GUIDE: How to get water and airtight prints on the first try with just 2 perimeters and the default (0.4mm) nozzle

GUIDE: How to get water and airtight prints on the first try with just 2 perimeters and the default (0.4mm) nozzle  

Eminent Member

(Skip to the bold text for the good part)

I live in a fairly dry environment, the state of New Mexico in the US.  The part I live - in the month I write this, June, the average afternoon relative humidity has been just 18%.  

So indoors, we actually have central humidifiers.  They work in tandem with the air conditioning which sucks the humidity out of the air, so you can actually regulate the indoor humidity fairly well by simply having the AC drip the condensation into a small tank with a little plastic float sensor that measures the water level.  

The problem I'd been having was this float kept failing at the same weak point and breaking off, almost like clock work, once a year.  

So, of course, 3D printing to the rescue, right?  The trouble is that this float's function is totally dependent on that it is a large, hollow, blimp shape filled with air that is water tight.  Water can't get in.  

Anyone else who has played with making watertight prints probably knows this struggle well:  prints leak.  Typically, they leak a lot.  Sure, they'll hold water, but it'll drip out over a few minutes.  


I watched youtube videos, read guides, and all of them involved significant trial and error, required huge nozzles or slicer settings so strange that it severely limited what one could even print, or simply didn't work with any reliability.  The general consensus online seemed to be that you had to print using vase mode, and had to use extra wide perimeters.  The thing is, even that never really worked for me. 

Well, I figured out how to get water tight prints reliably with minimal changes to print settings! I've printed measuring cups with a spherical shaped bottom layer and walls only 2 perimeters thick, and not one has failed to be 100% water tight.  The water evaporates before any leaks out - I've let them sit filled with water to make sure it wasn't just a very slow leak.  And my float?  It's been in service since April and hasn't had any water ingress.

Here is how to get watertight (and air tight, in the case of my float) every time, at least with PLA:

1. Use the standard (default) 0.4mm nozzle.  Larger nozzles also leave larger gaps. 

2.  TURN OFF LINEAR ADVANCE. I cannot stress this enough.  If linear advance is on, essentially nothing you try will yield water tight prints.  You can turn it off by changing the 'K' value to zero.  Do this in the filament custom gcode section, or just add this gcode: M900 K0. Linear advance does improve print quality at higher printing speeds, but at the expensive of leaving some gaps (and it only takes one to render a print unwaterworthy).

3. Bump up the PLA temp to 220°C.  This won't have an appreciable impact on print quality, but it will enhance the flow a bit to help seal up any gaps.  

That's it.  It is really that easy.  All other settings can stay the same.  Adjust flow rate as you would normally (or not at all, if your extruder is calibrated and generally doesn't need any flow rate tuning).  If you still aren't getting water tight prints, then you're probably under extruding slightly and you might try bumping the flow rate/filament multiplier up by a % or two.  But don't do it if you don't need to - again, you shouldn't need to bump up the flow rate unless you're actually under extruding.  


I know it seems too easy, but give it a try!


Do note that I haven't tried this with anything besides PLA, but conceptually, I imagine it would be similar for other materials.  The important thing is to turn off linear advance, and bump up the temperature to get a little bit lower viscosity and better flow of the bead that gets laid down while printing.  PLA only needs a 5-10°C bump, other materials may need more.  Or they might just not work well for making water tight prints.   

Posted : 18/06/2019 7:28 pm
Reputable Member

Great work, metacollin!  I would add that I think increasing the extrusion temperature also means that when the newly extruded layer is squished onto the previous layer- which has cooled by now - the hotter plastic in the new layer will do a better job of partially melting the underlying previous layer and getting the old and new traces effectively heat-welded together.

I base this theory on experience with the opposite problem:  if the extruder temperature is too low for the material you are using, the layers do not adhere well and the print is easily broken along layer lines.  If the extruder temperature is high enough, layer separation is much less likely and the layers are much better bonded.

The amount of "squish" -i.e. the force with which a new layer is pushed down onto the previous layer - depends on both the layer height and the trace width, so even though you didn't have to make adjustments to your settings, you should share those settings so that others can duplicate your results.

Posted : 18/06/2019 10:19 pm
Active Member

Good job.  This is very useful information.

Mechanical Design since June 1973 3D Printing since November 2016 :D...
Posted : 19/06/2019 3:50 pm
Estimable Member

I had always read that PLA was somewhat water-soluble, so it doesn't seem to be the best choice for this application.

Posted : 19/06/2019 5:57 pm
New Member

Hey everyone I'm new here. I'm looking to 3d print water tight / air tight stuff. This is a huge help thank you so much. Does anyone recommend any different filament materials? It's very important that they lost a long time and don't biodegrade as water will be inside it for years. 

Posted : 24/07/2020 5:38 pm
Eminent Member


I would not choose PLA for sure. It dissolves in water nor is it UV tolerant. I have used PETG myself and so far it's held up pretty well in the hand full of months I have had the prints outside. But ABS/ASA would be better and even nylon would be a better choice I think.

Posted : 25/07/2020 6:59 pm
New Member


Thanks man! I appreciate the help!

Posted : 25/07/2020 8:15 pm
Active Member

Trying this now on a .6 nozzle - hopefully I got the correct M900 set to 0 - I chose this one to change (Red bold was changed from 18 to 0)

*PRINTER_HAS_BOWDEN.*/}M900 K200{elsif nozzle_diameter[0]==0.6}M900 K0{else}M900 K30{endif} ; Filament gcode LA 1.0

Ill report back once the print is done.

Posted : 12/11/2020 12:58 pm
Active Member

1st trial print is complete - the seam is nearly invisible, this is a HUGE improvement and unexpected. Waiting for the PLA to cool off a bit then i'll test it with water for leaks.

Posted : 12/11/2020 2:32 pm
Active Member

no water leaks 🙂

Posted : 12/11/2020 6:20 pm

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