Caulking Tips: Cohesive Failure With 3 Point Adhesion

What is cohesive failure?
Cohesive failure is when the caulk line cracks or tears down the center.

Caulking Tips: Possible causes & solutions to cohesive failure:

Problems with 3-point adhesion of sealants: they can’t properly stretch.

Cause #1: 3-point adhesion
The caulk bead is sticking to the back of joint, as well as the sides, and the caulk can’t stretch correctly. Avoid this by inserting backer rod (foam rope, widely available at hardware stores) into any joint that is 1/4″ wide and 1/2″ deep or larger.

Cause #2: Rapid or Extreme Movement

If the surfaces the caulk was applied to undergo extreme or sudden movement, it can cause the caulk to get stressed. It relieves that stress by splitting down the middle. This is often the case with caulk applied indoors during the winter, before the heat is turned on. When the heat is turned on, it causes the surfaces to move a lot and quickly, stressing the caulk line and causing some splits.

Cause #3: Caulk Not Allowed to Properly Cure
Caulk applied in freezing temps or hot temps can’t properly cure and form all of its necessary performance characteristics, compromising elasticity and adhesion of the caulk. Be sure to carefully follow the manufacturer’s application instructions where it states the type of temps you need during application.

Cause #4: Too little caulk applied
A tiny 1/8″ wide joint does not accommodate enough caulk to both adhere to the sides of the joint and leave enough in the middle the stretch properly. Or, as is the case with big round logs, a small 1/2″ bead isn’t wide enough to accommodate the shrinkage and movement those big logs undergo. Try to apply enough caulk from the get-go, but understand that there may be some repairs to do when you can’t.

Solution:
For each instance, the solution is the same:

• Where the caulk has split, release the pressure by slitting open the tear with a razor blade.
• Where possible, insert backer rod. It should always be used in any joint 1/4″ wide or wider and 1/2″ deep or deeper. If you couldn’t fit it in before but the joint is now big enough for backer rod to fit, put some in.
• If your caulk will stick to itself, simply apply more caulk over the existing bead. All of Sashco’s products will stick to themselves, making repairs quick and easy. Some products can’t do that. In particular, silicone won’t stick to itself (and nothing will stick to silicone). In these cases, you’ll have to completely remove the caulk and start over. Sashco makes a great alternative to silicone called Lexel®. It’s crystal clear and won’t tear out of joints like silicone because it stretches.)

Related articles

• Caulking 101: Keys to Success (sashcoinc.wordpress.com)