Author Topic: OTC "Silasitc"?  (Read 5893 times)

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Offline ender4171Topic starter

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OTC "Silasitc"?
« on: February 04, 2019, 05:26:49 pm »
Dave and others often talk about components being tied down with silastic.  I have found the OG Dow/Corning 732 stuff, but it is pricey and not available in small quantities (way more than I would use in time without it going bad).  Is there anything really special about it other than it is a neutral cure silicone?  I was thinking of grabbing some GE Silicone II, which is also neutral cure and is available at any home store in small tubes.  Does anyone have experience with that product, or have any recommendations for an alternative that is readily available?
 

Online coppercone2

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Re: OTC "Silasitc"?
« Reply #1 on: February 04, 2019, 05:32:24 pm »
Ill give you a cookie if you make mechanical mounts for your parts rather then hosing it down in xenomorph juices
 

Offline ender4171Topic starter

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Re: OTC "Silasitc"?
« Reply #2 on: February 04, 2019, 05:41:42 pm »
Maybe "hold down" was a bad choice of words.  This is for vibration mitigation on things like capacitors.  Hard mounts would of course be ideal, but they aren't practical for small-medium sized parts, especially when the board is densely populated.  I am talking about this sort of thing:

 

Offline wraper

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Re: OTC "Silasitc"?
« Reply #3 on: February 04, 2019, 05:53:06 pm »
Ill give you a cookie if you make mechanical mounts for your parts rather then hosing it down in xenomorph juices
Please show your 'mechanical mounts' for PCB mounted capacitors, transistors, resistors, inductors...  :bullshit:
« Last Edit: February 04, 2019, 05:56:30 pm by wraper »
 
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Offline rdl

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Re: OTC "Silasitc"?
« Reply #4 on: February 04, 2019, 07:12:26 pm »
I'd never heard the term "silastic" until watching EEVblog. I think it just refers to a type of silicone glue that cures to a rubbery state and is non-corrosive. I'm pretty sure a lot of manufacturers just use hot glue of some kind, which is what I do.
 

Offline wraper

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Re: OTC "Silasitc"?
« Reply #5 on: February 04, 2019, 07:28:50 pm »
Hot glue is used rarely and usually only in crappy devices. Usual cheap hot glue will not only melt at elevated temperatures, it will also delaminate in a few years at most. And if vibration or freezing temperature is present it may fail almost instantly. What you normally see is RTV silicone adhesive.
 

Online coppercone2

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Re: OTC "Silasitc"?
« Reply #6 on: February 04, 2019, 07:45:19 pm »
Ill give you a cookie if you make mechanical mounts for your parts rather then hosing it down in xenomorph juices
Please show your 'mechanical mounts' for PCB mounted capacitors, transistors, resistors, inductors...  :bullshit:

you can make them? what do you want me to , bend some thin aluminum bar stock and take pictures of brackets? amazing technology.

here, its photoshopped


you can also make them smaller  :scared:

and yea the best way to actually secure a transistor is to put a bar on it tensioned with screws from the side.
« Last Edit: February 04, 2019, 07:47:58 pm by coppercone2 »
 

Offline wraper

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Re: OTC "Silasitc"?
« Reply #7 on: February 04, 2019, 08:06:09 pm »
Ill give you a cookie if you make mechanical mounts for your parts rather then hosing it down in xenomorph juices
Please show your 'mechanical mounts' for PCB mounted capacitors, transistors, resistors, inductors...  :bullshit:

you can make them? what do you want me to , bend some thin aluminum bar stock and take pictures of brackets? amazing technology.

here, its photoshopped


you can also make them smaller  :scared:

and yea the best way to actually secure a transistor is to put a bar on it tensioned with screws from the side.
LOL, I'd like to see such abysmal PCB where most of smallish inductors and caps are attached with that crap. FYI silicone adhesive works very well against vibration. It's especially useful for single layer PCBs where solder joints are much more prone to cracking. Also I would like to see how production engineer hires an assassin after you submit such design for assembly  :-DD. Oh, and I guess people with trypophobia better to not look on that PCB ridden with mounting holes.
« Last Edit: February 04, 2019, 08:14:15 pm by wraper »
 

Online coppercone2

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Re: OTC "Silasitc"?
« Reply #8 on: February 04, 2019, 08:31:31 pm »
your right about it being considered high quality and high repair ability.  Of course they will dislike the design.

