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A guide to manual coating application

The rehabilitation of pipes damaged by corrosion has resulted in the creation of innovative and effective solutions. The following provides a “˜how to’ guide for the manual application of mortar coatings.

The coating of drinking water pipes has been offered within Germany since 1970. Cement mortar coatings, as per DWGW W 343, DIN 2880, DIN 2614 and EN 805, are carried out in situ on pipes from DN 80 diameter upwards. The centrifugal spray technique is a clear favourite application method.

Sewer pipes have been coated with mortar in Germany since 1982. The applications methods are:

1. Manually applied coating
2. Wet spray coating
3. Centrifugal spray coating
4. Displacement process

Shafts and other installations in the German public drainage system have also been coated with mortars since 1982. Manually applied and wet spray coatings were the predominant methods, however the centrifugal spray M-coating process has gained more popularity recently.

Manual Coating

Equipment:

Mortar mixing container, bucket, two-paddle mixer, trowel, steel float, sponge board, coarse sponge, graduated water container, brush or soft broom

Applying the bond layer:

The first step is to create a bond layer using the renovation mortar. The grout needs to be mixed to a consistency between soft and plastic and then brushed onto the prepared substrate. The bond layer should be approximately 1-2 mm thick. If the substrate shows signs of damage or cavities, these must be filled in with mortar.

Mixing the pipe renovation mortar:

The appropriate ERGELIT-KS mortars are mixed according to their particular instruction sheet. Always take care to put the water into the mixing receptacle first. The amount of water, calculated as a percentage in relation to the dry weight of the mortar must be exact in order to guarantee the desired water-solid ratio of 0.4 or less. The water-solid ratio is usually provided as this is more practical for mixing dry mortars on site. It is also extremely important to mix the mortar for the recommended time.

Coating:

The mortar coating is applied by trowel and float, wet-on-wet, to the bond layer applied previously. Using the trowel to apply the mortar, as is done with ordinary cement mortars, is difficult in this case because of the high adhesion factor and is not advisable. However, there are often occasions when technically there is no alternative. As a rule, several wet-on-wet applications are required depending on the depth desired.

It is essential that the surface be lightly roughened between coats with a sponge or sponge board to ensure the application of the next coat. The surface of the final coat is smoothed with a damp brush in order to prevent water and air becoming trapped during the final steel coat smoothing.

When repairing damage caused by biogenic sulphuric acid, if using ERGELIT-KS 2b as coating mortar, the fresh mortar’s high thixotropy must be taken into account. This means that the fresh mortar will stiffen in the mixing container after about 5-10 minutes if mixing is interrupted. If this occurs, the mortar can be re-mixed for 20-30 minutes to recover its original consistency.

In order to speed up the setting time, some mortars can be modified by the use of compatible accelerators, however the manufacturer should be consulted.

Ambient temperature influences working time and must be observed. Working times for the different mortars can be obtained from technical data sheets available from the manufacturer. As manual coating has little impact energy, it is generally considered to be a top surface coating technique.

In the past manual coating was the most popular technique. In the future it is anticipated that the wet-spray technique will be used for larger and irregularly shaped installations.

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