+1 for clean bare glass. No cleanup and easy removal + sticking is the way to go. You just need to be fairly good at bed leveling and clean glass cleaned with alcohol occasionally like stehpan suggested will do wonders.
Even works for PET, PETG, some copoly. ABS, Nylon and the weird stuff usually requires more work though...
Going commando-style! 
(Sticks just fine on the naked glass at 60°C)
In the beginning it really was a problem for me indeed: I often have difficult prints: long, 100% filled, with chamfers or roundings at the bottom, 5 to 15mm high. These excert a lot of warping force, even when using PLA.
Printing on bare glass sometimes worked in cold dry weather, when it was freezing outside. But it never worked in rainy weather: then the filament would curl up immediately. I disliked the glue-stick methode: too messy, and bonding was still poor. And I could not use blue tape, since the underside of my models had to be totally flat. So I had to find something else...
It took me some time and some testing to discover the "salt method": now I just wipe the glass plate with very salt water before a print. When dry, this leaves a very thin, even mist of salt stuck to the plate. Since then I have no more problems: models stick very well when the glass is hot (60°C), and they pop off by themself when at room temp (25°C). I only print with PLA, so I don't know for other materials.
Also, I don't know why it works, but it does. Could it be surface tension? Soap decreases surface tension and decreases bonding. So I thought salt might help since it works in the opposite way of soap: it increases surface tension. Other things that might play a role could be surface roughness, or electrostatical charge?
since installing the extrusion kit on my U2, i've found that I have to add a nice layer of glue to my bed for pla to stick.
I am trying multiple brands that I've seen pass by on here so no idea if it's the fault of that or my printer but it's certainly...weird.
In the beginning it really was a problem for me indeed: I often have difficult prints: long, 100% filled, with chamfers or roundings at the bottom, 5 to 15mm high. These excert a lot of warping force, even when using PLA.
Printing on bare glass sometimes worked in cold dry weather, when it was freezing outside. But it never worked in rainy weather: then the filament would curl up immediately. I disliked the glue-stick methode: too messy, and bonding was still poor. And I could not use blue tape, since the underside of my models had to be totally flat. So I had to find something else...
It took me some time and some testing to discover the "salt method": now I just wipe the glass plate with very salt water before a print. When dry, this leaves a very thin, even mist of salt stuck to the plate. Since then I have no more problems: models stick very well when the glass is hot (60°C), and they pop off by themself when at room temp (25°C). I only print with PLA, so I don't know for other materials.
Also, I don't know why it works, but it does. Could it be surface tension? Soap decreases surface tension and decreases bonding. So I thought salt might help since it works in the opposite way of soap: it increases surface tension. Other things that might play a role could be surface roughness, or electrostatical charge?
Havent tried Salt.
I got tired of the glue method. Too messy and many times didnt really work or change anything. Florida here so it's very humid.
printer is in my room so I tend to use the ceiling fan. My first prints curled a ton because of it. After I installed the door and cover all I use is tape. Cleaning takes maybe 2 mins? Just peel off and replace. 300 hours later I havent had a print fail.
Sometimes I cant get my prints off the bed now XD
Going to 3D and design a damn wall system that lets me put my glass bed against the wall and pull my prints off!
I like glue. I dilute elmers wood glue with 10 parts water and spread it with a paint brush. This dries to an invisible layer and lasts for 20 to 50 prints. When I'm printing a large print that makes me nervous about curling corners I will wet the paint brush in the sink and then spread the water around on the glue spreading the glue around again (it becomes visible again when you get it wet). There's nothing messy when the layer of glue is about 1/10 the thickness of a sheet of paper. Maybe around .01mm thick.
Have you tried re-levelling your bed? Just installing the upgrade itself should not change anything to the amount of adhesion you can achieve. It could be that your new printhead is of a different size then your previous one due to the Olsson Block. Are you still printing at 60ºC?since installing the extrusion kit on my U2, i've found that I have to add a nice layer of glue to my bed for pla to stick.
I am trying multiple brands that I've seen pass by on here so no idea if it's the fault of that or my printer but it's certainly...weird.
If you upload a picture showing your first layer it could help us see if it is bed levelling, or maybe something else..
Good luck!
