For the past year or so, I put aside all the used tanks from my Form 1+, and even bought a few used ones for a cheap. This past week I finally got with the program, and bought a package of Sylgard 184 and began recoating my used tanks.
First let me say, this is a pretty simple and easy job t do, and it save you quite a few $ over buying new tanks, although they don’t last forever and sooner or later, you’ll have to buy new tanks anyway.
Here is a very important thing to know for those that are storing their used tanks for future reconditioning. Either store them without the black cover on, or make sure the edges and side of your tanks are clean. If there is any resin trapped between them, over a period of time, that resin will harden enough and stick to he cover and side of tank, and when you’ll try to get it off, you WILL break the top edges of the tank. No amount of soaking in soapy water will prevent this from happening.
I was able to salvage 3 tanks out of 6 that I had stored. Aside from the Sylgard the only tools you will need are a pair of tweezers, a level, a scale capable of measuring in grams, and a container to mix the Sylgard in
Removing the original PDMS is about as simple as it gets. I sued a pair of tweezers to grab a corner and lift the whole layer off. I then weighed the old PDMS layers They all came up to 63 grams. I’m not sure, but I seem to remember some say that over the life of the PDMS, it actually looses some weight, and since just about every FAQ I found on recoating mentions 65 grams as the amount needed to recoat, I would assume that 2 gram difference accounts for that loss.
Some FAQs suggest cleaning the clear acrylic on both sides. I suggest cleaning the bottom of the acrylic only, then once you remove the old PDMS, put a cover on the tank until you’re ready to refill it. The only thing I did was to inspect really close to make sure there are no little pieces of the old PDMS still stuck anywhere. But it should already be as clean as it gets, as that surface was previously sealed under the old PDMS. No sense in possibly introducing any micro scratches or smudges. It was clean enough when the original PDMS was added, it’s just as clean now.
For the sake of easy match, I measured 190 grams of Sylgard, the added and additional 19 grams of the hardener. I mixed everything for about 3-4 minutes making sure I rotated the container every few seconds and scraping the liquid from the sides to make sure every thing was thoroughly mixed. I then poured 65 grams in the first 2 trays, and then I was barely able to scrape off 65 gr for the last tray. Depending on the size of you mixing container, you may have to mix a bit higher quantities. If I had to do it again, I would go for 200 + 20 next time.
Anyway, you’ll have to manually tilt each tray to make sure the coating covers the glass and the edges of the tank, then place them on a perfectly flat surface. Use an actual bubble level, do not rely on a digital/Phone level app. The big fallacy of those apps, is they only work AFTER they’ve been calibrated on a perfectly level surface, so they pretty much require a bubble level to start with.
Back to the filled tanks. During the mixing, there will be millions of micro bubbles in the liquid, and I don’t have a vacuum chamber to degass it. I saw someone mention they used a hair drier to remove the bubbles, and I tried it too. Unfortunately that only works on larger surface bubbles, it has no effect on the micro bubbles inside the liquid. So I was a bit worried, but after a few hours, all the bubbles were gone. Apparently no degassing is needed.
So now I have 3 tanks waiting for the new PDMS coat to cure. They are about 36 hours into it, and should be ready by tonight.
Once I get a chance to use one, I’ll post a followup here.
P.S. After about 24 hours, I pulled the leftover layer of PDMS from the mixing container, and the first thing I noticed is that the Sylgard is a quite a bit “softer” than the original. Maybe that will change after its full cured, maybe not. Maybe the original layer got harder due to it being subjected to use. Don’t know for sure, only an actual printing test will tell.
