Need Help Need help please.Best adhesive for mounting acrylic backer to routed ACM panel for exterior lit sign

[BrianH311]

Hello everyone,

We have had a failure with this sign. The acrylic white backer separated from the DiBond panels in areas. We used tape (not VHB) and silicone adhesive to mount the acrylic to back of ACM panels.

The two acrylic panels per side were 4’x4’ for top panel logo and 2’ x 7’ for bottom text. Overall sign was 8’ tall x 9’ wide.

Since we can’t use a stud welder with the DiBond and secure with nuts and fender washers, what would be the best way to bond these dissimilar materials together for outdoor longevity?

I would be so thankful for any help with this problem.

Thank you!
Brian H

 

[Hero Signs]

Lord adhesive, welding make great 2 part expoys.

 

[BrianH311]

Lord adhesive, welding make great 2 part expoys.

Thank you! Will get hold of some.


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[astro8]

You need way, way more vhb and way, way more silicon under that acrylic. Just putting around the edge won't hold it. Use 1mm vhb and large dobs of silicon so it spreads out under the acrylic.
I'd split that bottom acrylic panel into 2 or 3 pieces as well.
Run a continuos bead of silicon around all the edges.

 

[BrianH311]

You need way, way more vhb and way, way more silicon under that acrylic. Just putting around the edge won't hold it. Use 1mm vhb and large dobs of silicon so it spreads out under the acrylic.
I'd split that bottom acrylic panel into 2 or 3 pieces as well.
Run a continuos bead of silicon around all the edges.

Thank you!

I had the middle piece of the “O” fall off sign. Along with other areas separated as well. I noticed all the silicone was stuck great to back of DiBond, no trace of it on the acrylic backer though. Great idea about making smaller panels for backer. Will do that, hopefully take a lot of weight off as well.

We will definitely use VHB and a lot of it next time. We used Iron Grip Silicone from GE. I don’t want to use that again with failure had.

What silicone do you use? Or two part epoxy? Worried about expansion of materials.

Thanks again!


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[astro8]

Sikaflex. Acrylic has roughly 2.5 -3 times the expansion of the acm so you need an adhesive with a lot of give, like the vhb with the sikaflex combo. Sikaflex is polyurethane based...seems to be the best we have used so far. Breaking down your acrylic panels into smaller pieces really helps with the expansion issue.

We use a lot of two part epoxy on rigid jobs, not jobs like these where thermal expansion will be a problem.

 

[BrianH311]

Sikaflex. Acrylic has roughly 2.5 -3 times the expansion of the acm so you need an adhesive with a lot of give, like the vhb with the sikaflex combo. Sikaflex is polyurethane based...seems to be the best we have used so far. Breaking down your acrylic panels into smaller pieces really helps with the expansion issue.

We use a lot of two part epoxy on rigid jobs, not jobs like these where thermal expansion will be a problem.

Great info! I was worried about epoxy, due to expansion, but also can’t have another failure like this. Will see where we can get Sikaflex here in the states. Thank you so much!


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[ams]

Unless I am reading this wrong, shouldn't that sign have a retainer?

 

[BrianH311]

Unless I am reading this wrong, shouldn't that sign have a retainer?

Usually, yes. This is an extremely old sign that had flush mount .080 aluminum faces.

Being such a large sign, we are having to use two separate panels per side. If it were a smaller one panel sign we could have added retainer and slid in single face.


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[BrianH311]

We usually use 3m clear vhb and ge 100% silicone, or lords/ASI industrial adhesive. Also, try to rough up both sides of the material that you are adhearing together, it gives the adhesive something more to cling to.

Funny story, I'm right there with you on popping studs to dibond being impossible, but last year we took down an old church sign that my father and grandfather had put together about 20 years ago, and it had studs popped to the dibond and through the acrylic. I was stunned. Now don't get me wrong, most of the studs had failed at the surface of the dibond, and you could tell on multiple occasions someone had gone to site with the trusty roll of vhb tape. If I remember correctly the alum on the dibond was about .020 thick.

Also, I'm glad to see I'm not the only one worried about work on a Sunday!

Good morning,

Thanks for reply! Great idea about roughing up both surfaces. Will do that for sure. It’s crazy how well the silicone stuck to DiBond, but no trace of it on acrylic.

You are correct about .020 aluminum face of DiBond. Good story too My dad was a sign-painter for many years and just recently retired. I love the trade. Always learning.

I will use a real good VHB tape as well along with adhesive. I found a Ge 100% silicone for “plastic sheets”. (In a red tube) Is that the one? If it will bite good onto DiBond as well, that could be a great match.

I’ve got some real good advice on the thread. Going to try the Sikaflex with VHB as well.

And yes, signs, signs & signs. Even on Sunday. Ha! Just hoping to get a real solid solution for these type of projects.

Hope you have a great rest of the day, and I sure do appreciate your help!


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[BrianH311]

NOT the stuff in the red tube! The gold/blue tube is the way to go.

Note the lifetime guarantee on shrinking and cracking, as well as the list of exterior uses (window, trim, flashing)
The red tube says something similar, but we had much better luck once we switched to the gold/blue line exclusively. The red tube also has stuff like sink & bath as uses, which may mean something along the lines of uv resistance have been added to the blue product. Honestly though, I have no clue what the difference is in the two other than labeling. Both are 100% Silicone...

Thanks for responding with pics too! Have a great week.


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[ams]

Usually, yes. This is an extremely old sign that had flush mount .080 aluminum faces.

Being such a large sign, we are having to use two separate panels per side. If it were a smaller one panel sign we could have added retainer and slid in single face.


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A retainer can still be added to this sign. I am confused as to why there are two pieces of polycarbonate glued together.

 

[BrianH311]

A retainer can still be added to this sign. I am confused as to why there are two pieces of polycarbonate glued together.

True. Hope to add retainer soon. Will post updated pics when finished.

We are using 3/16” white acrylic for backer on each panel. The other white is the back of DiBond face.


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[Nuagedesigns]

we have had better luck with Lexel Silicone than GE

 

[bowtievega]

Definitely need to sand the surface of the acrylic for most adhesives to stick well and clean thoroughly. The RP-25 vhb is what we have been using, is general purpose adhesive and is much less expensive and allows you to not feel like you need to skimp with the expensive tape lol
I believe the blue label GE silicone is the silicone II. Neutral cure silicone, doesn’t have the ascetic acid so it smells different, works on masonry substrates.