Assuming the photo is fairly representative of the entire firebox, what's it going to take to repair all of the mortar joints in terms of time/cost? The width at the back is 24, the front is 30, and the height of the area needing repair is 30.
When dry skin is the cause of an itching back, it is easily remedied by applying a lotion or cream to moisturize the area. When chronic dryness and itchiness is an issue, a person may need to increase hydration efforts.
Drugs and chemicals can cause itching when taken internally or when applied to the skin. Usually the itching is caused by an allergic reaction. A few drugs, such as morphine and some radiopaque contrast agents used when taking certain x-rays, can also cause itching without causing an allergic reaction.