Method for repairing sewer pipes

Claim 1

In a method for repairing a substantially horizontal sewer pipe, which has an upstream portion and a downstream portion, wherein a flexible liner is inserted within the sewer pipe, said flexible liner having an outer diameter less than the inner diameter of said sewer pipe; the flexible liner is supported in a spaced relationship from the sewer pipe, whereby an annular space is formed between the flexible liner and the sewer pipe, and the annular space is filled with cement, the improvement comprising, (a) filling the annular space by digging a hole about the sewer pipe at the upstream portion of the sewer pipe, removing a section of the upper half of the sewer pipe, and filling the hole with cement to a sufficient height to form a hydrostatic head, whereby the hydrostatic head will cause the cement to flow into the annular space, thereby filling the annular space as the cement flows downwardly to the downstream portion of the sewer pipe, (b) the cement comprising a low viscosity magnesium based cement selected from the group consisting of magnesium oxychloride cement and magnesium oxysulfate cement, whereby the liner is bonded to the sewer pipe and point-load collapsing of the sewer pipe is prevented.