might be one location to try for plaster specifically intended to be white as cast.

On this side of the pond, "Plaster of Paris" seems to be pretty consistently white (it also sets relatively fast, which can be good or bad depending on the project, and is usually higher priced.) I don't know if that term is used in the UK or if means the same thing if it is.

Incidentally, all the plaster manufacturer mixing instructions I have read mix a specific weight of plaster to a volume or weight of water, NOT a volume of powder to a volume of water, but that has no bearing on the color with clean water.

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  • ok thanks so it is normal to get light grey plaster ?
    – test test
    Commented Jan 1, 2022 at 23:43
  • Not if you buy white plaster. Otherwise, yes, that's a normal color. I poured 20+ kilos of about that color under/around a tub last year. Also some white, I wasn't too picky about color as it will never be seen.
    – Ecnerwal
    Commented Jan 2, 2022 at 0:27
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Plaster is a mixture of different elements (minerals) such as lime, sand, clay, gypsum, and cement, that all have their own colors, and the color is affected by the location of the mine and the mixing proportion of ingredients by the manufacturer.

You can ask the hardware store, they might be able to point out which product is whiter than the other. And, yes, painting is the solution to get the color you want.

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