UltraTech Fixoblock
Thin joints, tight walls — a precise 3 mm bond line built for AAC block and fly-ash brick masonry.
What is it?
A polymer-modified cement mortar for laying AAC blocks and fly-ash bricks in thin 2-3 mm joints instead of a conventional 12-18 mm bed.
Where is it used?
AAC block, fly-ash brick and lightweight concrete block walls, from individual homes to multi-storey projects across India.
Why use it?
Thinner, uniform joints mean straighter walls, lower mortar consumption and fewer shrinkage cracks than conventional mortar.
How is it applied?
Mixed with water into a lump-free paste and combed onto the block face with a notched trowel for a controlled 2-3 mm layer.
About UltraTech Fixoblock
Conventional block masonry still relies on a 12–18 mm bed of ordinary cement-sand mortar, and on an AAC block wall that thickness consumes real material while adding little to bond strength. UltraTech Fixoblock changes that. It’s a ready-mixed, polymer-modified cementitious mortar — cement, graded sand and admixtures blended at the factory — meant to be spread in joints just 2–3 mm thick. Because the bond line is thin and consistent, block-to-block tolerance improves on its own: walls come up straighter and masons spend less time correcting uneven beds.
On site it behaves more like a tile adhesive than traditional mortar. Powder is mixed with roughly a quarter of its weight in clean water and combed onto the block face with a notched trowel so every joint gets the same thickness before the next block is tapped level. The mix stays workable for about an hour, so batches need to match masonry pace. It’s built specifically for AAC blocks, fly-ash bricks and similar low-strength units — not a general substitute for structural concrete or waterproofing mortar.
The technical insight
The performance comes from particle grading and polymer chemistry working together. Fixoblock’s sand fraction is finer and more tightly graded than ordinary masonry mortar, which is what lets it spread in a 2–3 mm film without tearing — a standard 1:6 mix can’t be troweled that thin and still bond. A redispersible polymer admixture forms a flexible film as the mortar sets, improving adhesion and letting the joint carry useful tensile and splitting strength (around 0.75 N/mm² at 28 days) well beyond a thin smear of plain cement mortar. That film also retains enough mixing water to hydrate the cement fully, which is why the joint doesn’t need external water curing.
Where it is used
- AAC block walls in residential and commercial construction
- Fly-ash brick and calcium-silicate brick masonry
- Lightweight concrete block partition and infill walls
- Internal partitions in apartments, offices and institutions
- External masonry walls ahead of plaster or texture finish
- Infill blockwork in renovation and retrofit projects
- Mass and affordable housing sites where masonry speed matters
- Dry-wall style partitions built with lightweight blocks
Key advantages
- Joint thickness drops to 2–3 mm against 12–18 mm for conventional mortar, cutting material use
- Higher bond and tensile strength than plain cement-sand mortar
- Self-curing formulation removes the need for daily water curing
- Thinner, uniform joints reduce shrinkage cracking
- Factory pre-blending keeps the mix consistent bag to bag
- Faster wall-raising since masons aren’t waiting on thick beds to firm up
- Straighter walls that need less plaster to true up
- Ready for the next construction stage in about 24 hours
Limitations & considerations
- Meant for AAC blocks, fly-ash bricks and similar low-strength units — not dense solid concrete blocks or engineering brickwork
- Needs clean, dust-free block faces; dusty or wet blocks weaken the bond
- Can’t bridge wide or out-of-plumb gaps the way a thick mortar bed can
- Roughly one-hour pot life, so batches must match laying speed
- Once a batch stiffens it shouldn’t be re-tempered with water — that weakens the joint
Selection & best practice
Keep blocks dry and dust-free before jointing — a quick brush-down visibly improves bond. Mix only what a mason can use within the one-hour pot life, at close to the 25%-by-weight water ratio, using a mechanical stirrer for 2–3 minutes until lump-free. Apply with a notched trowel so the joint stays a consistent 2–3 mm, and check level and plumb every course since a thin joint won’t hide error. Discard any batch that starts to stiffen rather than adding water back, and protect fresh blockwork from sun and heavy rain for the first day.
Specifications
| Composition | Cement, graded sand and polymer admixtures (pre-mixed dry powder) |
| Pack Size | 40 kg bag |
| Joint Thickness | 2–3 mm |
| Mixing Water Ratio | Approx. 25% by weight of powder |
| Pot Life | Approx. 1 hour at 27°C |
| Compressive Strength (28 days) | 6–7 N/mm² |
| Splitting Tensile Strength (28 days) | 0.75 N/mm² |
| Bulk Density | 1450–1550 kg/m³ |
| Coverage | Approx. 60–230 sq.ft per 40 kg bag at 3 mm joint (varies with block size) |
Industry use cases
Residential construction
Homes and villas using AAC blocks get straighter walls with less mortar wastage.
Multi-storey apartments
Infill walls hold consistent joint thickness across large areas, speeding handover to plastering teams.
Affordable and mass housing
High block-consumption projects gain from lower mortar volume and no water-curing downtime.
Commercial and institutional buildings
Partition walls in offices, schools and hospitals get thinner joints that reduce finishing time.
Renovation and infill work
Adding AAC block partitions in existing structures, where fast set-up matters.
Frequently asked questions
Is Fixoblock only for AAC blocks, or can it be used with fly-ash bricks too?
How much water goes into a 40 kg bag?
Do the joints need water curing like normal mortar?
How soon can plastering start after the wall is laid?
How far does one 40 kg bag go?
What tools does a mason actually need on site?
How we position UltraTech Fixoblock
Fixoblock covers the block-laying stage; it isn’t meant to carry through to finishing or waterproofing. Once the blockwork is up, UltraTech’s Tilefixo tile adhesives are the natural next step for tiled areas, and UltraTech Readiplast suits the plaster coat over AAC and fly-ash brick surfaces. For terraces and external walls, UltraTech’s Weather Pro waterproofing systems pair in well. Where a specification calls for Fosroc instead, Space Arc also stocks Fosroc Conbextra Block Jointing Mortar, a comparable thin-bed AAC/fly-ash brick mortar with a similar self-curing formulation.
Fosroc Fosroc Conbextra Block Jointing Mortar — A factory pre-blended, self-curing thin-bed cement mortar for AAC blocks and fly-ash bricks at a similar 3-4 mm joint thickness — a like-for-like swap where a project specification calls for Fosroc rather than UltraTech.
Compare with Fosroc Fosroc Conbextra Block Jointing Mortar →
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