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-   -   removing excess cured silicon (http://www.plantedtank.net/forums/showthread.php?t=108964)

bycatch 05-24-2010 12:34 AM

removing excess cured silicon
 
Hi all,
The tank I'm setting up has some (in places way too much) excess silicon.
This is well and truley cured. I have had the tank full of water for 14 days to see if it leaks. This is when i noticed the excess.

The guy who built it used braces in the corners as he used 6mm Optiwhite and needed the strength.

Can I remove the excess by using a blade and carefully, without cutting into the joint 'scape' off the excess?

I imagine I'll have to run another bead around where i've been - and clean off excess before it cures?

Mike

dbosman@msu.edu 05-24-2010 07:18 PM

Unless it's really annoying, leave it alone.
If you start scraping, continue until you have removed all the silicone and start fresh as silicone will not stick to silicone.

JWA 05-24-2010 11:55 PM

What dbosman said. Learn to live with it.
Not only will fresh silicone not stick to old silicone it will also not bond well well to the glass that you thought you had cleaned off well. Silicone is almost impossible to to completely clean off glass. There is always a microscopic filling of the pores in the surface of the glass

Craigthor 05-25-2010 01:44 AM

Quote:

Originally Posted by JWA (Post 1075423)
What dbosman said. Learn to live with it.
Not only will fresh silicone not stick to old silicone it will also not bond well well to the glass that you thought you had cleaned off well. Silicone is almost impossible to to completely clean off glass. There is always a microscopic filling of the pores in the surface of the glass


Not completely true, I have resealed a dozen tanks at this point and all are still up and running 2-5 years later with no leaks. If you strip the silicone make sure you use lots of clean razor blades and plenty of rubbing alcohol to clean the glass with just prior to siliconing it to remove and oils from touching the glass.

JWA 05-25-2010 05:13 PM

Quote:

Originally Posted by Craigthor (Post 1075521)
Not completely true, I have resealed a dozen tanks at this point and all are still up and running 2-5 years later with no leaks.

Until 2 years ago I was an engineer for Corning. For the last 12 years our section worked on various ways to bond glass to everything under the sun, including other glass products. Very simply put silicone adhesives bond to glass by filling the microscopic pores on the surface. This gives them the "claws" to hang onto. Once silicone adhesive is on the glass those pores are filled. You can cut the excess off and rub all day with various chemical but it just doesn't give up the original purchase.
The only way to remove it completely is to mill the glass down 1/000 of an inch.
I am looking around here for the engineering data but 2 years gone is a long time to keep things sorted. By memory, I think you can expect that cleaned up glass will have a lower bond strength by 20%-25% Just plain silicone adhesive to cured silicone adhesive is about 65% percent that of a new and clean bond.
Soon as I find all that data I will post. There is a lot of bad info out there.
One caveat. I am speaking only of Dow-Corning Silicone adhesives.

dbosman@msu.edu 05-25-2010 05:28 PM

Darn engineers!
Spoiling yet another good argument with facts. ;-)

I'd not thought about the pores in glass being the reason RTV Silicone works.
That fills a void in my knowledge. Thanks.

bycatch 05-26-2010 01:58 AM

thanks guys.
My father and father in law are both engineers (retired), so I get the picture...
My father in law did some plans for our kitchen and when the builder and I came to construct, the builder asked me how he was supposed to measure and cut to 0.25mm accurately!
I cut my hand twice on an unpolished edge and pulled the pin on the silicon removal. I did manage to clean up a little up the front sides and left it be.

Cheers.

Diana 05-26-2010 02:53 AM

Builders usually do well to measure .25 inch reasonably, and .125 (1/8)" is not too difficult. but anything smaller, and the comment is, "I am not building a piano here!" or else, "The inspector will never see it!".

I do Autocad plans for landscape installation, including the construction of patio covers, retaining walls and a lot more. Autocad can be accurate to so many decimal places it has become a joke at the office. I have set it to be accurate to 1" for most things, and 1/4" for the most sensitive things. I almost never use the 1/4" sensitive setting.

kid creole 05-26-2010 03:02 AM

Quote:

Originally Posted by JWA (Post 1075947)
I am looking around here for the engineering data but 2 years gone is a long time to keep things sorted. By memory, I think you can expect that cleaned up glass will have a lower bond strength by 20%-25% Just plain silicone adhesive to cured silicone adhesive is about 65% percent that of a new and clean bond.
Soon as I find all that data I will post. There is a lot of bad info out there.
One caveat. I am speaking only of Dow-Corning Silicone adhesives.

A bond strength reduced by 25% doesn't mean we shouldn't reseal tanks. They're generally 50%-100% bigger than they need to be.

kid creole 05-26-2010 03:04 AM

Quote:

Originally Posted by bycatch (Post 1076303)
thanks guys.
My father and father in law are both engineers (retired), so I get the picture...
.

What it THAT supposed to mean. Engineers everywhere just got defensive. :)

bycatch 05-26-2010 06:36 AM

LOL!
Don't worry, as a result of not being an engineer myself, i have successfully over-engineered every possible task I have understaken - just to make the walls never come down, no matter what...

I am still measuring a wall to see if it has developed a lean 10 years after structural changes left it vunerable...

Engineers....can't really do without them...no matter how many times we're told 'i told you so'!

:proud:

deeda 05-26-2010 03:10 PM

JWA,

I love to hear that kind of info regarding using Dow silicone for resealing a tank. So as to not hijack the OP's thread, when you find the info, could you start a new thread? That would allow us to find your specific recommendations better.

I never really thought of glass as having pores but I realize that only makes sense. I do my best to get the glass as clean as possible when doing a reseal. My thoughts are that on a COMPLETE tank disassembly, it would be preferable to stone (or sand) the mating glass surfaces to remove the remaining silicone 'claws' to allow better adhesion between the glass panes. Just a thought.

Now, back to the original thread.

bycatch 05-27-2010 10:07 PM

All sealed up and running.
See bulkhead post for details.
Cheers for info and feedback.
Mike


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