Swimming Pool Blog

Problems with Pool Plaster

 Problems with Pool Plaster
by Rob Cox, September 6, 2012

Problems with Pool Plaster

contract for pool plaster"Since pool plaster is composed of natural materials that have certain inherent characteristics, some amount of shading or color variation is a natural occurrence which should not be construed as a defect and which only enhances the natural beauty of your pool. Homeowner agrees that the plaster is NOT guaranteed for evenness of color and may not be the exact shade anticipated. The shade and color may vary and fade over time. The plaster may become streaked, blotchy, or have a mottled appearance over which the contractor has no control."

                                                                               Date:______   Signed:_____________________

If you have had your pool replastered in the last 15 years, it's likely that you were presented with a statement similar to the one above, adopted by the National Plaster's Council, IPPSA, NSPI and NPSF. In the years since this disclaimer became the standard, more has been revealed.

More has been revealed about the likely causes of pool plaster problems. It seems that it's not always something that the contractor has no control over. Certain "Defects in Materials or Workmanship" can cause plaster discoloration, cracking, etching and delamination.

Now, with all due respect to plaster, a fine pool finish - I have to say that issues with a plaster finish are rare. Most new plaster finishes are flawlessly brilliant and without any visible defects for years. This post is not meant to discourage you from using plaster as a pool finish, even white plaster - but merely to discuss the problems that can occur with new pool plaster, so that the pool owner can be better informed - beyond the disclaimer statement offered by the plastering company.

Problems with Pool Plaster

  Discoloration of Pool Plaster

discolored pool plasterMaking a distinction from surface staining, discoloration is within or beneath the plaster. When attempts to acid wash the stain fail, this confirms that the discoloration is not caused by mineral or organic deposits on the surface.

Discoloration of a newly plastered pool can occur within the first few months and years of plastering, and can be more pronounced on colored pool plaster. Discoloration or variations in hue or shading of your pool plaster may be caused by one of the following.

  1. Excess use of Calcium Chloride to speed up setting time; with more than 1-2% added calcium.
  2. Adding water while finish troweling, known as "wetting". This disrupts surface aggregate bonding.
  3. Water content variation in the plaster mix.
  4. Thickness variations in the plaster application.
  5. Over troweling, which can also produce trowel marks on the surface
  6. Rain or surface wetting before pool is filled.

  Cracking of Pool Plaster

Check cracking or "Crazing" as it's sometimes called, is most often seen on the top step of a plastered pool, but can also run rampant through the walls and floors in some cases. These are not usually indicative of an eminent plaster failure, but if large enough, will provide a nice foothold for dirt and algae, and they sure are ugly!

Ideally, a pool will be full within 12 hours of plastering. Slow fills, on very hot days, can dry out the plaster before the fill water has a chance to cover it. And spraying it down before it's full can create discolorations. In the best scenario, the pool is plastered on a cool, foggy morning, and filled by truck 6 hours after the plaster is applied.

Cracking of pool plaster, outside of slow fill times, can also be caused by:

  1. Excessively "wet" plaster mix, with high water content.
  2. Excessively "hot" plaster mix, with high calcium content.
  3. Late stage hard troweling, with a wetted trowel.
  4. Alkali-Silica Reaction (ASR) within the plaster mix.
  5. Expansion of the Substrate beneath the plaster.

  Etching of Pool Plaster

plaster etchingMaking a distinction from delamination or spalling of the surface, where spots of new plaster have separated from previous plaster layers, "Spot Etching" is a symptom that is almost universally blamed on pool owners, or service companies performing water balance or new plaster start-up.

But etching of pool plaster indicates a soft spot of plaster that has degraded or deteriorated, and is also most prevalent on steps and swimouts, around wall fittings, pool lights and under the tile line.

Spot Etching of pool plaster can be caused by:

  1. Excessively "hot" plaster mix, with high calcium content.
  2. Late stage hard troweling, with a wetted trowel.
  3. Excess sand or fine aggregate used in the plaster mix.
  4. Excess water or low cement concentrations in the mix.
  5. Lime on the surface or in the plaster mix.

  Delamination of Pool Plaster

plaster delaminationAs the name suggests, pool plaster delamination is a situation where the new coat of plaster has separated from the old layer beneath. Small pop-off areas the size of a quarter may not be indicative of large scale bond failure.

Spray a hose on an empty plastered pool, and you may "hear" areas of delamination in the pool, which produce a hollow sound. However, delaminations can go unnoticed for years, unless they crack and begin to flake off.

Clearly a case of bond failure, the causes of plaster delamination are usually:

  1. Surface not properly cleaned, or no bond coat applied.
  2. Late stage troweling of a dry plaster surface.
  3. Plaster coat is too thin.
  4. Overtroweling.
  5. Excess heat or cold on day of plastering.

If you are planning to have your pool plastered again soon, chances are you'll have no problems. Most plastering crews are highly skilled applicators - and they have to be - pool plastering is as much an art as it is a science. Prep, Timing and Touch are all very important for a proper pool plastering job.

So, let's give our pool plastering companies a break. Pool plaster is a difficult medium to work with, with hundreds of variables affecting the outcome. It's one of the few pool repairs which should not be a DIY project. Contract with a trusted local plasterer and you should have no problems.

Be careful with the start-up procedure and follow the plastering company's advice to the letter - fill the pool rapidly without stopping, balance the chemistry, brush twice a day, and backwash as needed - and you should never need refer to this blog post. But, if you do find yourself in a disagreement about the condition or appearance of a new plaster coat - I hope that you find this little article helpful.