I tried the archives but didn’t find the info I was looking for. I wanted to know, for epoxy, how much difference there is between chem and mech bonding? And how much time you can wait, say, between laminating and hot coat, or between lamination and lamination. I remember someone somewhere said something (this is what happens when you spend too much time on Sways) about the conditions for chemical cross linking to be so complicated that I thought “Why even worry about it?”
Anyone, engineers and scientists, want to give an artist some guidelines?
ChemE, 15 years building boats and countless hours logged in seminars around Epoxy here.
The short of it for surfboards - doesn’t matter, either way you are golden.
The long of it - Depending on the epoxy used, media materials, bonding materials, environments after bond do you get swings in the sheer, impact, force and other forms of “breakage”. Typically in harsh environments (aviation, marine, submarine and space) chemical is preferred or a combination of the two if a mechanical bond can be added through a fastener. When is comes to lamination you have less of an opportunity for a point of failure in a chemical bond rather than a mechanical. This is due to 3rd party oils (human skin), airborne material (dust biological and non-biological) and gassing from curing lamination. These can weaken a bond, will a surfer expose this bond? Probably not, unless the flaw is enormous. Epoxy does cure in 24 hours but it can gas out for up to a week (usually after 48 hours it is stabile). Since the board is not going through extreme temperature, vibration and shock it will be fine. Bad bond on a 120mph boat or 50,000 ft airplane you are looking at a different story. It is a surfboard at the end of the day.
Chemical (hot coating) will save you time and works well unless you are really stacking materials. In surfboard construction you “should” never be in place where you can stack too much material.
Mechanical (sanding) is exposing you to more harmful stuff and takes a lot of time. I would try to avoid as much as possible.
When in doubt that you passed a window for a chemical bond let it cure and sand away. Remember that Epoxy does form a film on the outside after cure that has to be sanded and cleaned off before anything will adhere to it well.
Great question!!! I am sure someone else will feel differently than me but hey that is just life.
Great answer. So if I laminate and then have to wait a few days before doing another lam I should try to key up the surface a bit? And the strength will be for all practical purposes the same as if I did the second lam after a few hours?
That’s what I do with epoxy… a clean sheet of 80 grit on a soft block, scratching diagonally across the axis of the weave at a 45, from both directions… nose to tail one way, and tail to nose the other. I don’t call it “sanding,” so people don’t get the wrong idea. I call it “scuffing” or “scratching,” because the idea is not to remove material. Just add texture for a better physical bond. I’ve been doing that for almost 10 years with no bonding issues, and I’ve occasionally had to wait several days between laminations and hotcoats.
Keep in mind that if you use Resin Research’s Additive F, it is a surfacing agent. But if you limit it to 1cc per oz of hardener, which is the manufacturer’s recommendation for laminations, you won’t have any bonding issues like you might have with poly if you were to lam with sanding resin.
As nj surfer pointed out - the more course the sand paper the less pressure. He put it 100x better than me.
You are just creating a tooth for the bond to take place. Hand sanding always works out better than random orbital, most tend to cut into the fiberglass with a machine. I am not saying that sometimes a machine is not needed, but between lams that have no flaws just scuff it. Just make sure to avoid human skin oils (touching with hand before epoxy or paint) that can cause fish eyes and lessen the bond. To avoid human oil gloves and/or wipe with denatured alcohol/wash with water/acetone - I always reccomend denatured alcohol, it evaborates fast without leaving residue.
If the general population on Swaylock's saw how much bare hands work I do you guys would all just roll over and flip out! All wet resin gets handled with gloves. I wash my hands often. Try to never touch your face when working in the shop or Lab. My training says that a wipe down with Denatured Alcohol will just thin out and spread around the dirt aka contamination. I agree with Arag44 and NJ 98% of the time......
Proper planning Jeff. You can lam and hot coat a board in less than 24 hours. It's May. Temp is not an issue right now.
I use glass cleaner (like Windex) as a de-greaser (hand oil etc. remover). Spray, wipe down, wipe off. Then I use a damp paper towel or fine-weave soft cloth (wetted with water) to wipe the glass cleaner residue off the resin surface. Seems to work fine for me.
Scuffing with sandpaper increases the available surface area for bonding (many small grooves with peaks, valleys and wall faces), improving adhesion.
Never had an issue with epoxy hot coats bonding to an epoxy lamination when Add F was used. When I didn’t sometimes the epoxy hot coat would peel, and if it is going to peel you’ll find out for sure when sanding the board. Ways around this issue include scrubbing with 3M white commercial scouring pad or sanding the lam with 220 grit and a soft pad. Wiping the lam with denatured alcohol avoids peeling hot epoxy coats too apparently.
Also polyurethane chemically bonds to epoxy, though I don’t know if this includes PU foam. If it doesn’t then it’s a mechanical bond as epoxy on PU works just fine. This leaves polyurethane sprays (finish spray) if you’re that way inclined, which chemically bonds to epoxy. Or if you spray an “epoxy board” (can’t believe I just said that) with one of those polyurethane varnishes in a can, you certainly need to fine sand the board to get it off again.
As for chemical crosslinking in the epoxy as it cures? If you’re building the next space shuttle it would probably be worth worrying about.
I am not a Chemist. I am not an Engineer....I flunked on spelling... As stated... it is a surfboard not a super sonic flying object. My goal to Lam and hot coat in less than 24 hours is to forget about contamination...less steps less stress....fewer problems. My glassing methods were not invented by Stingray. I follow the rules set down by the guy that makes Resin Research Epoxy Resin....I use 1/2 cap full of add F for 15 oz of mixed resin. temp matters
No solvents...never...even if you need to sand between layers...no solvents.....Ray
Stingray no like solvents, I snuggle with solvents at night. each his own. Stingray makes better surfboards than I do but I can touch my tounge to my nose.