Silicone Adhesive Stick to Plastic?

Thread Starter

MrAl

Joined Jun 17, 2014
11,389
Hello there,

Anyone do this? I have to do a repair and it involves using silicone adhesive to glue to a plastic plate.
I've read around the web but would like to hear any experiences anyone might have had.
This has to be permanent or it could be bad.
Cant screw, cant drill, etc. Only way is to glue it. I have clear silicone so i thought about using that.
Thanks to other members for any ideas.
 

MrSalts

Joined Apr 2, 2020
2,767
Hello there,

Anyone do this? I have to do a repair and it involves using silicone adhesive to glue to a plastic plate.
I've read around the web but would like to hear any experiences anyone might have had.
This has to be permanent or it could be bad.
Cant screw, cant drill, etc. Only way is to glue it. I have clear silicone so i thought about using that.
Thanks to other members for any ideas.
You have clear silicone adhesive or do you have clear silicone caulk/sealant?
What plastic is the plate made of? If made in the past 20-years, it likely has a recycle code.
What is the expectation of the glued plate (how will it be used? How will it appear?)
What kind of break (clean two or three pieces or is the edge chattered to dust?)?
 

Thread Starter

MrAl

Joined Jun 17, 2014
11,389
You have clear silicone adhesive or do you have clear silicone caulk/sealant?
What plastic is the plate made of? If made in the past 20-years, it likely has a recycle code.
What is the expectation of the glued plate (how will it be used? How will it appear?)
What kind of break (clean two or three pieces or is the edge chattered to dust?)?
Not sure what you mean.
The silicone is clear adhesive but can also be used for caulk.
Not sure what kind of plastic it is unfortunately.
The plastic is not broken, a piece of glass has to be glued to the plastic. About a total of 20 square inches of surface area, so there is plenty of area where the glue can hold on to.
 

Ya’akov

Joined Jan 27, 2019
9,069
Hello there,

Anyone do this? I have to do a repair and it involves using silicone adhesive to glue to a plastic plate.
I've read around the web but would like to hear any experiences anyone might have had.
This has to be permanent or it could be bad.
Cant screw, cant drill, etc. Only way is to glue it. I have clear silicone so i thought about using that.
Thanks to other members for any ideas.
actrivity Do you have access to the other side of the glass while gluing? While RTV will adhere to glass, what you mean by "permanent" will determine if it is suitable.
 

MrSalts

Joined Apr 2, 2020
2,767
This an interesting post. I guess you now understand how difficult it is to be an "OP"
Your title mentions "repair" and your first post says only "plastic plate" - I guess I made the leap to assume the plastic plate was broken. "Glass" is only mentioned in your second post.

Today I learned, someone who posts thousands of answers doesn't necessarily ask clear and complete questions.

is there any other key pieces of information missing? How is this used? Decorative, functional (how)? Indoor at constant temp/humidity vs outdoor in range of temps and UV exposure? Do you expect an optically clear bond or is a milky white/hazy adhesive ok?
 

Ya’akov

Joined Jan 27, 2019
9,069
What do they stick car windscreens in with? That seems like what you need!
Actually, the first candidate in the absence of more information, is not the glue used for to hold glass to the car (which is a specialized RTV) but the glue used to hold the rearview mirror to the glass, which is specialized cyanoacrylate.
 

KeithWalker

Joined Jul 10, 2017
3,063
Cyanoacrylate (crazy glue) will stick well to most plastics and to glass but not to teflon. I use it extensively because I usually construct my own project cases and cabinets. If the plastic surface is flat and clean, a layer of thin CA will do the job. Put the two surfaces together along one edge and then close them together like a book. The high surface tension of the CA will eliminate most bubbles but if you do get any, they can be squeezed out when you clamp the pieces together. Be ready to catch the excess glue or your work area will get very sticky very quickly.

Sticky.jpg
 

Thread Starter

MrAl

Joined Jun 17, 2014
11,389
This an interesting post. I guess you now understand how difficult it is to be an "OP"
Your title mentions "repair" and your first post says only "plastic plate" - I guess I made the leap to assume the plastic plate was broken. "Glass" is only mentioned in your second post.

