External coatings on historic buildings

I am having doubts regarding the correct way of applying lime-based
coatings on historic buildings, so that the coating would resist for
a reasonable number of years in environmental conditions which
consist of pollution, sea air and a warm climate (no frost
problems). I would apply several layers of lime-based mortar
(containing perhaps some hydraulic lime, or an aggregate such as
terra cotta powder), and use lime milk mixed with pigments or fine
stone powder and possibly a small quantity of an organic binder as
the final layer.

I would apply every layer before the preceding layer has completely
dried out yet, so they will carbonise together and  will be
chemically connected to each other.

However I heard conservators who recommend to wait several months
before applying the final coating layer.

I don't really understand the logic behind such recommendation. Can
anyone share their experience on the subject?

Orit Soffer
Conservator
Israeli Antiquities Authority


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                  Conservation DistList Instance 17:2
                  Distributed: Thursday, June 19, 2003
                        Message Id: cdl-17-2-018
                                  ***