Online Enquiry

Do you want to find out more? Give us a few details below so we can contact you...
Remove Cookies


PROTECTA Mag™ - Manhole Corrosion Protection Technology

  • No Confined Space Entry - No Network Shutdown
  • Provides an enduring high pH surface with anti-bacterial properties
  • Life-long corrosion protection to the asset







Corrosion of concrete assets such as pump stations and manholes.

Corrosion caused by sulpher oxidizing bacteria that oxidize H2S gas to sulphuric acid, leading to acid corrosion.

Low pH causing an increase in bacterial colonies.



PROTECTA-Mag, based on Calix’s Magnesium Hydroxide Liquid (MHL), is derived by mixing additives to MHL.

PROTECTA-Mag applied via a spray mechanism, gels quickly on the concrete surface and forms a hard coating.

Calix has designed a mobile "Vertical Spray Rig", which carries all required equipment, can be used for spraying PROTECTA-Mag either manually or by lowered winch in deep manholes.

Depending on the depth of the manhole, coating thickness of 1.5 to 2 mm can be achieved in 90 minutes to 3 hours.

Surfaces which have an epoxy coating, PROTECTA-Mag can be applied after removing the epoxy coating.



PROTECTA-Mag neutralizes the sulphuric acid present on the concrete, which causes corrosion.

It also increases and maintains the pH level of the concrete surface, thus inhibiting growth if acid-oxidizing bacteria and provides corrosion protection to concrete surfaces.

It inhibits root ingress. 

Even after 12 months, the PROTECTA-Mag layer strongly adhered to concrete walls, thus providing long-lasting protection to concrete surfaces.



     APPLICATION             TEST




PROTECTA-Mag™ is derived from Calix’s high surface area magnesium hydroxide liquid mixed with additives that allow spray application and fast gelling characteristics for concrete surfaces. When sprayed on the surface of corroding concrete, PROTECTA-Mag raises the pH and firstly neutralises the sulphuric acid. Secondly, it eliminates bacterial colonies that oxidise hydrogen sulphide and generate sulphuric acid. When sprayed on manholes, Calix guarantees the pH will be at or above 7 for 7 yrs.


Calix has designed and purpose built mobile spray rigs for “vertical spray operations” which are used for coating sewage assets such as manholes and wet-wells. The corroded asset is spray cleaned with pressurised water jets and then coated with a PROTECTA-Mag spray using an airless pump. Multiple coats are carried out to achieve opacity and a coating thickness of 1 to 1.5mm. Depending upon the depth of the manholes, the operation can be carried out manually or by auto spray heads lowered on a winch.


Trained operators carry out a detailed site risk assessment before starting the work and a site clean and sign off before concluding the project. For manholes up to a depth of 3 metres, the entire process lasts around 60-90 minutes. For deeper manholes and wet-wells, the process time is 2-3 hours. All required MSDS documents, safety equipment, harnesses, gas meters etc. are available on the mobile rig.


The process is straightforward and can be carried out without stopping the sewer flow and without confined space entry. Along with manhole walls and benching, accessible areas of the flow canal are also coated. PROTECTA-Mag provides lifetime corrosion protection for sewage assets, because the coating can be easily reapplied on the existing surface; unlike other technologies such as epoxy, where the old coating needs to be chiselled out.


The coating does not have structural properties, thus structurally compromised manholes cannot be protected using the PROTECTA-Mag technology.



Product PROTECTA-Mag:


• Provides an enduring high pH surface coating

• Penetrates the surface of the concrete to neutralise residual acid

• Inhibits the growth of specific acid forming bacteria (e.g. thiobacillus concretus)

• Inhibits any root ingress

• Spraying is carried out without stopping flow of the sewer and without confined space entry

• The over spray of PROTECTA-Mag entering the sewer flows is complementary and beneficial for any downstream Sewage Treatment Plant (STP) and odour control

• Safe to handle and, non-hazardous

• Provides life-long corrosion protection to the asset





Calix presented their spray PROTECTA-Mag™ technology for corrosion protection to Gold Coast City Council (GCC). The technology was found to be cost- effective and safe. Thus GCC decided to test the coating on a designated manhole in Ormeau.



