AAC Block Adhesive

Masonry Block

 Adhesive – Complete Guide

1. Definition

Masonry block adhesive is a ready-to-mix, polymer-modified cementitious mortar specially formulated for laying AAC blocks, CLC blocks, hollow blocks, and solid blocks.
It replaces traditional thick cement–sand mortar (1:6) with a thin joint layer of 2–3 mm, ensuring:

• High bonding strength
• Reduced material consumption
• Faster construction speed

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2. Types (as per Indian Standard & Practice)

Currently, IS 6041:1985 (Code of practice for construction of autoclaved cellular concrete block masonry) and IS 15477:2019 (tile adhesives, adapted for thin joint mortars) are referred for guidance.

Block adhesives are generally classified by application area:

Type	Description	Typical Use
Cementitious Thin Bed Adhesive (Standard)	Polymer-modified cement-based	AAC / CLC blockwork in dry or damp areas
High-Strength Adhesive	Increased bonding for load-bearing walls	High-rise, heavy-duty walls
Fast-Setting Adhesive	Quick strength gain	Urgent works, repair jobs
Weather-Resistant Adhesive	Higher water & temperature resistance	External walls, exposed areas

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3. Technical Specifications

(Typical industry values – refer to manufacturer data + IS standards)

Property	Requirement
Compressive Strength (28 days)	≥ 6 MPa
Tensile Adhesion Strength	≥ 0.5 MPa
Pot Life	2–3 hours
Open Time	20–30 min
Water Retentivity	≥ 95%
Mix Ratio	Powder:Water ≈ 3:1 by weight
Application Thickness	2–3 mm
Coverage	1 bag (40 kg) ≈ 12–15 m² (for 2–3 mm)

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4. SOP – Application Method

Step-by-Step:

1. Surface Preparation
   • Ensure block surfaces are clean, dust-free, and slightly damp.
2. Mixing
   • Add adhesive powder to clean water (approx. 3:1 ratio).
   • Use slow-speed mixer for 3–5 min until lump-free.
   • Rest 5 min, remix.
3. Application
   • Spread adhesive with a notched trowel (6–8 mm notch).
   • Maintain a 2–3 mm joint thickness between blocks.
4. Block Placement
   • Place block, tap gently for alignment.
   • Check vertical & horizontal level with a spirit level.
5. Curing
   • No water curing required; light misting in hot/dry weather.

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5. Thickness Guidelines

• Vertical joint: 2–3 mm
• Horizontal joint: 2–3 mm
• Avoid exceeding 3 mm — thicker joints reduce bonding performance.

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6. Types of Tests

(as per IS 15477 / IS 6041 / ASTM references)

1. Compressive Strength Test – IS 4031 (Part 6)
2. Tensile Adhesion Strength Test – IS 15477 / EN 1348
3. Shear Bond Strength Test – ASTM C952
4. Workability Test – Flow table method
5. Open Time Test – EN 1346
6. Water Retentivity Test – IS 2250 method
7. Durability / Weather Resistance Test – Exposure cycles

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7. Key Points for Site Engineers

• Thin joint = less mortar, faster work, better accuracy.
• Always use a notched trowel for uniform thickness.
• Do not mix more adhesive than can be used in 30 min open time.
• Keep blocks slightly damp before application to avoid moisture loss from adhesive.
• Store adhesive bags in dry conditions to prevent lumps.