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Quick Tips For Mitering Corners

What is mitering?

Mitering is defined as making a joint between two pieces of a material. In this tip-sheet, and in most cases with RV or boat seals, a miter is made by cutting the end of the seal at a 45 degree angle. When you join two of the similarly cut pieces of rubber together, it will form a 90 degree corner.

Is mitering the only way to go around corners?

There are three ways you can tackle corners:

  1. Formed
  2. Continuous
  3. Butted
Example of Mitering

Mitering is a “formed” method. Mitering is ideal when you are working with tight 90 degree corners. This method also gives you a clean and finished look.

Example of a Continuous Seal. Notice how it is puckered

Continuous means that you will round the corner with a seal without making any cuts to the rubber. To make it look seamless, you have to round the corner in a way that doesn’t kink pucker up the rubber, which can be a pain to accomplish. A continuous section of rubber that is kinked or puckered can allow for leaks and openings for pests to get in.

Example of Mantling

Butted, or ‘mantling’, is similar to being formed like mitering, because the seal is cut to length, but in the corners the ends are pressed against each other without being glued.  In a 90 degree corner, one seal end will set on top of the other seal end. This method makes a much less ‘finished’ look, and more importantly, with an open seam, can also allow for leaks.

How to miter your rubber seal

The following steps are for mitering the corners of a ramp gate - but they can also be used for compartments and doors, too.  The tools needed are:

  • The seal you’re going to install
  • A pencil
  • Super Bonder 495 (or similar instant glue)
  • A knife or sharp pair of scissors, and
  • A small 90 degree triangle template (see the image below for an example).  The template can be made of paper, but something stiffer like the edge of an envelope or business card will work better. 



NOTE: remember, the surface must be clean and dry to ensure the best adhesion of your seal.

With the pencil, make a 45-degree line in the corners of the surface that you are sealing, marking from the outside to the inside edge. If the seal will sit in a channel or in the middle of a ledge, make sure the line is longer than the seal is wide.

Lay the seal along the edge of the surface that it will be applied to, overlapping thecorner, and mark the outside and inside edge of the seal where it meets the line.

Using a triangle template, place the 90-degree tip of the triangle on the outside edge mark and line up the edge of the triangle with the inside edge mark.



Carefully mark a line across the seal on both sides of the triangle.

Using a knife or sharp scissors, trim the seal along the marked lines from the inside edge towards the outside. NOTE: don’t cut all the way through to the outside edge of the seal. You want to leave the outside edge holding the seal together. This makes the mitered corner look seamless and further ensures a leak-proof corner!

Carefully apply Super Bonder 495 to the cut edges and fold the seal together to form a 90-degree corner. TIP: Super Bonder 495 does not quickly dry when exposed to air so you have some ‘work’ time to align the edges correctly- but once the edges touch, the bond sets immediately.



**With compartment doors, after all four corners are finished, the two edges of the seal may be similarly bonded. Trim the seal to the correct length and glue together.

Ready to try your hand at mitering? Head over to our free resources page to download a copy of these mitering instructions which comes with a cutting template!

For all your RV or boat weatherstripping needs, Steele Rubber Products provides high quality products made from EPDM rubber.  You can find a complete list of all of our marine seals and RV seals on our website  Additionally, you can download a free parts catalog online or give us a call to request a mail catalog 800-230-6752.

*For more help check out our How To series on YouTube!

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