Rusty brown spots in newly installed fiberglass pools

We had a fiberglass pools installed. Work is still undergoing around the pool. Anyway, after backfilling and filling the pool with water, a concrete collar was poured around the pool, although the actual patio around it will be pavers. This was done, I was told, mainly to keep the stairs and seating areas from sagging and partly to accomodate an on-deck automatic pool cover (keep the cover tracks from sagging with the pavers).

We just had the pool cleaned and have noticed thousands of rusty brown spots all over the steps, the seats and basically all around the edge of the pool. These appears to be consistent with splatter from pouring the concrete. There are also a lot bits of concrete on the edge of the pool that is above the water line, but these can easily be removed with the finger nail.

However, the rusty brown spots that are present on the surface of the pool underwater do not come off with either the finger nail or a stiff plastic brush. It has been raining for the past few days and the contractor has not been back on site so we didn't get a chance to ask him about this. I just wanted to get the opinion of the members here as to what they are so I can have an informed discussion with the contractor when he comes back. Thank you in advance.

You can test with a vitamin C tablet or, better, some Iron Out (laundry section) held in a wet rag against some of the spots. If either of those lighten the spots, it's iron. Thousands of rusty brown spots sound like someone was grinding or cutting something -- maybe rebar for the deck? -- and didn't watch where the filings went. Do NOT let the contractor take a pass on this one; they may not be possible to remove completely.

Ben

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Originally Posted by PoolDoc

You can test with a vitamin C tablet or, better, some Iron Out (laundry section) held in a wet rag against some of the spots. If either of those lighten the spots, it's iron. Thousands of rusty brown spots sound like someone was grinding or cutting something -- maybe rebar for the deck? -- and didn't watch where the filings went. Do NOT let the contractor take a pass on this one; they may not be possible to remove completely.

Ben

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Yes, I believe you are right. We had a concrete deck around the pool with steel mesh. This was cut and removed in order to re-set the pool (pool was off-level and was settling over time - different and long story).

While still under (current) construction the contractor lowered the water level to work on the pool light. At that time he applied muriatic acid to the rust spots that were above the (lowered) water line and than sanded with a 600 grit sand paper and was able to remove those spots. He did try to remove the spots that were still under water with just the sand paper but that didn't work. He told me he would try to lower the water level more when he comes to close the pool for the winter (in a month or so) and get at those spots. Does this sound right to you?

I was afraid the sand paper would scratch the finish, however, after inspecting the places where he removed the spots the finish looks intact and smooth still. He told me that this is the same sandpaper that is used to "finish" the fiberglass after a repair.

I don't know about FG finishing, so I can't comment about whether it will or won't hurt the finish.

However, it may be the only way to remove the spots. You can TRY Iron-Out. If that removes the spots, then that might be a less damaging option. (And easier, too.) BTW, you can buy 25# pails of Iron Out from the mfg, over the Internet.