A special system was created for large cracks that appear at the web walls. The crack is routed out and built up on one side with Planitop XS. A piece of foam is placed next to it and Planitop XS built up on the other side. The renovation team will monitor the cracks over the winter for expansion and contraction and the proper crack filler will be chosen based on the results of the monitoring. Weiss explains that this is an unconventional attitude in usual concrete crack repair. "One attitude is 'concrete is strong and you should use strong repair materials, and concrete is rigid and you should use rigid materials.' But that attitude has also failed. We're taking a different attitude, which is 'you see that crack, we have that crack in a photograph 20 years ago and we're not going to fill it up with cement and sand; we're going to fill it with something that will allow the building to stress and move where it needs to'."
The Guggenheim restoration will be finished in the spring of 2008, with the scaffolding coming down and any visible evidence of the changes gone for the 50th anniversary celebration.