Today I learned, someone who posts thousands of answers doesn't necessarily ask clear and complete questions.

is there any other key pieces of information missing? How is this used? Decorative, functional (how)? Indoor at constant temp/humidity vs outdoor in range of temps and UV exposure? Do you expect an optically clear bond or is a milky white/hazy adhesive ok?
I hope you didnt cry too long :)
Text is always like that. You need back and forth to get the full picture. A single reply is rare unless the OP does not come back.

Actually, the title says it all. Does silicone adhesive stick to plastic. Very simple. Doesnt matter what else is going with it. That means it has to have some strength anyway, and if anyone wanted too they could list the things that may go with it. Someone with experience with silicone might say, "I glued a bottle cap to the underside of my plastic shelf so i could unscrew the bottle to get the contents, then screw it back up, and the silicone held for years now". Alternately they may say, "and it fell down the second day and the bottle broke and contents all of the floor. I am throwing my silicone in the garbage".

Your tone seems to be mixed with a lot of mockery. That's not good etiquette for text discussions.
Text discussions take more time than a face to face meeting or phone call, you have to be patient.
 
Last edited:

Thread Starter

MrAl

Joined Jun 17, 2014
11,389
Actually, the first candidate in the absence of more information, is not the glue used for to hold glass to the car (which is a specialized RTV) but the glue used to hold the rearview mirror to the glass, which is specialized cyanoacrylate.
Thanks for the reply Yaakov.

Oh yeah i know what you are talking about i should probably look that up.
I do have to cover about 20 square inches surface area. That's roughly 3 inches by 7 inches rectangular.
I guess i was hoping silicone would work because i have some already :)
I was also thinking of using some backup method, such as thin stainless steel wires. If the glue gives out, the wires hold it and i will see it shaking around so i know to work on it again.
I would like to drill a tiny hole in one corner and use a wire to hold it if the glue gives out, but i know drilling glass is not that easy.
 

Ya’akov

Joined Jan 27, 2019
9,069
Thanks for the reply Yaakov.

Oh yeah i know what you are talking about i should probably look that up.
I do have to cover about 20 square inches surface area. That's roughly 3 inches by 7 inches rectangular.
I guess i was hoping silicone would work because i have some already :)
I was also thinking of using some backup method, such as thin stainless steel wires. If the glue gives out, the wires hold it and i will see it shaking around so i know to work on it again.
I would like to drill a tiny hole in one corner and use a wire to hold it if the glue gives out, but i know drilling glass is not that easy.
If you are going to sandwich the RTV between the plastic and glass you will find the RTV has problems curing properly. Does it have to be clear? A good possibility is UV cured glue because can be cured through the glass. Alternatively a good quality epoxy will work.

If you want to avoid the exotic epoxy options, I can readily suggest J-B Weld ClearWeld. In general the J-B Weld products are really good. Their steel reinforced epoxy is a beast and can be used for a lot of things, it's unreasonably strong.

1647372875902.png1647372830891.png
 

Ya’akov

Joined Jan 27, 2019
9,069
Beat me to it, I always use J-B Weld steel where extra strength is needed.
Joins just about anything
Though I would want something less viscous to coat a large area.

I use a variety of adhesives. A few different types of cyanoacrylate and activators, UV cured (tbough my go to, Loctite AA 349 has dramatically risen in price. I am glad I have a reasonably large supply), a few different epoxies including J-B Weld, of course but also Loctite Hysol 1C which is a white, room temperature curing epoxy with excellent strength and exceptional chemical resistance (it’s the stuff you sometimes see on trimmers when a manufacturer wants to be sure you don’t play with calibration), a few RTVs including including, importantly ASI 388 electronics grade silicone that doesn’t outgas acetic acid when it cures (don’t use the normal stuff inside electronics!), polyurethane and PVA glues for wood, a variety of purpose made glues for shoe repair and the like, and of course hit glue (I keep two glue guns, one with transparent and one with black glue sticks).
 

