The following installation makes use of the 90 degree inside corner bracket (also known as the hidden, concealed, or floating bracket). It's primarily used in floating counter top and floating vanity applications where you wish to hide the support structure to achieve a modern and clean look for your surface without sacrificing strength.
Step 1: Preparing the wall
As with any installation, you need a good solid foundation prior to installing your brackets. Hidden Inside Corner brackets to create a floating vanity or counter top effect MUST be installed directly to your studs. For light applications, you may get away with installation using gypsum board anchors; however, this is not recommended as repeated load cycling can cause the drywall to crumble and fail over time.
It is recommend that brackets be installed on straight, even, and plumb wooden studs. If any warping, bowing, or other distortion of your studs is present, it is strongly advised to have that fixed before continuing with the installation.
Step 2: Bracket Levelling
Position the first bracket directly against the wooden stud. Place a level across and along the cantilevered arm of the bracket and ensure that the arm is plumb and level. If any deviation from straight and level existis, either return to step 1 and adjust the studs, or shim the bracket as required.
Step 3: Fasten Bracket
Use the appropriately sized countersunk screws to fasten your bracket in place to the stud. For 1/4" through holes, use #14 X 1.5" wood screws.
Step 4: Fasten other brackets
Repeat steps 1-3 for any other supporting brackets. Individually installed brackets should be checked for plumb and level, in addition to the levelling between bracket cantilevered arms. It is recommended that any counter top be supported at every stud; however, the precise number used is left to the installer's discretion.
Step 5: Extra support
Should you require additional support for your installation, A mirrored bracket installation can be done above the existing brackets to effectively double the bending stiffness. Doing so minimizes deflection when under high loading conditions.
Step 6: Finishing Up
After all brackets are installed, install gypsum/drywall sheets around the brackets by cutting out sections that interfere with brackets. To hide brackets, use your standard drywall patching techniques - For example, successive coats of drywall compound and fiberglass mesh tape works well. Install your choice of counter top on the brackets after the wall is patched.