Fundamentals
Expansive mortar: splitting rock and concrete without detonation
Working principle, history, applications and limits of a method that has been used since the 1970s wherever blasting and hammering are not an option.
- Expansive pressure
- over 5,000 t/m² of expansion pressure
- Reaction time
- 8–24 hours depending on temperature
- Hole diameter
- typically 30–45 mm
- Vibration
- none – no flying debris, no bang
Working principle
How expansive mortar works
Expansive mortar is a finely ground mineral powder based on calcium oxide and further additives. Mixed with water it forms a pourable slurry that is poured into pre-drilled holes. During hydration, calcium hydroxide crystals form whose volume is greater than that of the original components. Because the borehole leaves no room for this expansion, an enormous radial pressure builds up – with sufficient hole depth and correct spacing, far more than the tensile strength of rock or concrete can absorb.
The material therefore cracks along the axis of the boreholes. The process is slow, silent and free of vibration: no bang, no shock wave, no flying rock. It stays predictable for the user because crack formation and opening width are controlled through the drill pattern and hole spacing.
Instead of a detonation that releases energy within milliseconds, pressure acts here over hours. That is exactly what makes the method usable in residential areas, inside buildings, underneath existing structures and in security-sensitive facilities.
History
From the 1970s until today
The idea of using the swelling behaviour of quicklime is an old one: in ancient quarries, wooden wedges were soaked with water to split blocks. Industrially usable expansive mortars emerged in the 1970s, when formulations allowing a controlled and reproducible build-up of pressure were developed in Japan and Europe in parallel.
The foundations of KUBATEC BMT AG were laid during that period. The demolition industry's need for a method without a blasting permit gave rise to BETONAMIT® – today one of the globally established brands for expansive mortar, complemented by ROCKSPLIT® for rock applications. Production and testing take place in the Principality of Liechtenstein; deliveries go to more than 60 countries.
An early defining field of use was the dismantling of reinforced concrete structures in densely built-up areas. Where blasting was ruled out and hydraulic hammers were unsuitable because of noise, vibration and access, silent splitting offered a practical alternative – an argument that has gained weight over the decades as emission regulations became stricter.
Procedure
Application in five steps
01
Plan the drill pattern
Define hole spacing according to the material and the desired fragment size: in rock typically 8–12 × hole diameter; in reinforced concrete use tighter spacing and drill along the planned separation joint.
02
Drill and clean
Drill as parallel as possible and over the full height of the element. Remove drilling dust and water – a clean hole that is not filled with water improves pressure transfer.
03
Mix
Dose cold mixing water exactly as specified by the manufacturer and mix into a lump-free, pourable slurry with a stirrer. Too much water significantly reduces the achievable pressure.
04
Fill
Fill the holes quickly and completely up to just below the top edge. Observe the working time: the material should react in the borehole, not in the bucket.
05
Wait for the reaction
Secure the area and leave it undisturbed for 8–24 hours. Once cracking has occurred, the material is broken out with an excavator, a grab or by hand and removed.
Applications
Where expansive mortar is used
- Rock excavation for building pits, utility trenches and road construction
- Boulders and rock fragments in agriculture and landscaping
- Foundations, concrete plinths and machine bases in industrial halls
- Dismantling of reinforced concrete walls and slabs in occupied buildings
- Natural stone and block extraction with minimal material damage
- Work in tunnels, shafts and underground without blasting fumes
- Use in security areas, power plants and chemical facilities
- Recovery and dismantling of concrete and rock parts after incidents
In-depth application pages with drill patterns and field experience: rock excavation, splitting boulders and concrete demolition.
Assessment
Advantages and limitations
Advantages
- +No detonation, no bang, no shock wave and no flying rock
- +As a rule no blasting permit and no licensed blaster required
- +Vibration-free – even next to existing buildings and sensitive equipment
- +Minimal equipment: drill, stirrer, water
- +Separation lines can be controlled precisely through the drill pattern
- +Usable in confined, enclosed or hard-to-access areas
Limitations
- –Reaction time of several hours – requires construction scheduling
- –Drilling is a prerequisite and determines the effort involved
- –Less economical than blasting for very large daily volumes
- –Material consumption scales directly with borehole volume
- –Application is tied to a temperature range and the matching product variant
Safety
What to observe during use
Expansive mortar is strongly alkaline. Safety goggles, gloves and closed clothing are mandatory, especially when mixing and filling. Never look into filled boreholes from above at head height: under unfavourable conditions material can be ejected from the hole. Never seal or plug boreholes.
Mixed material that is no longer used must be left to harden and disposed of as mineral construction waste. Safety data sheets and instructions for use for individual countries are available for download on our product pages.
FAQ
Frequently asked questions about expansive mortar
+What is expansive mortar?
Expansive mortar is a powdered, cement-like material that is mixed with water and poured into boreholes. As it sets it increases in volume and generates a pressure of several hundred bar inside the hole, cracking rock or concrete in a controlled way. No detonation takes place – the force is produced purely by chemical and physical crystal growth.
+Is expansive mortar an explosive in legal terms?
No. Expansive mortar contains no explosive components and does not detonate. In most countries it is not classified as a blasting agent, which is why no blasting permit and no licensed blaster are required. National regulations at the place of use are always binding.
+How long does it take for the rock to crack?
Depending on the material, hole diameter and temperature, the first cracks usually appear after 8 to 24 hours. Low temperatures extend the reaction time, high temperatures shorten it.
+Which temperatures are permitted?
The usual application window is a rock temperature of roughly 5 to 35 °C. Different product variants are available for cold and warm conditions; if the mixing water is too warm or the rock too hot, the material may react prematurely.
+How much material is required?
Consumption follows from the borehole volume. As a rule of thumb, about 1 kg of powder fills roughly 0.55 litres of borehole. A hole of 40 mm diameter and 1 m depth therefore requires about 2.3 kg.
Read on
Related topics
Alternative demolition methods
Hammer, wire saw, splitting cylinder, conventional blasting or expansive mortar: when each method pays off.
Rock excavation
Building pits, road construction, tunnel re-profiling – breaking rock without vibration and without a blasting permit.
Splitting boulders
From field stones to 50-tonne blocks: drill, fill, wait – without flying debris and without vibration.
Concrete demolition
Separating foundations, plinths and mass concrete in a controlled way indoors and in populated surroundings.
Business location Liechtenstein
Highly industrialised, politically and financially stable, globally connected: the location behind BETONAMIT® and ROCKSPLIT®.
Mechanical application
Mix and pump BETONAMIT by machine: tonnes instead of kilograms – process, MAI mixing pump, water setting of 1.0–1.2 litres per 5 kg and safety.
Discuss your project in detail
We support you with drill patterns, quantity calculation and product selection – from a single boulder to industrial dismantling.