Every infield will need additional material added to the existing infield frequently. The question I usually hear is: "How often will I need to add material?" That question is not easy to answer for a few reasons.

Adding new infield mix to an existing infield

Every infield will need additional material added to the existing infield on a frequent basis. The question I usually hear is: “How often will I need to add material?” That question is not easy to answer for a few reasons. First, what type of mix are you using on your existing infield? Often, local and less expensive mixes are used. A mix that is not balanced will not hold a grade as well as a balanced infield mix. What is your sand/silt/clay and SCR in your mix? Secondly, how close do you want the transition for turf to dirt to be? At the highest levels, mix is added at least once a year to ensure good ball roll and to ensure correct surface drainage. If your infield mix is low, the back edge will create a dam for water after rain events.


So, with all that said, how do you add new mix? The first task is to test your infield mix. A test will cost about $100 per test, but when a good, balanced mix can cost $1,500+ per load the $100 test is well worth the expense! You need to know what you have before you decide what to add. (Consult Infield Mixes, Vol 3 for more info) If you have questions, please let me know. I will work with you to ensure that a correct mix is added to your existing mix. After the mix that will be added is determined, it’s time to go to work. 
The first step is to remove all the topdressing from the infield. This topdressing may be able to be re-used if the material is clean and free of the existing mix. Next, if the infield grade is in poor condition a rough laser grade should be performed to move the existing mix into the correct location. The new infield mix should then be added to the existing infield using a topdresser to ensure consistent application of the new material. Blecavating the infield is the next step. Blending the new material into the existing material at a 4 inch depth is CRITICAL! Furthermore make sure all the edges are tilled by hand. After the blending takes place, the infield is rolled with a 3 ton duel drum roller to ensure proper compaction. Then, the process of laser grading and rolling is performed until the infield reaches the proper grade. Finally, infield topdressings are added and the infield is finished with a mat drag.
Adding new mixes to existing mixes is a very labor intensive operation. With skilled labor and the correct equipment, this process will take between 8-12 hours to complete. To be honest, this is a job that is best to leave to professionals. 
Play on!
–Jamie
@JamieMehringer