Cementos Molins

Creating a one-coat render in cold or damp weather

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When one-coat mortars are applied in certain environmental conditions, like rain, low temperatures or high relative humidity, there is a higher risk of whiteish stains appearing.

These stains, called efflorescence, are the consequence of a mechanism called carbonatation, and usually occur between 7 and 10 days immediately after the material has been applied.

Carbonation occurs when the salts released during the setting of the cement, dissolve in the kneading water, migrate to the surface of the monolayer mortar and react with the atmospheric carbon dioxide, giving rise to calcium carbonate, white.

In the appearance of the stains, the drying rate of the mortar is especially influenced. If it is fast enough, the setting salts remain in the capillaries and do not come out. On the contrary, if it is slow (because of the environmental conditions mentioned), they reach the surface of the mortar and form whitish deposits or efflorescence.

The dry wind has an important influence on the appearance of the spots.

Although carbonation does not alter the mechanical performance of the monolayer mortar, it creates an aesthetic problem, the more noticeable the darker the color of the coating.

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The solution is to use PROPAM® ACEL, that is to say, a product that allows to adapt the drying of the product to the exposed environmental circumstances, so that the finishing can be done as if it were worked under environmental conditions.


Wait until the material has completely set and hardened (28 days after application) and remove stains by washing with acidified water (1: 4 hydrochloric acid with water).

Once this solution is applied, wash with plenty of water.

In case the carbonation has been severe and the stains are difficult to remove, apply REVAT® FILM, to restore the aesthetic characteristics of the monolayer mortar respecting its texture and properties.


  • Do not apply under the following conditions: at risk of rain or frost, at temperatures below 5 ° C, with high humidity.
  • Protect the coatings against the risk of rain and / or frost, until the tenth day after its application.
  • Try applying light colors, in which efflorescence is less visible.



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