I talked to Great Lake Carpet today. He said the reappearing spots could be the result of an original spill that soaked the pad. When the carpet is cleaned, it looks good for a while but the pad is still not clean and the stain eventually comes up thru the carpet again. He thought professional cleaning should take care of it. I'll try it.

Carpet black spots
 

I will add the following to my first post on the subject. We cleaned the carpet the first time and the spots came back. The next time we had ours professional cleaned and the spots came back. This time the carpet will be removed and we will replace it with something other than carpet. This is a shame as we are part timers and the carpet has had very little usage. While I do not know the cause I will say I am pretty sure it is not from something being spilled on it as mentioned in a earlier post. At least not while we owned the home. I guess it is possible when the carpet was installed something was spilled on the padding. I am tempted to cut the spots out when removed and try to find a lab to send it in to be analyzed to determine what it really is. Not that it will do anything other than solve the mystery. There is too many houses including some neighbors that have had the same issue with no clear cause. Our carpet was a also a light beige color also as mentioned in a earlier post. We bought new and the house was built in 2009. The spots showed up after the warranty was up. I will say this has been one of only two small issues with the house. I would do it all again the same way. It is a great home with even greater neighbors.

so here's another icky mildew problem for those thinking about wood flooring. the same problem with carpet can happen to wood on a concrete slab.

I am fairly sure that it isn't mildew. Mold spores produce color that can be blotted. I have cleaned and then blotted and no color. Also no odor.

Also OUR carpet is not installed, it is a bound piece of carpeting with a backing applied and placed over wood floors. We had it made. (Two of them)

It was made in Ocala. It does release the stain with Spotshot, but it returns in about six weeks.

Unfortunately, the latex adhesive used to laminate the backing on the carpet seems to be a nutritious environment for fungus. It will grow in, as opposed to on or under the carpet. A unit in Naples that was closed up for the summer without AC actually had 2"-3" mushrooms growing out of the carpet. Granted that was a bit extreme, but the black spots sound like a similar problem.

I wonder if this does occur when we are not running heat and air.....

The color of the carpet appears only to indicate that such spots woud be more readily found.

Everyone seems to be describing mold/mildew which indicates moisture. Mold grows above 50% humidity especially in dark areas combined with enough heat to allow the spores to grow. Remembering that mold/mild spores are ever present and needing the aforementioned to grow they therefore were present in the carpet in question. That is why for instance wallpaper and especially vinyl wallpaper was never a good idea installed in a bathroom.

We had beige carpet in our three bedrooms and owing to traffic patterns deided to replace them. We hemmed and hawed over the three most obvious options wood, tile and carpet. After much discussion for almost a year we opted for a very high grade carpet and pad. I did make it a point to inspect the slab before they installed the carpet two of the bedrooms had a slight but lengthy crack. I am told that it would do litle good to fill them as movement would only open them again. Since they both were slight in width I acquiesced. Perhaps my information was faulty?

I have lived here for better that six years and have not found "black spots" to be a problem for us. However, given the number of those responding in the affirmative it would appear that there is obviously some commonality (defect) here. It would seem that perhaps a water restoration expert upon visible inspection could unravel the mystery.

I am sorry that you are having difficulty here and hope you all can get it permanetly resolved.

Personal Best Regards:

I lived in CA in a house with a concrete slab foundation. Even though humidity wasn't a problem, moisture wicking through the foundation was. When vinyl flooring was removed, even though it was applied properly, mold and mildew were under the sheet. Carpeting, white I might add, did not seem to be impacted UNLESS there was a heavy piece of furniture on it and only if a very large area was covered, and it had to be for a long time. Our chair mats caused a problem....they stayed down for about a year and the carpet became moldy....and smelly in the area impacted. Never did we have spots just appearing like I saw on our neighbors' carpeting....black spots with absolutely no odor, not in a traffic area and not covered with furniture, etc. We lived in our CA house for over 30 years....had a dark green shag initially (it was an in color at the time...:D) and if any spots ever showed up on that carpeting, you couldn't see it....there was no moldy smell, ever.....even where furniture sat on it for years.

I'm beginning to wonder if the "spotted" carpeting showing up here is defective. Is it predominantly one color, one manufacturer?

I am wondering too.

Carpet problem
 

You might have to pull the carpet back and see what type of spot there is on the secondary back of the carpet. If its mold you could clean it with bleach and water. If its permanent you might have to replace that area of the carpet. The other problem you might have is, in the concrete someone might have spilled a solvent that keeps wicking through the carpet, if thats the case, you have to clean that area of the concrete. Being in this field before I retired I think this might be you problem.