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Technical Bulletin
What Causes Yellowing of Tile Under Mats?
From time to time we are asked about mats causing the floors
beneath them to discolor. This is common for both carpet and hard surface floors
such as vinyl or tile. The discoloration is usually a brown or yellow color. The
most likely cause for this is moisture. There are several potential ways that
moisture can cause discoloration.
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Lack of exposure to sunlight and/or restricted air flow. It is
common to see floors change color when they are covered by anything, whether
it be a mat, or a counter, a file cabinet, etc.
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Placement of mats on freshly cleaned and still damp carpet.
This prevents carpet from drying, thereby causing discoloration.
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Moisture comes from the ground up through the floor until it
reaches the floor surface. This moisture normally evaporates and goes
unnoticed. Placement of a mat on the floor prevents the normal evaporation and
traps moisture, thus causing the discoloration. This seems to be most common
at building or home entrances where cold or warm air enters buildings when the
door is opened causing condensation (sweating).
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Moisture from the back of mats. If mats are not properly dried,
the damp mat can provide moisture to cause discoloration.
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Chemical reaction between the chemicals in the rubber backing
and the floors or floor finishes used on hard surface floors can cause
discoloration.
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In most instances where mats are placed and floor discoloration
results, the customer is faced with a difficult decision. Use no mat and the
floor doesn't discolor, however, the floor is damaged by tracked in soils,
moisture and dirt, and the entire area deteriorates. Or use a mat and protect
the floor with resulting discoloration in the area underneath the mat. Of the
two, most customers select the latter.
Corrective actions. Discoloration can usually be removed by stripping the
floor and rewaxing. In the case of carpet, professional carpet cleaning can
usually remove the staining.
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