How to Stop Leaks in a Black Pipe Cement Block

Inspect the pipework installation on both sides of the cement block wall, and locate the nearest fittings, one on each side. You may have to dig away soil from the outside of the wall if it is an external wall. Clear the areas around and beneath both fittings so that contamination cannot fall into the open pipe during repairs.

Close off the supply of gas or water to the pipework installation. This is typically done at the meter for gas; with water, it is often possible to isolate just the part of the system that you are working on.

Use a pipe wrench to remove the leaking pipe from the system. It is often easier to remove the fittings from each end individually, rather than trying to rotate the pipe itself, which is held in place by both fittings. Turn the pipe or fittings counterclockwise to release the male threads from their female counterparts.

Retract the released pipe through the cement block wall, moving it in the direction that allows for easiest maneuvering. Tape over the open fittings to prevent contamination from entering the system.

Replace the leaking pipe. Although wrought-iron pipe can be welded, the cost and complexity of the project is unviable. Use a fine-toothed hacksaw to cut a new pipe to the correct length, and a proprietary threading tool to create male threads on both ends. Alternatively, obtain a pre-threaded replacement from a plumbing supply store or home improvement warehouse; such outlets often have many different ready-to-use lengths in stock.

Remove the protective tape if you used any to temporarily cover the open fittings, then install the new pipe: Seal the threaded joints with Teflon tape, sometimes packaged as PTFE tape, or with proprietary jointing compound, called “pipe dope” by some professionals. In either case, apply the sealant to the male threads of the pipe, then install the thread into the female threads of the fitting. Tape must be applied in a clockwise manner, so that it is not stripped from the threads as they are engaged and tightened. Turn the pipe into the fitting until it is hand tight, then use a pipe wrench to continue turning at least one full rotation.

Reinstate the pressurized supply -- be that gas or water -- and test the repaired installation for soundness. If working with water, a simple visual check of the pipe-to-fitting joints is sufficient. If working with gas, use a specialty pressure-testing tool according to the manufacturer’s instructions to ensure no gas is escaping from the joints.