Bandhanam means fixing an idol to its pedestal or peetham, inside the sanctum sanctorum of the temple. Ashtabandhanam is bandhanam made with a mixture of eight elements.
Ashtabandhanam is by nature flexible like rubber. Through repeated pourings of abhishekha dravyams, and the action of atmospheric oxidants, the Ashtabandhanam loses its flexibility, becomes rigid and causes a lot of fissures. Through these fissures the abhisheka dravyams seep in and attack the yantra embedded under the Upapeetam, hiding the Bijaksharamantras inscribed on the yantra, which results in lowering the pranic spiritual power of the deity. Therefore it is highly recommended that Bandhanam should be done regularly at 12 year intervals to infuse the deity with divine power.