I'm halfway through replacing a 16mm sealed double glazed unit in a fixed window timber frame in an upstairs bedroom due to a cracked pane. Following removal of the unit I found there was rot at the corners so I removed all the dead wood and spliced in new hardwood and sealed with an expanding adhesive. The frames look good now after sanding and filling. The new sealed unit fits well with 3mm either side width ways and about 7mm on top. My plan was to use double sided butyl tape laid onto the timber frame then fit the glass onto this, then apply the butyl tape onto the beading and tap this into the frame. Firstly the tape I tried (Flexistrip) doesn't want to stick to the timber at all and just falls off which has got me scratching my head. I've tried pre-heating the timber before applying which helps or should I be applying this directly to the glass?? Secondly I was going to use plastic packers to lift the frame up about 5mm- do I just cut these to fit and leave them in? Thanks in advance for any help.