Large rolls of glass mat are used in the shingle manufacturing process, and a splice is a glued or taped lap of the end of one roll to the beginning of the succeeding roll. Rolls of glass mat must be spliced together to maintain continuous shingle production. Each splice is marked for rejection before the shingles are packaged. Occasionally, an error or oversight occurs where that splice gets packaged along with the shingles. Shingles containing a splice may delaminate on the roof, and should be replaced.