Most cementitious surfaces are laden with free lime. When cured properly, this free lime is securely trapped inside the plaster... but if the surface is not properly cured with sufficient wetting the lime can be transferred through the topcoat system causing undesirable lime staining. Thin polymer-modified plasters are most prone to the problem as they often dry out during the curing process resulting in an incomplete cure.
The problem has little to do with the paint or the painter... the problem is the improperly cured substrate. How do we know this? Simple... when the substrate is properly cured, there is no problem. Unfortunately though lime staining only shows up as a problem after the substrate has been coated.
Rather than sit back and point the finger the Resene Technical team got onto the job and figured out a product that will fix the problem and, as an added bonus, reduce the downtime before coating plaster. Environmental Choice approved Resene Limelock is a preparatory coating designed to cure and seal cementitious substrates. It promotes curing by producing a water barrier, which, unlike traditional curing membranes, can be overcoated with acrylics at any stage.
Its outstanding ability to cure and seal the substrate means you don’t have to leave the plaster to cure for seven days before painting. You can cure and seal the surface using Resene Limelock while the scaffolding is still up, allow it to dry and then start painting on the acrylic topcoats. You’ll be finished the job while others are still waiting seven days before they can start using traditional products. If you’re planning dark, heat-absorbing topcoats we recommend you still wait seven days before painting just to be on the safe side.
Free lime is aggressive and can affect some pigments too. Application of Resene Limelock can help with colourfastness as well.
Resene Limelock traps free lime in the cementitious substrate protecting the paint finish against the appearance of ugly lime staining, and providing a perfect base for subsequent Resene finishes. Part of the surface preparation process, Resene Limelock should be applied as soon as possible over plaster systems to achieve maximum potential.
You can’t tell just by looking at a plaster whether it has been cured correctly, but adding a quick coat of Resene Limelock as part of the surface preparation process will give you the assurance that the surface is properly cured and sealed ready to take the topcoat system of your choice. No more having to worry about what might show up after you hang up your tools.
See Resene Data Sheet D809 for more technical information on Resene Limelock. Data Sheets are available from Resene ColorShops or from the Resene website.