They kill the root tips they touch and do nothing to the defect. Copper sulphate and foaming herbicides burn back roots inside the pipe, which restores some flow for a while. The opening stays open, moisture keeps escaping, and new growth follows it straight back in.
Foaming herbicides coat the pipe wall and kill root tissue on contact. Copper sulphate crystals dissolve and poison roots as the solution passes them. Both work on what they reach, which is the root mass sitting inside the line on the day you pour it. Neither travels far enough into the soil to stop the tree, and neither closes the crack.
Manufacturers are reasonably clear about this in their own instructions, which tell you to reapply every few months. That reapplication schedule is the honest description of the product. It is maintenance, not repair.
There is a second problem nobody mentions. Copper sulphate corrodes metal pipe, and the lines most likely to have root intrusion in North Texas are cast iron laterals in homes built before the mid-1970s. Those pipes have already lost wall thickness from the inside. Pouring a corrosive compound down a corroding pipe treats this year’s symptom and shortens the life of the pipe underneath it.
As a holding measure between a camera inspection and a scheduled repair, chemical treatment is reasonable. As the plan, it means paying forever and losing the pipe faster.
Nuflow DFW is a licensed trenchless sewer contractor serving 25 Dallas-Fort Worth cities, RMP# 46694. We run the camera inspection that shows whether the defect can be lined, and you keep the footage. Call (469) 701-0597.