Hidden concrete cracks and leaky down pipes

Membrane hiding cracks

Zenith had come across quite an interesting problem with one of its client’s buildings during a site inspection that was a part of our tendering process for a commercial coating project. The damage that exists is well hidden and only a few clues were available for us to see.

But with the use of clever deduction, our wits and our knowledge of the way concrete works were able to uncover serious defects in the buildings concrete pillars

Hidden cracks and defects

Zenith had been asked to provide a quotation for the exterior re-coating of a medium sized office block.

Zeniths undertake a robust consultation process during the tendering stage for all projects.

During our site investigations we had uncovered many water ingress issues that would have affected the effectiveness and life span of the coatings that we were going to apply.

As a part of our commercial recoating service Zenith offer life time warranties for the coatings that we apply, this means that we must apply the coatings to the manufactures specifications as well as ensuring that any existing defect in the substrate will not affect the coating after we apply it.

We have all seen large bubbles in commercial buildings appear within a week or two of a new paint job being applied Zenith avoid this occurring with our projects by ensuring that the substrate is fit for paint to adhere to it.

Once the defects in the substrate had been identified we notified our clients and tendered a report with what we had found, our client then asked us to develop a proposal to rectify the problems and then apply the coatings with our life time warranty firmly in place.

The following explanation will outlay what we had found and detail how it had occurred.

  • Situation

The building in question in a 1980s built commercial office two stories tall.

It has poured floors and precast walls with these poured pillars at the corners and every 6 meters along each face.

The building is rectangular in shape and is 50 meters long by 18 meters wide making the roofed area approximately 900m2 .

Each corner pillar has a square galvanized down pipe cut into the pillar so that it matches the pillars original profile and is hidden.

The down pipes travel up the pillars and into the eves where they connect with a large internal gutter that runs across each long side.

  • Case study of damages

The damage that we had first identified was presenting as bubbles in the paint on each pillar that had a down pipe.

The paint was textured and a dark blue, this had made it harder for us to identify the cause of these bubbles.

In most cases bubbles in paint is due to the substrate being wet at either the time of application of the paint or constantly after the paint has been applied.

After closer inspection we had found that the pillars had been coated with paint on water proofing membrane over the top of a fiberglass mesh reinforcing sheet.

The membrane had been damaged by water penetrating out from behind it.

This had meant that the pillar was leaking water from the inside and expelling it out through the repair.

The reason for these original repairs was to seal cracks in the concrete pillar, the repairs had hidden the cracks well however they had not addressed the reason for the cracks in the first place, which was the presence of water in the pillar that had caused the reinforcing rods to rust, and while rusting expand and crack the pillar.

Membrane hiding cracks
  • Case study of causes

This finding of course had warranted further investigation.

After inspection we had found that the inside profile of the pillar (behind the down pipes) was not sealed or painted.

The existing down pipes where the original down pipes and had never been replaced but had been repaired in a number of places with steel patches and rivets but only on the outside profiles of the down pipes that are accessible without removing the down pipes where repaired.

The inside profiles of the down pipes (between the pillar and the down pipe) where still leaking badly onto the unsealed face of the pillar.

This had caused the pillar to soak up water for at least 20-25 years which in turn had caused the reinforcing inside the pillar to expand while rusting and crack the pillar.

The previous repairs had hidden the extent of the cracking.

The previous repairs had also not addressed the issues of the leaking down pipes or the rusting reinforcing and had allowed these to continue to the point that the cracks where large enough to allow the liquid flow of the water to travel through the pillar and break the waterproofing membrane easily over time.

This had lead us to believe that the pillar has been thoroughly cracked right the way through its cross section due to the reinforcing rusting.

The fact that the last tradesman had not understood what was occurring or did, and did nothing beggars belief and may have caused the building extreme amounts of structural damage over time.

This is most apparent due to the fact that they had sealed the pillar with water proofing membrane and in doing so had stopped water from escaping the pillar through the cracks in it, causing it to fill up with water completely and be constantly full of water.

The owners, without the knowledge of this defect where not able to correctly plan and budget to maintain the building which in turn has resulted in the requirement of a large scale concrete remedial repair project and possible structural repairs to the building.

  • Investigation of extent of damages

Zenith had submitted a report detailing all of our findings and proposing remediation of the damage and the situation that had caused it to occur.

The client had no idea that this was happening and had praised our thoroughness, especially as we had been asked to provide a commercial painting proposal and had instead identified a potential asset devaluing situation and then offered an in-depth report detailing it.

  • Repair solutions

The best and most fit for purpose repair and remediation solution is to remove the offending down pipes.

Remove all of the existing membrane to uncover the damage to the pillar.

Depending on the size of the cracking, (which I can estimate to be extensive due to the amount of water travelling through the pillar) chisel out all cracks to expose the rusted reinforcing.

If the rusting is more than ¼ of the diameter of the steel the rusted portions of the reinforcing will have to be replaced, properly tied in with the correct overlap, the pillar boxed (concrete formwork)  and new concrete poured.

If the rusting is less than ¼, then proper removal of the rust by mechanical means and the application of a suitable rust preventative coating (zinc based), then  followed by the boxing and pouring of concrete into the holes or large open areas of concrete made by removing the cracked concrete

Followed by the application of a water proofing membrane to the inside of the pillars and new down pipes.

  • Summary of how to prevent

Commercial property, facilities, asset managers and owners can prevent this type of degradation by regular onsite inspections and the replacement of any defective items in good time.

If our client had replaced these down pipes many years ago the pillars would not have cracked so badly and the opportunity to seal the inside of the pillars would have presented itself.

Regular onsite inspections and identification would also have allowed the owners to budget for these repairs well in advance of any sever degradation to the pillars; a simple replacement of the steel down pipes would have saved many thousands of dollars and possible break down of the buildings structural integrity.

Instead a band aid repair was performed by covering the cracks, therefore sealing the water inside the pillar and thus causing more extensive damage because the reinforcing would have been covered in water the whole time instead of just getting wet some of the time.

In summary band aid repairs cost more than thorough and fit for purpose repairs in the long run.

Zenith is currently awaiting the go ahead for this project and if anyone is interested in seeing what we find when we open up the building and how we remediate it please let us know and we will make a series of articles on this project.

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