3.1 Manhole coating equipment

The coating trial was carried out on the 15th of August, 2015 using Calix’s purpose-built mobile rig, designed for vertical spray operations (similar to the rig shown in figure1). The mobile spraying rig was equipped with :


• Petrol driven high-pressure water pump

• Hose Reel

• Airless spray pump for PROTECTA-Mag coating

• Automatic spray head lowered in the manhole using a winch for water spray and PROTECTA- MAG spray

• Handheld lance for spraying water and PROTECTA-Mag for the top portion of the manhole and manhole cover

• Water and PROTECTA-Mag storage containers

• Safety equipment – tripod, harness, gas meter, traffic signs, manhole cover, spill kit

• Safety documents including material safety data sheets and risk assessments

Manhole coating equipment                                                                                    Fig 1


3.2 Application Process



After arriving at the site, Calix team carried out a detailed site risk assessment including H2S levels around the manhole, and other nearby manholes in the Ormeau pump station. Around the manhole on the southern edge of the pump-station the H2S was found to be above acceptable levels (fig 2). This area was assigned as a personnel exclusion zone in the risk assessment.


Tripod was set around the manhole, manhole cover removed and replaced with safety cover (fig 3).



manhole with high H2S levels

Fig 2 – manhole with high H2S levels

tripod setup

Fig 3- tripod setup


The manhole and its conditions were surveyed and accordingly, the operators formulated a cleaning and coating plan. The manhole featured a metal grill and an overflow pipe. Additionally, the walls showed extensive corrosion, especially the top area (fig 4).


manhole conditionmanhole condition

 manhole condition

Fig 4 – manhole condition


Water cleaning

The high-pressure water cleaning head was lowered into the manhole (fig 5). The cleaning head with its rotating nozzles was moved along the depth of the manhole cleaning loose concrete and any other dirt on the concrete walls (fig 6). The cleaning pressure and speed is adjustable as per the degree of cleaning that needs to be achieved. The top 500mm of the manhole and the underside of the manhole collar were cleaned using a handheld lance. All cleaning was conducted without confined space entry.


 Cleaning head

Fig 5 – Cleaning head

 Cleaned manhole walls

Fig 6 – Cleaned manhole walls


PROTECTA-Mag Coating

A spray head was lowered into the manhole (fig 7,) and the PROTECTA-Mag was applied using an airless pump. The coating was applied in multiple passes (fig 8). The underside of the manhole collar and the rear of the manhole cover were coated using a handheld lance. All coating was conducted without confined space entry.


 Coating head

Fig 7 – Coating head

 Coated manhole walls

Fig 8 – Coated manhole walls


Sign off

The coated lid was placed back on the manhole. All equipment was stored back on the rig and any waste removed from the site. A signoff procedure was carried out before leaving the site.


sign off sign off
Fig 9 - sign off




4.1 The Corrosion Process

The pH on the surface of any concrete sewer asset is the measure of the corrosion rate; lower the pH higher the corrosion rate (fig 10). Low pH allows colonies of Sulphur Oxidising Bacteria (SOB) to thrive. These SOBs are responsible for oxidising the H2S gas to sulphuric acid leading to acid corrosion. As pH reduces, more bacterial colonies are formed, thus more sulphuric acid generated leading to more corrosion (fig 11). PROTECTA-Mag has a high pH; once it’s sprayed onto the cleaned manhole concrete, it neutralises any residual acid. Additionally, it quickly gels to form a strong bond with the concrete, thus creating a protective layer. The high pH inhibits the formation of bacterial colonies. The high surface area of Calix MgO imparts anti-bacterial properties thus the PROTECTA-Mag coating can resist bacteria much longer.


 Relationship wall pH to corrosion rate

Fig 10- Relationship wall pH to corrosion rate
(Source- LA County San District & Thioguard TST

 The pH reduction process

Fig 11- The pH reduction process
(Source – SCORe: R Melchers, T Wells 2014)


4.2 Calix test method

The direct relationship between concrete pH and corrosion is an established fact, Calix checks the corrosion protection efficacy of its coating technology by testing the surface pH. Calix follows Australian Standard AS1289.1.1.2001 “Methods of testing soils for engineering purposes” for conducting a surface pH test.

The pH test involved Calix operators scraping the coated layer which also included some concrete behind the coat. These samples were tested for pH as per the test method specified in the standard mentioned above.



4.3 Test 1 - 16th of December, 2015

A detailed site risk assessment was carried out. The H2S levels in the manhole were acceptable. Refer fig 12, the manhole was found to be in good condition. The PROTECTA-Mag coat had adhered very well to the concrete. Brown lines on the side of the upper part of the manhole were marks of water entering through the manhole cover. There had been an entry in the manhole since the coating for removing steel overflow grate. This work had not disturbed the PROTECTA-Mag coat.

