Canvas Flats

For Princess Ida (2003/4), we built canvas flats. We did this to allow us to get them into the Dancehouse (up 3 flights of stairs). The biggest flat we built was 6'x10', double sided. This would have been way too heavy if it was covered with hardboard.

For reasons that nobody can quite remember, we decided to build the flats with the timber on its edge, as shown in Fig.1. There were problems with this:
Frames were built from rough sawn 3x1.

Joints - 3.5" No 8 PZ2 woodscrews. PVA was used in joints also, which made them extremely strong and doesn't, as has been suggested, make the flats too difficult to take apart.

The flats were canvassed with Scenic Cotton Canvas, Natural NDFR (Non-Durably Fire Retardant) 72? wide roll (approx £4/metre).

The canvas was stretched very tight over the frame dry, and tacked in place with staples. The material was then sized with a 3:1 warm water-PVA mix. This has the effect of shrinking the fabric, making it drum tight. The edges were sealed with neat PVA (we should have taken out shares in Bostik!) to stop them from fraying.

The frames had a tendency to warp, due to the tension in the canvas. We put stretcher bars in at regular intervals, but some of the larger frames were still considerably out of alignment.

The flats were painted with a combination of regular emulsion, mixed to form a stone grey base, and the detail was done with Rosco acrylic paint. This stuff is much more highly saturated than regular emulsion. It needs to be watered down as per the instructions, as it is very concentrated (and £20/litre!)

Once dry, the flats were treated with flamebar. It is important that this is done after painting, as the flamebar does funny things to the canvas surface. Also, the canvas is non-durably flame-retardant ? i.e. it's not flameproof once it gets wet. As I am well aware of the flammability of canvas (no further comment m'lud), IT IS VITAL THAT THE FLATS ARE TREATED.

The flats were fixed together with pin hinges as usual. They weren't totally true, having been warped by the canvas, so putting pins in was a real struggle at times. However, the flats looked ok, and were very strong, and pretty light.

Painting canvas flats

A very thin coat of black emulsion followed by a thin coat of white should prevent the canvas being translucent (though this isn't a major problem on double sided flats.

Submitted by Ben Seaby.