I have a big jar of Slime rubber cement and slather that on liberally after a light abrading. I put on the patch and then lightly clamp in my bench vise until I remember to take it out which is about 1 day or a week. Very low failure rate, also use Rema patches. I take the plastic bit off but have thought about leaving it on quite a bit but I think the Germans would disapprove.
Germans make Rema patches right? That would be a weird post if they didn’t, in which case I apologize.
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N = '96 Colnago C40, '04 Wilier Alpe D'Huez, '10 Colnago EPS, '85 Merckx Pro, '89 Merckx Century, '86 Tommasini Professional, '04 Teschner Aero FX Pro, '05 Alan Carbon Cross, '86 De Rosa Professional, '95 Gios Compact Pro, '95 Carrera Zeus, ‘81 Masi Gran Criterium, ‘81 Merckx Pro, ‘89 Cinelli Supercorsa, ‘83 Bianchi Specialissima, ‘VO Randonneur, Ritchey Breakaway Steel, Rivendell Rambouillet, Heron Randonneur, ‘92 Ciöcc Columbus EL