Caulking Guns, Tile Cutters & Sealants

What is the purpose of installing closed-cell foam 'Backer Rod' in deep gaps before caulking?

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 Correct IncorrectBacker rod controls sealant depth and prevents three-sided adhesion. Sealant must adhere only to the two opposing joint faces so it can expand and contract without tearing.

What is the purpose of installing closed-cell foam 'Backer Rod' in deep gaps before caulking?

• To control sealant depth and eliminate 3-sided adhesion so the sealant can stretch freely
• To make the joint fireproof
• To soak up water leaks like a sponge
• To support heavy foot traffic directly