Need Help Silicone failure? Opinions needed!

[nolanola]

We are a sign shop located in New Orleans, LA.

A popular type of sign that we have been producing in the last few years is a painted aluminum cabinet sign with dimensional acrylic lettering. We attach the acrylic lettering to the face of the aluminum cabinet with double sided tape (3m VHB) and silicone. If the lettering is very fine, we leave off the VHB tape and only use silicone so the lettering is flush with the surface of the sign.

A sign installed a year ago where dimensional lettering was installed with only silicone has recently had the acrylic fall of the face of the sign despite using high quality silicone. The acrylic is cast, black, 1/4".

Has anyone else had this experience? Do you know why that may be happening?
What are recommendations on how to apply acrylic lettering to a sign panel and have it not fail?
Are studs our only option?

Any recommendations or shared experience is appreciated.

 

[Moze]

Silicone doesn't adhere well to acrylic/polycarbonate/plastics. Use Lexel (available from Lowes, not Home Depot) or stud-mount.

 

[TimToad]

We are a sign shop located in New Orleans, LA.

A popular type of sign that we have been producing in the last few years is a painted aluminum cabinet sign with dimensional acrylic lettering. We attach the acrylic lettering to the face of the aluminum cabinet with double sided tape (3m VHB) and silicone. If the lettering is very fine, we leave off the VHB tape and only use silicone so the lettering is flush with the surface of the sign.

A sign installed a year ago where dimensional lettering was installed with only silicone has recently had the acrylic fall of the face of the sign despite using high quality silicone. The acrylic is cast, black, 1/4".

Has anyone else had this experience? Do you know why that may be happening?
What are recommendations on how to apply acrylic lettering to a sign panel and have it not fail?
Are studs our only option?

Any recommendations or shared experience is appreciated.

It costs more, but we've been using LEXEL instead of silicone for several years for that type of installation and find it to be a superior product in many ways. Faster setting, more resilient, stronger bond, less mess because you can use a smaller bead and get the same adhesion strength.

 

[bannertime]

We had this happen with a project that was acrylic to black ACM. Was about 3 months before the GE Silicon II failed. It looked as if some of it hadn't cured yet. It was probably too thick of acrylic for the size. The letters have been perfectly fine. Just the logo fell. We brought it in, removed all the silicone, refinished the acrylic, and mounted with the one part Lexel. Let it sit over the weekend. It failed before the installer got back to the shop. Not sure what was up. Ended up mounting it with counter sunk screws and re-applied graphics. Been a year now.

Still not sure why the original silicone wouldn't cure. The rest of the sign has been trouble free. Not sure why the Lexel failed so fast either. At the shop, it didn't seem to budge. The customer wouldn't give us any more time to look into it so we had to go the physical fastener route. I believe we even tried some VHB and Killer Red tapes we had.

We've not had anything like that happen before or after that.

 

[Billct2]

another vote for lexel and you could lightly scuff the back of the lettrs and clean cabinet with alcohol

 

[nolanola]

Thank you all for the recommendation. Sadly, we have tried Lexel and had it fail on us several times on indoor and outdoor applications so we no longer use it.
Are there any other thoughts?

 

[bannertime]

Thank you all for the recommendation. Sadly, we have tried Lexel and had it fail on us several times on indoor and outdoor applications so we no longer use it.

Glad to know we aren't the only ones that have had Lexel failure.

 

[MikePro]

silicone has ZERO strength when pressed-flat.
vhb tape is a solid pairing because it holds the letter in place while the silicone cures AND allows for the silicone bead to be at least that thick.

for smaller letters, I take some vinyl backing paper and lay-out some strips of VHB, peel the liner to save some effort later, then cut the vhb into smaller 1/4" squares. place the tabs on the letter, drizzle on the silicone, and place on wall/panel.

 

[nolanola]

Mike--thank you for clarifying about silicone adhesion. It seems like that is our problem here.

Is there a product out there that would allow us to apply acrylic seamlessly / flush onto a panel?
What types of glue or products like liquid nails do you use at your shops?

 

[Moze]

Coming from someone who has had to remove a number of signs over the years that I have personally installed with Lexel, I would love to see a product that adheres as well in the situation being described.

The stuff does not let go. If it does, you did something wrong.

For those of you with failures, did you ONLY use Lexel? If so, did you allow it to cure for a week before moving stuff around, flexing panels, etc? Did you mount something perfectly flat to another substrate without an additional means of attachment (ie: VHB tape)?

If you want dimensional letters to be installed perfectly flat on a panel, stud-mount them.

Liquid Nails is a horrible option.

 

[Texas_Signmaker]

STUDS

 

[kcollinsdesign]

Mechanical fastening is the only thing that works. You can use glue (Lexel), but you need to drill holes into both surfaces so the glue can grab onto something. With non-porous surfaces, sanding is not enough. You can also attach pads to your acrylic using plastic cement or MEK, then attach the pads to your surface (little holes in the pads, holes in the surface - the glue squishes through the holes and grabs everything tightly when dry).

 

[bowtievega]

We have used silicone for attaching letters and panels to most substrates for as long as i can remember. I can't recall ever having a letter or panel fall off of a wall or sign after it has cured properly. Can they be physically removed by someone? Sure. I feel success is mostly due to proper substrate prep and application. You can get away with thinner beads (meaning squished flatter so there is less gap) if you are bonding similar materials, ie aluminum letter to aluminum face. When you have dissimilar materials like the OP stated with the acrylic letters to aluminum face thats where the different expansion and contraction rates of materials can bite you. Silicone doesn't grab well to smooth acrylic very well to begin with either, really needs a pretty aggressive scuffing to create enough tooth for the silicone to adhere. We typically will drill and tap letters to our cabinet faces to eliminate this issue all together and to ease assembly. We bond panels all the time with silicone, alot more surface area for adhesive compared to backs of letters. Silicone also requires some pretty clean and dust free surfaces to adhere properly. Paint overspray on the backs of letters can be an issue, a quick scuff and a wipe down with solvent (be careful with alcohol on acrylics) can make a huge difference as well.

 

[TimToad]

These are very common sign types for us and we have been using a combination of LEXEL and VHB on the raised letters for years and years and have never to my knowledge had a failure that I am aware of.

To be totally clear, we use mechanical fasteners WHENEVER possible to be 100% certain of our process.

As MikePRO and several others have affirmed, the trick is to not press the letter into the surface so hard that your adhesive film thickness narrows to nearly nothing.