We had to re-glaze A LOT of windows and Chris got pretty damn good at it by the end. Here's his helpful tutorial if you've got the same task to do. Without further ado...
hehehehehehe. Okay NOW without further ado....
tools/materials you may need:
stiff putty knife or glazing tool
dap 33 glazing putty (for wood windows)
dap 1012 (for metal framed windows)
replacement glass (in case any is broken or break when chipping out the crusty stuff)
finishing sander (aka 1/4 sheet sander)
80 grit sandpaper
scraping tool with straight razor
1. if you're redoing the whole window then you'll want to give the windows a good scraping and sanding before you apply any putty. (if you're just replacing a broken pane skip to step 2). i prefer to use a painter's tool to get the big flakes and then a finishing sander for this step. finishing sanders get into the corners of the windows better than orbital sanders and are more powerful than those little mouse style detail sanders or the multi-tool (fein, dremel, bosch) oscillating tools with sandpaper attached. at the same time, finishing sanders don't bounce all over the place so the glass won't end up looking awful. sand all the rails, stiles, and especially muntins that need to be sanded in order to be paint-ready. you're doing this now so that none of the dust or flakes ends up in the glazing later.
2. after the wood is all sanded and paint-ready you can start chipping out the old glazing. most of it will be fairly easy to take out. if it's not cracking or difficult to get out, then you can probably leave it. you want to inspect it to ensure it still has a good seal with the glass and muntin, if it does then you may leave it. however, an aesthetic consideration is having to blend the new glazing into the old on a single side of the window pane. if you can blend it then no worries, otherwise you might want to just remove the glazing from the whole side for a better look.
there are probably many ways of getting the old glazing out, but the way that works best for me is using an old chisel. i work from the muntin side of the window (not on the glass side) making sure i don't gouge the wood muntin while chipping away at the old glazing. once you get it started, the older stuff is really easy to get off. patience is key here. some will suggest heating the putty with a heat gun, but that's just a waste of time and energy. elbow grease and patience work best. i like to use my bench grinder to keep the chisel fairly sharp at all times, as it makes the work go faster. a word of caution, though, that also makes it easier to gouge the muntin, and you want to avoid that.
3. once all the glazing is out you can replace the glass if necessary. when replacing the glass there's no real secret. just carefully take out the old one along with the old glazier's points.
put in the new pane of glass and firmly push it against the trim which should be intact on the inside of the window. use a stiff putty knife or painter's tool to attach new glazier's points every 6". make sure they're tight against the glass and completely seated into the muntin.
4. brush or blow the window clean of all debris and dust. pre-prime all the wood that the glazing will be touching. no need to be overly cautious here. the excess on the glass can be scraped and the excess on the wood should just be thinned with your brush so it blends in with the final top coat.
5. after the primer has dried, scrape the glass panes with a straight razor scraper so that no primer will show after the glazing compound has been applied.
6. take a chunk of glazing compound in your hands and knead and roll it around to warm it up. roll it into a snake and pinch it into the corner between the glass and muntin. don't be shy, it's better to have too much than too little.
i like to do one pane at a time. so repeat this step until all four sides of the pane are covered. take your glazing tool or putty knife and work the putty into the corner, running the tool perpendicular to the muntin. the goal here is to get the compound into all the nooks including the keyway which is hopefully still intact on the muntin.
7. the draw. the next couple steps are critical and the ones where the experts really earn their money. starting in one corner, draw your glazing tool at approximately a 45 degree angle relative to the muntin and firmly apply pressure while working towards the opposite corner.
with a steady hand and some (lots) of practice you'll get good at making it look good and getting it done quickly. repeat this step on the other 3 sides of the glass. you want to make sure that your glazing doesn't extend too far past the trim on the interior side of the glass, so make sure you start your draw at the same-ish angle that was originally used on your windows.
(on the top of this pane the glazing extends too far, on the left it looks perfect)
with practice you'll see that a flatter angle relative to the muntin will make the glazing too skinny and a flatter angle relative to the glass will make the glazing too fat.
8. finishing. after you have drawn the line for all sides of the glass you can remove the excess compound and cleanup the glazing.
i like to use as big a drywall knife as the window will allow to make sure that the edge is nice and straight. you can't make corrections more than 1/16" or so, so this isn't a tool to fix a really wavy line, just to get a way of getting a nice line to look great.
(this is an example of a good angle and a smooth draw)
after you're happy with the straightness of the lines you can work on the corners.
the corners are the tough spot. i've found that doing a short, light draw from the corner towards the middle of each side smooths the corner nicely.
the important thing here is that it needs to shed water efficiently. some people prefer a rounded corner to a sharp ("mitered") corner. experiment with each and see which is easier and more preferable for you.
the last finishing step is to follow up your draw with a finger to smooth and seal it all to the glass and muntin. lightly use your index finger to smooth the glazing compound. there shouldn't be any bumps or fingerprints and it should be tightly sealed against the glass.
this is your last chance to fine tune. use your drywall or putty knife to make sure the line is straight and true
9. after a week or more (depending upon the weather) the compound should be ready for primer and paint. dap recommends an oil-based primer, though i've had no problem using latex in the past. prime and paint. whatever you use, make sure you extend the paint onto the glass just a bit to seal up that transition.
So there you have it, a tip from the pro. I mean Christopher. Same thing.