I went to the Liquid Nails for Projects and Foamboard website to peruse the tech data on the product to try and figure out how long, when glueing foam to foam, until it is dry and safe to remove the weights I have in place on it. I found this information"
Extrudability: Good
Shear Strength: 24 hours – 300 psi
48 hours – 350 psi
28 days – 400 psi
R.T. Static Load in Shear:
10 lbs. No failure in 72 hours.
Tensile Strength:
24 hours – 60 psi avg.
7 days – 75 psi avg.
but I have no idea what extrudability, or static load in shear or tensile strength mean as far as drying time, if any.
Any one here know?
Jarrell
For removing weights, the only real data of interest is the tensile strength. In 24 hours the stuff will resist 60 pounts of pull-apart force for every square inch of properly adhered adhesive. You can certainly remove the weights after 24 hours, and probably quite a bit sooner, though the data you listed doesn’t indicate tensile strength at earlier periods.
I’m not sure what “extrudabliity” actually infers either. But it looks like that shear strength doesn’t improve all that much after 48 hours. (Jarrell, I believe that “shear strength” would be the amount of force needed to shear an object off the surface - either vertically or horizonally - from which it is adhered to, either by pulling or pushing it.)
Unless you and your dear wife plan on dancing on top of your layout (in bare feet, mind you), I would think you should be fine to work on your layout. Do you have any spare or scrap pieces of EF(extrude foam) as a control? Granted it’s a larger surface area but that would be the quickest and easiest way to keep tabs on how well the Liquid Nails is curing.
I used some of the Projects glue and had the foam down for a year or so. I then had to go back and do some modifications to the area as I was changing the track layout.
I needed to remove some sections of the foam and decided to try and use a putty knife to slide in between layers of the foam. Figuring that I would destroy most of the foam doing this, I was surprised that it just popped off the layer below.
I could then just peal off the glue that had held the top sheet on. And it did not affect either piece of foam. Now I have to admit that I did not put the glue down in a solid film but just made beads around the area and then took the top sheet and smoosched it down onto the glue beads.
It was good that the foam layer came off so easily and I was able to reuse the foam! But what I worry about is what is going to happen years down the road. Is the glue going to just reales and all of the foam layers come loose?
Tensile strength measures the force required to pull something such as rope, wire, or a structural beam to the point where it breaks."
In structural engineering shear strength is a term used to describe the strength against the type of structural failure where a component fails by shearing when it splits into two parts that slide past each other.
Thanks fellas for the answers. Tom, it’s been a while since my wife and I, or me and anybody for that matter, did the boogaloo anywhere…
Bob, I know what you mean. Sometimes, especially along an edge where the foam doesn’t seem to adhere well enough to suit me, I’ll take a long screw and get an oversized washer, cut out a little round piece of the foam, use the screw and washer to ‘snug’ the edge of the foam down, then glue the little piece back in place over the screw and washer. I try to be careful to NOT do this in an area I may have to do drilling later.
Jarrell
The shear and tensile strength numbers only apply only when used as specified on the data sheet. If you are using less adhesive it will be weaker. The fact that they are testing with only 10 lbs in static shear should tell you that this stuff is not all that good for structural connections. That means that if you put more than 10 lbs of load on a glue joint it may fail at anytime.
Yes, Lee I think they recommend using a 1/4 inch bead spaced 12 inches apart. I guess for the model railroaders use, where we’re placing more weight on the foam and trying to be careful not to bump it sideways in a shearing action, or lifting on it in a separating motion, it does ok for our purposes.
Jarrell
I used Elmers wood glue to glue down all of my foam on our layout. It seemed to hold, almost TOO good! The problem I had was when I went to cut out the large section for the river I was going to make, the foam didn’t “pop” loose like you guys had reported, it was down so firm I had to chisel the foam off the OSB board. I think I’ll use the Liquid Nails stuff on our new layout.
Not entirely correct. The “psi” means pounds per square inch. If you have two square inches of glue, you’re joint will be able to resist twice the values listed. Half a square inch of glue - half the value listed. So if you have 100 square inches of adhesive, you’ll be able to resist 1000 pounds of static shear in theory. In reality the number will be less, because the elasticity of the materials means that the loading at the glue joint wll not be entirely uniform - some areas will see lower forces than others, because of the movement between the two surfaces will mean greater shear forces at some locations than at others. The elasticity of the adhesive may more than offset this, however… it does get a little complicated.
But basically you can figure how much hold you’ve got by multiplying the allowable loading by the number of square inches of adhesive contact between the two parts.
Actually, gentlemen, “extrudability” is the ease with which it can be forced (squirted) out of the tube, and “extendability” is the extent to which it can be spread thin and still retain its intended properties.
Extrudibility is another term for ductility, or the amount that a material will stretch under tensile stress. Ductile materials (rubber, chewing gum,etc.) undergo a reduction in cross sectional area as they stretch in order to maintain a constant volume. When the material finally does break, the area of that break is far less than the area of the unstressed material. The percentage of this area reduction is usually the the value given for the extrudebility or ductility of the material. Brittle, or non-ductile materials, such as glass or concrete, break apart with no reduction in area.
Incidentally, the area reduction requires an expenditure of energy to accomplish. This energy absorption is what enables crush zones to absorb crash impacts. They are made from ductile materials.
Don’t you just love it when engineers start talkin’ shop? [:)] Actually, I do. I enjoy learning about stuff like this. It’s the remember part I have problems with. [:(]
Tom’s idea of using a couple of small scrap pieces is an excellent one which I use constantly on many non-railroading projects. To me it’s the best test of when an adhesive sets up and how the curing process is going.
One thing to keep in mind when talking about tensile strength of an adhesive, especially when you use it to attach two pieces of foam together. If you glued two pieces of foam together with the Liquid Nails, and after 24 hours applied a tensile force, the foam would most likely fail before the glue joint.
Most of the forces involved on a layout with respect to the adhesive used to join two pieces of foam are compression (the weight of the stuff above the foam countered by the benchwork pushing up). There should be very little shear stresses on the adhesive and probably zero tensile stresses.
This goes out the window if the foam is flexed, whereby the adhesive would be seeing all three. Of course if the foam is flexing to the point where the adhesive joint is compromised, I would think there would be bigger problems to worry about. [:D][:D]