Because of the desolation of forests and the dearth of building lumber, the people resorted to the use of cement for construction and also imported lumber from the land southward (see verse 10).
While this is not significant doctrinally, it does give an additional external evidence of the truthfulness of the book, since Joseph Smith could not have been aware, as a result of his own intellect and learning, of this important item that has since been substantiated by modern scientific findings.
For an in-depth discussion of the role of cement in ancient construction see Hugh W Nibley, Since Cumorah, p. 254; An Approach to the Book of Mormon, pp. 347-48; and the research findings of Matthew G. Wells and John W. Welch in “Concrete Evidence for the Book of Mormon,” in Insights [a newsletter and research update published by the Foundation for Ancient Research and Mormon Studies, Provo, UT], May 1991, p. 2.