Home Pool Services Cracking and Discolouration in Gunite Swimming pools – Blupool Swimming Swimming pools

Cracking and Discolouration in Gunite Swimming pools – Blupool Swimming Swimming pools


Uneven plaster and pitting in swimming pool

Pitting and Discolouration in a gunite pool.

Discolouration in gunite swimming pools is worrying. This precipitated concern for a swimming pool proprietor in Durban. He additionally had issues about his swimming pool which had a crack, uneven paster and marking.

1. Attainable Cracking within the Nook of the pool
2. Marble plaster discoloured
3. Marble plaster pitting and floor uneven in locations.

Jason Sanders proprietor of BLUPOOL Durban, and a member of the National Spa and Pool Institute of South Africa, attended to the pool inspection and reported the next, amongst which was the discolouration in his gunite pool:

Cracking within the nook of the pool:

cracking in the corner of a gunite pool

There was a crack within the tile within the nook of the pool. Based mostly on a visible evaluation, we weren’t sure whether or not this crack was proper via the concrete shell of the pool.

Floor motion could cause cracks. In some instances, elevating the swimming pool ranges after the shell is forged or united could cause the pool to crack. The tile genearly cracks on the joint.

It may be that the pool or the paving round that nook is settling. Even when there isn’t a signal of the pool or the paving settling, the crack may develop into a priority later, particularly if it widens, or continues additional down into the shell.

On this particular case, the proposed pool location was modified from its unique place to a brand new space within the yard. The pool was designed with piling beneath it in its unique place, nonetheless, we can’t be certain whether or not piling was performed on the new place.

We really useful that the builder (or engineer that signed the pool off) confirms that the pool was correctly underpinned and complies with the specs, though the pool location has moved.

Associated Article: Why does a Swimming Pool Crack?

Discolouration in Gunite Swimming pools

discolouration of marble plaster

The marble plaster has gray stains. Causes of discolouration in gunite swimming pools:

1. Drop Out (Precipitation of metals within the water.)

Metals can get into the pool from a number of completely different sources, fill water, sanitising merchandise, algaecides, soil and many others.

If the metallic content material within the pool water is excessive, a sudden change within the pH might trigger the metals to come back out of resolution. The metals then connect to the pool floor.

2. Slag Stains (Discolouration in gunite swimming pools.)

Black cement (which is often used for guniting the pool shell) has about 38% slag in it, and this will migrate to the floor of the marble plaster beneath sure situations.

Ensures towards discolouration in gunite swimming pools with marble plaster finishes are normally by no means coated by the builder. The extra respected builders have this very clearly spelt out of their contracts.

There are measures one can put in place to forestall stains from getting worse. Good water stability and a upkeep dose of a metallic chelating agent, resembling Pool Magnet by BioGuard, may also help.

We advocate that pool water absolutely analysed quarterly by a pool store that could be a member of the NSPI, and that has adequate testing tools.

Marble Plaster pitting and uneven in sure locations.

There are noticeable pits within the marble plaster. Brought on by:

  • poor water stability (low Calcium Hardness), or by
  • inferior high quality white cement, or by a
  • negligent applicator.

Calcium Hardness.

A good BioGuard supplier and NSPI retail member examined this. Calcium Hardness is appropriate at 198ppm (Preferrred vary 200 – 275ppm)

Inferior white cement.

If the white cement is of inferior high quality or has expired, then the pool marble plaster can pit prematurely.


In our business, we’ve got skilled some specialist plastering contractors, sprinkle water onto the marble plaster when trowelling to provide it a clean ‘polished’ look.

This creates dilution of the cement and weak spots within the bond between the marble mud and the white cement.

After a yr or two, this turns into evident. Corrosive water (poor water stability – Calcium Hardness beneath 200ppm.) aggravates this.

The uneven marble plaster in locations seem like the trowelled end of the marble plaster was beneath normal.

Most contractors assure their workmanship on plaster for less than a yr or two.

One can’t reverse pitting. Hold pool water effectively balanced and the saturation index in test. It will decelerate the additional deterioration of the marble plaster.

The pool will want re-plastering at some stage. Use a registered NSPI member firm to re-plaster the pool. Use at high-quality marble plaster combine.


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