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Aug 01, 2019, 06:26 AM
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Discussion

Getting a decent finish on Depron


Hi all, just starting to work with Depron (I hate balsa!)and I'm wondering what are the options for getting a smooth finish on Depron sheet that isn't tape? I really don't care for the idea of tape except from the obvious strength point of view. So, what do people use to seal up that granular look for a nice finish?
Or is it necessary to use some sort of covering (car skin vinyl?)

Cheers,
Martin
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Aug 01, 2019, 08:58 AM
An itch?. Scratch build.
eflightray's Avatar
First you need to prepare the surface of Depron as it has an 'greasy like' surface that paints, and adhesives don't always stick to. A light sanding seems to work best for me.

There is this method ---

Newspaper-glue covering improvement

which I have used on large models.

But all these things add weight.

The lightest method I have used is to prime the Depron using a matt ceiling emulsion, slightly thinned with water, then add some talcum powder to thicken it up slightly.

This is suitable for rubbing down lightly prior to color, I have been using artists acrylic paint for the color, then a protective coat of a polyurethane varnish.

Ray.
Aug 01, 2019, 12:00 PM
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jumo004's Avatar
Quote:
Originally Posted by eflightray
The lightest method I have used is to prime the Depron using a matt ceiling emulsion, slightly thinned with water, then add some talcum powder to thicken it up slightly.

Ray.
Just curious, what is a 'ceiling emulsion' ?

Thanks.
Aug 01, 2019, 12:13 PM
Registered User
psychedvike's Avatar
I'd use the newspaper method. Doesn't add too much weight but it adds a lot of strength. Other way of filling and painting don't add the tensile strength that the paper dose. Hoppy's thread explains it well. There is a link to a video of how to do it that I made. It is really a good way to finish any foam.
Aug 01, 2019, 01:04 PM
An itch?. Scratch build.
eflightray's Avatar
Quote:
Originally Posted by jumo004
Just curious, what is a 'ceiling emulsion' ?

Thanks.
It's what we paint ceilings and some walls with here in the UK.

Emulsion is water-based paint, with vinyl or acrylic resins added to make the finish hardwearing

Because it's water based there is no chance of any solvents eating the foam.

.
Aug 01, 2019, 02:05 PM
Registered User
Silkspan and WBPU is an option (lighter than newspaper, problem is finding silkspan--but can use a different lightweight tissue), or you can use lightweight spackle (apply with credit card on flat surfaces, sand after drying overnight--then paint as desired), Foam Finish is another option, or you can just cover with a low-temp lightweight film (example here: https://www.rcgroups.com/forums/show...=27873)...Pete M
Aug 02, 2019, 03:49 AM
Registered User
Thread OP
I was wondering how you fill the surface grain of Depron, for instance. I have had little luck in getting lightweight filler to set on non absorbent surfaces.

Martin
Aug 02, 2019, 08:06 AM
An itch?. Scratch build.
eflightray's Avatar
Are you sure it's Depron ?

I have been using the original white Depron for years and never had a surface that needed filling.

Below is one of my Depron builds painted with just acrylic paint and then a coat of polyurethane varnish. No filling was required.

Sounds more like you have expanded polystyrene, or polypropylene if it needs filling, not Depron, the current grey Depron has a slightly rougher surface but should still not need any filler.

.
Aug 02, 2019, 08:12 AM
I Look, Listen, and Learn
Timbo383's Avatar
Surface preparation is the key to getting any type of adhesive....paint, spackle, glue...to stick to any surface. Its alot of work but the end results will make it worth it. First, cleaning the surface is a priority, get the oils off wiping the foam using an alcohol damp rag....I use denature alcohol, it doesn't melt the foam and it flashes off fast....then a light sanding with fine sandpaper to scuff the surface and open the pores of the foam. Then apply the spackle in light coats, sand, reapply some more to fill in, sand again. Top coat it with a light coat of water based polyurethane, sand, second light coat, sand and you'll have a glassy finish.....Too much work, then glue the plane together go fly and have fun...
Aug 02, 2019, 02:10 PM
The Junk Man
Quote:
Originally Posted by jumo004
Just curious, what is a 'ceiling emulsion' ?

Thanks.

My Aussie relatives call our "Latex" paint "Emulsion". Pommies probably do the same.

Tom
Aug 02, 2019, 05:36 PM
Registered User
Thread OP
I prefer enamels to anything water based, but whilst Depron is OK from a distance, It's noticeably "grainy" close up. I can still get the white one from SLEC, who are near me and have boxes full of it, but have said Depron will become grey when they run out and won't be doing the 2mm any more.
But it's definitely Depron. I'll try the lightweight filler first.

Martin
Aug 03, 2019, 01:43 AM
Registered User
I use 25gm glass cloth with water based polyeurethane. High build spray primer can then be used as the depron is now protected, sand smooth and paint.
Works for me and can get whatever level of finish you want depending on the effort you put in. Adds a small amount of weight but nothing drastic.
Aug 03, 2019, 07:59 AM
Registered User
wijwoj's Avatar
Lowish temp films also give a nice finish on depron and mpf. Here's my version of Lockey's BD-5 from some time ago covered in Solarfilm.

Wij.
Aug 04, 2019, 08:53 AM
Registered User
Thread OP
Thanks, chaps. Nice Bede there.

M
Aug 08, 2019, 05:15 AM
Danish? Don't U eat that??
DKChris's Avatar
Did an FT Mustang in Depron some time back and decided to cover it with standard iron on shrink film. Used some scraps of red oracover and some "surplus" old gray metallic Graupner brand film that I got for cheap at the hobby shop. Worked just fine with the iron on a low setting and a bit more patience than what's usually needed for a balsa plane. The black bit is packing tape.

Not quite as neat as the Bede, admittedly. The plane was intended to be a "beater" from scratch with the intention of using it for streamer combat, so I didn't put a huge amount of work into the prework before covering.
Last edited by DKChris; Aug 08, 2019 at 06:01 AM.


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