Properties and Performance Comparison of Backing Materials

The choice of backing material is a primary consideration in an elastomeric log joint sealing system. The backing material performs five key functions in the joint design: 1. It limits the depth and amount of applied sealant. 2. It assists the sealant in forming the proper shape for optimum adhesion and depth/width ratio. 3. It acts as a bond breaker to prevent three point (bottom side) adhesion. 4. It provides insulation to the joint. 5. It strongly affects the aesthetic appearance of the finished joint.

Backing Material	R-Value Typical 1-1/2" per side	Repels Moisture	Bond Breaker	Typical Joint Design	(+)Strengths (–) Weaknesses
TRI-ROD®	> 12	yes	yes		+ Triangular shape design provides flat even chinking surface + Rounded edges provide strong adhesive "footprint" for sealant + Does not distort or bulge + Highest R-value – May add slight initial cost to chinking system
Trapezoid Rod	> 5	yes	yes		+ May have slightly lower initial cost – Splayed edges do not fit well & reduce chinking footprint area – Design configuration can fold and bulge at edges – Does not provide strong adhesive "footprint" at edges of joint – Significantly lowers R-value
Grip Strip	> 5	yes	no		+ May have slightly lower initial cost – Does not provide strong adhesive "footprint" at edges of joint – Open cut cell surface does not meet ASTM bond breaker joint design requirements – Open cells may contribute to blistering of slow-curing sealants – Significantly lowers R-value
HBR Round Rod	> 12	yes	yes		+ May have slightly lower initial cost + Highest R-value – Greater quantity of chinking material is needed to cover round backing – Joint often tears due to too thin center and too thick edges – Round configuration creates bulging chink joint
HBR - Split	> 6	yes	no		+ May have slightly lower initial cost – Does not provide strong adhesive "footprint" at edges of joint – Half round configuration can tip and bulge in joint – Open cut cell surface does not meet ASTM bond breaker joint design requirements – Open cells may contribute to blistering of slow-curing sealant – Significantly lowers R-value
Foam Pak	> 6	no	no		+ May have slightly lower initial cost – Round configuration creates bulging chink joint – Joint often tears due to too thin center and too thick edges – Open cut cell surface does not meet ASTM bond breaker joint design requirements – Greater quantity of chinking material is needed to cover round backing – Does not provide firm, durable joint