My home was built in 1914 (Portland, Oregon). In 1948, the house was moved 200 feet to its current location. The 750 square foot house has a concrete basement with a concrete floor. The concrete basement walls are approximate 7 feet tall.
A view from the inside of the basement shows the concrete was poured in layers. Some of these layers are crumbling. 1/2 to 1 inch aggregate is falling from the wall. Other layers are in great condition.
Interior and exterior "tapping" with a screwdriver reveal most of the the concrete is solid - even though the aggregate can be seen in some areas. Other areas sound hollow. This is where the aggregate will crumble from the wall.
The exterior has a skim coat, but half of it has fallen off, or is ready to fall. Again, other exterior section where the skim coat remains appear and sound solid.
What is happening to the concrete?
How can this deterioration be stopped?
Does the concrete need to be replaced?
What type of trades person should look up to make the repairs?