Impression siding defects

Yesterday’s inspection the house was built in 2010. The impression siding has rows of white dots. Checking with a local siding specialist he had not seen this defect before. It appears to be a manufacturing defect. I have 30 years experience in injection molding of plastics. Not of siding. The marks are consistent with marks that are from knockout pins that are used to push the molded part out of the mold. Can one of you confirm, or explain the cause of the marks?


Lap siding or shakes?
Looks like shakes hung on battens.

Round White circular rings appear to be from conductive thermal transfer, affecting the paint.
Could be the wrong fasteners.
Just a hypotheses.

Get the type of and manufacture of the siding.

Refer to a siding contractor for evaluation.

1 Like

It is impression siding installed over plywood. My siding professional has not seen this before. His thought is that it is most likely a manufacturing defect.

1 Like

Defect like that would have never have left the pant.
Good luck.

Robert young,
The defect that Kurt described (failed to remove knockout pins) might not show up visibly for some time because there is no pressure on those pins until the siding is installed on the wall. Over time, the localized pressure leads to strain at those locations which discolors the material.
You would not see these white dots in the manufacturing plant.

If Kurt’s guess is right, the discoloration is the symptom, not the root cause.

It is possible that QC at the manufacturing plant made a mistake.

Further evaluation needed. Let us know what you find out, Kurt. This is interesting.


It sure shouldn’t.

I second Bert’s opinion

1 Like

Kurt, it definitely looks like a manufacturing defect. The mold may have been to cold when separated and pulled, leaving white stretchmarks. The pictures are of a similar or even same product that I have installed. You can see there is a stamp mark or injection point at the same level as the defects shown in your pics.

may also be nail heads sticking out behind the siding, probably from a foam or high R board. I have seen this happen before but it looks to consistent on each panel to be from random nailing.


It is consistent across the front of the house. Yup. Those are KO Pin marks that you are point out.

1 Like

I spent some time injecting molds with platinum cured silicone where we used air to release from the mold but agreed it definitely looks as if caused by the knock outs.

1 Like

If I could see the back side of the siding I would be able to tell with out a doubt.

Right, I figured the siding was almost identical so it would be a good reference. The sad thing is that they probably installed it that way :sleepy:

1 Like

Remove a piece and look behind it :slight_smile:


Probable cause, improper warehouse storage, too many pallets stacked on top of one another, they are single course 7 in. exposure,
images (25)


To remove cedar impressions vinyl siding, you have to start at the top and work down.


Thanks, Bert.
Never ran into plastic siding North of the 49th parallel.