In Coyle's book on Armstrong, he makes some mention of this:
"...Postal's Belgians...did it the old-fashioned way, buying tires called sew ups, which had to be glued to the rim. But first they had to be aged in the sacred darkness of [head mechanic] DeVriese's basement--two years at least, which added to their suppleness and strength. Then they had to be sorted and selected to be attached to the rim of a wheel, a process that took four days and four coats of a gluelike varnish applied with a special brush, the last a double coat. Then, and only then, was the tire worthy of sitting beneath a Postal bike."