When installing new vinyl windows as a replacement I want to find out what experienced DIYers or contractors think about the protruding plastic that exists on the plastic welded mitered corners.

Here is a typical picture:

enter image description here

What is a better choice when installing wood trim boards around the insides of the rough opening so that such trim boards can fit right up to the rest of the vinyl window frame?

  1. Trim off the protruding ridge with a sharp chisel
  2. Cut some relief notches in the edge of the trim boards
  3. Leave as is and use silicone caulk to fill the resulting gap between the window and the trim board
  • I rolled it back because the question is asked 100% correctly. My vinyl windows are made from individual pieces of extruded vinyl material that is then cut with ends at 45 degree angles. The pieces are then butted together in a vinyl welding process which fuses the corners together. As a result of that the melting of the vinyl causes a raised ridge along the miter seam. My question was all about those seams and how best to safely remove the ridges at the seams. Your misguided rework changed the whole understanding of what I was specifically asking about. Please leave it be.
    – Michael Karas
    Mar 15, 2023 at 2:38

2 Answers 2


We trim it back with a razor knife. You can (should) leave a little bit protruding (maybe 1/8" max) so you don't effect the integrity of the window. Seems like this is always the case with vinyl windows these days.

All your trims should be caulked to the window frame so having a little gap is good. I would use a siliconized latex caulk rather than 100% silicone. Silicone does not take paint and is difficult to use (can easily make a mess).

  • I do use the "siliconized latex caulk" as recommended by the window manufacturer. It is very paintable. It can still create a mess using it though. :-(
    – Michael Karas
    Oct 10, 2022 at 23:15
  • Why are they there in first place if you cut it
    – Traveler
    Oct 11, 2022 at 2:05

Vinyl windows always have extra material anymore. Usually we just leave them as is. If they are exceptionally long, (extending 1/2" or more past the miter), we will have our window guy come back and trim them with his knife.

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