Adventures in waterproofing 3D prints

I’ve started printing 3D vases which look really nice in metal filaments.

3D prints are prepared by making the shape in software and then ‘slicing’ it into layers which can be understood by the printer. Usually this means that several layers are placed on the bottom, the side walls are built up by multiple passes of the print head, the top is a repeat of the bottom and the middle bits which are not seen are filled by ‘infill’ in special patterns. All this makes for strong objects.

There is a special mode of slicing which ensures that the print head never lifts off the work being printed, and never ‘retracts’ the filament nor moves backwards. This is sometimes called ‘vase’ mode and makes the print into a long spiral all the way to the top. There are few objects for which this works properly since it makes the sides only one layer thick and there is no infill. On vases or drinking glasses, cups this is ideal however and with the proper sized nozzle and good filament the results are great.

One issue is that usually these are not waterproof. Filament and deposition manufacturing by their nature leave microscopic holes in the print and while tuning the slicing parameters and the printer can have some effect, generally it is just luck when things hold water.  I’ve decided to look into lining the inside of objects to see if their water-tightness can be improved and so far I’ve read or seen of a few ideas:

  1. A wax or waxy substance rubbed into the surface then allowed to dry,
  2. liquid latex, of the type used for face painting,
  3. PVA wood glues of different types,
  4. general purpose epoxy resin, sometimes used in the fibreglass manufacturing industries. One I have found is called ‘Epolam,
  5. acrylic conformal coating used in the electronic industry for coating PCBs,
  6. … or general spray paint coatings.

Of these, the conformal coating sounds good but is very expensive. I’m going to try some of the other ones first to see if they are effective and attractive, starting with the cheapest which seems to be the wood glue and liquid latex. I wouldn’t want to mar the appearance of a beautiful vase by having a thick visible coating, but I also don’t want that vase to leak.

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