Starches, Binders & Paper Bond
Hold the paper-to-core bond through the kiln and through decades of service.
The interface between gypsum core and facing paper is a starch problem. Migratory pregelatinized corn starch travels with bleed water during setting and deposits at the paper line; non-migratory starch stays in the core and builds compressive strength. For water-resistant Type H / WR cores, silicone hydrophobizers (poly(methylhydrogensiloxane) / PDMS emulsions) or paraffin wax emulsions are added; EN 520 defines the water-absorption threshold for Type H at ≤ 5% (surface plus total-immersion methods per that standard).
Pregelatinized acid-thinned starches dissolve in the slurry, migrate with water, and form a film at the paper-core interface that survives kiln dehydration. STMP-crosslinked starches stay in the core and reinforce inter-crystalline bonds. Silicone emulsions hydrophobize the gypsum surface. For fire-rated Type F / Type X cores, chopped E-glass fiber and vermiculite are added — see EN 520 for the classification and ASTM E119 for the fire-endurance test method.
Paper bond failures typically trace to insufficient migratory starch, kiln overdrying, paper sizing changes, or foam reaching the interface. Correct diagnosis of the failure mode should precede any product change.
- §EN 520 — Gypsum plasterboards: definitions, requirements and test methods — CEN
- §ASTM C1396 — Standard specification for gypsum board — ASTM International
- §ASTM E119 — Standard test methods for fire tests of building construction and materials — ASTM International
- §ASTM C473 — Physical testing of gypsum panel products — ASTM International