Concrete cancer rectification step by step

Hi All

Thought I would post some pics showing what concrete cancer can look like and also the sort of work that's involved in rectifying it.

Here you are seeing some mild spalling of concrete from the ends of the reo rods. The concrete cancer is caused by the rusting of reo rods that happens when the reo rods have insufficient concrete cover. The concrete actually protects the reo rods from the air and sets up an alkaline environment which also deters the rusting. With insufficient cover the water leached away the alkaline environment and allows the reo rods to start rusting. Rust takes up way more space than the original steel rod and as a result expands the concrete and cracks it. This in turn allows more water and air to enter and cause further damage.

If you see cracks in concrete which is generally dry and this crack has any rusty colour about it then there is likely to be a rusting reo rod within.

If you look closely at the left corner of the balcony you see a small crack. This is the corner that in the next set of pictures is completely opened up.

To be continued........
This corner needed very little encouragement to 'fall off'. This is the corner that you can just see in the left of the picture in the previous post.

This was after the first section of concrete was removed. It doesn't look to bad until we followed to unsound concrete further.

It appears that when they poured the slab the hot and cold water pipes were able to float in the wet cement and actually washed towards the edge of the slab. This movement also encourage air pockets around the pipes. The closeness of the reo to the surface and then the air pockets allowed substantial rusting of all the surrounding reo rods.

So all this area had to be opened up back to sound concrete and clean reo rods. The rust then had to be removed from the rods back to bare metal. It ends up being a substantial hole where we had to insert some extra rods as some of the previous rods were to far gone. The hot and cold copper pipes were cut out of the area and both will be rerouted on the underside of the slab.

To be continued ..........
Here we have opened up all the unsound concrete and treated the reo rods with a primer ready for the rebuild of the concrete. As can be seen the water pipes have been removed.

This next pic is of a partial rebuild. It is very time consuming as you can only do about 50 -60 mm per build then have to let it set before applying the next layer.

The final result before any repaint.

Hi HandyAndy,

What was used to clean back the reo, and prep before reconcreting?

Did you have the treat the surrounding concrete with Bondcrete or does the new concrete bond to the old without this?


We use the Sika system which are Sika Monotop 610 and SikaMonotop 615HB.

The job shown in the photo sequence was the first concrete cancer job we did so we were still finding our feet.

The reo we cleaned mechanically on this job, namely angle grinders with metal grinding blades and sandpaper for the back. Took forever.

Nowadays, we use a sandblaster which does the job more thoroughly and much quicker. We just bought a 10 gallon sandblaster like this one

we already had a compressor. The sand blaster uses ceramic tips which wear out and are super expensive. It also wears out the taps and seems anything else associated with this equipment.:eek:

Another problem is the safety gear as the stuff is so abrasive that any mask gets blasted very quickly, to the point that you can no longer see through the shield. We use the Triton powered face respirator for which we need to buy a new face shield.

Ones the steel is cleaned then you coat it with 610. You also coat all the old concrete as this form the bond layer. You need to coat it multiple times and then finally follow up with the first layer of 615. You repeat with the 610 between each layer of the 615. The brochures available from Sika are very helpful.

What would you do with this? :D


  • stump.jpg
    58.7 KB · Views: 401