While drywall is porous, plaster is not.
This means that mold will grow on the drywall, and often times on both sides since it is an organic porous material; in fact the rich carbon paper back that holds the gypsum together is the preferred food source for Stachybotrys to grow and decompose given enough moisture.
If you have visible mold on the exterior of the drywall, is almost certain a larger amount of mold growth is present in the back of the drywall.
There are no products that can guarantee the successful cleaning of mold on the drywall due to the porosity of the material. Often times, it must be cut off and removed.
Mold on plaster walls on the other hand are cleanable since it is not a food source, and not porous. The mold is usually feeding on your paint and dust. However plaster walls can contain paper backing and if moisture penetrates the back of the plaster, the walls will need to be removed.
You must always consult with a mold remediation specialist to ensure you can determine the extent of the contamination.
Call us for a free inspection at 416-791-8020.