I probably can't claim to have dealt with as many Duo-Art pianos here
in the UK as Mike Boyd, but over the last 40 years I have encountered
quite a few.

In many pianos, particularly uprights, the accordion pneumatics
were undoubtedly made originally in rubbercloth, and some were still
serviceable after more than 50 years.  I believe this was because the
rubbercloth was of excellent quality and orientated correctly so it did
not stretch, but more importantly the corners had suffered no cracking
because the cloth had not been pulled too tight round the corners of
the boards and the folds were not crisp with excess glue.

Most of the original tan and red leather-covered accordions I have
encountered had long since rotted away.  The few remaining were without
exception very porous and stretched, the rubbercloth-covered 5-board
accordions being the UK factory specified 3-1/2 inches tall overall,
but the leather-covered ones often significantly taller.

No accordions I have re-covered in tan pouch leather have ever
performed as well as those in rubbercloth.  As the leather stretches
the zero level must be raised to stop notes missing; the increments
go inconsistently out of kilter and, unless they are re-adjusted, the
piano plays louder and louder; and they soon become porous unless
regularly treated with Hydrophane or proofed with rubber solution,
which can make them stiffer and slower.

Knowing a bit about acoustics, and after much listening, I do not
believe that leather-covered accordions are any quieter than thin
rubbercloth ones -- rather the opposite -- so I invariably re-cover
accordions in best quality striker-pneumatic rubbercloth.

I have in the past re-covered accordions perfectly well using hot glue,
but PVA (not PVC-E/Elmers' White Glue!) gives far superior results.
PVA allows just sufficient time before it grabs for the rubbercloth (or
leather) to relax without leaks at the corners: this gives very even
results without any skew in the accordions.

Any slight excess PVA will not make the cloth stiff; it never sets into
sharp fillets which eventually cut the cloth; the final overlap in the
cloth remains flexible yet airtight; and when the accordions need to be
re-covered again the cloth can be easily peeled off and the PVA wetted
and removed easily without damage.  I re-covered the accordions of my
Steinway O in rubbercloth using PVA about 25 years ago and they are
still in perfect condition.

Personally I never use spacer blocks but mark up the cloth with the
correct positions for the boards and find I get better results.

Limiting straps tacked to _every_ board may overcome stretching
problems in leather-covered accordions, though they are hardly original
and surely a waste of effort when full rubbercloth works so well.  But
attaching limiting straps between only the accordions' top and bottom
boards was and is a huge mistake absolutely contrary to the logic of
their operation: when the leather stretches the intermediate boards
invariably wobble about and the lost motion prevents the accordions
releasing and contracting by their full amounts, so the dynamic
permutations do not build up correctly and the piano does not
reproduce.

Paddy Handscombe
Wivenhoe, Essex, UK