Trouble with Bonding Foam to Plywood

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briangb

Seneca Junction
#1
I'm bonding foam to plywood using Liquid Nails for Projects. I'm using a blob of Liquid Nails about an inch in diameter every 8 inches or so and using moderate weight on top of the foam for 2-3 days. The problem is that after about a week or so the foam de-bonds from the Liquid Nails. Tips and tricks on how to overcome this would be most welcome. How do you go about bonding foam to plywood? Am I using enough adhesive?
 

D&J RailRoad

Professor of HO
#2
Is the liquid nail spot of glue still wet when ya pull the foam off of it. Is the glue covered with the foam, in other words, is the foam pulling a patch out of the foam board?
 

Motley

Active Member
#3
What kind of foam? Is it the builders blue/pink extruded foam? Or is it the white beaded type foam?

I use the pink exctruded builders foam, with the regular latex caulk. Maybe its your liquid nails?

Also, did you remember to peal off the protective sheet from the foam? Just asking, because I didn't know about it, until my first layer and the foam came unglued because of that plastic peel.
 

briangb

Seneca Junction
#4
The Liquid Nails is a little pliable after the foam comes off, and the foam comes off nearly clean from the adhesive. I'm using pink extruded foam. Protective sheet?!?! Wow! This is news. I've never read anything about it in any article about using foam!! Is it on both sides? I'll certainly look for it; that may be the key. I've already painted the top side (primer and color paint) and that seems to be sticking quite well.
 
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Motley

Active Member
#6
The Liquid Nails is a little pliable after the foam comes off, and the foam comes off nearly clean from the adhesive. I'm using pink extruded foam. Protective sheet?!?! Wow! This is news. I've never read anything about it in any article about using foam!! Is it on both sides? I'll certainly look for it; that may be the key. I've already painted the top side (primer and color paint) and that seems to be sticking quite well.
Ahhhh thats must be it. Yes I know, I had no clue about the protective sheet. Its very thin, and unless you get a knife or something to break it loose, you will never notice it.

Its on both sides also.
 
#7
Something to consider with Liquid Nails and other similar adhesives. Many require you to press the foam firmly in contact with the surface being bonded to, then pull the foam away for a set amount of time before pressing the foam firmly in place for the final time. Be sure to read and follow all directions thoroughly for good results.
 
#8
The plastic film on the foam serves as a vapor barrier when the foam is used as house insulation -- its intended purpose. But glue does not adhere well to the film.

To remove the film, I usually start at a corner, using a hobby knife or my fingernail to begin separating the film from the foam. Once you get it started, you can sometimes pull off the film in one big piece.

- Jeff
 

RCH

Been Nothin' Since Frisco
#9
You might try Loctite PL300 Foam Board Adhesive. I used that on my Free-mo module a few years ago and have had no ill effects with the strength of foam-to-foam or foam-to-plywood bonds.

Since 2" thick foam is not available in my area, I had to laminate two sheets of foam to get the desired thickness. I spread the adhesive with a putty knife and then laid a large and very heavy speaker cabinet down on the two sheets for a couple days. I used the same technique to get the laminated foam sheet to adhere to the plywood frame.

I would caution you against laying track/roadbed on the foam surface. It does degas over time and will shrink regardless of whether you paint/cover both sides or just one. This will cause the track to come out of alignment, particularly on curves. I'm at a point now where I will have to remove and replace the module endplates to get them perpendicular to the track. Either that or rip up and replace the track.
 

briangb

Seneca Junction
#10
I looked, and scraped with a knife, and tried my fingernail but couldn't find a plastic film. Then I called Dow Corning and spoke with their insulation tech rep. Turns out their pink styrofoam sheets are marketed in two versions -- with and without a plastic film. The with version is highly shiny, the without is dull, and the rep said that you will know if you have the with version. It looks like I have the without version. I was told by the rep that the with version does not need to be stripped before being bonded to another surface. My piece of foam is somewhat bowed, so I'm going to try CaptSuperCow's suggestion of cutting part way through the piece, and I'm going to use A LOT of adhesive. I'll be away for a couple of weeks, but I'll let y'all know what happens. Thanks for your help!
 
#11
I too used very inexpensive white caulking. I think it was about $1.50 per tube. I put that on my benchwork in long 1/4 beads. Then I let it sit with some weights holding everything in place (5 - 25 pound weight lifting plates). I ended up needing to take the layout apart because we were moving... I needed to saw between the wood and foam in order to get it apart. Where I couldn't reach with the hand saw, I needed to pry and in some cases break the foam. Sometimes parts of the foam stayed stuck to the wood, other times the foam and caulk pulled splinters of wood.

You can get fancy with special foam glue, but the white caulk worked for me.

Doug
 
#12
Try using The BULLDOG adheasive brand. I have used it to bold the same styrofoam to a sheet of playwood and it works like peanut butter in a blanket! Not sure if that liquid nails stuff really adds up to its name.
The only thing is when you use the "BULLDOG" stuff, make sure you spread it around either surface - foam or wood and then scatter weights (I use several 2 - 5 gal buckets of water) to press both surfaces together.
Hope this helps!
 

fcwilt

Active Member
#13
Read the label on any adhesive. It should tell you if it is rated for foam-to-wood.

Also check if it is rated for foam-to-foam - that is a different case.

Normal LiguidNails adhesive will dissolve foam - not good - don't ask me how I know.
 

gregc

Apprentice Modeler
#15
i use wood glue (titebond).

i use it to glue 1" white foam to 1/4" luan plywood as a base (i use up an 8 oz bottle and then some for a 2'x8' piece). You must clamp or weight the pieces down to hold them in place.

i use it to glue homasote to the foam.

i've also used it on curved surfaces (RC airplane wings) by letting it dry for 30 mins, heating it and then attaching and holding the materials in place until the glue cools (quickly).
 





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