Step 1: The Scratch Coat in Stucco Application
The scratch coat is the first layer in a traditional three-coat stucco system. Applied over galvanized metal lath, it creates a strong base for the brown and finish coats. This step is critical for bonding, durability, and long-term performance.
What Is the Scratch Coat?
The scratch coat is applied over metal lath and scored while wet to help the next layer adhere. It sets the foundation for the entire stucco system.
Why the Scratch Coat Matters
A proper scratch coat:
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Anchors the stucco system to the lath
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Prevents future cracking
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Supports the structure of the wall
Failing to apply it correctly can lead to delamination and costly repairs.
Mix and Thickness
Standard mix:
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Portland cement
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Clean sand
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Water
Apply at a uniform thickness of 3/8 inch and score horizontally with a scarifier. This rough texture improves bonding for the next layer.
Curing Time
Let the scratch coat cure for 2 to 3 days before applying the brown coat. Curing allows the mix to harden properly, ensuring long-term strength.
Lath Preparation Tip
Before applying the scratch coat:
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Fasten lath securely
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Overlap seams properly
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Avoid loose areas
Good lath prep improves adhesion and helps avoid future issues.
Who This Is For
This guide is for:
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Homeowners planning stucco work
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Contractors ensuring proper application
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DIYers learning the correct process
Summary
The scratch coat is not optional. It gives structure to the stucco system and prevents failure. Ensure proper materials, thickness, scoring, and curing to get it right.
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