Choosing the repair materials
Weiss explains the process for choosing a repair system was quite exhaustive but necessary for a building such as the Guggenheim. The design team looked through industry magazines, talked to various people and groups within the industry and used their knowledge from previous jobs to come up with a list of eight companies to invite to the materials selection process. All eight companies offered the three products needed for the project - a patching material, crack filler and a coating system. "We knew we would feel most comfortable if we could get all those products from a single manufacturer for a variety of reasons - developing a relationship with the company through the construction period, issues with warranty, legal questions and so on," explains Weiss.
Two companies declined to participate in the Guggenheim project, so the remaining six underwent extensive laboratory testing using a "Guggenheim gunite" replica mix. The renovation team put the materials through artificial weathering, hot and cold cycling, wet and dry cycling, condensation tests and freeze/thaw cycles. The team was looking at how the repair materials held up to peeling and blistering, discoloration, coating adhesion, failures and tears in the cracks, loosening of the patching materials, and so on.
At the end of laboratory test, the race was narrowed to three companies and field mock-ups began. The results of the field mock-ups brought the design team to choose MAPEI for the Guggenheim restoration. "After the testing we were ready to say we have a manufacturer of product, and more importantly a manufacturer we can work with. In other words, not just a company that's going to sell us products and go home but one that's going to have people on site and be there to train contractors to handle the products properly, to examine any problems that might arise in the field and work on modifications," explains Weiss.
Weiss admits the average contractor might wonder about the lengths to which the Guggenheim design team went in choosing a repair product, but he says the rigorous testing was necessary. "This is an extraordinarily high level of research and scientific review and field testing on this project, but the level of importance dedicated to it equaled the international importance of the building," Weiss says. "It might seem over the top to the average person in the concrete field. On the other hand, if we're right there on the forefront testing how the best concrete repairs can be accomplished, then we're making a contribution to the industry."
Executing the repair
With repair materials chosen, the job progressed to addressing cracks throughout the rotunda walls. Bruce Burton is business development manager with MAPEI and the company's key contact on the Guggenheim project. With the support of MAPEI's global Concrete Restoration Systems team, he's been working on this project for nearly three years and explains the uniqueness of the situation.
"MAPEI has met the challenges of many important restoration projects around the world, and the Guggenheim has challenged us to continue providing unique solutions," he says. "This is restoration as it would compare to architectural sculpture or restoration of a piece of artwork. That's the level of emphasis we're putting on the repairs that are going on here."
The crack repair is happening on three fronts with MAPEI products. Burton explains the roles his company's materials are playing in the repair, "One, we're here to protect the steel with Mapefer 1K, a corrosion inhibitor. Secondly, we have our patching materials Planitop XS, a repair mortar that can be applied in lifts that ramp up to 4 in., and Elastocolor Rasante SF, an acrylic-modified patching compound with sand that fills the smaller, non-moving cracks on the building. Beyond that we had to design a coating system that would protect the building from chlorides, carbonation and water intrusion but would not change the visual appearance of the building." That coating system combines a layer of Mapelastic, a flexible cementitious membrane for concrete waterproofing and protection, and the color coating with its product
Elastocolor Rasante, a high-build elastomeric finish coating. (Mapefer 1K is a new product for MAPEI Americas, to be introduced at the World of Concrete; Elastocolor Rasante SF and Elastocolor Rasante are currently only available in Europe.)
In addition to repairing the concrete, MAPEI and the repair contractor have to work together to ensure the original texture of the concrete is retained through the repair products, even though it will be covered up by the coating system. That original texture includes all the little flaws Wright was disappointed about after the formwork came off, including visible lines in the concrete left behind where two plywood forming panels met. That means the contractors have to apply the repair materials in a way that any visible joints or other surface textures show through; if that texture is lost, the contractors must build it back up.