QUESTION

We have a plaster pool that was re-done about 7 years ago. the health department made us make the pool shallower. We are in the mountain and have lots of snow. We have a row of tiles under the coping. Two years ago, in the spring we noticed that many of the tiles had fallen off. We had them all removed and had workers install new tiles. This spring now we have pitted holes in the tile. Some are large and some small with no pattern. What could cause this? One of the workers on the re-do of the pool had said something about water behind the tiles?
Thanks for any advice.

ANSWER

ANSWER - Being in the mountains and having your pool subjected to snow and freezing conditions would suggest that your pool waterline tiles are not freeze-thaw stable.

Meaning that the tiles are porous enough that they absorb moisture.  If the tile absorbs moisture, then when there is freezing temperatures the moisture freezes.  When the moisture freezes it expands and can cause the tile surface to spall/pit.

Nothing you can do about it.  If you replace the tile make sure you use a porcelain tile that has less than 0.5% absorption and is rated as freeze-thaw stable.