There was a gun-manufacturing foundry at Windmill Hill, now Tabernacle Street EC2, until an explosion in 1716. Captured French guns were being melted and the liquid metal was poured into moulds which were (unintentionally) damp. The moulds exploded, killing Mathew Bagley, the founder, and 16 others, and injuring several important visitors.
In 1739 John Wesley took a lease on the building, presumably repaired, and, as the Foundery, it became his first London chapel and the first Methodist Book-room. He had the City Road Chapel built and moved his congregation there in 1779. The Foundery pulpit and some pews can now be seen in the City Road Wesley Chapel.
Londonist has a good post about this building and reports, 2015, that the EC2 plaque has gone missing.