MP2070 Adhesion to Paper Tape

MP2070 is a hard VAE powder with a minimum film forming temperature of 5 °C. In a gypsum joint compound the hard film is the point: it grabs the paper and holds the edge of the board.

The Paper Interface

Paper tape and gypsum board liner are porous, fibrous surfaces. A compound bonds to them mechanically, by penetrating the fibres and drying around them.

A hard polymer film forms a stronger mechanical key than a soft one. That is why joint compounds are built on rigid grades rather than flexible ones.

Dosage and Cohesion

Joint compounds usually carry 2 to 4 percent of MP2070, higher in the taping pass and lower in the finishing pass. The taping mix needs adhesion; the finishing mix needs sandability.

Cohesion inside the compound matters as much as adhesion to the paper. A compound that crumbles cannot hold a feathered edge, whatever its bond strength.

Shrinkage and Cracking

Gypsum sets by hydration and loses volume as it does. The polymer film has to accommodate that without opening a crack along the tape.

Application thickness controls the risk more than dosage does. Two thin passes behave better than one thick pass, because the second pass fills the shrinkage of the first.