PDMS does not stick to VAT bottom



I have very frustrating problem that I have been fighting with for a while.

I try to recoat my VAT’s, but I always fail, because PDMS does not stick to the bottom of the VAT… At first, after a few hours, it seems OK, but later on, especially in the corners, it starts to come off and that continues along the edges until very big areas of “floating” PDMS are visible. I simply do not know what to do… I live in Europe, so most stuff that is available in US I cannot get here.

Thanks for any advices.


I don’t have experience with this but maybe lightly sanding the acrylic would give the PDMS substance to adhere to better.


Two thoughts: 1) is the acrylic clean, and 2) are you following the manufacturer’s mixing ratios precisely? It is possible that the PDMS is shrinking excessively during curing, which may be due to an incorrect resin to activater ratio. Alternatively, if there is contamination, such as oil or soap residue that may interfere with bonding. If you are using denatured spirits to clean the vat, check what the denaturant (s) is/are. It may be a long chain alcohol or oil that doesn’t evaporate readily.

If you want to try the resurfacing route, search for the thread on recoating the vat, it is involved because optical clarity is essential for good prints.


I would recommend putting tray on a glass warming tray after being poured, and leave overnight for it to cure properly. Make sure its level!


someone correct me if i’m wrong, but that seems like the worst thing you could possibly do. the laser needs to pass through the material clear, the prints would fail because you’ve scuffed up the surface.


well not the worst thing, but definitely a desperate thing to do. The goal is to add a micro abrasion that is not very visible at all. Probably not the best idea and I would look for other options first.


what pdms are you using?
I would def look at degreasing the vat, just as a start- or changing cleaning agent.
Ive got a scratched vat and to be honest, the scratch disappears with the addition of the PDMS layer,visually at least, so i wonder how much you can get away with with a light surface abrasion, such as 1200 wet and dry- but agreed, it should be sticking enough without anything else.


Yes, the first things to look out for is properly mixing the PDMS materials and also making sure the vat is squeaky clean. Then ambient temperature is something to look into as well.


I’ve never had a problem with it sticking! All I do is use pure Alcohol and make sure its clean and dry before I pour. Also be sure that you mix the mixture very well before pouring, and use a heat source (Heating tray temp 150-175 to dry Silicon for 24 hours. I use a food warmer tray and I put a piece of foil over the top of the vat while curing.


I was just looking at this page: https://www.chemical-concepts.com/qsil-213.html which states:

Designed for superior adhesion with use of primer

That being said, you could rough up the acrylic around the edges beyond the print area. You might think of using a Dremel tool using a fine cutting tip at high speed because you could end up with melted protrusions in the acrylic that the PDMS could lock in around.

I am cutting out some trays using a laser cutter (Artwork to laser cut replacement vat) and after your topic will add some texture to the outside walls and edges of the bottom. I don’t get the PDMS till Monday, so it will take me a little to confirm how it works.


If the silicon cures in the center but not the corner it’s clearly a residue like resin that inhibits cure there. Before sanding anything, try cleaning with denatured alcohol.


Hi, once again. Thanks for answers.

Well, I mix those carefully. I have 0.0001g scales and mix quite well according to recommendations. I clean with IPA and let is stay for a while until it vaporises. Maybe I should go with simple soap for cleaning… not sure.

I also tried to change mix ratios as a desperate measure, but with no luck…

P.S. I am familiar with post about recoating VAT.