Okay, let's break this down and figure out the best approach for mounting your non-metallic round box in stucco.

Understanding the Challenges Stucco Thickness

Stucco is generally thicker than drywall, so a standard old-work box designed for drywall might not have the ears or mounting depth to securely grip the stucco.

Security

Stucco is a rigid material. Simply screwing into it without proper support can lead to cracking, crumbling, and an insecure mount.

Weatherproofing

Stucco is meant to protect the house from the elements. You want to make sure that the hole you create does not create a route for moisture to get in and cause damage.

Code compliance You want to make sure you are installing the boxes to the local code in your area.

Here's a breakdown of your options and considerations



1. Try the Old Work Box (Carefully)

If you can find an old work box that is larger and deeper, it might still work to mount the box to the stucco.

2. The Best/Most Secure Method: Access from Behind (Your Suggestion)



Open the Drywall

Cut an appropriately sized access hole in the drywall directly behind the stucco mounting location. Make it large enough to work comfortably.

Install Blocking

This is the ideal solution. Securely mount a wood block (2x4 or similar) between the studs in the wall cavity. Make sure it's flush with the outer surface of the stucco.

Mount the Box

Screw the non-metallic round box directly to the wood block. This provides a very solid and secure mounting point. Use screws appropriate for wood.

Close the Drywall

Repair and patch the drywall you opened.

Reasons Why This is the Best Approach



Solid Mounting

The wood block provides a rock-solid base for the box.

No Stucco Stress

You're not relying on the stucco for structural support.

Easy Wiring

Makes wiring connections easier and safer.

3. Alternative if Access Behind is Truly Impossible



Use a "Stucco Box" or "Masonry Box"

These boxes are specifically designed for mounting in masonry and stucco. They often have deeper mounting flanges and may come with shims or other features to accommodate the uneven surface of stucco.

Appropriate Anchors

Use heavy-duty masonry anchors or screws designed for stucco. Tapcon screws are a common choice. Make sure the anchors are long enough to penetrate the stucco and embed deeply into the wall sheathing behind it. The length will depend on the thickness of your stucco.

Sealant

Apply a generous bead of exterior-grade sealant (like silicone caulk) around the box where it meets the stucco to prevent water intrusion.

Important Considerations



Electrical Code

Always follow local electrical codes. They dictate box fill requirements, grounding procedures, and other safety regulations. If you're unsure, consult a qualified electrician.

Weatherproofing

Stucco is designed to protect your home from the elements. Make sure your installation doesn't compromise that. Use sealant liberally around the box. Consider a weatherproof cover for the box, especially if it's exposed to direct rain or sunlight.

Safety First

Turn off the power to the circuit before doing any electrical work. Use appropriate safety gear, including gloves and eye protection.

In summary



Best Option

Accessing from behind and installing blocking is the most secure and professional method.

Second Option

A stucco box with appropriate anchors and sealant is acceptable if rear access is not possible.

Avoid: Just screwing into the stucco with standard screws is likely to fail and could damage the stucco.Let me know if you have any other questions! Flag for review