black spots on floor tiles - microvision labs,...
TRANSCRIPT
Black Spots on Floor Tiles
Problem:
A client responsible for maintaining the facilities in a public school district called with concerns of a possible mold
problem. Areas with high foot traffic, especially those where students tracked water in, were showing dark black
spots in the floor tiles. Aggressive cleaning and buffing of the floor would remove the problem for a while, but after
several few weeks, the problem resurfaced. The facilities management staff was convinced it was mold related, but
sending samples, swabs, and air grabs to a mold lab for culturing showed no sign of fungal structures on the tiles.
Approach:
An affected floor tile was submitted to determine if the previous mold
testing had missed a source on the tile backing or mastic. Additionally, a
new tile from the same manufacturing lot was submitted for comparison.
The process of preparing and examining the sample and reference tile
was documented. Areas with darkened surface features were imaged and
then cut out and examined.
Analysis and Results:
While the dark spots looked very discrete when examined by eye, under
top light polarized microscopy they appeared more diffuse at the outer
edges. The darkest areas surrounded what appeared to be particles
embedded in the surface.
Scanning electron
microscopy with
energy dispersive x-
ray spectroscopy (SEM-EDS) was used to identify the
particles. The SEM showed an elevated concentration of iron
and iron oxide in the impacted areas. The backscatter electron
(BSE) image which correlates brightness in the image with
atomic density, highlighted the iron particles that were
embedded in the tile and the EDS spectrum confirms the
PLM Image
chemical composition of these higher density particles.
Also, the color EDS map highlights the iron particles in the
mineral filled PVC floor. These iron particles were
concentrated in areas were the tile showed signs of impact
which indicated some metallic object impacted the tile
leaving behind small particles and over time the materials
oxidized which created darker spots in the tile.
EDS Spectrum
BSE Image EDS Map
Conclusion:
The client was able to determine that there was no sign of any mold or fungal growth in the tile or mastic. Knowing
that the iron was largely responsible for the dark spots, the client was able to apply a thicker wax coating in order to
avoid particles from being embedded in the tile itself.