The phrase "applied to the underside" is correct and usable in written English.
It can be used when describing a process or action where something is placed or attached to the bottom surface of an object.
Example: "The adhesive was applied to the underside of the panel to ensure a secure fit."
Alternatives: "attached to the bottom" or "affixed to the underside".
I couldn't resist touching the delicate corrugated bump that rose from the surface of the fluid when a magnet was applied to the underside of the beaker.
A medical skin-safe adhesive (from the first prototype) is applied to the underside of the patch.
The shipping industry is already experimenting with microbubbles, applied to the underside of ship hulls, to reduce friction and improve fuel efficiency.
The Klingon cruiser first seen in 1979's The Motion Picture was altered to suggest an important flagship, with a flared design applied to the underside of the vessel.
The spinal nociceptive tail-flick reflex was evoked by radiant heat (Columbus Instruments) applied to the underside of the tail.
100 µl Microscint 20 was added to each well, a white sticky base applied to the underside and a sealant top applied to the top of the plate.
To ensure the cleaning agents (both AHP and SHP) were applied to the toilets, a UV visible marker (UVM) was used on the underside of the toilet seat following the protocol of Alfa et al [ 18].
The underside of the uncover-slipped slides was marked by a pathologist and the pinpoint matrix capture solution (Zymo Research Corp) was applied to the slide and allowed to air dry.
Using a pneumatically driven dispensing system, an average 232 ± 64 μm (mean ± SD) thickness layer of silicone adhesive coating was applied to stiffen the underside of polyimide multisite arrays.
Ensure that there is sufficient glue applied to firmly stick the patch to the underside of the hole.
If you do see rust or mildew, spray with Ortho's Funginex, applying to both the top and undersides of foliage.
