How to Stiffen a Sagging Canvas

Written by brenda priddy
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How to Stiffen a Sagging Canvas
Tightening a sagging canvas will restore it to usefulness once more. (Jupiterimages/Comstock/Getty Images)

If a canvas was improperly stretched, or has loosened over time or with changes in the weather, it can be stiffened to restore it to a tight, smooth look. Stiffening a canvas can be done in two ways: with hot water or by using small, thin pieces of wood known as "corner keys." The keys stretch a canvas by tightening the corners of the stretchers. Only use the wet stretching method on canvases that have not been painted.

Skill level:
Moderately Easy

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Things you need

  • Tea kettle
  • Water
  • Spray bottle
  • Corner keys
  • Rubber mallet
  • T-square

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    Water Method

  1. 1

    Boil water on the stove. Fill a spray bottle with the hot water.

  2. 2

    Spray the back of a blank canvas with water. Soak the canvas, but do not apply so much water that the canvas drips.

  3. 3

    Dry the back of the canvas with a hair dryer. This will cause the canvas to shrink slightly, tightening and stiffening any loose areas. Do not use this technique on canvases that are painted.

    Corner Key Method

  1. 1

    Locate the slots next to the seams between the stretcher pieces at the corners.

  2. 2

    Insert a corner key in each slot.

  3. 3

    Gently tap the wood keys into the slots with the rubber mallet. Do not drive the keys in too far, or they will cause the corner joint to pull apart. Drive the keys in equally, at all four corners, so that the stretcher and canvas stay in square. Use the T-square to ensure that the corners are square.

Tips and warnings

  • If the canvas is old and fragile, or valuable, do not attempt to tighten it yourself. Bring it to a professional restorer.

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