It's also in the beginners forum.

you know you can stamp a big piece of metal to fit over the entire PCB to sandwich everything?

If you buy aluminum bar stock you can cut it with bolt cutters, bend it in a vice with a hammer and drill holes, in a few minutes.

actually faster then curing shit.
« Last Edit: February 04, 2019, 08:35:58 pm by coppercone2 »
 

Offline wraper

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Re: OTC "Silasitc"?
« Reply #9 on: February 04, 2019, 08:50:25 pm »
your right about it being considered high quality and high repair ability.  Of course they will dislike the design.

It's also in the beginners forum.

you know you can stamp a big piece of metal to fit over the entire PCB to sandwich everything?

If you buy aluminum bar stock you can cut it with bolt cutters, bend it in a vice with a hammer and drill holes, in a few minutes.

actually faster then curing shit.
Nor it will be high quality, nor it will have good repairability. It will be hell to disassemble and assemble back. On the other hand you can simply cut silicone adhesive with a knife and remove the component. Not to say your suggestion would have abysmal effect on size and weight.
Quote
you know you can stamp a big piece of metal to fit over the entire PCB to sandwich everything?
The only way it would somewhat work is if you put pieces of elastic material between it and components. Pressing them down and adding mechanical stress on parts and solder joints. Also it would obstruct airflow this preventing heat dissipation. Adhesive on the other hand fixes components in their natural position after soldering and does not add any stress.
IMO you don't know a tiny bit about DFM (design for manufacturability).
 

Online coppercone2

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Re: OTC "Silasitc"?
« Reply #10 on: February 04, 2019, 08:51:42 pm »
its design for prototyping because its a blog and its the beginners forum.

Putting two screws on something is not hell. Having to use a exacto blade is. It's ridiclous.
 

Online Ice-Tea

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Re: OTC "Silasitc"?
« Reply #11 on: February 04, 2019, 08:55:13 pm »
I'm pretty sure a lot of manufacturers just use hot glue of some kind, which is what I do.

Please don't. Once had a PSU manufacter that also considered it a good idea. The stuff would just run out of the vent holes if you put it upside down..

Offline wraper

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Re: OTC "Silasitc"?
« Reply #12 on: February 04, 2019, 08:55:20 pm »
its design for prototyping because its a blog and its the beginners forum.

Putting two screws on something is not hell. Having to use a exacto blade is. It's ridiclous.
Are you suggesting that if it's beginners section, suggestions should be such that no sane engineer would do that.  |O

Quote
Putting two screws on something is not hell
Putting 2 screws, then multiplied by many tens as minimum  :palm:. And creating custom fixture for every different component.
« Last Edit: February 04, 2019, 08:56:57 pm by wraper »
 

Online coppercone2

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Re: OTC "Silasitc"?
« Reply #13 on: February 04, 2019, 08:57:58 pm »
what no sane engineer would do is put silastic in a 1 off.

chirst it would be so dirty and if you need to rework it you need to peel fucking glue off of everything.
 

Offline wraper

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Re: OTC "Silasitc"?
« Reply #14 on: February 04, 2019, 09:01:20 pm »
what no sane engineer would do is put silastic in a 1 off.

chirst it would be so dirty and if you need to rework it you need to peel fucking glue off of everything.
You don't need to place it on prototype to begin with. It's usually used to prevent damage during transportation. And there is nothing dirty about it. What would be really insane is spending half of your time one making stupid custom fixtures instead of doing what matters.
 

Online coppercone2

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Re: OTC "Silasitc"?
« Reply #15 on: February 04, 2019, 09:04:34 pm »
half your time? really? are you refining your own aluminum or something?

get real. Are you drilling the holes with a sharp stick or are you trying to cut metal with a butter knife here?

absolutely preposterous.
 

Offline wraper

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Re: OTC "Silasitc"?
« Reply #16 on: February 04, 2019, 09:07:39 pm »
half your time? really? are you refining your own aluminum or something?

get real
Feels like logic falling apart when written by you. IMO you should look in the mirror.
 

