Mounting Screws in Stucco

Question

Does anyone here have experience putting mounting screws into stucco?

I want to mount a light plastic box to the exterior of my home to protect a coax junction. My house's exterior is stucco.

The box is not heavy but I want it to be secure and not come loose over time. Also, I want to minimize the damage to the stucco.

I'm thinking I should use mounting screws, pre-drill the holes using a masonry bit (i read a hammer drill is better but i don't have one and read a regular drill should work for smaller holes), and put some type of sealant into the hole.

But I'm not sure if a masonry screw or masonry anchor is best. Also, I'm drilling blind as I don't know where the studs are. Any other tips welcome.

Answer 1

First off, buy a good studfinder. They should be able to detect the stud even through a layer of stucco.

When you do find a stud, put on your safety glasses and pre-drill the locations of your screws with a standard bit, use just enough force to gently go through the stucco, it's not as hard as cement and this should be fairly easy with a standard bit. You probably won't need a mason bit and certainly not a hammer drill.

When you mount the box, use a blob of silicone sealant between each screw hole and the box and use a good stainless screw, phillips or torx, with a wide washer, like a pan washer. This will maximize the surface contact if you can only get two screws into a stud.

Once the box is mounted run a bead of clear silicone around it, if you feel the need to smooth out the bead dip your gloved finger in mineral spirits or rubbing alcohol and do it that way. Silicone doesn't like to be smoothed with a dry finger and will make a mess of the project.

Answer 2

For stucco I would consider using plastic expansion anchors. For a smallish screw these should work well and minimize the size of hole you have to drill into the stucco.

You have to be rather careful when drilling in stucco in that it is rather easy to find your hole getting larger diameter than you want. This happens when the carbide cutting tips on the masonry drill hit the wire embedded in the stucco. The stucco material is rather soft and the drill bit likes to walk to the side instead of going through the wire.

Plastic anchors use regular pan head type sheet metal style screws. This can be an advantage if you need to re-work a mount point at some point. Using a masonry specific type of screw tends to be a one shot deal and they also require a drill hole with very close tolerances (review comment above regarding the wire in stucco).

Answer 3

Have you considered other ways of fastening? My limited experience with stucco is that you really don't want to put holes in it.

Alternatives: Create some form of protrusions on the box. Bolt and nut comes to mind. Sanding and scratching the back of the box might work.

Rig up a way to hold the box in position.

Meanwhile, mix up a small quantity of thin set mortar, and make a neat square slightly larger than the box on the stucco wall. Get it as flat as you can. Let set overnight.

Now mix up another small batch, and butter the patch on the wall, and apply with a notched trowel to the back of the box. The combined thickness of the mortar on the wall and on the box must be thicker than any protrusions you made to anchor into the mortar. Press in. Prop up.

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Variations on a theme: Can you stick the box onto the wall with silicon seal? Construction adhesive?