I like glue. I dilute elmers wood glue with 10 parts water and spread it with a paint brush. This dries to an invisible layer and lasts for 20 to 50 prints. When I'm printing a large print that makes me nervous about curling corners I will wet the paint brush in the sink and then spread the water around on the glue spreading the glue around again (it becomes visible again when you get it wet). There's nothing messy when the layer of glue is about 1/10 the thickness of a sheet of paper. Maybe around .01mm thick.
I don't need it for PLA, but I am going to keep this method in mind for when I would print other materials (I doubt if my salt method would work then), it seems interesting.
I haven't seen Elmer's wood glue here in Europe though (but I haven't searched either, so just from memory). Is it that kind of general liquid white honey-like glue that is also sold as general kid-safe wood/paper/cardboard glue, and is water-soluble?
Do you remove the glass plate to apply it, or just apply it while in the printer? And how well do parts come off after cooling down, do they pop-off from themselves, or do you need to pry them off?
The one for children and the one for wood both have PVA as the primary ingredient. This is also the key ingredient in hair spray and glue stick. Any of these work but my favorite is "wood glue". For wood glue mixed with 10 parts water I use a paint brush and paint it right on the glass inside the printer. Heat the bed and it dries quickly:
2
Oh - and parts just pop off once the bed cools.
since installing the extrusion kit on my U2, i've found that I have to add a nice layer of glue to my bed for pla to stick.
I am trying multiple brands that I've seen pass by on here so no idea if it's the fault of that or my printer but it's certainly...weird.
Have you tried re-levelling your bed? Just installing the upgrade itself should not change anything to the amount of adhesion you can achieve. It could be that your new printhead is of a different size then your previous one due to the Olsson Block. Are you still printing at 60ºC?
If you upload a picture showing your first layer it could help us see if it is bed levelling, or maybe something else..
Good luck!
I have the bed leveled and the bed heats to 60C.
(i still had this picture of the first layer, i was curious about the little points on the brim but i forgot about it)
There's "level" and then there's "level".
The latest leveling procedure with the card makes it so that when the z=0.3mm the nozzle is 0.3mm off the glass and that is where it prints the bottom level (by default in Cura anyway) and that is how much filament is extruded (enough to make a bottom layer .3mm thick).
This works great when you need dimensionally PERFECT parts - where the absolute bottom layer can't have a skirt - not even .1mm of skirt (not visible without a microscope or micrometer).
However this results in parts that don't stick well. So instead I level things a little lower (a lot lower). This way the bottom layer is extruding pancake-like brim or skirt. To achieve this - anytime after doing the leveling procedure (I rarely run it anymore) just adjust the 3 screws counter clockwise about a half turn. The next time you print something make sure the brim or skirt is squished flatter than nominal. It will stick much better.
Edited by GuestThe one for children and the one for wood both have PVA as the primary ingredient. This is also the key ingredient in hair spray and glue stick. Any of these work but my favorite is "wood glue". For wood glue mixed with 10 parts water I use a paint brush and paint it right on the glass inside the printer. Heat the bed and it dries quickly:
Thanks. I saved this as PDF for the future (=easier to find back than searching through hundreds of posts). We can never know too much usefull methods. 
I've had good experience with 3DLAC in an aeresol can. Similar to using hair spray, but it's water soluable and easy to clean the glass.
I print a lot of PET in my U2ext+, and some tall objects just need good bed adhesion
With PLA, no, it's generally not a problem. Once you start experimenting with other materials you might find it's a different story though.
As for glue being messy. If it's messy, you're doing it wrong I think the biggest mistake people do when using glue is that they use way too much of it. The way I do it is to put the glue on with _very_ light pressure, left to right, once. I don't go over the same spot multiple times. Then I use a piece of wet paper and spread the glue around. Once the water dries (which it does while heating the bed for a print) you're left with a very thin layer of glue that isn't messy at all.
For glue I've used and use the included Pritt-stick, wood glue (the classic orange Casco bottle), and when I need extra stickage I go for Tesa Easy Stick.
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StephanK 30
With PLA, I don't even bother with Painters Tape. Sticks just fine on the naked glass at 60°C. No glue, no brim, no hairspray, no nothing. That's why I love PLA ;-)
(I do wipe the glass with a bit of isoprop alcohol on a paper towel before every other print, cause there's always fingerprints and lots of dust.)
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