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Replacing PDMS - Form 2 vs 1 size & Amount needed


So I will be refinishing some tanks soon after reading through the forums but something not specified is whether more PDMS is needed for Form 2 vs Form 1 tank. To date everything I have read said to use about 69 grams of PDMS mixture. Then just today while skimming through the ApplyLab site I found a VAT refinishing section and it very clearly states Form 1 use 68 grams base + 6.8 grams hardener & Form 2 Vat use 105 grams+10.5grams hardener.

Had I not seen this I would have been pouring 69 grams into each Form 2 tank. Now I am unsure.

Can anyone clarify amount needed for a Form 2 tank?


Carefully remove the PDMS material and weigh it. Now you know.


Also add approximately 3 grams to that weight. I found that The weight of the cured PDMS is about 3 grams lighter than the liquid mix.

I recoat my tanks, and the standard FormLabs Form 1+ tank holds 67-68g (total) of mixed liquid PDMS. When it’s time to replace it, and I pull it out of the tank, it’s about 3 grams lighter or about 64-65g.


I have replaced the PDMS layer on many Form 2 tanks I have been using 103-105 grams and that works great. I have also switched from using Slygard to using ML solar-cell guard ($59.00 on eBay) with no issues. The ML solar does take longer to cure.


Thanks for confirming mlabird. I too will be using ML solar Guard…already have it in fact. So after mixing you are adding ‘about’ 104 grams, leveling it, and letting it cure?


How long does it take ML to cure? with Sylgard it’s basically 2 days at room temp.


same thing Dudemeister…2 days


Here is my process which I have learned by trial and error.

  • clean the tank, this step is the most important. I use IPA and small pieces of old bath towels, and keep wiping with IPA until every corner is clean like new, I know that some say that IPA can weaken the tank but I have cleaned many and not notice any issues using it. I leave the old PDMS layer in the tank until the tank is completely cleaned. this will protect the window from the IPA and I also find that the window does not need any addition cleaning after carefully removing the PDMS layer. I have ruined tanks trying to clean a small smuge. Do not use IPA on the window period it will cloud the window.
    -i use a piece window glass as my level table, I use a standard 3’ level and shim it in both directions to get it level.
    -ii mix the ML solar in a throw away cup and then use a scale that I can zero out. I place the tray on the scale and zero the scale and add 103-105 grams of ML solar. I have not noticed any problem with having a gram or two more or less of the ML solar when printing.
    -i then take the tray and tilt it around until it covers the bottom being careful not to let the liquid get on the sides of the tank, Not that its and issue but it will leave a layer on the sides if your not careful.
  • I place the tray on the level table and place a tray cover over the top at an angle so that is can breathe, if you don’t the ML solar will not dry (lesson learned)
    -don’t worry about any air bubbles they will all work there way out before it drys.
    -ML solar stays tacky for 24–30 hour for me and I wait a solid 48 hours before I move the tank. I also put the tank at the bottom of the pile so it does not get used for days to let cure even more. I have attached a picture of some of the tanks I have refinished.
    Good Luck,
    Mike A.
    Scout 3D Printing


Thank you Mlabird. Excellent write up and much appreciated.


Has anyone replaced the acrylic window with glass? I’ve got one with a crack…