Need Help I Need A Plan B For My Failed Installation Of Foam Letters

calbanner · Feb 28, 2017

Hello Fellow signmakers,
Although I have been making and installing signs for 31 years, I am still learning and need
your suggestions for a better installation for these foam letters with plexiglas face.

I previously had made this type of letters before and they lasted 10 years plus.

This logo is falling off after 8 months.
Letters are 2 inch thick dense foam (not bead)
Foam was painted with Glidden brand primer (Gripper) front and back.
1/8 inch acrylic glued to foam with Dow Corning 732 clear silicone adhesive.
Wall was painted with exterior Behr paint from Home Depot. Paint is sticking well to wall.
Logo and letters glued to wall with Dow Corning 732 clear silicone adhesive and some 3M VHB Tape.
The section that fell off did not break.
The wall had no silicone residue and had a couple of sections of VHB Tape still hanging on.
The silicone removed pretty easily from the back of the foam logo.

So it appears my adhesive is not working well in this situation, although i have been
successful with the mounting method previously.

My thoughts for a Plan B remount of logo is:
Remove all silicone adhesive from both surfaces and wipe clean.
Paint back of foam and wall where logo goes using one shot enamel paint.
Add 4-5 plastic anchors into wall per section and leave a 1-1/2 screw sticking
out with the head cut off.
Slam logo over the screws sticking out and adhear again with adhesive. (not sure which though)

BIG EASY DOES IT · Feb 28, 2017

Sounds like wrong silicone. Dow Corning 732 is more of a sealent then an adhesive. It has adhesive properties but it's more for seal in place gaskets and sealing industrial equipment. Not for holding plexiglass on the side of a building. I would go with liquidnails Construction Adhesive. Either Extreme Heavy Duty or FUSEit. Personally haven't tried the FUSEit on anything yet but the Extreme Heavy Duty does the trick. Stick it and it's never coming down.

ChaseO · Feb 28, 2017

I would also agree wrong silicone, but with the weight of those letters, I would feel better if it had a stud or two going through the wall for the sheer weight.

solock · Feb 28, 2017

I would offer up lexel,its a silicone with a solvent that adds some real bite, its crystal clear and is available at Lowes everywhere. Works well even in the cold. Its my goto for unknown bonding circumstances.

signbrad · Feb 28, 2017

Dissimilar surfaces usually call for a soft adhesive, like silicone, rather than one that dries hard. This allows for movement.
Many paints for exterior walls contain additives that repel dirt and moisture, allowing the film stay cleaner and last longer. The same chemicals that prevent dirt from adhering may interfere with the adhesion of glue.

The only real failsafe method, in my opinion, for mounting exterior letters to a wall is a stud mount, especially if the letters are of any size. The shearweight of the letter can be carried indefinitely by the studs, leaving the adhesive to simply hold the letter snug to the wall.

Brad in Kansas City

Sign Works · Feb 28, 2017

I have always used GE Silicone II, never a problem except when it comes to removing the letters. I have used it many times along with Home Depots Behr Premium Plus Exterior Paints, got jobs out there using these two products going on 15-20 years and nothing has fallen down.

Marlene · Mar 1, 2017

it looks like all your tape and silicone is sticking OK to the logo but not the wall. it might be the wall finish isn't all the receptive to anything that sticks to it. they are adding stuff to paint to keep it dirt free and that also means it isn't as receptive as it used to be. for something that size and being an exterior sign, I would never use tape and silicone, I'd stud mount it.

GaSouthpaw · Mar 1, 2017

+1 on the stud method. I'm always leery of putting letters up on exterior walls using only adhesives.

ddarlak · Mar 1, 2017

I'm gonna go with bad/old silicone.

I have used clear silicon as adhesive for close to 30 years and only one time did this happen to me, it was a bad batch of silicone. I had "glued together" about a hundred coro real estate signs back to back and I had about 20-25 fail, looked just like your silicone failure. This was the only time I have ever had clear silicon fail. I have used different brands of clear silicon, as long as it's clear, it works...

Johnny Best · Mar 1, 2017

I am in agreement with everyone, Lexel, better 3M (4941) VHB, some studs if possible and good luck sleeping and not thinking of it falling off again

calbanner · Mar 1, 2017

BIG EASY DOES IT said:
Sounds like wrong silicone. Dow Corning 732 is more of a sealent then an adhesive. It has adhesive properties but it's more for seal in place gaskets and sealing industrial equipment. Not for holding plexiglass on the side of a building. I would go with liquidnails Construction Adhesive. Either Extreme Heavy Duty or FUSEit. Personally haven't tried the FUSEit on anything yet but the Extreme Heavy Duty does the trick. Stick it and it's never coming down.