Track 4: This New World: Preservation technology and emerging issues within our historic buildings and built landscapes

General Abstract

2 - Good Clean Fun: An Evaluation of the Effect of Various Laser Pulse Durations on the Surface Cleaning of Historic Architectural Terra Cotta

Tuesday, September 25
10:30 AM - 12:00 PM
Location: BNCC-106BC

Laser cleaning technology continues to rapidly evolve allowing for increased use of laser cleaning in architectural preservation. Concurrently, environmental concerns, regulation, and restriction of many chemical and micro-abrasive architectural cleaning systems are increasing. Other factors, including the necessary protection of adjacent building materials, and the relatively narrow range of acceptable working temperatures and environmental conditions further limit and complicate the use of many chemical and micro-abrasive systems. Additionally, chemical systems and some micro-abrasive systems are used with water which may enter to the interior of a building through a compromised facade and contribute to the distress of interior finishes. The use of water and chemicals may also introduce harmful salts into the surfaces being cleaned. All of these concerns indicate a likely future shift away from chemical and micro-abrasive cleaning methods where feasible.

Modern laser systems offer control of many variables to optimize the cleaning process and achieve the desired visual results. Laser parameters such as wavelength, pulse duration, pulse energy, pulse frequency, scan speed, fluence, and spot size can be tuned to achieve a range of results. Although several studies have been published reviewing the effect of 1064nm wavelength laser cleaning on stone surfaces, fewer studies exist for the laser cleaning of other exterior architectural materials. This study characterizes the soiling and substrate of terra cotta samples with a vitrified (glossy) white colored glazed surface which were removed from historic buildings. The samples were spot cleaned at different fluence levels with pulse durations ranging from 10 to 400 nanoseconds. Additionally, areas were cleaned in both damp and dry conditions to evaluate the effect of water-laser interactions and the potential benefit of laser induced micro-steam cleaning in removing soiling present on the surface and in recesses of the crazed glazing.

Each sample was documented with photographs and photomicrographs prior to and after cleaning. The cleaned surfaces were visually evaluated relative to uncleaned surfaces and the interface of cleaned area relative to uncleaned area was also evaluated in 2D and 3D using a Hirox 3D digital microscope. The gloss of the cleaned surface was evaluated under magnification with various light conditions. Once successful trials were completed, larger scale trials were performed on-site to evaluate the schedule and cost efficiency of the laser system relative to typical chemical and micro-abrasive systems.

Learning Objectives:

Jamie Morris, AIC PA

Project Manager
CSOS, Inc.

Jamie Morris is a licensed architect and architectural conservator and works as a Project Manager at CSOS Inc. She has over ten years experience testing, evaluating, and specifying architectural cleaning systems. Her recent work has been focused on studying and using laser cleaning systems on a variety of architectural materials and soiling types. Jamie also serves on her local Preservation Commission, and is the President of the Western Great Lakes Chapter of APT.


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Rachel L. Will, P.E.

Senior Associate
Wiss, Janney, Elstner

Rachel Will, PE is a Senior Associate with Wiss, Janney Elsnter Associates in Chicago. She participates in various projects including facade evaluations, condition surveys, structural analyses, repair design, construction document preparation, and construction observation. Ms. Will’s expertise includes preservation and repair of historic masonry (terra cotta) building facades.

Rachel currently serves as the Past-President of the Western Great Lakes Chapter of the Association for Preservation Technology (APT) and a member of both the strategic planning committee and preservation engineering committee, along with member of the student design build competition subcommittee of APT.


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Dan Worth

Mr. Worth is Principal and Historical Architect with BVH Architecture with offices in Lincoln and Omaha, NE. Dan has 40 years of experience with an emphasis in historic preservation, rehabilitation, urban design, master planning, programming and project management. He has extensive experience with managing public facilitation and community engagement process. Over the last 35 years, Dan has completed dozens of master plans and designed / implemented large complex historically significant projects with civic and institutional clients including the National Park Service, Smithsonian Institution, State of Nebraska, University of Nebraska and the Nebraska State College System. Dan has been a leader locally, regionally and nationally in community and non-profit professional organizations promoting the best practices for planning and preserving our communities.


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2 - Good Clean Fun: An Evaluation of the Effect of Various Laser Pulse Durations on the Surface Cleaning of Historic Architectural Terra Cotta

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