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
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 |
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) |
4. SOP – Application Method
Step-by-Step:
- Surface Preparation
- Ensure block surfaces are clean, dust-free, and slightly damp.
- 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.
- Application
- Spread adhesive with a notched trowel (6–8 mm notch).
- Maintain a 2–3 mm joint thickness between blocks.
- Block Placement
- Place block, tap gently for alignment.
- Check vertical & horizontal level with a spirit level.
- Curing
- No water curing required; light misting in hot/dry weather.
5. Thickness Guidelines
- Vertical joint: 2–3 mm
- Horizontal joint: 2–3 mm
- Avoid exceeding 3 mm — thicker joints reduce bonding performance.
6. Types of Tests
(as per IS 15477 / IS 6041 / ASTM references)
- Compressive Strength Test – IS 4031 (Part 6)
- Tensile Adhesion Strength Test – IS 15477 / EN 1348
- Shear Bond Strength Test – ASTM C952
- Workability Test – Flow table method
- Open Time Test – EN 1346
- Water Retentivity Test – IS 2250 method
- Durability / Weather Resistance Test – Exposure cycles
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.
