How to Remove Carpet Yellowing Due to BHT.

1. BHT yellowing is characteristically a bright canary yellow on carpet.
2. Spray with Brown Out^® diluted 1 part product to 2 parts (up to undiluted) with water to the area.
3. Allow to work 15 to 20 minutes.
4. You should see the yellow gradually fading away.
5. Once the yellowing is gone, make a single wet pass with water only to remove most (but not all) of the Brown Out.
6. Follow with two dry passes.
7. If the yellow does not fade away, the yellowing is probably not due to BHT, but rather to optical brighteners, mill oil or asphalt.

What is BHT?

• BHT, a phenolic, is Butylated HydroxyToluene.
• BHT is commonly used as a preservative in bread and other processed food and used to be commonly used as a preservative in carpet cushions and padding.

Why Does BHT Yellow Carpet?

• BHT used to be commonly used as the preservative in carpet padding or cushion, primarily rebond urethane foam padding.
• Normally, BHT, a solid, sublimes up from the padding through the carpet and off-gases into the air without causing a problem.
• However, if BHT is trapped and cannot escape into the air, the BHT reacts with chemicals on the carpet, forming bright yellow derivatives.
• This may occur where part of the carpet is covered with a large couch with a skirt, piano or rug and the BHT has nowhere to go. That means that the BHT stays close to the carpet and will cause a yellowing to occur.
• When you go to move a large item or rug, you may see this yellowing effect. This may also occur in a small carpeted closet.
• BHT yellowing is rather rare these days because the padding manufacturers have moved away from BHT preservative
• The carpets involved are almost invariably light colors because it is more visible on light colors.
• BHT also reacts with atmospheric contaminants such as those created by the burning of fossil fuels to form yellow by-products.
• Carpet may also turn yellow if it is cleaned with a detergent with a pH over 10.

How to Prevent BHT Yellowing of Carpet?

• While newer carpet installations should not exhibit this problem, older carpet might.
• Move the rugs often so the BHT can escape.
• Move furniture at times so the carpet can “breathe” and the BHT can escape.
• If the problem is in a closet, leave the door open as often as possible.
• You want to expose as much carpet as possible when having your carpets cleaned to allow the carpet to breathe.