Silicone Rubber Mixing, Pouring & Smoothing Tips (For Sorta Clear 40 Type Rubbers)
Posted: 06 July 2008 04:57 PM   [ Ignore ]
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Seeing as I’ve just completely wasted half a tub of Sorta Clear 40 and destroyed a nice piece of acrylic, I thought I’d start a thread for everyone to share some tips for those wishing to give this method a go.

On Speed....
Work fast and don’t be a perfectionist… The mistake I made was to keep making passes with my smoothing bar to correct minor issues. Sorta Clear 40 sets very quickly. I didn’t time it but you probably want to finish the whole surface within 20-30mins of mixing. Do not try and smooth the surface anymore if you notice it’s starting to stick to your smoothing bar. Basically: As soon as you get one clear smooth pass, think very carefully before making another one.

On Smoothing Bars…
Also, use a thin flat smoothing bar. I made the stupid mistake of trying to use an aluminium pole. Whilst it did have a flattening effect, the rubber just started to cling all around the pole and dripping on to the smoothed surface. I also suggest that you use a few layers of electrical insulation tape to get a thin <1mm compliant surface, as when I checked all of the aluminium/plastic profiles at a local diy store and found that they were all at least 1mm thick.

Also, make sure you remove any rubber left on the bar from each pass, as this can drip and ruin your surface.

On Mixing…
Use two containers to mix the rubber in. In one container, cut a small (1/2") hole in the bottom of the container and cover it with sticky tape, you will be using this to pour the rubber out into a thin stream to pop the bubbles. After mixing for half the time in the first container, transfer the mixture to the pouring container and continue to mix. This will ensure that all of the rubber around the edges of the container gets thoroughly mixed.

On Measuring…
I heard some members on this forum mention that it might be easier to mix all of the two pots in one go rather than to weigh it out on your own. I’d probably advise against this for two reasons:
1. The weight of the two pots might actually be different to the amount specified on the containers - you certainly can’t guarantee a good mix using this approach.
2. The trial size of Sorta Clear has just enough rubber to coat approximately two pieces of medium sized acrylic and it’s expensive - so only use the amount you need and you should have enough left over for your second project… or second attempt!! By the way, does anyone know how long this stuff lasts for once the seals have been broken? 

On Pouring…
Use the ‘Bombs Away’ method of pouring to remove all of the bubbles. Simply remove the sticky tape from the bottom of the pouring container and then let the rubber slowly pour onto your acrylic from a tall height. As the rubber falls it will thin out into a really thin strand and all of the bubbles present in the mixture will pop on the way down. You might want to stand on a chair to get some extra height.

If anyone else has some tips to share, please post below!

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Posted: 06 July 2008 08:25 PM   [ Ignore ]   [ # 1 ]
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Too bad about your acrylic. What a price to pay to learn.

I admire your perseverance though, and thanks for taking the time to post your project details so others might be able to pull this off!

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Posted: 06 July 2008 09:19 PM   [ Ignore ]   [ # 2 ]
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Good tips =)

How did you destroy the acrylic though? Or is that not related to the silicone.

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Posted: 07 July 2008 06:56 AM   [ Ignore ]   [ # 3 ]
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Actually I’ve just realized that the acrylic is fine, which leads me on to the next tip:

Sorta Clear 40 peals off acrylic quite easily - which is good if you mess up! But be very careful when you are cutting around the edges of the rubber because if you don’t cut deep enough the rubber will tear off the acrylic quite easily, taking your nice new compliant surface with it.

So I’m about to try again with the remaining rubber - hopefully things should go ok this time. I’ve also noticed that when you ‘shake’ the small bottle it introduces loads of tiny little bubbles into it. For my first attempt, I didn’t actually shake it and instead poured it into a mixing bowl and mixed it for about 3mins with practically zero bubbles. It seems to have set ok so i’d recommend that you avoid shaking it and instead try mixing in a bowl to minimize the bubbles you introduce into the rubber.

