The yellow stain in the sheet vinyl flooring was caused by a chemical adhesive remover that got into the cracks in the concrete and then worked its way through patching compound into the backing of the flooring. Photo courtesy Christopher Capobianco.

Resilient floors have been experiencing discoloration problems for many years. They became more visible/noticeable when the industry went to lighter-colored products. While most of the discoloration occurs in rotogravure (printed) products, inlaid, heterogeneous and homogeneous materials are also subject to this problem. Most of the discoloration comes from the bottom-up.

The following are some causes of bottom-up discoloration. Use this information to identify potential causes of these problems and find ways to avoid them.

Adhesives:While once a big problem, bottom-up discoloration has lessened considerably during the past few years. In an attempt to save money, installers and/or retailers will choose an adhesive not recommended for use under resilient materials. Caused by antioxidant or processing oil ingredient in the adhesive, this discoloration will be yellow and appear in various shapes and sizes.

Alkali discoloration:Associated with moisture migration, alkaline salts usually travel with water vapor and attack the printing and PVC components of resilient material. This alkali attack bleaches out the material and gives the floor a milky appearance.

Bacterial discoloration:Mold and mildew are associated with moisture migration, appear to be bluish-gray to black in color. Promoted by an accumulation of stagnant moisture, micro-organism growth produces a spot that will continue to expand. Bacterial discoloration can be confirmed by removing the wear surface; the backing will be damp and have a pungent, musty odor.

Construction adhesives:Some of these adhesives contain butylated-hydroxyl-toluene (BHT), an antioxidant which has been known to sublime (off-gas) up into the material and cause a yellow discoloration. This often surfaces as spots where the gas from the adhesive has migrated up around nail heads or in a straight line above the underlayment joints. Sometimes, it mirrors the pattern of the adhesive application straight over the floor joists and swirled beneath underlayments.

Fungal discoloration:Fungal activity requires three components: a fungi spore, a food source, which can be found in some gypsum-based products (i.e. taping compound, wall texture overspray and some gypsum patching compounds) and excessive moisture. This discoloration is often found over concrete and gypsum substrates too wet to install over. The discoloration is in the form of a pastel-pink, blue, green, blue, and yellow or tan-colored spot that grows larger over time.

Patching compounds and embossing levelers:Installation of resilient materials over un-dried patching compounds and embossing levelers can create either a bacterial or fungal discoloration often yellow or gray in color.

Residuals on the substrate surface:Many reagents cause discoloration and/or damage to resilient materials from beneath. Among the culprits are: adhesive residues – cutback (asphalt) and latex (SBR based); adhesive removers – oil and citrus based; concrete markers – spray paint, felt tip markers and wax marking crayons; concrete waterproofing sealers – oil based; equipment leaks – oil and grease; heating products – kerosene, diesel and heating oil; painting products – paint thinner, mineral spirits, oil-based stains, and paint spills; plumbing residues – PVC pipe primer, oil from threading machines and oil residues from pipe; and roofing tar and other asphalt products - driveway sealer.

Solvent attack:Installation of resilient materials over a recent solvent spill permits solvent to migrate up into the material where it distorts the material’s surface that diffuses light differently. This usually creates a dull spot.

Underlayment edge treatments:Some wood panels used for underlayment are treated with a preservative or sealer. Some of these edge treatments contribute to debonding, discoloration or both. Rarely are these products designated for underlayment usage. This type of discoloration is generally in a straight line directly over the underlayment joints.

Underlayment fasteners:Often underlayment fasteners will promote resilient discoloration that appears as yellow spots. This problem is the result of one or more of the following:

• BHT migration –Discoloration is caused by off-gassing of BHT found in construction adhesives

• Coated nails (sinkers) –Sinkers which are not a proper fastener for underlayments are a leading cause of floor discoloration. The anti-rust coating on the nails, usually gold or black in color, will off-gas up into the material and affect both felt- and vinyl-backed materials. Most sinkers can be identified by their diagonal checkered pattern on their heads.

• Coated staples –As with sinkers coating on some staple fasteners will also affect resilient products. In this case the discoloration is either pink or tan.

• Oil residue from pneumatic nailer or staplers –During use, over-oiled, worn out or poorly maintained air driven fastening equipment will often spit a small residue of oil onto the substrate. This residue migrates up into the material and creates a yellow spot in the material.

• Rusty fasteners –Excessive moisture in the substrate will allow fasteners to rust, creating a reddish-brown discoloration.

Foreign matter in wood underlayments:Occasionally, foreign wood chips get into the mix used to make oriented strand board (OSB) or waferboard underlayment. These chips can cause discoloration. Red cedar and redwood chips will leave a reddish color. Chips that contain creosote and pitch will leave a yellowish color, and chips from bark and pine cones will leave a brownish discoloration. It is extremely difficult to determine which chips will cause discoloration. Even worse, no one wants to accept responsibility when the problem occurs.

Wood filler (plastic patch):Plywood manufacturers that use synthetic wood filler must exactly mix the patching compound components to the specified portions or the filler may off-gas and migrate up into the resilient sheet material where it leaves a yellow discoloration that mirrors the shape of the synthetic patch. Over time the patch will shrink and create a show-through problem, as well.

While I have attempted to cover many causes of bottom-up discoloration, there are many yet to be identified. Hopefully, the information presented here will give you knowledge to identify potential causes and remove them. The installer and flooring contractor need to be aware of these concerns. The general contractors also need to be accountable for using the right products and protecting substrates from possible reagent exposures prior to the start of the installation.