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Old 13-03-2012, 05:06 PM   #1
Neo-Uk
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Default Help needed please

I need help from somebody who knows about rtv molding rubber.
As you can see by this picture I got big wad of rtv on my diving bell on top of the main viewport which took me ages to get right.
Problem being it's been like that now for three days and I'm starting to panic.
I dont think its going to go off so the question is how do I get it off without damaging whats underneath (a sculpt of the window in plasteline ).


Last edited by Neo-Uk; 13-03-2012 at 10:22 PM.
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Old 13-03-2012, 09:44 PM   #2
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I feel for you Neo....

If it hasn't catalysed by now it probably won't.

Try to remove as much as you can by draining the material out with a small hole drilled as low down as you dare in the retaining wall, use a clean bucket to catch the rubber. Leave it to drain overnight. Take a small sample of the drained RTV and add a new batch of catalyst as per the volume or weight instructions. If it cures, throw away your old catalyst.

Once you have drained as much as possible carefully removed the retaining wall, you will need to strip down and clean everything. White spirit will remove rubber and not affect the plastics. Use kitchen roll turning or folding to a clean face after every wipe. Scrub the detailed surfaces with clean white spirit and an old toothbrush.

Make sure every trace of the old material has been removed, replace the retaining wall and try again.

WARNING: If you have any white spirit (aka mineral spirit) that can mix with the RTV it will cause it to shrink, so watch for any spots where the cleaner has seeped under details or into joints with gaps. Use a compressor and air nozzle to blow dry if possible.

Good luck mate...
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Old 13-03-2012, 09:50 PM   #3
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DON'T PANIC!! If I understand correctly the rtv hasn't set up yet. If that is the case it should just wipe right off. You may need to use mineral spirits too. That shouldn't hurt the plastic sphere. ( I assume it's plastic). If the rtv has set up, it should peel off and not leave any mark at all. Liquid rtv will wipe off non porous material easily; it's porous material you have to be careful of. Rtv that has set up will peel off of wood let's say but it will stain it. It will ruin clothing btw. I hope this helps. let me know

Joe
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Old 18-03-2012, 02:37 AM   #4
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Neo, you can also turn that over and let every drop drain that will for a day or so. Then, mix up just a very small batch of RTV and pour it in there again making sure you get everything coated your trying to keep from getting damage. Make sure the new batch of RTV is fresh and follow the mixing instructions TO THE LETTER. If it calls for mixing by weight and you DON'T have a scale/balance, then GET ONE.

A new fresh batch of RTV poured into that mold will 9 times out of 10 cause that little bit of remainder to set. You can then pull out what you used to "clean" the mold, throw that away and start over.

If, for some reason that doesn't work, you will have to tear everythying apart and start cleaning everything, but some fresh, properly prepared RTV should solve your problem.

Rob.
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Old 18-03-2012, 02:57 AM   #5
Neo-Uk
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So I got fed up of waiting and decided to get this useless lump off so I can move on with the build. After I go most of it off this is what is left to clean up.



It must be the stickiest substance in the world. What a $h!t job I've got in front of me..I feel like crying
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Old 18-03-2012, 11:52 PM   #6
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That looks partially cured to me, I would test a small amount off the model, maybe on a kit part or something. It really looks like it is just under catalysed.

It's the most annoying & heart breaking thing and I have done it myself, thankfully it's a mistake you probably won't repeat., I store, measure, mix and weigh RTV in near surgical conditions these days.

Keep going mate, we are all watching you pull this up despite the problems.
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Old 19-03-2012, 03:40 AM   #7
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Quote:
Originally Posted by Captain Sci-Fi View Post
It really looks like it is just under catalysed.
Yes it does. Neo, what brand/type did you use?

Rob.
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Old 19-03-2012, 06:55 PM   #8
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Thanks for the encouragement Captain.
I was going to ask if someone on here would be prepared to mold this for me when (and if ) I get it clean back up.Any ideas who would ?
It says Moldsil on the tub Rob but it's gone in the bin now.
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Old 19-03-2012, 10:48 PM   #9
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I use this from Alec Tiranti - never had any problems:

T20 RTV Silicone Moulding Rubber
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Old 21-03-2012, 10:24 AM   #10
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OK so after the major cock up I was glad to see the window sculpt was relativity undamaged.
It's a bit rough here and there but I think it will be easier to just sand the resin version later.
Ready for round two.

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Old 22-03-2012, 10:34 PM   #11
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Next time you do it try this, Mix up a small amount of rubber as normal and pour it over the part you want to mould using the surround as you did before. do just enough to cover the part and no more. when its tacky and just going off do this again untill youve built up about a few mm thickness. then mix up a larger amount of rubber and add a thixotropic addative which will make the rubber go like butter (You can see where this is going) Butter it all around untill your happy with the thickness and let dry. After that add a fibreglass jacket around the rubber to retain the shape when removed.
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Old 22-03-2012, 10:44 PM   #12
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neat rubber without the addative on the mobile shell before butter mix.
Attached Images
File Type: jpg 2011-05-30 17.59.21.jpg (171.8 KB, 25 views)
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Old 23-03-2012, 01:59 AM   #13
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Thanks for the tips.
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Old 25-03-2012, 03:29 PM   #14
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My rtv turned up yesterday so after checking and double checking everything I began round two.
Taking The Captains advice I measured everything with surgical precision (I even brought a new set of scales).
Everything went according to plan and this morning I've ended up with this...


Round two to me I think

Last edited by Neo-Uk; 25-03-2012 at 10:23 PM.
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Old 26-03-2012, 07:06 PM   #15
Glenn Allen
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Glad it all worked out for you Neo , the first time i used RTV i had the same problem ... what a mess that was , still you learn ..
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Old 30-03-2012, 09:54 PM   #16
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Quote:
Originally Posted by Neo-Uk View Post
Round two to me I think
By a straight knock out...

What diameter is that sphere or is it an EMA part no.?
I want to cost a build cause you are making this look really good..!

Inspiration resides between the covers of the EMA catalogue..
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Old 31-03-2012, 01:53 AM   #17
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Cap the sphere is ten inches across. It was originally a lampshade from B&Q which I stumbled on while shopping there (not for diving bells).


I'd searched for ages for something to base this build on.
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Old 31-03-2012, 02:00 AM   #18
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Updates to this will now go back on the proper thread
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