Silicon membrance doesn't stay vacuumed (but only for coasters!)

[Samstables]

As per the title, I have found that when pressing flat items (well I've only wasted coasters so far), the silicon vacuum membrane goes baggy when pressing flat coasters. It's not a vacuum problem, per se, as I managed some phone cases and didn't have the problem occur. The pressure stays up throughout on the dial and the centre remains pulled into the vacuum hole! (I have an ST3042)

I tried putting the coaster on top of 3 waste coasters to make it taller (I thought it might work as the phone cases are less flat than coasters) but it reoccured. Obviously if the vacuum isn't holding the paper tight, you get pale bits.

I tried using teflon over the coasters, but it didn't help either. I have to stop and start the vacuum during the cooking process about every 45-60 seconds. Given it worked fine for the phone cases, it's not because the silicon is too used/ baggy in my opinion.

Has anyone else had this problem? If so, what was your solution? I want to do placemats, but don't want to waste them!

[Samstables]

Weirdly I found I can sublimate onto other flat things without issues, such as fabric (not great quality though) and through experimentation found that I can keep the vacuum sealed and successfully create coasters in the 3d press by putting a layer (fabric worked, as did a large 1mm silicon sheet) underneath the coasters. Still no idea why the vacuum lost pressure without anything underneath but pleased to have a solution.

[socialgiraffe]

Sometimes covering the hole with a piece of paper can help the vacuum, might be worth giving that a try...