Yellow Stain under rug

This has been something I have been wondering for a while and have just forgot to ask until now. I am sure all of you have seen it. A yellow area where a rug used to be. I like to be able to educate my customers but I don't know what to tell them as to what caused it. Does anyone know what causes this yellowing under some rugs? Also while I am at it, has anyone been able to successfully remove that yellowing and if so, what did you use? So far I have tried every chemical I can think of and it never breaks loose.

Thanks

I do know the yellowing is ALWAYS caused from rubber backed rugs, or more like rubber backed bath mats since that's what they're for, hard surfaces.

But exactly why they turn carpet yellow, I'm not sure.........I suspect some kind of chem reaction, or some sort of moisture trapping.   

And no, it can't be removed, it's permanent.

It's from the rubber backing of the rug. Probably had some moisture under there and it allowed the transfer of chemicals to create that yellowish tint. I've seen it on tile a lot around here, but too often on carpets.

As for removal, you already threw the sink at it and it will probably never get better. I would use a peroxide on it and hope for the best. If it doesn't work (it probably will not), at least you can say you tried.

It is one of the situations where you don't get to be the hero, all you can do is be an educator for your customer. What color was the carpet? Maybe you can dye your way out?

Always on light colored carpet too right?

Vacuum a new Oriental rug as you would carpet and wool area rugs. Use special care with delicate vintage or antique rugs. Protect them from the vacuum by placing a piece of nylon screen over the rug and weighting it down with books or bricks.

l was originally told it is what's called 'off gasing' where the rubber in the backing of the rug reacts with the carpet.

As far as l know it is permanent.

I was told if it's bright yellow, it's BHT browning.

Carpet & pad manufactures use BHT just like processed food manufacturers use it - as a preservative - to preserve latex backings, urethanes in pad/cushion. The BHT off-gases and gets trapped under the impermeable membrane of the rubber backed rugs turning the carpet fibers yellow. More noticeable with light colored carpets.
It even occurs under with beds & sofas with skirts around them, trapping BHT; esp noticeable sitting on light colored carpet.

Prevention is best remedy: head it off by teaching them never put rubber-backed rugs on top of carpet.

You get brownie points for pointing it out, maybe heading off a disaster, but usually it's too late by the time they are ready to listen cuz they've already done and it and you're probly gonna fail with the recommended procedures of citric acid... makes money for the suppliers who recommend/sell it to you, when you come back to tell them it didn't work "well it must just be you Joe..."

oxalic - better than citric but still see the banana. This is where I (accidentally) discovered oxalic as the most cost effective rust remover ever for our trade.

peroxide - dilute, like 3%, misted 2-3 times seems to bleach it outa there pretty good. Teach your people to buy the drug store stuff and drop in a trigger and get with it, else be prepared to hire you, THE PROFESSIONAL - to come and do your thing with dilute Sally's or Aquasilk.
Let it dry on its own; no forced air. Keep the pets and bare feet away til dry.
Not good idea for wool but may be the only solution.

The day carpet cleaning suppliers start selling 27-34% H2O2 (and at the same prices that spa & pool suppliers sell it to homeowners and the poolboy)... that'll be the day you will realize they were lying to you all along about anything & everything they could get away with. Board owners who pocket their hush money are just as guilty. The only real answer is real cleaners coming together solving our own problems.

Joe Bristor wrote: you will realize they were lying to you all along about anything & everything they could get away with.  Board owners who pocket their hush money are just as guilty. The only real answer is real cleaners coming together solving our own problems.

Amen brother.

"...better than citric but still see the banana"

I may have to use that phrase, Joe.  It goes in the great quote file 

you will never find another supplier to give it to ya straight like Joe Bristor. wither you want to hear it, it helps, or you just realize you made a mistake, Joe is gonna lay it on the line every time.

Thanks so much for the info Joe. You are a wealth of knowledge.