black Marble 36 inch Matte vanity top bathroom

What Happens During Installation

You are absolutely correct. Walls are rarely perfectly straight (plumb), square, or flat. When placing a rigid, pre-cut slab of marble against an irregular wall, the result is an uneven gap along the backsplash.

This gap will be wider in some areas and tighter in others. If not addressed, this leads to:

• An obvious, wavy, and inconsistent caulk line.

• A potential water-damage channel if not properly sealed.

• An unprofessional finish that detracts from the beauty of the stone.

What We Need To Do When Installing (The Process)

The solution is a professional installation technique that compensates for these imperfections. Here is the essential process:

1. The Non-Negotiable First Step: Templating

• Never order a vanity top based on standard dimensions. The cabinet must be fully installed and level, and the walls must be finished (painted, tiled).

• A professional fabricator will then create an exact physical template of the vanity base and the wall. They use strips of wood, cardboard, or plastic to transfer the exact, irregular shape of your wall to the shop. This template accounts for every bulge, dip, and out-of-square angle.

2. Fabrication Based on the Template

• Using this template, the fabricator cuts the Portoro marble slab to fit the actual conditions of your bathroom, not the idealized drawing. The backsplash edge is custom-cut to mirror the wall's contour.

3. Dry-Fitting and Scribing

• Upon installation, the team will first dry-fit the top-placing it without adhesive to check the fit.

• Even with templating, minor adjustments might be needed. The installer may scribe the top. This involves using a tool to trace the wall's profile onto the stone (if necessary) and carefully grinding the edge for a perfect mating surface.

4. Setting and Securing the Top

• Once the fit is confirmed, a bead of 100% silicone adhesive is run along the top of the vanity cabinet.

• The slab is then lowered into place. The silicone acts as a flexible adhesive and sealant, preventing movement and squeaking. It is not screwed down tightly.

5. The Final, Crucial Step: Caulking

• The seam between the marble backsplash and the wall is never perfect-this is where the skill comes in.

• The installer will fill this uneven gap with a high-quality, color-matched silicone caulk (often grey or black to complement the Portoro). They tool it to create a clean, consistent, and waterproof seal that looks intentional and finished.

Special Note for Matte Finish:

• The honed (matte) surface is more porous than polished. Ensure the installer uses a non-staining silicone and immediately cleans any squeeze-off with isopropyl alcohol to prevent residue from embedding in the surface.