Fastening Rigid Foam: Glue vs. Fasteners
I’ll be installing 2 inch Thermax to the inside of my poured concrete foundation. I don’t yet own a hammer drill, but I’m looking for advise on the best way to attach this material to the wall. I’ve read about glue only, plastic fasteners, metal fasteners, and strapping. Which are the easiest to install and will last the life of the house?
GBA Detail Library
A collection of one thousand construction details organized by climate and house part
Glue is the easiest to install. I used glue to hold 2-inch rigid foam to the concrete walls of a crawl space 30 years ago, and the glue is still holding well.
If you are worried about longevity, I suppose that either plastic fasteners or furring strips and Tapcons might help you sleep at night.
Hilti IDP fasteners are white and blend in with Thermax WF (white finish): https://www.hilti.com/anchor-systems/insulation-anchors/r217
Take a look at the Ramset T3IF system
Ramset had a “demo” tool that they allowed me to use when I bought the fasteners.
This tool made for a fast and neat job on my Thermax.
We used a foam gun and the appropriate glue (some glues dissolve the foam). You wouldn't be able to use cap nails in cement, and I would think that tap con or other screws is considerable overkill and a lot of extra trouble. We waited a short time for glue to be starting to dry, making it tacky enough to hold the foam sheet up without much effort. You can figure ways to support the sheets while drying if needed, but that seemed to us unnecessary. 5 years later not one has dropped off the wall.
Seems like tape could be used at the edges to hold the foam up while glue dries.
I will be using these for my rigid foam installation.
I should be installing the insulation this week so I can let you know how it goes.
I have easy access to regular great stuff gap and crack. Should I special order a special adhesive like enerfoam?
David Meyer.........How did it go using those Rodenhouse fasteners. Better yet do you have any left over from your project that you would like to sell for a modest price?
They certainly have the market cornered by making you purchase 250 of them! I would be looking at needing 50-60.
Let me know and we can exchange contact info
I'd like to report that I had good luck using the Dow Enerfoam. I misted the board and the wall with water to increase the stickiness and the rate of cure. I just ran a bead around the perimeter on the side of the board facing the concrete wall. Between sheets of Thermax I used regular large gap Great Stuff to fill the gap to prevent any loss in R-value at the seams. The boards are stuck on very firm and do not budge. I used a few 2x4's to hold the Thermax in place while the foam cured. It was set within 10-30 minutes.