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I've got some curious marks on my heatbed.

It appears to be from my black Sunlu PLA+ (I can just feel it if I scrape my finger nail over it) but I can't scrape it off with the metal spatula.

When I try and print over it the filament won't stick.

Any suggestions as to what it is and how you get rid of it? enter image description here

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  • $\begingroup$ Try isopropyl (rubbing) alcohol. If that doesn't work, try acetone. $\endgroup$
    – Mick
    May 30, 2019 at 14:14
  • $\begingroup$ Have you tried naptha and a razor blade? $\endgroup$
    – Davo
    May 30, 2019 at 15:48
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    $\begingroup$ that's the PEI sheet, yes? $\endgroup$
    – Trish
    May 30, 2019 at 21:55

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Prusa ships (or has shipped) with two types of PEI build plates. The original (and what I was shipped in February 2019) is a PEI sheet held in place with an adhesive. The marks I've gotten seem to be places where the adhesive has been displaced slightly from long term pressure by the object being printed.

In your case, it actually looks like scratches in the PEI. If, after cleaning with water, then 95% Isopropyl alcohol, and finally acetone the scratches still appear, I'd check if they are a problem. Do they transfer onto objects printed on the plate?

If you decide you have a problem, I would use a mild kitchen scrubby sponge to "sand" out the scratches. I have two types in my kitchen. The yellow ones are too abrasive. The blue ones are better. Gently use one to make the surface uniform.

If you have an adhesive based plate, Prusa sells replacement PEI sheets, with adhesive. The process of changing them seems onerous. Although I bought two spare sheets when I got the printer, I have never been tempted to use one. When my build plate becomes unusable, I will buy another one.

Prusa3D also offers a textured build plate, which is more expensive and in short supply. These are a powder-coating process and from pictures and their blog, I infer they are particles of PEI which are melted onto the steel surface. I have no experience with these.

I don't know if they are making the current smooth plates with a powder coating process, or if they are still using the adhesive.

The adhesive is the weak link in the heated bed. It is only rated for 110 degrees C, which is the temperature limit of the bed. I find that when I print with a hot bed (such as for PETG), the visible ripples in the surface are worse than when printing PLA on a cooler bed.

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It looks like you may be a little bit too close with the nozzle. Does the first layer calibration look alright?

The steel sheet with coating is a consumable. It will get marks. Even with long PLA prints. However, these will slowly fade and should not interfere with print quality.
I can still see my first benchy on my sheet.

When you're no longer satisfied with the state of your sheet, use some acetone to clean to bed.

Note: PETG will case bumps since this sticks a bit too much to IPA cleaned coating. Causing the coating to bubble on removal. These damages can fade. If not too bad. So don't clean with IPA for PETG, use window cleaner.

What you can do is move the print around, instead of always print in the center.

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  • $\begingroup$ Prusa beds are PEI surfaced or Powder coated $\endgroup$
    – Trish
    May 30, 2019 at 21:55
  • $\begingroup$ @Trish Yes, I own one. $\endgroup$
    – Jeroen3
    Jun 2, 2019 at 11:21
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Edit: As Trish noted, apparently Prusa printers don't ship with Buildtak stickers like the other printers I've used, so this is probably a bad idea in your specific case. For others reading this, only do the sanding shenanigans with buildtak or other stickers that you can easily replace and don't mind wearing down over time.

Used to happen to me printing PETG on Buildtak. I ended up using a medium grit sanding sponge to remove the PLA layer. Related, you might want to grab some 1k grit sandpaper for the same reason, it does a great job of freshening up your build surface once builds stop sticking well.

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  • $\begingroup$ Prusa beds are not buildtak but either coated with PEI or powercoated. treating them like buildtak easily destroys them! $\endgroup$
    – Trish
    May 30, 2019 at 21:52
  • $\begingroup$ The last time I looked into it, Buildtak was listed as a PEI surface, I have no idea about the powdercoat though. I was under the impression Prusas shipped with the same sticker surfaces that basically everyone else was using - I'll edit accordingly. $\endgroup$
    – Nach0z
    May 30, 2019 at 22:04
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    $\begingroup$ BuildTak is not PEI at all. PEI is a smooth plastic surface, BuildTak has a distinct rough surface. $\endgroup$
    – Trish
    May 30, 2019 at 22:06
  • $\begingroup$ Duly noted, I've no idea why I thought it was this whole time. $\endgroup$
    – Nach0z
    May 30, 2019 at 22:07
  • $\begingroup$ I've just had this issue whilst writing the tag usage for PEI. If you google for PEI film, some sites (the first search item returned) call it BuildTak PEI, which, as @Trish states, would appear to be incorrect. Ultem PEI is the correct term. $\endgroup$
    – Greenonline ♦
    May 31, 2019 at 1:37

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