IF Mastic is used to seal an hvac joint, do you still need to tape and mastic the tape?

If mastic is used to seal an HVAC joint properly, there is generally no need to apply tape and then mastic over the tape. Mastic alone is considered sufficient for sealing duct joints when applied correctly12. Here’s why:

1. Mastic is more durable and long-lasting than tape, often lasting up to 20 years or longer3.
2. It creates a flexible, airtight seal that can withstand temperature changes and vibrations1.
3. For small gaps (less than 1/4 inch), mastic can be applied directly to the joint without additional reinforcement4.

However, there are some situations where using both tape and mastic might be beneficial:

1. For medium gaps (1/4-3/4 inch), you can first apply fiberglass mesh tape over the gap, then cover it with mastic4.
2. When sealing flexible duct connections, some professionals recommend using high-quality duct tape first, then sealing with mastic for added protection2.
3. In cases where immediate temporary sealing is needed before mastic can fully cure, tape might be used as an initial layer4.

Remember, when applying mastic:

• Clean the surface thoroughly before application5.
• Apply a generous amount, ensuring complete coverage of the joint or seam16.
• Allow 24-48 hours for the mastic to fully cure3.

In most cases, properly applied mastic alone is sufficient for sealing HVAC joints without the need for additional taping.