Online coppercone2

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Re: OTC "Silasitc"?
« Reply #17 on: February 04, 2019, 09:11:29 pm »
your telling my its going to take long to drill a few holes and bend a piece of metal ???

yea half my time
quarter of a cigarette break?
 

Offline wraper

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Re: OTC "Silasitc"?
« Reply #18 on: February 04, 2019, 09:14:25 pm »
your telling my its going to take long to drill a few holes and bend a piece of metal ???

yea half my time
quarter of a cigarette break?
You could solder a whole pcb faster than bending that stupid metal and drilling holes. Also you need to spend a lot of time when designing PCB just to make that those fixtures would fit. Insanity squared  :palm:. Please show an example of actual PCB with this stupid crap.
 
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Online coppercone2

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Re: OTC "Silasitc"?
« Reply #19 on: February 04, 2019, 09:15:16 pm »
 

Offline Nerull

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Re: OTC "Silasitc"?
« Reply #20 on: February 04, 2019, 10:33:12 pm »
OP never specified this was for a one-off, you seem to have made that detail up in your head.

And yes, bolting capacitors to a big piece of metal is moronic. How many expensive custom machined or stamped parts are you going to put on your cheap, one-off board?
 

Online coppercone2

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Re: OTC "Silasitc"?
« Reply #21 on: February 04, 2019, 10:46:25 pm »
ones that you make with a hammer in 5 minutes?

expensive? custom machined? your competing with glue ffs.
« Last Edit: February 04, 2019, 10:48:26 pm by coppercone2 »
 

Offline wraper

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Re: OTC "Silasitc"?
« Reply #22 on: February 04, 2019, 10:51:59 pm »
ones that you make with a hammer in 5 minutes?
And you call that crap better and more elegant than using silicone adhesive? I ask again, show a photo of PCB where your suggestion is actually realized. And not something like a one huge axial cap bolted down while other components are not on PCB from 70's-80's . Not just products of your imagination.
 

Offline RobertHolcombe

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Re: OTC "Silasitc"?
« Reply #23 on: February 04, 2019, 10:57:43 pm »
Someone has had a bad experience with silicone...

Only applied where needed it literally takes 5 seconds to sever/remove with a knife or side cutters. If you are doing rework but don't have either of those but you have metal fabrication tools and spare metal, perhaps crafting a blade from scratch would be more time efficient for you than making custom brackets  ::)
 

Offline timelessbeing

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Offline timelessbeing

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Re: OTC "Silasitc"?
« Reply #25 on: February 04, 2019, 11:14:13 pm »
This looks like adhesive specific to your application
https://www.rpelectronics.com/1035-85ml-rtv-silicon-clear-adhesive.html
 

Offline westfw

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Re: OTC "Silasitc"?
« Reply #26 on: February 06, 2019, 07:48:41 am »
I'd think the GE Silicone II would work OK.For somewhat more flexibility, the crafts industry sells a wide variety of two-part silicone mold-making resins.For example: https://www.amazon.com/Smooth-Silicone-Making-OOMOO-30/dp/B004BNF3TK/https://www.smooth-on.com/product-line/mold-max/
 

Offline stj

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Re: OTC "Silasitc"?
« Reply #27 on: February 06, 2019, 02:23:39 pm »
there is a chinese company that specialises in silicone products.

705 is a specially usefull one because you can seal windows, leds etc.
https://www.ebay.co.uk/itm/302814126123
 

Offline timelessbeing

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Re: OTC "Silasitc"?
« Reply #28 on: February 06, 2019, 09:39:40 pm »
There's also this stuff



Available for cheap from the usual suspects.

It's thermally conductive which is good if you need to spread the heat around. (But it cures firm like adhesive.)
 

Offline Gary350z

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Re: OTC "Silasitc"?
« Reply #29 on: February 07, 2019, 10:01:20 am »
I'd never heard the term "silastic" until watching EEVblog. I think it just refers to a type of silicone glue that cures to a rubbery state and is non-corrosive.

Silastic (a portmanteau of 'silicone' and 'plastic') is a trademark registered in 1948 by Dow Corning Corporation for flexible, inert silicone elastomer.
https://en.wikipedia.org/wiki/Silastic

Where I used to work, everyone called it RTV (room temperature vulcanizing).

If I recall correctly, I have heard that as it cures it gives of ammonia(?) which corrodes copper. I don't know if this is true or not.
 

