What is chemical used for AAC block joints in construction?
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Dnyan Deshmukh
Staff member
AAC blocks are stick together with a thin polymer modified mortar or acrylic base polymer adhesive.
Cement base adhesive comes with a fine sand, cement, cementitious material and polymers which create dispersion in mix, provide great workability, polymers to retain the water inside it to give self curing property to it.
Acrylic polymer base adhesive make bond stronger as they dries. Disadvantage which i observed in past with purely polymer base adhesive (chemical adhesive comes in liquid form) is, it softens the bond and loose its strength when it comes in contact with water. a seepage or leakage in wall where high wind pressures are there, the walls constructed with that adhesive might fall on the clients who lives in that rooms.
Cement base adhesives are best for construction of AAC block masonry and also wont require any curing to it, if had self curing additives in it.
Cement base adhesive comes with a fine sand, cement, cementitious material and polymers which create dispersion in mix, provide great workability, polymers to retain the water inside it to give self curing property to it.
Acrylic polymer base adhesive make bond stronger as they dries. Disadvantage which i observed in past with purely polymer base adhesive (chemical adhesive comes in liquid form) is, it softens the bond and loose its strength when it comes in contact with water. a seepage or leakage in wall where high wind pressures are there, the walls constructed with that adhesive might fall on the clients who lives in that rooms.
Cement base adhesives are best for construction of AAC block masonry and also wont require any curing to it, if had self curing additives in it.
Sir to avoid cracks at RC wall and block work junction what is the procedure can I know it
ferrer.vicente1997@gmail.
Newbie
Dnyan's distinction between cement-based and acrylic polymer systems is spot-on — that warning about pure polymer adhesive softening on water contact is critical and often overlooked.
I'd add the specification layer that determines whether the system performs as designed: joint thickness and application method.
Cement-based thin-bed mortar for AAC is designed for 2-3mm joints, not the 10-12mm of traditional brickwork. The polymer content (RDP — redispersible polymer powder) needs to be minimum 2 kg/tonne to provide the flexibility AAC's higher thermal movement requires compared to standard brick. Using the right product at wrong joint thickness defeats the system's advantage — thicker joints increase shrinkage cracking and thermal bridging.
The reason AAC needs polymer-modified systems at all: AAC has very low suction (0.5-2 kg/m²·h vs 5-8 for standard brick). Traditional OPC-sand mortar cracks because water doesn't get absorbed by the block, which extends curing time and increases shrinkage. The RDP in thin-bed mortar solves both issues: improves water retention so the adhesive cures properly, and adds flexibility to handle movement.
For walls with any moisture exposure (external walls, bathrooms, kitchens), cement-based thin-bed is mandatory as Dnyan said — not optional. Pure polymer has its place for interior partition walls in absolutely dry conditions only.
I've worked extensively with AAC block systems in India. More at builtbychemistry.com
builtbychemistry.com?utm_source=forum&utm_medium=comment&utm_campaign=civil4m
I'd add the specification layer that determines whether the system performs as designed: joint thickness and application method.
Cement-based thin-bed mortar for AAC is designed for 2-3mm joints, not the 10-12mm of traditional brickwork. The polymer content (RDP — redispersible polymer powder) needs to be minimum 2 kg/tonne to provide the flexibility AAC's higher thermal movement requires compared to standard brick. Using the right product at wrong joint thickness defeats the system's advantage — thicker joints increase shrinkage cracking and thermal bridging.
The reason AAC needs polymer-modified systems at all: AAC has very low suction (0.5-2 kg/m²·h vs 5-8 for standard brick). Traditional OPC-sand mortar cracks because water doesn't get absorbed by the block, which extends curing time and increases shrinkage. The RDP in thin-bed mortar solves both issues: improves water retention so the adhesive cures properly, and adds flexibility to handle movement.
For walls with any moisture exposure (external walls, bathrooms, kitchens), cement-based thin-bed is mandatory as Dnyan said — not optional. Pure polymer has its place for interior partition walls in absolutely dry conditions only.
I've worked extensively with AAC block systems in India. More at builtbychemistry.com
builtbychemistry.com?utm_source=forum&utm_medium=comment&utm_campaign=civil4m
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