Intumescent backer rod

A construction assembly comprising:

• a first construction element defining a first end surface and formed of at least one material, the first element having a first fire-resistant rating, and a second construction element defining a second end surface and formed of at least one material, the second element having a second fire-resistant rating, wherein the first end surface and said second end surface are opposing and adjacent to define a void, the height of the void defined by a top plane and a bottom plane;
• a backer rod press fit into said void to a depth to define a sealant collection cavity within said void, said backer rod having an external shell defining a total rod volume and a hollow interior, and a core disposed within said hollow interior, wherein said external shell is formed of a combustible material and said core is formed of an intumescent material;
• and
• a sealant layer within said sealant collection cavity forming a bond between said backer rod and said first surface, said backer rod and said second surface, and said first surface and said second surface;
• wherein exposed to fire on a side opposite said sealant layer, said external shell disintegrates on said side opposite said sealant layer and said core expands within said void in a direction away from said sealant layer to occupy the void and break the bottom plane of the void on said side opposite said sealant layer to form a fire-resistant barrier within said void between said first element and said second element.