Top 2" of my concrete wall has eroded. How do I fix it, so it will last, and make sure new concrete bonds to the old?

Hi.

There are different kinds of concrete coating. The choice of product varies, depending if the wall is interior or exterior and on the location of the wall (for example the product used in a bedroom's wall will be different from the coating adopted in a garage).

Epoxy coating are great products that can be used in exterior or interior. Epoxy products however may smell and trigger allergies. Epoxy is one of the strongest coating for exteriors.

If the space is a living room, then it is probably better to use acrylic cement. Acrylic coatings do not smell and do not release volatile compounds. Acrylics look similar to Portland cement and are generally less strong and adherent than epoxy paste.

The application method is usually illustrated in the coating product's container. The procedure consists in cleaning the wall (you can use a power washer), applying the product with a trovel, and then checking the results after 24 hours or when prescribed in the coating's instructions.

After applying the coating you can finish the wall with paint and sealer product.