Technical Discussion

Understanding Modulus of Elasticity in AAC and Applied Coatings

The importance of Low Modulus of Elasticity for External Plasters over AAC is well known.

Because AAC is a lightweight highly insulating material, plasters are subjected to high stresses and must be formulated to be compatible with the AAC and resistant to stress induced damages. As a result, plasters with a low modulus of elasticity are necessary over AAC. A low modulus of elasticity indicates that a material is more malleable or less brittle and as a result is more resistant to cracking. For a cement plaster to exhibit a low modulus of elasticity it must be lightweight and intentionally made to low strength. ACI 523.3R recommends using the following empirical formula to determine the modulus of elasticity for cellular of lightweight concretes of unit weights ranging from 23 to 90 lbs/cf.

      Modulus of Elasticity (Ec) = 33 W1.5 Öf’c

      W = dry weight lbs/ cf
      f ‘ c = compressive strength-psi

      For Autoclaved Aerated Concrete:

        Ec = 33 (35)1.5 Ö350 = 127,739 psi

      For Litewall® SL:
        Ec = 33 (38)1.5 Ö350 = 144,401 psi

      For Normal Stuccos:
        Ec = 33(100)1.5 Ö2000 = 1,475,100 psi


Litewall® SL exhibits a modulus of elasticity similar to that of AAC and is therefore recommended for construction utilizing AAC.