Getting Plastered
New plaster undergoes a fair bit of preparation and protection to allow it time to cure into limestone.
One of the questions we get asked most often is whether all the prep and care we put into lime plaster is really necessary. The answer is no. One does not NEED to prepare substrate meticulously and maintain lime plaster walls while they are curing. But doing so will extend the life of your lime plaster by years and probably even decades. Therefore, we think it’s well worth the time, attention, and care put into the plaster when you first install it.
A good rule of thumb for plastering: Only 1/3 the time you invest in plaster involves putting the material on the wall. The other time involves a laundry list of essential tasks:
Infill of substrate to create a consistent, flat, continuous substrate. This can be done with substrate material, or with a plaster using some substrate as an aggregate. Consider this step as plastering 0.0, with curing requirements akin to plaster that need to be considered in the project timeline.
Protection of surfaces from plaster - windows, doors, trim, walls, other items that you don’t want to have covered in plaster.
Mixing lime putty (for hydrated lime plasters only) and mixing plaster. Mixing plaster is an art and a science, worthy of a blog post all its own.
Saturating the substrate. Wetting the walls the day prior is best practice, and again just prior to plastering. For the 1st round, you’ll wet the wall until it’s dripping, and just before plastering you’ll re-wet until there is a moist sheen on the entire wall.
Your level of smoothing and finishing will determine how the plaster looks on the wall for years to come. To get a smooth, flat, even finish, expect to spend a good deal of time with a large trowel or darby to even out the plaster while it’s fresh on the wall.
Once plastered, the wall needs to remain moist. This means wetting the walls for 3 - 10 days, depending on type of lime material, and protecting the walls from wind, sun, or rain.
While the walls are curing (5-14 days, depending on type of lime material) avoid knocking the plaster or leaning into it. The plaster is still soft and can be indented, damaged, or scraped off the wall. Repairs are simple, but need to be protected throughout their curing cycle.
Protect the walls from freezing for 28 days. Use canvas or burlap protection to shield from light frost, or engineer heating systems as needed in case of a sudden cold snap.
