Need Help With Painting Plastic Plugs

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PostPosted: Fri Dec 18, 2015 5:50 pm
Hi All,

I am hoping to get some knowledge from the community here. I am trying to paint plastic plugs (3/4" round head plastic hole plugs). I am having trouble with the edges of the plug chipping.

Here is my current process:

Sand head of plug quickly/lightly with 1000 grit
Wash with dish soap and dry
Wipe with 70% IPA
Spray 2 light coats of Adhesion Promoter
Spray Acrylic Basecoat (4-5 light to medium coats)
Spray 2 wet coats of acrylic clear

I don't know if I just need to be more intentional about sanding the edges or making sure adhesion promoter get's on there but the paint is just not sticking.

Any advice?

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PostPosted: Fri Dec 18, 2015 11:17 pm
Just a few problems that I see there... 1000 grit is too fine, drop down to 400 to 600 grit. Plastics like that need more "profile" for the paint to grip on to.... I'm assuming the IPA is isopropyl alcohol?.... too strong... try max. 50/50 with water.... and last but not least... are we talking acrylic lacquer here? Spraying lacquer too wet on a plastic like this will have "shrink back" from the edges which means thin edges. Also try to do only 2 to 3 coats max. If it is lacquer, try a lighter "dry" coat first, ample dry time, then a couple of wet coats. We do various size plastic plugs, knockouts, etc., on commercial furniture and there is a little bit of technique involved in getting the coatings to adhere properly. Oh, and keep the AP to one light coat....
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PostPosted: Sat Dec 19, 2015 1:07 am
Ok, thanks for the tips.

The reason for 1000 grit is my AP says to prep with 1000 grit or finer sandpaper on the instructions but will try more course next time..

Yes, I was talking about isopropyl alcohol - will try the 50/50 mix.

Yes the paint is acrylic lacquer.


I appreciate the feedback. The center has great adhesion. You can't get it to flake off but around the edge it is not sticking to the plastic like the middle.

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PostPosted: Sat Dec 19, 2015 10:03 am
Yeah, a lot of AP stuff says that about 1000 grit but I think that's more from them not wanting calls from sand scratch problems on their 800 numbers. Yep, lacquer will "crawl" back from edges as it shrinks on a lot of plastics. You should see some improvement with dong the few things I've mentioned. If you don't I'd consider going to polyurethane with these....
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PostPosted: Mon Dec 21, 2015 8:11 pm
Thanks again for your advice Darrel. I have to correct one item I said - it's actually Acrylic Enamel that I'm using not laquor. I don't know if that changes any of your advice but I gave it a try and we'll see how they hold up this time!

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PostPosted: Mon Dec 21, 2015 11:38 pm
Enamels can be somewhat harder to bond to plastics but most of the same advice I gave you should help with them, too. Let us know if it improves the bond.
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PostPosted: Tue Jan 05, 2016 4:32 pm
Darrel - Thanks for your help! These tips significantly improved the durability of the painting!

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PostPosted: Tue Jan 05, 2016 4:53 pm
Glad to hear it.... plastic is some strange stuff sometimes, a little tweeking with prep. can make a big difference.
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PostPosted: Tue Feb 16, 2016 2:29 pm
Hi Darrel,

This method is still working great. I am wondering if you have any suggestions for a faster way to sand the rounded head plugs?

This might sound crazy but I am currently sanding them with a sheet of sandpaper on a towel (to help contour). I am doing each plug individually to make sure that I get the entire surface well scuffed.

Now that I am adding more volume this isn't sustainable. Any suggestions?

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PostPosted: Tue Feb 16, 2016 3:16 pm
Well, if they've got a rounded profile to them it's going to be tough to adapt any type of machine method to sanding them. Even most stationary sanding machines will generate too much heat and melt your plug. You might be able to take a mold off a plug using epoxy, mount that form as a jig, then take some psa type sandpaper and line your form.
I would think a couple of quick twists with each cap in that jig with the appropriate grit paper would work.....
Metal, wood, fiberglass, we work it all... www.furniturephysicians.com We can restore the irreplaceable!
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