Sealant blisters are a common sight on construction projects — but they don’t have to be. These unsightly bubbles may look like trouble, but with the right techniques, they can be prevented and fixed easily. Let’s explore what causes sealant blisters and how to deal with them effectively.

What Causes Sealant Blisters?

Blisters form when gas becomes trapped between the substrate (such as logs, wood siding, or concrete) and the sealant. This typically happens during the early stages of curing, when the surface of the sealant has skinned over but the material underneath is still soft. Heat — often from direct sunlight — causes any trapped gas to expand, pushing the sealant outward and forming a blister.

The source of the gas can vary. It might come from:

• Water vapor trapped in the substrate or backing material

• Sap or pitch from wood

• Moisture within closed cracks

Common Scenarios That Lead to Blisters

1. Trapped Water Vapor
Water-based sealants release water vapor as they cure. If that vapor gets trapped due to high humidity or direct heat, it can form a blister under the sealant skin.

2. Dead-End Cracks
When moisture accumulates in cracks that don’t go through the full depth of the substrate, heat can cause the trapped moisture to expand — resulting in blisters.

3. Pitch Pockets in Logs
Logs often contain sap pockets, sometimes holding several gallons of pitch. When exposed to heat, the sap can vaporize, move through internal cracks, and create blisters under the sealant.

How to Prevent Sealant Blisters

Control the Heat

• Apply sealants during cool, shaded times of day.

• Avoid applying when surface temperatures exceed 90°F (32°C).

• In hot and humid conditions, cover surfaces with light-colored tarps or cloths to block sunlight, ensuring proper ventilation underneath.

• Prime or stain the substrate before sealing to help close off moisture-prone cracks.

Control the Backing Material

• Use blunt tools to install closed-cell backer rods without puncturing them.

• For foam board or insulation, cover any dents or holes with clear packing tape before applying the sealant.

How to Fix Blisters

If the Sealant is Still Fresh

• Puncture the surface to release trapped gas.

• Push the sealant back into place.

• After 2–3 days, apply a skim coat over the area and smooth it out.

If the Sealant is Fully Cured

• Use a razor blade to cut out the dry blister.

• Reapply sealant in the affected area.

• If it shrinks after curing, apply a thin finish coat after 2–3 days to match the rest of the bead.

Why It Matters

At Shandong Noid Building Materials Co., Ltd., we don’t believe in “good, better, best.” We believe in building the best every time. That means creating durable, high-performance sealants that withstand real-world conditions. Understanding and preventing issues like blisters helps ensure your projects not only look great — they last.

If you have technical questions about our sealants or application tips, our experts are here to help.

Contact Us

If you have any questions or need more information about our products and services, feel free to reach out to us through the following contact details:

Phone/WhatsAPP:
+86 15853657921

Email:
cy971109@gmail.com

Address:
No.198 Yishan Road,Dongcheng Street,Linqu County,Weifang City,Shandong Province,China

Customer Service Hours:
Available 24 hours a day, 7 days a week