stringy wrote:
What does AP stand for on your test samples? Is it alcohol prep?
Sorry I neglected to explain "AP". It stands for Adhesion Promotor. It's a primer that is supposedly good on plastics. This is the product I used:
This particular product requires immediate application of the next product, as it is essentially a tack coat. I don't know if it works better than other primers, but apparently it's commonly used with plastics. Krylon makes a similar product but I'm told it is not flexible so I chose the DupliColor.
In my use, the ultimate goal was to apply a hydrophilic coating. This required a base (primer coat) and I used the AP to help stick the conventional primer. So it was a 3 coat process. In your case it might be interesting to pre-test whether or not to use a primer or go directly from flame treatment to adhesive. Using an intermediate coating may provide two ways for the bond to fail (surface to primer or primer to adhesive. Your application requires a better bond than just paint!
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watched a few of the clips you linked to and flame treatment looks to be another essential step in prepping PE. I’ll definitely be doing it. It’s not mentioned in 3M’s guides so thanks for the heads up!
Sorry the intended videos didn't show up. There are a variety of philosophies (and wives tales) about how to go about bonding to PE, as you've probably seen. I've done two hulls now and applying the hottest part of the flame to the surface while moving your propane torch quickly seems to work well. For a larger job I used a weed burner (bigger flame).
Regarding the alcohol prep, I pre-clean and then use isopropyl 70% (= 30% water) right out of the bottle. I chose that over 91% and denatured because it was easiest to reach on the shelf. I don't think it makes any difference other than cost and how fast it evaporates. It's just a solvent that leaves no residue.
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intend to prep as follows, being very careful to avoid contamination.
1-Clean area thoroughly using 50/50 mix water/Isopropyl alcohol, wiping in one direction only as recommended by 3M and dry thoroughly.
2- Flame treatment
3- Apply Primer 94 and let dry thoroughly.
4-Apply VHB taped skegs with uniform pressure ensuring no air bubbles.
5- Leave for 72 hours before on water testing
I am undecided about scuffing which is recommended for some surfaces but not for PE according to 3M’s guide.
I used a scuff pad between primer and top coats -- don't know if it matters in your case. I had previously sanded one hull with 900 grit sandpaper but not the other. They both bonded well.
I'm excited to see how your project turns out. Finding alternative ways to bond to PE for different purposes is great to know!