Gunite Pool Maintanence

[masanori]

We just decided to buy a gunite pool. We heard different things about how often one needs to acid wash the pool. Assuming good pool chemistry, can it last 10-15 years? How often are we re-plastering, too? Thanks

[Pool Clown]

We just decided to buy a gunite pool. We heard different things about how often one needs to acid wash the pool. Assuming good pool chemistry, can it last 10-15 years? How often are we re-plastering, too? Thanks

Yes, but with a heavy accent on the "Good pool chemistry" part. Almost needs to be "Excellent pool chemistry", for 15 years. There are also variables to the actual application of the plaster that come into play as well. So to be honest, good chems may or may not be the sole variable of your plaster life.

does that make sense? I tend to ramble...

[quantumchromodynamics]

My opinion is that you should almost never have to acid wash. As long as you maintain good chemistry and keep metals out of the water, I don't see any reason to ever have to acid wash. I don't think that acid washing should be considered something that needs to be done periodically.

With the proper chemistry, you should be able to get up to 20 years on your plaster.

[quantumchromodynamics]

Here is a good resource for information about plaster. It is the National Plasterer's Council.

[waterbear]

The above info is all well and good but under real world conditions a good number of plaster pools do need to be acid washed every 3-5 years or so. Much depends on the makeup of the fill water and how well you maintain the water chemistry (and how much the look and feel of the pool surface bothers you). Each time you acid wash you remove a bit of plaster and shorten the life of the plaster finish so you really do want to do it as infrequently as possible to lengthen the times between replastering the pool. However, if you develop scale deposits or certain other stains it will become necessary.

I completely agree with Pool Clown on this one!

Then again, vinyl liners do need to be replaced every 7-10 years and fiberglass is prone to cobalt spotting and iron staining so no pool surface is maintenance free. There are tradeoffs that much be considered. With a plaster pool you need to consider the cost of acid washing and replastering (or repainting every year or two) as part of the normal maintenance of your pool.

[quantumchromodynamics]

I really don't see any reason that plaster would need to be acid washed, ever. Proper maintenance should keep the plaster in good shape. I think that acid washing should be avoided, if at all possible.

Proper maintenance will prevent scale. Metals should be removed before the water is introduced to the pool. Many metal stains can be prevented with sequestrant. An ascorbic acid treatment will remove most metal stains.

Of course, it requires very good maintenance of the pool and chemistry, but I don't think that it should be considered beyond what a homeowner should be able to do.

[masanori]

I really don't see any reason that plaster would need to be acid washed, ever. Proper maintenance should keep the plaster in good shape. I think that acid washing should be avoided, if at all possible.

Proper maintenance will prevent scale. Metals should be removed before the water is introduced to the pool. Many metal stains can be prevented with sequestrant. An ascorbic acid treatment will remove most metal stains.

Of course, it requires very good maintenance of the pool and chemistry, but I don't think that it should be considered beyond what a homeowner should be able to do.

I will keep my ph under control...after all I am a urethene chemist

[quantumchromodynamics]

It's important to maintain a positive CSI to prevent the plaster from dissolving.

Although, it is also important not to allow the CSI to go too high. I recommend that you maintain a CSI of between 0.0 and 0.4.

You can use the Pool Calculator to calculate your CSI.

I prefer to keep the pH between 7.6 and 7.9.

[waterbear]

I really don't see any reason that plaster would need to be acid washed, ever. Proper maintenance should keep the plaster in good shape. I think that acid washing should be avoided, if at all possible.

No arguments here but in the real world even the best cared for pools often need acid washing after a period of a few years. Theory is all well and good when it comes to pool maintenance BUT situations DO occur.

Proper maintenance will prevent scale.

It will HELP prevent scale but nothing is foolproof! Scale happens if the water is balanced to be non aggressive to plaster (slightly positive saturation index and/or higher pH).

Metals should be removed before the water is introduced to the pool.

In a perfect world yes, BUT metals do end up in fill water and in pools for various reasons. It is often impossible to remove the metals from the fill water without special, expensive ion exchange filtration or by causing them to precipitate out on the filter media, essentially staining that. If the stained media is not completely changed the metals can redissolve into solution.

Many metal stains can be prevented with sequestrant.

Sequestrants only 'deactivate' the metal ions, not remove them and sequestrants break down from sunlight and chlorine and need constant redosing. It just takes one missed dose...

An ascorbic acid treatment will remove most metal stains.

Ascorbic, Citric, Oxalic and other organic reducing acids are very effective against iron, somewhat effective on manganese and cobalt, and effective on some types of copper stains. If the copper stains are black or brown then an acid wash is the only thing that will remove the stains. The other metal that needs an acid wash to remove is the most common one and is calcium stains or scale (let's not forget that calcium is also a metal and one that we often ADD to a plaster or fiberglass pool!)

Of course, it requires very good maintenance of the pool and chemistry, but I don't think that it should be considered beyond what a homeowner should be able to do.

Yet things happen that can throw the water balance off just enough and for long enough for problems to happen in ever the best cared for pools! In theory it sounds good but as reality rears it's ugly head the truth surfaces that plaster pools DO need to be acid washed every so often!