Offline BurningTantalum

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Re: OTC "Silasitc"?
« Reply #30 on: February 07, 2019, 10:28:07 am »
Just to clear this up: Dave is Australian, and the term 'Silastic' is, as detailed, a trade name of Dow Corning, but is used in Australia as a generic term for any sealant goop (Viz: Hoover, Doona, Graviner etc.)
BT
 

Offline graeme.c.payne

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Re: OTC "Silasitc"?
« Reply #31 on: February 07, 2019, 02:46:35 pm »
My memory is that "Silastic" was (is?) an early brand name for some silicone adhesives. (USA)

For electronics, silicones are widely used for hording parts in place, vibration damping, and encapsulating parts or assemblies.

For use in electronics, the silicone must NOT create any acid while curing. If it smells like vinegar at any time, don't use it! It will eventually cause corrosion. A silicone adhesive safe for electronics WILL cost more than what the home center carries, because it is a specialty product.

An example of a suitable product is this, from Amazon (USA): GC ELECTRONICS 19-155 ADHESIVE, SILICONE, TUBE, 3FL.OZ.(US) (1 piece) https://www.amazon.com/dp/B004SPJN6K/ref=cm_sw_r_cp_apa_i_ZnexCb4WZPT1X




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Offline LukeW

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Re: OTC "Silasitc"?
« Reply #32 on: February 10, 2019, 12:18:46 am »
Generally, when choosing a material like this, these are the factors we're interested in:

- Neutral-cure silicone. A lot of hardware-store 1-pack silicones are acetoxysilane based which will release acetic acid in the curing reaction, which will corrode nearby things - you don't want this, you really want a neutral-cure silicone. This is probably the most important thing, and if you can buy a neutral-cure Home Depot silicone for a couple of bucks it's probably fine.

- One-pack, because it's more convenient than mixing a binary system.

- RTV (room-temperature vulcanising), i.e. it chemically sets and crosslinks by itself at room temperature, going hard with the desired shore and mechanical properties.

- Has some "bounce", which is the main motivation for choosing a silicone over a polyurethane.

- Cheap and locally available for you in a non-bulk pack.

- High dielectric strength, although if you're not using it for HV applications anything is probably fine.

Personally, I like Dow Corning 738, which is available in a small tube.

It's actually documented as an engineering material - it has a datasheet, and if we want to know, say, the dielectric strength, it's documented.

https://www.ellsworth.com/products/by-manufacturer/dow/sealants/silicone/dow-738-electrical-sealant-silicone-white-90-ml-tube/
 

Online xavier60

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Re: OTC "Silasitc"?
« Reply #33 on: February 16, 2019, 09:40:14 pm »
Dave and others often talk about components being tied down with silastic.  I have found the OG Dow/Corning 732 stuff, but it is pricey and not available in small quantities (way more than I would use in time without it going bad).  Is there anything really special about it other than it is a neutral cure silicone?  I was thinking of grabbing some GE Silicone II, which is also neutral cure and is available at any home store in small tubes.  Does anyone have experience with that product, or have any recommendations for an alternative that is readily available?
I have been using ThreeBond(Japan) 1530C for years. It is moisture curing and non corrosive. Because it self levels, it gives a neat result.
The product isn't easily available in Australia. It is now available on ebay in retail blister pack. Be certain to read the review.
https://www.ebay.com/p/2-Pcs-Tube-Tb1530c-All-Purpose-Adhesive-Glue-Clear-Extra-Strong-Wood-Elasticity/18024574076?iid=173609103986
« Last Edit: February 24, 2019, 07:31:43 am by xavier60 »
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Offline djacobow

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Re: OTC "Silasitc"?
« Reply #34 on: February 17, 2019, 01:24:46 am »
What do you guys think of zip ties for caps? Just put a few extra holes in the PCB design and feed the tie around the back. Seems like it would work nicely for elcos on their sides. Maybe with some silpat or other foam to provide tension.
 

Offline stj

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Re: OTC "Silasitc"?
« Reply #35 on: February 17, 2019, 05:28:22 am »
that's not new, it was common in the 70's, 80;s etc when linear psu's had bigger caps.
 

