Dimensional changes of rugs during the cleaning process can occur when natural fibres are used to make the rug, when borders are attached at 90° angles to the body of the rug and when the weaving process creates a propensity for an irregular shape.
Natural fibres used in a rug’s backing or foundation absorbs moisture during wet cleaning or from humidity in the home. The fibres swell with water and as the rug dries it can shrink in overall length and or width as much as 5%. Overall dimensional shrinkage is most pronounced after the rug’s first cleaning.
Borders attached at 90° angles to the body of the rug have a propensity for differential shrinkage during or after wet cleaning. When the warps and wefts shrink in different directions, the rug buckles along the seams. Humidity in the home can also cause differential shrinkage.
Not only can hand-woven rugs shrink in overall width and length, they can also shrink in isolated areas. If a section of warps or wefts is not pre-shrunk before the weaving process, then it will shrink in one area across the width or length and create an hourglass effect along the sides or ends of the rug.
Ripples down the side of a hand-woven or hand-knotted rug are usually an indication of a weaving defect. During the weaving process, warps and wefts should be under even tension on the loom. If there is uneven tension during the weaving process, the rug will have ripples that are difficult to permanently correct. Blocking may help but after washing or exposure to humidity, the rug will most likely return to its original shape.