Skin material? [Canvas, Muslin, Calico?]

You may have a problem with canvas, depending upon it?s weight!

While unbleached calico is preferable for easier working!

Also what widths of flats are you planning to double skin & the loom width of the material?

How are you planning to attach the skin, with glue, tacks/staples &/or both?

Assuming the flats are constructed in3"x1" pine & have diagonal & toggle brace rails!

Also ensure they do not have corner gusset or keystone plates, holding the but or halving joints of the pine frame, on the back face side, as these will become proud on the surface, when covered by the skin. Fix 1" angle flat furniture brackets, [fairly cheap from any hardware shops] on the inside edge of the frame rails, replacing the keystone & corner gusset plates.

Get some PVA [wood] glue & mix it with water until it is a milky consistency. Then paint the face & side of the top. Bottom & left & right stile rails. Not the toggle or diagonal ones!

Lay the muslin on to the frame, with about a 2" over hang. Secure it in place, on the side of the pine at the either the top or bottom rail, only holding it in place with just enough staples or tacks. Pull the wrinkles out loosely, do not over stretching the muslin. Put the odd staple in the edge of the rails, only to hold the cloth until it dry?s to the frame!

Ensure that the toggle & other bracing rails have not been glued to the muslin accidentally. Trim off the excess muslin about ?" from the back edge of the rails of the frame, leaving a ?" of the pine bare!

Turn the flat over & do the same to the other side.

Mix up some wallpaper size [glue] & paint the muslin on one side. Allow it to dry & shrink naturally, even if the muslin starts off slack, it will do this evenly & become as tight as a drum! Do the same to the other side!

You will find the skin overlap, on the outside edges, will be smooth & secure!

As your looking to hinge & book them. Cut up some 3/4" strips of old carpet to the underside of the bottom rails, with a 2 part epoxy glue. Stick the back of the carpet to the flat, leaving the pile side to contact the stage. This will make it much easier & smoother, when moving the flats, while being book hinged.

If you use 2" square hinge?s, known as Flap or But hinges [these usually have 3 screw holes on each flap half of the hinge], if you can get the type with removable pins, even better. If not get someone to grind the end of the pin & remove them! Purchase some steal mild steal rod, of the same diameter, cut them into about 5" lengths, then bend 2" on one end of the rod, into a circle, grind off the edge of the other end straight end of the rod. This will make it easier to remove & replace the pin, in the 2 halves of the hinge.

Normally I would make up a template or jig, to ensure each hinge is in the same position on the flats, so each flat will mix & match with each other!

I hope this helps Aimee!

Your right!

The muslin is virtually preshrunk, because of the retardant process!

I?d suggest you size the skin on the face & rear &/or paint the flats in a base colour emulsion!

It make tighten up more than it has when retardant was added?

This is one of the reasons we use unbleached calico, as it shrinks very well & evenly!

The only other thing is re tighten the skin, but it can still look a bag of spuds, unless you can make up stretchers or be able to apply even pressure grip on the material!

It may be easier to replace the muslin for the untreated type!