Online coppercone2

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Re: OTC "Silasitc"?
« Reply #36 on: February 17, 2019, 02:26:01 pm »
What do you guys think of zip ties for caps? Just put a few extra holes in the PCB design and feed the tie around the back. Seems like it would work nicely for elcos on their sides. Maybe with some silpat or other foam to provide tension.

its better then goo
 

Offline timelessbeing

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Re: OTC "Silasitc"?
« Reply #37 on: February 18, 2019, 01:02:45 am »
I think goo helps dissipate heat from caps
 

Offline stj

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Re: OTC "Silasitc"?
« Reply #38 on: February 18, 2019, 01:29:05 am »
I think goo helps dissipate heat from caps

so does putting ceramic caps in parallel with them to remove high frequency noise the electrolytic cant deal with.
(another old trick from the 70's)
 

Offline timelessbeing

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Re: OTC "Silasitc"?
« Reply #39 on: February 18, 2019, 01:36:33 am »
I thought ripple current causes them to heat up.
 

Offline stj

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Re: OTC "Silasitc"?
« Reply #40 on: February 18, 2019, 01:49:37 am »
they heat because the esr is not low enough to react in time to fast ripple.
these days we have low esr caps for that - back then you put several in parallel along with some ceramics.
 

Offline jc101

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Re: OTC "Silasitc"?
« Reply #41 on: February 19, 2019, 02:27:37 pm »
I use Dow Corning (now DOWSIL) 744, it was designed to be safe on electronics etc.
 

Online xavier60

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Re: OTC "Silasitc"?
« Reply #42 on: November 26, 2019, 11:26:05 pm »
Dave and others often talk about components being tied down with silastic.  I have found the OG Dow/Corning 732 stuff, but it is pricey and not available in small quantities (way more than I would use in time without it going bad).  Is there anything really special about it other than it is a neutral cure silicone?  I was thinking of grabbing some GE Silicone II, which is also neutral cure and is available at any home store in small tubes.  Does anyone have experience with that product, or have any recommendations for an alternative that is readily available?
I have been using ThreeBond(Japan) 1530C for years. It is moisture curing and non corrosive. Because it self levels, it gives a neat result.
The product isn't easily available in Australia. It is now available on ebay in retail blister pack. Be certain to read the review.
https://www.ebay.com/p/2-Pcs-Tube-Tb1530c-All-Purpose-Adhesive-Glue-Clear-Extra-Strong-Wood-Elasticity/18024574076?iid=173609103986
I have just received my first order for 2X 150g tubes from this Japanese online store.
https://global.rakuten.com/en/store/marunishi-online/item/3552896/
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Online T3sl4co1l

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Re: OTC "Silasitc"?
« Reply #43 on: November 27, 2019, 02:21:33 am »
Hmm, shopping between Digikey and MG Chemicals, isn't easy, but this seems a likely candidate... if pricey.
https://www.digikey.com/product-detail/en/mg-chemicals/RTV162-300ML/473-1203-ND/1972157
The thermal conductivity is specified, though with some kind of bastard unit that can't be written correctly.  If it's what I think they mean, it's close to 0.21 W/(m K) which isn't bad as adhesives go (comparable to say, FR-4).
Also RTV102 and 103 (black) I guess; cheaper.

This is cheaper, but poor thermal conductivity (average as sealants go),
https://www.digikey.com/product-detail/en/mg-chemicals/1035-85ML/473-1370-ND/1972170
probably comparable to the Dow 738 and similar, listed above.

https://www.digikey.com/product-detail/en/chip-quik-inc/NCS10W/NCS10W-ND/9836748 too,

Can't seem to find anything harder.  These are pretty flexible (Shore A 20-30ish?).  Saw one Shore D something.  Would be nice to have options for more rigidity, like for glopping between electrolytic capacitors.

Probably the kind of thing you need to old fashioned read catalogs or phone up the manufacturer to select products.. ::)

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Online xavier60

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Re: OTC "Silasitc"?
« Reply #44 on: November 27, 2019, 02:46:31 am »
It's difficult to find common products that are  flowable, transparent and non-corrosive.
This  product is easier to re-enter, https://www.permatex.com/products/adhesives-sealants/sealants/permatex-flowable-silicone-windshield-glass-sealer/
Like with most Permatex products, the tube cap is programmed to fall apart so that one is likely to find spoiled contents the next time it is needed.
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