Spots have been observed on finished liners which may be associated with pin holes allowing water to pass through.
Causes: Spots on the surfaces of liners may be in some cases caused by a combination of the choice of resin and in particular, the choice of curing agent and the curing method (e.g., steam as compared with hot water and the choice of liner undersize).
Spots are formed by the filtering out of impurities in the water passing through tiny pinholes brought about under the conditions explained above.
Figure 1: Spots on liner. (Click photo to view video.)
Figure 2: Spots associated with a change of section (e.g. manhole). (Click photo to view video.)
Solutions: Spots on liners are uncommon and can be avoided by an informed choice regarding the combination of resin, curing agent/catalyst, liner specification and curing method.