Restoring historic plaster isn't just about fixing cracks and holes—it's a meticulous process aimed at preserving the essence and beauty of our architectural heritage. Each project is unique, but our approach to plaster restoration and stabilization follows a structured process designed to ensure durability. From the 17th through the early 20th century, three-coat plaster was widely used in the interiors of buildings, reflecting the craftsmanship and historical significance of the era. This traditional method involved applying three distinct layers to create a durable finish. Remarkably, we still use this three-coat process today, as it continues to provide a reliable and authentic method for preserving the integrity and character of historic structures. Understanding and maintaining this technique is central to our plaster restoration process, ensuring that we honor both the historical craftsmanship and the building’s unique heritage. Here’s an inside look at our plaster restoration process and the careful steps we take to breathe new life into these timeless structures.
Restoration vs. Replacement
When deciding how to address damaged plaster, there are two primary options. One being a full demolition and replacement which involves removing the existing plaster, setting up scaffolding, cleaning, and replastering. This extensive process can take months, be expensive, and result in the loss of historic fabric. On the other hand, many owners opt for restoration methods. Restoration is more cost-friendly, allows the building to remain in use while work is being done, and preserves the historic fabric of the building, making it a popular choice for maintaining both the structure and its historical value.
Understanding the Structure
The journey of plaster restoration begins with understanding the history of the structure. Our first task is to delve into research. By knowing the building’s past, we can make informed decisions that enhance its longevity. Although not always necessary, this step is fundamental for projects where the historical context is complex or unclear. Typically, plaster surfaces were applied to wood lath and frames substrates, however, plaster could be applied directly to masonry.
Assessing the Plaster
With a solid understanding of the building's history, we move on to assessing the current state of the plaster. This involves a comprehensive plaster conditions survey to evaluate both the plaster itself and the underlying structure. These are our main goals:
Assess the Underlying Structure: We examine whether the underlying support (typically wood) for the plaster is stable and sound. If the structure is not in good condition, it needs to be addressed before we can proceed with restoration. Often this will included stabilizing the wood structure with the addition of fasteners, metal brackets, hangers and sister-ing or wood members.
Identify the Cause of Failure: We investigate the reasons behind the plaster’s deterioration. This could be due to structural issues, or poorly executed previous restoration attempts. Addressing these causes is essential to prevent future problems and to provide a restoration plan. Often, a combination of factors culminate in degradation of plaster. Along with age and gravity, building movement and cracking are typically the leading causes.
Quantify Failures and Types: We document the extent and types of damage to create a clear plan for restoration. These findings are annotated on architectural drawings with supporting photography.
Specify the Work: We determine the specific steps required for the restoration based on our findings. This will include specific materials, formulas, methodologies, and appropriate conditions to make corrections or installations.
Implement the Work: We carry out the restoration process according to the plan and specifications we have established. Mockups are always prepared and evaluated to confirm correctness, quality and durability.
Stabilization & Repair
Once we've identified the causes of failure and ensured the underlying structure is sound, we proceed with plaster stabilization and re-attachment. Stabilization is crucial as it ensures that the plaster is secure and will provide a stable base for the restoration work. This step may involve various techniques such as:
Consolidation: Using specialized materials to bind loose or crumbling plaster.
Reinforcement: Re-adhere plaster back to its separated members and to the substructure, such at wood lath.This strengthens the existing plaster to prevent future failures.
We start by applying liquid acrylic polymers as a consolidant over the entire surface, which reconstitutes the plaster and provides a much greater tensile strength.This also provides the necessary bond to adhere the plaster to the wood substrate. Once the consolidant has dried, we reinstate any broken of missing plaster keys with a high adhesive polymer that has fillers in creating a lightweight, high strength yet flexible caulk that is injected between lath members.
Consolidation Notable Steps & Things to Look for
To consolidate plaster using the three-coat process, we begin by ensuring that the area is thoroughly cleaned and free of dust, debris, and loose plaster. This preparation is crucial for effective adhesion. The first stage is applying a low-viscosity acrylic polymer to the plaster and wood. This polymer penetrates deeply into the porous surfaces of the lath and surrounding plaster, creating a strong bond and reinforcing the base layer. Next, move on to the second stage with a medium-viscosity consolidant, which has a thicker consistency that is absorbed into the plaster matrix, as well as, smaller gaps between the lath and plaster. The third application of consolidant also is the highest viscosity.This application fill in cracks, voids and is typically absorbed by the plaster at the upper section of layering. This is also when the plaster system is adhered to the lath. Finally, we address the broken or missing plaster keys, by applying a lightweight, flexible yet strong bonding acrylic polymer. This grout like caulk product is applied like caulk between lath members to fill void that were once keys.This step ensures a secure attachment of the plaster to the lath and prevents future damage. Additionally, this acrylic polymer system offers elasticity, thus allowing the plaster to accommodate the natural expansion and contraction of the building. After all materials have fully cured, the restoration is considered complete, ensuring maximum strength and durability of the consolidation system.The plaster is applied in applications, from low, medium to high viscosities. Each viscosity finds their leveling place within the plaster matrix, cracks and voids.
Commitment To Quality
Having forty years of experience installing plaster consolidation systems, first with Rhoplex, and in recent years as a provider & installer of Historic Plaster Conservation Services (HPCS) products, we ensure every step leads to a durable and sustainable plaster system.To that end, HPCS offers a 25 year warranty that backs up their research, analyses, expertise and durability of work. We are proud to be certified in HPCS products, making us one of the select few authorized installers of these renowned materials.These products are known for their exceptional quality and reliability, essential for both modern and historic applications.