How to avoid damaging the walls when demolishing concrete floor? How to demolish concrete slab / roof?
How to break / demolish / remove concrete floor / screed between the walls?
Demolition of concrete or reinforced concrete floors and screeds inside the buildings can potentially damage the walls, ceilings and other structural elements. Chisseling concrete floors or concrete foundations with pneumatic or hydraulic hammer generates high levels of vibration and shockwaves being annoying for naighborhood and capable to develope significant damages of fragile structures. Concrete demolition can however be performed today with limited emissions, less noise and with reduced vibration levels. Drilling the holes and Dynacem expansive action will produce incomparably less damage to the house and walls, and less noise than heavy hammering. Dynacem method of expansive demolition is very well known in nordic countries. It is being acceptable there fo breaking hard rock in direct vicinity of inhabited houses and is there called "vibration free" demolition.
Step 1 - separation the slab from the walls
If the slab has free edges, go to Step 2.
The procedure is demonstrated on the sketch below.
If the slab has no free edges, you can drill inclined (45 degrees) holes in square drill pattern (according to Stage 2 procedure and beginning demolition from the center of the floor). Drilling all inclined holes you will use 45 % more Dynacem but you can fill all the holes in one step and potential damage to the walls will still be very limited. Otherwise there are three possible options of Step 1 to choose from:
Drill near the walls and fill the rows of inclined (45 degrees) holes A.
Alternatively, drill vertical holes B, located as close to the wall as possible, together with corresponding iclined holes A.
When extremal protection is needed for the walls, drill the holes C, B and A as sketched, and fill holes B and A only. Fill holes C after delamination and removal of cracked concrete from between the holes B and A.
Remove cracked concrete from the whole area near the walls and proceed to Step 2.
S - hole spacing in square drill pattern
h - drilling depth
Step 2.
To break internal part of the slab, holes D are used in square drill pattern.
Hole diameter: 30 mm in non-reinforced concrete above 10 deg C, 40 mm is recommended in all other cases. Smaller diameters may also work, but with worser results and in the longer time.
The following conditions must be met at the same time.
S < 2h when non-reinforced concrete slab rests on plastic foil/styrofoam/sand (any sliding support) and whole slab thickness is removed,
or S ≤ h in all other cases.
S < 10 hole diameters when the slab is made of reinforced concrete, or S ≤ 15 hole diameters when the slab is made of non-reinforced concrete.
h ≥ 5 hole diameters (holes can be drilled at an angle in thinner slabs to increase drilling depth).
h > 85 % of the slab thickness being removed (the deeper the hole, the better Dynacem action).
Hole spacing should not exceed 30 cm if the rubble will be removed manually or with hand tools (larger hole spacing can be used when larger chunks will be removed by the excavator).
One (preferably) or two outer rows of holes should be filled every 24 hours. Move the cracked concrete away from the uncracked inside of the slab every day.
Example 1
Non-reinforced concrete slab 30 cm thick, resting on sand, temperature 20 deg C.
Cracked chunks will be removed manually.
Hole diameter: 30 mm
Hole spacing S = 30 x 30 cm (you can drill holes in the 30x30 cm grid nodes or you can follow the sketch below where the holes are spaced 30x30 cm basing on the 26x30 cm grid)
Drilling depth h = 27 cm
Example 2
Reinforced concrete slab 50 cm thick, resting on plastic film, temperature 20 deg C.
Cracked concrete will be removed with excavator after Dynacem raction.
Hole diameter: 40 mm
Hole spacing S = 35 x 35 cm
Drilling depth h = 45 cm