An official website of the United States government
Here’s how you know
Official websites use .gov
A .gov website belongs to an official government organization in the United States.
Secure .gov websites use HTTPS
A lock (
) or https:// means you’ve safely connected to the .gov website. Share sensitive information only on official, secure websites.
The exposure test wall was built at the National Bureau of Standards in connection with a long-time project to study the action of various weathering agents affecting stone masonry. The project is a cooperative investigation between the National Bureau of