Stucco, Stage One

Pro prep tips for the scratch coat to make the job easier now and clean-up easier later

It’s time to say goodbye to all the exterior work we’ve watched go up at Custom Design & Construction's Sheldon Street house over the past several months—the studs, the AdvanTech sheathing and ZIP System tape, the black tar paper and stucco wire—because today the guys are here to cover the structure with stucco. The first step of the three-layer process is the scratch coat, and since the size of this job calls for a spray-on technique as opposed to a hawk and trowel method, it’ll go relatively quickly but also create one heck of a mess. 

As such, the crew has taken steps to ensure the ground around the home is adequately covered with drop paper and the scaffolding is draped with material to prevent adjacent structures from picking up any overspray. Tape and plastic sheeting covers anything that shouldn't get stucco, including hand railings, stairs, and door and window frames. Don't forget those holes for electrical boxes, lights, and so on. Stuffing them with paper prevents the crew from filling them with stucco. Just as with painting, when it comes to stucco, there are two words to remember: prep and protect.

The stucco material used here is a common mix: about one part plastic cement to three parts sand and water, combined in a mortar mixer and shot onto walls under pressure with a spray-gun applicator. As soon as it’s applied, workers follow with trowels to fill in any gaps. Scarifiers or scratch tools are then used to add horizontal grooves on the surface. Once the stucco fully dries, in about 2-3 days, these scratches will provide a solid mechanical surface for the second, or brown, coat to adhere to in addition to the chemical bonding that will occur. 

A float can be used to clean up and smooth out corners, but it sometimes pushes material from one side to the other. A better option on corners and under belly boards: a paintbrush dipped in water. It provides gentler contact and is less likely to push as much material from one side to the other, while the brush bristles clean up both sides of the corner at once, increasing efficiency and still providing the smooth coat needed for the subsequent brown coat.

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