Originally Posted by JohnBurke

Be aware that at one weekend a month, based on eight hours each day, it would take approximately 16 years to equal 18 months of full time employment (at 40 hours a week as a mechanic, necessary for either the airframe, or powerplant), or a combined 23 years to get the experience to apply for both ratings.

This is due to the FAA having defined the experience requirements spelled out in 14 CFR 65.77 as full time employment, based on a 40 hour work week.

eCFR ? Code of Federal Regulations

§65.77 Experience requirements.
Each applicant for a mechanic certificate or rating must present either an appropriate graduation certificate or certificate of completion from a certificated aviation maintenance technician school or documentary evidence, satisfactory to the Administrator, of—

(a) At least 18 months of practical experience with the procedures, practices, materials, tools, machine tools, and equipment generally used in constructing, maintaining, or altering airframes, or powerplants appropriate to the rating sought; or

(b) At least 30 months of practical experience concurrently performing the duties appropriate to both the airframe and powerplant ratings.