Unfinished Travertine Decking Erosion around entry and exit points

[arizona480]

So I have these clients with beautiful travertine around the pool which has been in place for almost 3 years. Around where swimmers get in and out there is heavy erosion. The water is about as "new" as the decking and it's in Arizona, so if anything we have a hard water issue.

Here are the current numbers on the pool chemistry:
FC: 7.0 ppm
TC: 7.0 ppm
pH: 7.8 ppm
TA: 70 ppm
CYA: 50 ppm
Ca: 350 ppm
TDS: 2400 ppm
Phosphates: 2500 ppm
NaCl: 1600 ppm

During Swim season when the water is being tracked over the travertine, the CL ranges from 3.0 - 10 ppm , pH and TA stay in their appropriate ranges (7.4-7.8 and 80-100 ppm).

Any ideas on what part of the water chemistry may be responsible for this?

 

[JamesW]

It might just be weak travertine. Can you post some better pictures?

How soft is the stone?

 

[arizona480]

Supposedly it is "outdoor grade" not sure on the softness or how to measure it. I need to get some info off one of their spare boxes. I'm back there Friday, hopefully I can get some more pics.

Would the high phosphates do anything to that stone? I'm not sure what the phosphates were during swim season, I never had any trouble maintaining FC though, so never was an issue to check it.

 

[kimkats]

Are you talking about the light spot? Or is there more that cannot be seen as easily?

 

[JamesW]

Try scratching a spot with your fingernail or something to see how hard the surface is. Better stone will be hard to scratch. Soft stone will be easy to scratch. Of course, do it in an inconspicuous place.

 

[tstex]

First, the picture you posted is very inconclusive, esp since it's far away and heavily shadowed.

Next, that is pecan/tumbled travertine, that is highly pitted in it's normal state anyway, more so if the softer cretaceous material is blown out w a powerwasher. Also, if the pool is salt-based, that can accelerate wear and tear, so it has to be sealed.

As noted, you need to post closer pics and from a better perspective w out the shadows and more uniform lighting

 

[arizona480]

Not a SWG pool, but has 1600 ppm due to normal acid/base reactions.

 

[JoyfulNoise]

Phosphates are not an issue with stone work but your number is probably 2500 ppb (parts per billion ) not ppm. It’s a secondary issue to treat phosphates and I do it in my pool. At 2500ppb that water can become reactive to algae growth so your choice is either to maintain the higher FC levels consistently and ignore phosphates OR give yourself some insurance against an algae bloom and treat them at some time later. It’s up to you and it sounds like you’ve been able to maintain this pool well enough.

So there’s no SWG...then how are you chlorinating this pool?

As JamesW alluded to, it could very well just be that the travertine that was used in that area of the pool is “soft” (ie, easily eroded) and there’s not much you can do about it. Travertine is a beautiful stone to work with but it can be subject to wear & tear. If travertine is to be used as an exposed form of decking (ie, not under a covered patio) then it should be sealed to prevent water absorption and help reduce wear. Your customer might just have to live with the wear and replace the stone pieces at a future date.

Your chemistry looks fine sand your water balance (CSI) is on the right range. So aggressive water is not an issue.

 

[duraleigh]

The light spot looks a lot like an acid spill.....but that travertine would have to have been coated and I doubt it is.

 

[jeffnhispool]

When I had my pool resurfaced with Marquis quartz about 12 years ago, we tiled the water line with 6x6 tumbled travertine that I had sitting around. The PB had no opinion on how smart that was but we did it anyway. I cant recall specifically that I sealed it although Im fairly confident that I did (knowing me) but even if I had it would probably not still be sealed after this long (and in a pool no less).

To this day the tile still looks new...better than my floors actually). Its a chlorine pool (soon to be swg) and I also have travertine on floors (Im on one now) and in the steam shower. Honestly I have never seen any signs of deterioration anywhere and we hit the steam shower with some pretty strong mold killers. Being naturally porous, it does have varying amounts of fill so Im wondering if perhaps thats whats breaking down.

Im actually considering travertine pavers for my deck so am interested to follow this

 

[arizona480]

Sanitized with mostly bleach and one or two trichlor pucks in the summer per week.

 

[JoyfulNoise]

If it’s just at the pool entrance, then it’s probably just a quality issue with the stone that has been brought out by the repetitive nature of people and water going in and coming out. Nothing you’ve posted so far reveals any gross chemical negligence. Natural stone quality can vary quite dramatically from region to region. Arizona flagstone can be very tough stuff and works well in my pool but flagstone in Texas can be a nightmare. It may just be an off batch of travertine that got installed.

 

[arizona480]

Are you talking about the light spot? Or is there more that cannot be seen as easily?

That's a patch they tried, the worn out looking area.

 

[kimkats]

The shadows are too dark to see any worn out area.

 

[arizona480]

The shadows are too dark to see any worn out area.

You can see in the sunlit part on the left, nice and smooth, most of the tile looks like that, in the middle of the sunlight is on the way to the pool steps, very worn on top. More pics later today.

 

[jeffnhispool]

I just enlarged your pic and IMO that sure looks like erosion or etching. If its strictly at the pool entrance, logic says it has to be chemical. I've never seen travertine do that

 

[arizona480]

Here are some pics from today:

 

[JoyfulNoise]

Has dry acid or sulfate containing chemicals ever been used regularly in this pool?

 

[JamesW]

It might just be soft stone. Have you tried the scratch test?

Does water pool in the affected areas or does it drain adequately?

 

[JoyfulNoise]

I truly believe this is a materials quality problem and not so much a chemistry problem. Not all travertine is the same, it's quality depend A LOT of where it was mined from and how it was formed. Travertine is nothing more than limestone that has formed from a flowing water source. True travertine comes from hot spring sources where superheated water that is saturated with calcium carbonate rises up to the surface. Once there, the excess dissolved CO2 rapidly outgassed and the pH rises. As the pH rises the calcium carbonate precipitates out of solution. There are two forms of calcium carbonate - calcite and aragonite (different crystalline structures). If the water that the travertine deposit forms in is hot (the hotter the better), then the aragonite is the preferred precipitate and the travertine will be harder, more dense and less porous. If the water is cooler, then the calcite form is favored where the travertine will be less dense, softer and more porous. In the extreme case of fluvial waters (free flowing cool waters like rivers and lakes), the deposit that is formed is very porous and weak; as such, it is not technically travertine but it is called tufa.

So, my gut feeling is that the homeowner simply has a poor quality batch of travertine that is likely more porous and soft. As such, the constant exposure to water, wet/dry cycling and chloride exposure (from the chlorine used in the pool) has simply caused the travertine to spall and disintegrate. Chloride and sulfate attack are well known problems in cementitious materials especially in arid climates where the rapid evaporation allows the pool water to deposit lots of chloride into the surface of the stone. Those tiles should have been sealed to prevent the damage you are seeing. My guess is they were not to prevent them from being slippery.