First Layer & Air Printing PLA. Also ABS curling  

RE: First Layer & Air Printing PLA. Also ABS curling

PLA requires an ultra clean bed. Alcohol only works if you use ounces to thoroughly rinse.  Soap and Water is easier, faster, and allows a deep clean and rinse.  

For ABS, people use all sorts of things: hair spray, gluestick (what Prusa recommends), and a product called ABS juice.

Warping ABS is why many build enclosures. The entire print needs to stay hot and the cooled evenly.

You probably didn't do a cold pull to remove the ABS before loading the PLA. Load some ABS, then do a couple of cold pulls to clear the nozzle.  Then load the PLA.   Or, you can try setting the nozzle to your ABS telp and extruding a 100 mm of PLA, the dropping the temp back to PLA temps.  Sometimes that will thin the ABS residue enough you can print at lower temps.

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Hot Water wash: often, as needed
Handle the bed only by the edges.
Wash the bed in hot water, use a fresh paper towel as a wash cloth, with a few drops of plain dish soap (Dawn, unscented, no anti-bacterial, etc.). Rinse well in hot water - if you have very soft water, rinse a bit longer.
Dry the bed with a fresh paper towel.
Handle the bed only by the edges.
Place bed on printer.

Alcohol rinse: every few prints
Once in a while, an alcohol rinse is helpful to remove PLA residue. It does not remove finger oils.
Pour a 5 cm puddle of 91%+ alcohol in the middle of the bed, with clean hands use a fresh paper towel to scrub the bed. Wipe up all the alcohol.

Streak test: when contamination is suspected
With a fresh piece of paper towel, and very clean fingers, dampen the towel with 91%+ alcohol, and wipe the bed side to side moving back to front, like you're painting it with alcohol. The alcohol should be thin enough on the towel it quickly evaporates. If you see any streaks, the bed is dirty and needs a wash.

Acetone wash: infrequent
Pour a 2 cm puddle of acetone on the bed, scrub it around with a fresh paper towel. It will evaporate fast as you clean. This step removes PEI oxides that form over time and with heat, and improves PLA adhesion to a like new state.

RE: First Layer & Air Printing PLA. Also ABS curling

Thanks for the detailed answer tim-m30! Looks like I need to improve my bed cleaning routines significantly. 

I'll give the bed a clean as suggested + cold pull and give the PLA print another go.

Cheers

RE: First Layer & Air Printing PLA. Also ABS curling

So I've tried:

1. Hot soap and water scrub with paper towel.
2. Isopropyl alcohol scrib with paper towel.
3. Ascetone scrub with paper towel.
4. Extrude 200mm of PLA to clear nozzle.

The nozzle appears to be functioning well however the bed isn't very sticky any more. 

To combat this I applied a mist of hairspray on the bed to increase adhesion.

After all these efforts this was the result from my latest attempt to print PLA: 

The corners lifted and after a few layers the entire print stopped sticking to the bed.

RE: First Layer & Air Printing PLA. Also ABS curling

The bed does not look at all clean in that photo but that may be the hairspray residue.

Hairspray on PEI is more commonly used to STOP material sticking too well to the bed by forming a layer between the plastic and the PEI sheet. If the bed is really clean, and z-level calibration accurate and still PLA will not adhere, a wipe with acetone (a little goes a long way) is recommended by Prusa to revitalise the bed. If you have no acetone available you can achieve the same result by gently rubbing with the green side of a ScotchBrite sponge or using 2000 (2 thousand) grit sandpaper and then cleaning again with IPA.

RE: First Layer & Air Printing PLA. Also ABS curling

Thanks @billcampbell. I tried cleaning the bed again:

1. Clean paper towel damp with hot water. Scrub.
2. New clean paper towel damp with isopropyl. Scrub.
3. New clean paper towel damp with ascetone. Scrub.

Following cleaning the bed looked like this

I then tried a print but the first layer eventually came unstuck again:

RE: First Layer & Air Printing PLA. Also ABS curling

OK, if the bed is clean, the only other adjustment using the standard PrusaSlicer profiles is the z level. Try following this thread - it's how I first achieved reliable adhesion.

life-adjust-z-my-way