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Posted: 07 July 2008 05:46 PM   [ Ignore ]   [ # 4 ]
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Well my second attempt went a lot better! My surface is at least smooth and clear, even if the rubber is not quite uniform. I’m just glad that I didn’t use the whole tub in one go on my first attempt. Also, I’ve noticed something interesting about the small bottle that comes with Sorta Clear 40… When you shake it vigorously, it does indeed introduce lots of small bubbles into the mixture. However, if you leave it to stand for a few minutes all of the bubbles rise to the surface and the bottle goes back to how it appeared before it was shaken. I would therefore suggest that you shake for quite some time then let it stand till all of the bubbles have completely risen to the surface and popped. Only then should you start mixing it with the other part. I’m sure this is where some people might be going wrong, they simply don’t let the bottle stand till all the bubbles disappear before mixing it with the other part.

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Posted: 08 July 2008 03:17 AM   [ Ignore ]   [ # 5 ]
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On Speed....
Work fast and don’t be a perfectionist… The mistake I made was to keep making passes with my smoothing bar to correct minor issues. Sorta Clear 40 sets very quickly. I didn’t time it but you probably want to finish the whole surface within 20-30mins of mixing. Do not try and smooth the surface anymore if you notice it’s starting to stick to your smoothing bar. Basically: As soon as you get one clear smooth pass, think very carefully before making another one.

You are right about the speed!!! I had read that it would take 2 hours before it starts curing. But after 15 min mixing and 20 min smoothing the surface it started to get sticky. We ended up with one edge that is a bit bumpy. It works fine though....

Oh and we used one pot of Sorta Clear 40 and that was exactly enough for our table. But because it was just enough we had to make extra runs to get it evenly spread. This probably was the cause of our time shortage. And somehow our mixture was a bit less fluid then I expected (and seen in Blaxwans tutorial).

We used Blaxwans tutorial about the pooring method. Can’t find it now, but maybe someone can post a link here.

Tip: If you have children in the house, explain them the whole proces upfront, so they can’t come and ask lot’s of questions while you are stressing to get everything smooth before it starts to dry....

...better, send them away for a weekend!!!! Because there are allways new questions to be found....

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Posted: 08 July 2008 02:45 PM   [ Ignore ]   [ # 6 ]
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Tunabreath - 08 July 2008 03:17 AM

Tip: If you have children in the house, explain them the whole proces upfront, so they can’t come and ask lot’s of questions while you are stressing to get everything smooth before it starts to dry....

...better, send them away for a weekend!!!! Because there are allways new questions to be found....

Haha...! I love this comment!

Tie them could be a solution? hahaha

I suffer the same =P

Cheers!

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Posted: 10 July 2008 10:17 AM   [ Ignore ]   [ # 7 ]
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I would also add that you should make sure you pour more rubber on the surface initially than you need, then scrape any excess off with the slide as this should hopefully result in a smoother surface. Unfortuantely I neglected this on my second attempt, so my surface is mostly smooth but it’s not a uniform thickness.

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Posted: 10 July 2008 02:34 PM   [ Ignore ]   [ # 8 ]
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I also found that the advertised drying time of over an hour was more like 15 minutes… 1/4 of my table ended up bumpy.

It still works but the it creates hot spots in the image and that means I have to compromise on sensitivity during configuration.  I eather have random touches or I need to press hard to create the blobs.

I’ve ordered another round of Sorta Clear and will give it another more informed attempt.

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Posted: 02 September 2008 06:00 PM   [ Ignore ]   [ # 9 ]
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The picture below should give you an idea of the difference made with the bombs away pouring method. On the right hand side, some of the mixture accidentally spilled over the pot I was pouring from in a big blob, so none of the air bubbles had the chance to pop. The left side however was poured from a great height and popped most bubbles successfully.

bea302e67c.jpg

By the way, you’ll probably only get about two attempts at this in a trial size pot, so try and get a friend to slowly pour the mixture out whilst standing on a chair when you smooth it out. It comes out like treacle, so it takes a long time to pour it via this method but it does pop most of the bubbles on the way down. Don’t try and do it on your own (like I did) because you won’t have enough time to ensure a good smooth surface.

Good Luck!

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