Definition- The downward flow of coating, also known as curtaining. May appear as runs or drips.
Causes of Sagging- Application of too heavy a coat of product.
- The over reduction of a product.
- Product is too thin, caused by a warming of the product.
- Cold and/or humid environmental conditions, leading to slow dry times.
- Cold and/or humid coating and/or substrate, leading to slow dry times.
- Improper spray technique, including the gun being manipulated too close to the wood or at the wrong angle in relation to the wood, or not releasing the trigger at end of stroke.
- Under catalyzed material.
Prevention of Sagging- Apply thinner coats of product.
- Thin the product to a lower ratio.
- Store and use all materials at room temperature, while keeping spray and drying areas at room temperature.
- Use the proper spray technique. Gun should be 8-12 inches from the wood and at a right angle to the surface.
- Catalyze at the correct ratio.
Possible Fixes for Sagging- Strip and refinish
- Sand and recoat
Questions to Ask- Has the product been altered in any way?
Thinners, retarders, colorants, additives, any other additional adds to the product? - Were there any products (water based, oil based, glazes, stains)used that may have left residual material behind?
- What are the environmental conditions, both during application and cure?
- Have things changed, including equipment and personnel?
- Are the products being used compatible?
- Are the products being used from the same manufacturer?
- Was there any preliminary testing of this system before it was used on a larger scale?
- When in the finish process did you notice the problem?
- What is the humidity, dew point, air movement, and temperature of environment and materials?
- Has this problem happened before?
If so, what were the conditions at that time, especially compared to the current conditions? - How much coating is being applied per coat?
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