Sealant that is too deep resists stretching and pulls at its bond lines; too shallow and it tears. For typical building joints the sealant depth at the center is kept around half the joint width, with a minimum near 1/4 inch and a maximum near 1/2 inch. Narrow joints under about 1/2 inch often go closer to 1 to 1. Backer rod placement sets the ratio.
Rod's sitting way too deep, you've got an inch of sealant in a half-inch joint, that width-to-depth ratio is backward.
Also heard as
- shape factor
- W:D ratio
- 2:1 rule
Related terms
Hourglass profile
The ideal cross-section of a sealant joint: thick at both bond faces and thinner in the middle.
Backer rod
A round foam cord pushed into a joint to set sealant depth and keep the sealant from bonding to the back.
Movement capability
How far a sealant can stretch and compress, as a percentage of joint width, while keeping its seal.
Rodding
Installing backer rod into joints ahead of the sealant crew.