Thread: Yellow stains on white vinyl siding

I am looking for some insight on what these yellow stains may be. I don't think it is related to air movement through the siding (weep holes or joints) because the stains are eveywhere. I have only seen this once before. The house is near a coal fired electric plant. Possibly acid rain?

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What type of insulation is in the walls?

Directly behind the siding is a foil faced celotex insulating/sheathing. product. The exact product was not determined. House was built in 1987.

Hi Greg,

I'm not really sure what it is, but it looks like something spilled out from behind. it resembles something like foam that came out and was peeled off. But I think if it was foam, it would have discolored from ultra violet exposure.

Sorry I could not have been more help.

Originally Posted by Greg Jenkins

I have only seen this once before.

And what was the cause?

On this house, describe the substance:

firm, sticky, tacky, hard, gooey, rigid, smelly, etc.

You were there, what was your impression of the origin?

Celotex sheathing fom 1987 could be polyiso board. It is a yellow/cream color if that is the sheathing. Acid rain reacting with the sheathing?

Sounds like Scott and Steven have it pegged, unless it was a tall dog.

This may work to clean:

Combine 1/3 cup of TSP with a gallon of water and a quart of bleach. Mix thoroughly. TSP is caustic, follow directions on container.

Protect plants and shrubs around the foundation of your house by covering them with a plastic sheet or tarp.

Scrub the stained area with a brush saturated with the bleach mixture. A long-handled car-washing brush works well.

Rinse the siding with a water hose to remove all remaining bleach.

I am still baffled. I think it is something environmentally related or an inferior siding. When touched, the stained areas did not have any abnormal texture and they would not rub off.

Did you notice how the stains stack up vertically? Not Random spots but a cascade from top to bottom. And each vertical location has similar stain throughout length but different from next vertical stack. And are they spaced horizontally in in units of 16 inches?
Could this mean varying amounts of moisture getting past past poorly installed insulation (e.g.not tight to studs)?

Well that is my biggest clue- the similarity of stains in the vertical with the difference of stains in the horizontal. Maybe you can work with it.

The staining could be caused by corrosion of the fasteners attaching the siding or the insulation underneath.

Originally Posted by Greg Jenkins

I am looking for some insight on what these yellow stains may be. I don't think it is related to air movement through the siding (weep holes or joints) because the stains are everywhere. I have only seen this once before. The house is near a coal fired electric plant. Possibly acid rain?

From what I was able to find on line, it yellow was related to deck stain, insect repellent and asphalt. However it does appear that it's a little darker in tone than what color they would leave.

First, to confirm or rule out acid rain from the near by power plant, do other homes in the area with vinyl siding show the same symptoms? If they do it's probably environment related. If not, it's isolated to the construction on this particular house. Personally, I don't think its acid rail, but one commenter may be close when he thought that the acidic mix from the local power plant may be reacting with the foam underlayment in some unforseen manner.

Whatever is causing it is definitely coming from behind the siding (otherwise the stain pattern would cover more of the surface.) It would appear that that the majority of the stain is related to the weep holes in the siding's bottom channel, indicating that the stain-bearing liquid is accumulating in the channels.

Is it worse on one side of the home than another?

I have found that frost will accumulate on the back side of siding in cold climates. The east side of a home will see the sun first and frost melts sooner here than on say the west side, creating more liquid to run off (vs. other sides where it evaporates more than melts.) I found this while conducting a research project for Dept of Housing and Urban Dev. on homes with failed hardboard siding. It was always worst on the side facing east.)

I don't know if any of this would play a factor, but it's been my experience that environmental conditions seem to favor one side of a home or another.

As it deteriorates from the homes retail value, and it will probably continue to get worse, I feel it justified to pull a sample of the siding to investigate what, if any thing, is behind the siding that may cause this. If its been on the home for any length of time, it's probably going to require

It could be simply from a roof leak.
There is a lot of dirty fallout on the roof, which makes a kind of tea out of the rainwater. Water runs along the top of the wall sill and down the back of the siding to the weep holes.

'Unzip' a vinyl siding edge and look behind it, where is the staining coming from? I.e., does the staining extend in, behind and over the top of the covered piece below the unzipped piece; does the staining stop at the underside of the overlocking piece of vinyl siding; is the staining on the backside of the piece of vinyl siding which was unzipped?

What does the sheathing look like behind it? Covered in honey? (just a wild thought there)

That pattern shows some areas where something 'ran down the face of the siding' like sags in paint.

The stains were on all sides of the house. Sun exposure did not appear to be a factor. Again, the stains did not correspond with weep holes or seams but were everywhere. At this point, all I could do was write up what I saw and make my client aware of the condition. Thanks for all of the input.

Greg
did you unzip to look behind the siding?

was there a WRB in place and what brand if there was?

what was its condition?