Scrape samples of the PROTECTA-Mag layer were taken at 4 locations, 2 each on the western and eastern side. Along with the PROTECTA-Mag, the samples contained concrete that the PROTECTA-Mag layer had adhered to. The pH values of these samples were tested in Calix’s laboratory. The results are tabulated below



 Virgin PROTECTA-Mag East 1East 2West 1West 2
9.5 pH8.65 pH8.8 pHpH 8.8pH 8.6


The virgin PROTECTA-Mag pH mentioned above is the value of non-contaminated product, as it is supplied to the site. The pH levels of the samples from the manholes are high. The reduction from the original 9.5 pH is due to the lower pH of the concrete that is mixed with the scraped samples.


 Manhole condition after 4 months Manhole condition after 4 months
Fig 12 – Manhole condition after 4 months


The conclusion from this test was that the PROTECTA-Mag layer is still strongly adhered to the concrete. A high surface pH means that there are no bacterial colonies present on the manhole walls.


 scraped area recoated and marked

Fig 13 – scraped area recoated and marked

 coated manhole cover rear

Fig 14 – coated manhole cover rear


All the scraped areas were re-coated with PROTECTA-Mag and marked (fig 13). The manhole cover rear was coated in August. The cover still has the PROTECTA-Mag bound to it and has no further corrosion as shown (fig 14).


4.4 Test 2 – 17th of February, 2016

The second scrape test was carried out in February 2016.


 Manhole condition after 6 months

Fig 15 – Manhole condition after 6 months 


South 1North 1
8.54 pH8.6 pH

As can be seen (fig 15), the manhole is in excellent condition. Scraped samples were collected 1 each from the South and North side. The pH values are in the table shown.



4.5 Test 3 – 19th of April, 2016

The third scrape test was carried out in April 2016, 8 months after coating.


 Manhole condition after 8 months Manhole condition after 8 months
Fig 16 – Manhole condition after 8 months



9.5 pH9.54 pH

As can be seen in fig 16, the manhole is in good condition, the applied PROTECTA-Mag coating is on the concrete and the pH, as shown in the table is high. The scrape sample did not contain any base concrete thus the reading is high, close to the virgin PROTECTAMag level.


4.6 Test 4 – 16th of August, 2016

The fourth test was carried out in August 2016, 12 months after coating


 Manhole condition after 12 monthsManhole condition after 12 months
Fig 17 – Manhole condition after 12 months


8.2 pH8.4 pH

It can be seen clearly in Fig 17 that the coating and the manhole is in a good condition. There has been no peeling or cracking of the coating and it continues to protect the asset. This manhole experiences high levels of H2S, and despite the high levels, there has actually been no change in the coated product over the last 12 months.


The pH is still high, around the 8 value due to base concrete mixed with the PROTECTA-Mag scrape sample.


4.7 Test 5 – 17th of January, 2017

The 18 month test results are given below.


 Manhole condition after 18 monthsManhole condition after 18 months
Fig 18 – Manhole condition after 18 months


Lower SouthUpper North
9.25 pH8.71 pH


Fig 18 clearly shows that there has been no degradation or wash off of the coating over 18 months. The pH readings from the scrape test are provided in the table.



The pH is still high, around the 8 value due to base concrete mixed with the PROTECTA-Mag scrape sample.



4.8 Test 6 – 12th of July, 2017
The 24 months test results are given below.


 Manhole condition after 24 months Manhole condition after 24 months
Fig 19 – Manhole condition after 24 months


On ConcreteOn Steel l ip
9.14 pH9.12 pH

The two-year testing was a significant milestone. As can be seen in the photo (fig 19), the coating has not undergone degradation. The change in colour is due to the staining from the water flowing over the manhole walls.


As it can be seen the pH of the wall surface is still high, unchanged since it was coated and it continues to protect the asset after 2 years.


4.9 Test 7 – 12th of June, 2018

The 36 month test results.


 Manhole condition after 36 months Manhole condition after 36 months
Fig 20 – Manhole condition after 36 months


9.5 pH9.45 pH

At the 3rd year after initial coating condition of manho still looks good with some increased staining but overall coating integrity still good. Higher pH results of scrape tests may be due to lack of base concrete dislodged during scrape.


High levels of H2S observed during testing but surface pH remains high preventing corrosion.



The objective testing parameters is the pH values noted at different points on the manhole. As can be seen from the results, the pH value of the manhole surface is high and PROTECTA-Mag layer continues to strongly adhere to the walls. Hence, we can conclude that the asset is protected and free from corrosion.


pH of Scrap Samples from Manhole


Original State of the MH 

Original State of the MH

Coated MH 07/15

Coated MH 07/15

MH Condition 4 months

MH Condition 4 months

MH Condition 8 months

MH Condition 8 months

MH Condition 12 months

MH Condition 12 months

MH Condition 18 months

MH Condition 18 months

MH Condition 24 months

MH Condition 24 months

MH Condition 36 months

MH Condition 36 months