How to Tighten a Slack Painting on Stretched Canvas with Hot Water
Paintings on stretched canvas can become slack over time due to environmental factors such as significantly varying humidity levels and temperature differences. Depending on how slack the canvas is, it may be possible to quickly and effectively tighten the canvas using this method. However, it must be noted that if a valuable painting is in need of tightening it should always be taken it to a professional framer to be maintained.
This method is only effective in tightening slightly slack stretched canvases. Alternative methods such as using canvas keys or reframing may be considered instead if the painting is considerably loose.
Apply the Hot Water
Caution: Considerable care must be taken when using this technique as it involves the use of boiling water.
Lay the painting face down on a flat surface and using a large bathroom sponge apply the boiling water to the back of the canvas. The back of the canvas should only be made damp and not saturated. It is also important to ensure the stretched canvas material is made evenly damp.
The canvas can now be allowed to dry naturally and as it does the canvas material will gradually tighten. Some artist recommend using a hair dryer to speed up the drying process but if this technique is used it is important to apply heat evenly all over the back of the canvas to prevent the stretcher frame from buckling.
This simple and effective technique can improve the appearance of your older canvases as the difference between a tightly stretched painting and a slack painting is significant.