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Stucco Hydration - Hydrating (Water Curing) Stucco (Preventing Soft Stucco Walls)

01 Jun 2019 4:32 PM | Anonymous

Hydration: The chemical reaction that occurs in Stucco when water is added and causes the liquid Stucco Paste to turn into a solid.

Stage 1 (Mixing)

  • Blending stucco in a mixer starts the hydration process.
  • Stucco should be mixed a minimum of 5 minutes (concentrate) or 3 minutes (premix) after all ingredients have been added (See mixing instructions on bag).
  • Empty the entire mixer after each batch.
  • All the particles in the mix are coated with water during mixing.
  • Soft stucco can result if the sand and stucco are not thoroughly mixed.
  • Over-mixing will entrain air and weaken the stucco.

Stage 2 (Application)

  • Stucco goes into a dormant stage after it is mixed.
  • The water coats the particles and cools the mix.
  • The stucco is now in a fluid (inactive) state and can be applied.
  • Stucco must be applied a minimum of 3/8 inches thick.
  • Stucco that is less than 3/8 inches thick will dehydrate easy and may not get hard.

Stage 3 (Hydration)

  • Stucco hydration begins once the water starts to dissolve the cement particles.
  • The temperature of the stucco will increase.
  • The dissolved cement particles start to form together.
  • The stucco begins stiffen and to form into a solid.

Stage 4 (Hydration/Curing)

  • Stucco must be kept moist for a minimum of 48 hours after application.
  • Stucco walls should be watered (fogged) in the morning and evening when the walls are cool.
  • Moist curing (watering) allows the hydration process to continue and the stucco to get hard.
  • Weather conditions (wind, heat, low humidity) may require more hydration (moist curing).
  • The hydration process stops if the stucco becomes dry and does not get re-hydrated.
  • The stucco may not get hard.
  • New (fresh) stucco that is dry can be re-hydrated.
  • Adding water to the dry stucco can restart the hydration process.
  • It is difficult to re-hydrate stucco after it is painted.

Potential Causes of Soft Stucco

  1. Improper Mixing
  2. Over sanding
  3. Using out of spec sand or sand with excess silt (dirty sand)
  4. Inadequate hydrating

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