MaxHeadRoom

Joined Jul 18, 2013
28,617
I too keep a good variety, one maybe not suitable for this topic, but one I discovered a few years ago and is apparently developed +80 years ago..
Namely Durhams Water Putty.
I use it primarily for wood and Gyproc projects, where you need to secure an anchor point in either for a fastener etc. Plus a few other applications.
Plus its cheap!!
  • Fill cracks, gaps, holes and voids in all surface types
  • Can be sanded, drilled, sawed and painted when dry
  • For long-lasting repairs indoors and out
 

MrSalts

Joined Apr 2, 2020
2,767
I hope you didnt cry too long :)
Text is always like that. You need back and forth to get the full picture. A single reply is rare unless the OP does not come back.

Actually, the title says it all. Does silicone adhesive stick to plastic. Very simple. Doesnt matter what else is going with it. That means it has to have some strength anyway, and if anyone wanted too they could list the things that may go with it. Someone with experience with silicone might say, "I glued a bottle cap to the underside of my plastic shelf so i could unscrew the bottle to get the contents, then screw it back up, and the silicone held for years now". Alternately they may say, "and it fell down the second day and the bottle broke and contents all of the floor. I am throwing my silicone in the garbage".

Your tone seems to be mixed with a lot of mockery. That's not good etiquette for text discussions.
Text discussions take more time than a face to face meeting or phone call, you have to be patient.
Those are the standard questions when discussing adhesives.

Strong rigid adhesives holding two substrates is a bad idea if the two parts have different CLTE and the parts will be subjected to many thermal cycles of 10°C or more in their lifetime. Most plastics have a high CLTE vs glass.

Many plastic adhesives use "solvent welding" to swell the plastic of each substrate and cause entanglement of the chains from each part. Thst doesn't work with glass as one substrate.

Most 1-component silicones need humidity to cure. Thst means, with glass or tiles, only the edges cure and years from now, the adhesive in the middle can still be soft. It also means the volume of the adhesive is expanding as water is added (or the density is increasing as the water adds to the matrix). Caulk/sealant is different than adhesive - caulk has little shear strength or compressive strength. There is really no problem if it doesn't cure, and it is kind of an advantage not to cure as a house shifts or acrylic tub deforms when full.
 

Thread Starter

MrAl

Joined Jun 17, 2014
11,389
If you are going to sandwich the RTV between the plastic and glass you will find the RTV has problems curing properly. Does it have to be clear? A good possibility is UV cured glue because can be cured through the glass. Alternatively a good quality epoxy will work.

If you want to avoid the exotic epoxy options, I can readily suggest J-B Weld ClearWeld. In general the J-B Weld products are really good. Their steel reinforced epoxy is a beast and can be used for a lot of things, it's unreasonably strong.

Hello again,

Hey that's interesting i have used JB Weld and JB Kwik for years now, at least 8 to 10 years i would say.
I had an old Hyundai and one of the pollution control valves had a tube that rusted off of the body of the valve so there was no tube left to connect to the rest of the system. I looked far and wide for a replacement valve, but none anywhere as the car was quite old. I went to Home Depot and picked up a short length of 1/2 inch steel threaded pipe and some JB Weld. I got JB Weld instead of Kwik because i wanted it to have the maximum working temperature because it was under the hood and contacted some things that get really hot.
I stuck the pipe into the rusted opening of the valve then used some JB Kwik in very small amounts to position the pipe correctly so once it dried there were still very big openings around the pipe end that had to be filled and liquid epoxy alone wasnt going to cut it because it would just drip through the gaps. So i got some medium steel wool and tore some off and draped it around the openings, then applied the JB Weld.
All of a sudden i had a working control valve again. So JB Weld really saved me that time because the car had to go through inspection and it would never pass without that value working correctly.
I still have several tubes around of both the Weld and the Kwik versions.

Yes i see what you mean about the large surface area and the ability of silicone to cure. I think the air would have a hard time reaching the center of the mirror underneath. I guess i would apply it in smaller circles like the size of a US quarter or half dollar so the air can get to the edges of all the circles and thus the shorter distance from a circle circumference to the center of the circle should allow all the circles to cure as there will be little air passage ways between all the circular patches. I am glad you mention this. I can do it when i dont have to use the car for a few days, which is almost always. Well, that is if using silicone that is.

