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Author Topic: Dope Over Epoxy?  (Read 3067 times)

Offline Chancey Chorney

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Dope Over Epoxy?
« on: October 24, 2015, 09:35:02 AM »
Hi all, yet again.  I am in the process of finishing up my White Lightening that I had started years ago and am wanting to try putting fillets on it with what I have on hand and available.  I have found and read that I can use epoxy.  I have a good quality 15 minute and 5 minute epoxy here to use. I planned on taping off the area, applying the epoxy and smoothening it using alcohol (read online). But the main question is in which order should I make the fillets?  Complete the model, dope it, then do the epoxy fillets, or is it alright to make the fillets then dope over it all? I could just not find out whether or not aircraft dope (Randolph Non-Tautening Dope) is ok to put over epoxy, or vice versa?  Thank you.
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Online David Hoover

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Re: Dope Over Epoxy?
« Reply #1 on: October 24, 2015, 11:51:58 AM »
You'll need to put in a filler of some kind (micro balloons is one kind, there are others) to turn the epoxy into more or less a putty otherwise your fillets will be HEAVY.  I generally use a finishing epoxy (Z-poxy or equivalent with a long cure time) and stir in the filler until I have a nice putty then do the fillets much as you described.  I haven't used dope in a long time but I don't recall any adhesion problems with dope over epoxy.  I generally do all the initial clear work before fillets then it's just primer/filler, colour and clear coat after.

Others may be able to give you more detail.
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Offline Avaiojet

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Re: Dope Over Epoxy?
« Reply #2 on: October 24, 2015, 12:48:45 PM »
I use 5 minute Epoxy for all my fillets and anything that has to do with micro-balloons.

Stuff sets quick so this is what I do.

Two paper Dixie cups cut off so I'm using a cup that is only 1" deep. One cup for hardener the other for the Epoxy.

Mix equal amounts in the cups with micro-balloons. Yes, two different "Starbucks" sticks. Get plenty of them for free.

Mix the two together and your good to go. Plenty of time to do one fillet, possibly two.

I don't use tools for the radius,  I use my fingers.

I press in a bit hard, that way I won't have much of a fillet at all. That's what I do. I don't like big radius fillets.

I apply the stuff about half way up with the stick, dragging your finger brings the amount the rest of the distance.

I may make a couple of passes if necessary. I use spit on my finger, there's plenty of it on your tongue but you could have a water glass.

Wipe with paper towels, start again.

Scratch it up before applying dope. Now some guys are using other stuff, including me.

I've been doing it this way forever. Proof of the pudding.

Here's a model done this exact way back in 1989.

The other three are recent.

Good luck with whatever you decide.





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Offline Dan McEntee

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Re: Dope Over Epoxy?
« Reply #3 on: October 24, 2015, 02:37:29 PM »
Quote from: David Hoover on October 24, 2015, 11:51:58 AM
You'll need to put in a filler of some kind (micro balloons is one kind, there are others) to turn the epoxy into more or less a putty otherwise your fillets will be HEAVY.  I generally use a finishing epoxy (Z-poxy or equivalent with a long cure time) and stir in the filler until I have a nice putty then do the fillets much as you described.  I haven't used dope in a long time but I don't recall any adhesion problems with dope over epoxy.  I generally do all the initial clear work before fillets then it's just primer/filler, colour and clear coat after.

Others may be able to give you more detail.

  David here is giving you the straight scoop. This method originated when Smooth N' Easy finishing epoxy was available. I use the 20 minute Finish Cure epoxy from Bob Smith products that most hobby shops sell with their name on it. You do need to add micro balloons like he mentioned to give it some body. I mix about 1/4 ounce of the two halves of the glue before I add the micro balloons just to make sure you have a good chemical reaction going on. This doesn't sound like much but by the time you add enough micro balloons to get to a cake icing consistency you will fill one of those 1 ounce mixing cups. Adding the micro balloons is also adding a contaminant to the glue so it slows the curing time and gives you some time to work carefully. Apply the mixture to the size you want and wait for it to start setting up. Play with the left overs in the mixing cup and when it starts to get sticky, you can start dipping you finger in alcohol and drag the fillets out until they are smooth and feather the edges into the wing a fuselage until there is no edge. You'll be able to get them as smooth as a baby's butt and I've never had a need to sand them, but if you do, they sand pretty easy. The surface when cured takes paint and dope extremely well and have never had paint lift from these kind of fillets. If I'm doing a iron on finish for the wings, I do the fillets the same way and over lap the edge of the covering about 1/8 to 3/16 inch, then finish the fuselage however I plan on it. If you have 15 minute epoxy, I would try that first. I leave 5 minute epoxy for field repairs and such and don't ever use it for any kind of construction, to short of a working time and it starts hardening before it has a chance to soak in the area you are working on. Sounds like you are wanting small fillets so the 15 minute should work out best. You may want to custom sand a Popsicle stick to a custom shape that you want to drag the mix with. I have a kit and plans for the White Lightning and will have to get to that one of these days.
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Offline Chancey Chorney

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Re: Dope Over Epoxy?
« Reply #4 on: October 24, 2015, 03:09:12 PM »
Thank you. I will search up Micro-Balloons locally to see if they're available. And as fro small fillets, yes that is what I would like and am shooting for. I do have small wooden coffee stir-sticks that I would use, approximately less than half of regular popsicle stir sticks.
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