WHEN TO PRIME THE BASE COAT BEFORE APPLYING FINISH ON EIFS
Some EIFS manufacturers recommend that a primer coat be used over their base coat on nearly every job. Other EIFS manufacturers do not require a primer coat on every job. They only recommend a primer for special circumstances. Why the difference? Here is one explanation:
A Primer can serve several functions:
- Increase bond of the finish.
- Reduce efflorescence from the base coat.
- Compensate for poor water resistance in the base coat.
- Compensate for low or high levels of lime and limestone in the base coat.
- Compensate for poor hiding power in the finish.
Total Wall has internal bond promoters in our finishes, highly water resistant and efflorescence resistant base coats, and high hiding power in our finishes. Therefore, the Total Wall system does not routinely require a primer to perform. Total Wall employs a primer to compensate for special job conditions, not to compensate for products in the system.
Consider a primer as an upgrade to an already good system. Therefore, the option for priming is always available. Occasionally, it is very desirable to prime the base coat before applying the finish coat. Here are a few instances when a primer coat is recommended:
- When spray applying any finish.
- When severe exposure conditions are anticipated, such as a section of sloped EIFS.
- When potential read‑through of fasteners or other system attachments due to thermal shorts may be a consideration.
- When any read through of a contrasting base coat tone in a swirl texture is undesirable.
The use of the primer coat can serve several purposes. First, a primer can alter the base coat color to better approximate the color of the finish. Any very thin spots in the finish from a swirl texture will not be visible because the primer has altered the gray base coat color. Second, a primer will be a slightly softer surface than raw base coat. This usually produces less bounce‑back when spraying a finish. Third, the prime coat will tend to even out the suction of the base coat. If variations in suction exist due to thermal shorts in the system, such as from fastener heads, the primer will work to minimize these variations.
What to use as a primer? Total Wall recommends that non‑textured standard Total Lastic be used when a prime coat is indicated. A single coat of Total Lastic at approximately 8 ‑ 12 wet mils thickness will do an excellent job as a primer. Total Lastic may be applied by roller, airless spray, or brush. Estimate coverage to be between 700 ‑ 800 sq. ft. per 5-gallon pail. Be sure the base coat is completely dry before applying Total Lastic. Allow the Total Lastic to dry before applying the finish coat.