I found a replacement mirror glass for sale online with the plastic backing plate already attached. That's the way this is normally done. You get a new glass with plate and 'pop' the old one off and 'pop' the new one on, maybe 60 seconds and it's fixed. It isnt that expensive either, rather cheap really. The problem is it will take at least 2 months to get here! Not sure where it is coming from, but i dont want to wait that long.
Too bad too, the other side mirror assembly would get here in about 3 days but i dont need that side, and the two sides are drastically different in shape.

Oh i also use Locktite super glue almost exclusively when i need super glue. I got a new type from them just a few weeks ago. It was made for plastic and came in two parts, one is the activator and the other is the super glue itself. The activator is supposed to do something to the plastic to make the super glue stick better to plastic. The first package i got the activator was all dried up but i got a new package and tried it, but it's hard to determine if it is stronger than just regular Locktite super glue.

My test of the silicone came out pretty good though and i also tested some Gorilla glue the clear non foaming type (but not super glue). I've used this G Glue several times in the past and it works pretty good so i decided to test that with the silicone.
Well, the silicone was applied to the side of a monitor, which is plastic, in a blob and spread out into a uniform thickness about 1/8 inch thick with a piece of index card. The Gorilla glue was applied to the side as well, and one end of a 3.5 inch razor knife blade was placed on top of the glue, but only about 3/4 inch of the razor blade was glued not the whole length.
Now about 36 hours later, i can not peel off the silicone blob without tearing the silicone the only way to get it off now is to repeatedly tear little pieces off until it is all removed, but it sticks incredible well much better than i would have ever thought. Thus silicone moves up one or two notches on my glue list.
Also, the Gorilla glue holds the razor blade to the side very well also. I can lift the free end of the blade up about 3/4 inch and all the thing does is bend, the glue does not let go, but i will bend it up farther to see if the blade bends sharply or the glue lets go. I didnt expect that to work that well either.
It's too bad though i dont know what kind of plastic either the monitor or the plastic back plate is, so i will remove the plate soon and try the same test with the actual plastic plate.
It's been interesting for sure.

Thanks again for the ideas and suggestions.
 
Last edited:

Thread Starter

MrAl

Joined Jun 17, 2014
11,389
I too keep a good variety, one maybe not suitable for this topic, but one I discovered a few years ago and is apparently developed +80 years ago..
Namely Durhams Water Putty.
I use it primarily for wood and Gyproc projects, where you need to secure an anchor point in either for a fastener etc. Plus a few other applications.
Plus its cheap!!
  • Fill cracks, gaps, holes and voids in all surface types
  • Can be sanded, drilled, sawed and painted when dry
  • For long-lasting repairs indoors and out
Yeah maybe not for this project, but still interesting to hear about different types of glues. I have a bunch of different types for different things including wood. My favorite for wood considering cost also is Elmers external wood glue. It is similar to white glue but much stronger and water resistant. I've used it a lot for wood and paper that might be subject to higher moisture.

Thanks.
 

Thread Starter

MrAl

Joined Jun 17, 2014
11,389
Those are the standard questions when discussing adhesives.

Strong rigid adhesives holding two substrates is a bad idea if the two parts have different CLTE and the parts will be subjected to many thermal cycles of 10°C or more in their lifetime. Most plastics have a high CLTE vs glass.

Many plastic adhesives use "solvent welding" to swell the plastic of each substrate and cause entanglement of the chains from each part. Thst doesn't work with glass as one substrate.

Most 1-component silicones need humidity to cure. Thst means, with glass or tiles, only the edges cure and years from now, the adhesive in the middle can still be soft. It also means the volume of the adhesive is expanding as water is added (or the density is increasing as the water adds to the matrix). Caulk/sealant is different than adhesive - caulk has little shear strength or compressive strength. There is really no problem if it doesn't cure, and it is kind of an advantage not to cure as a house shifts or acrylic tub deforms when full.
Yes i worried about that too, using a glue that is too rigid might just crack and let go.
After talking to Yaakov in this thread i now realize that i would have to apply the silicone to the surface in small circles maybe 1 inch or so diameter in several places rather then smear it over the entire back. That will leave small air passages so all the circle blobs should cure. I can leave the car sit for 3 days easy.

I see now how you got into this with a much higher level of thought. Originally i was talking more casually but i see your information pin points some details that are good to address. Thanks a bunch for your ideas.
 
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