Hello all,

I made a silicone rubber layer for my multitouch, but it really has bad - small but many many - bubbles.
See pic1
The camera sees it like this: pic2

This is bad and I have to make a new silicone layer.
I’m afraid to make the same mistakes again and I don’t want to waste too much money. So I describe here shortly what I did and hope to get some hints what I can do better.

I used Sorta Clear 40 that some guys here use, too.
I watched the movie by Blaxwan and tried to do all things right.

I shaked part B very well (pic3) and poured it to part A while weighing the parts with a digital scale 10:1 (A:B)
And I mixed about 10 minutes and not too quickly.
Actually I couldn’t mix very quickly, because the mixture was quite stringy - seemed tougher than the one in the movie.
See pic4
And you also can see in pic5, that the mixture doesn’t flow very well.

Why is that? Can it be due to the room temperature? Maybe was it too cold? Or was I too slow?

I read that you can vacuum the material to get the air out of it, but I have no idea how to manage this.

Any hints????

Thanks, Grit.

Hey Grit.
What was the ambiant temp when you did your mixing ?  Did you make the whole batch at one time ?
From what i can see from your pics, I think either the mix might have been incorrect .  Or the Temp might
have been too cool for the silicone to set up correctly. 
At this point, I dont believe there is anything you can do to the silicone layer to remove the bubbles. :(

I was getting ready to order the sorta clear for my current project and was curious if your order
came pre-measured 10:1 or if you NEEDED to adjust amounts supplied in order to remain 10:1 mixture ?

How thick did you make the surface? The thinner it is the easier for the bubbles to rise to the surface when curring.  Also, the reason that Blaxwan’s video looks like the silicone is more liquid and not thick is because the video is sped up by a lot. If you were to slow down the video you would see that the silicone is quit thick and not that easy to move around/stir. So don’t worry about that. Is the IR filter on your camera in the image you show?

daddyoli: if you don’t use the whole amount of silicone A + B then you have to measure out the 10:1. For my pour I only needed half so I had to measure it out.

Hello,

Thanks for replies.

If you use all of the SortaClear, than you don’t have to measure, because it comes 10:1. I didn’t use all of it so I measured.
I am not sure, but it was not cuddly warm. I guess it was about 20°C (68F). Does it have to be warmer???

My surface is 1mm (0.04 inches) thick.
And yes, there is the IR filter on my camera in the image so it works as an IR-camera.

I will order a new Sorta Clear and will give it a second try. I still would appreciate further hints.

Thanks, Grit.

Good news!
I gave it a second try. Got a new Sorta Clear 40.
This time I
- heated the room more (no clue if this had any impact)
- used all of the silicon parts, so I couldn’t make any mistake with the proportion
- mixed it even more gently with a big plastic spoon
- poured and flattened it even more carefully

The result is really good. Almost no bubbles.
I am happy.

Grit

HiGrit,
Happy to hear it workied out this time..
Any pics of the process ? I ordered a new batch of sorta on
friday. Going to try to make some “stand alone” sheets for testing.

Hi Daddyoli,

Unfortunately I took no pictures this time. But all in all I did the same as you can see above in the pictures I posted first, but all steps more carefully. And I think using a big flat plastic spoon is better than using a bendy plastic fork.

Good luck!
Grit.

after you mix, slowly pour into a second container.  if you pour a thin stream, a lot of the air bubbles will have a chance to escape.  do likewise when you pour onto the surface.  my local sculpture supply store suggested this to me, seemed to work well.

I guess what beeduul says is right, you gotta mix and pour steadily, slow and take your time. What sort of projection material are you planning to put on top btw? any professional material or just tracing paper? (sorry, bit off topic but just curious )

Hi,
I have the same problem with small bubbles in an 1.5mm thick silicone layer.
When I remove the silicone to give it another try, should I clean the acrylic surface with some special cleaner? Or can I remove it remainder-free? Does normal window cleaner do the job as well?
Is pouring the silicone to another container twice or more often getting better results?

Thanks for reading and hopefully for your replies.

Alex

nice pics grit, I’m glad you managed to have a good result

I had he same problems the first time, and now i am looking to use the vacuum chamber at my university.  That way I KNOW that there will be no bubbles

my silicone session was also a little bit hard.. i mixed the whole package together for my 75x45c, layer.. but mixing for 3 min the 2 ingridients is from my perspective a little short (3min is written in the official handbook). next time i would mix it for at least 10min.. also also drop the silicone from a very high distance to the acrylic and very slowly. then just take a spoon or something else and mix it again for a min ver slow. as the final part then just take a l profile (like in blaywan video) and make it all flat.

I mixed a batch two nights ago and have no bubbles at all on our surface. I think that a few things help account for that:

A) 1mm or less under the smoothing bar
B) dragging the bar very slowly to allow bubbles to catch with the passing silicon
C) Multiple passes
D) When mixing don’t lift the spatula or spoon stir with it under the surface. You are trying to reduce introduction of bubbles

I don’t think that the vacuum solves all of the problems - because no matter how you cut it there will be bubbles until you smooth. I did some tests and notice the bubbles will stay in thicker pours unless you make an effort to smooth them out.

” heated the room more (no clue if this had any impact) “:
Curing . . . Allow the mold to cure overnight (at least 16 hours) at room temperature (72°F/23°C) before
demolding. Do not cure rubber where temperature is less than 65°F /18°C..: quote from the SortaClear pdf overview

check Sorta clear 40 :
http://www.smooth-on.com/liqrubr.htm