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Prepping for Painting
- Thread starter Rolly9
- Start date
RV7Guy
Well Known Member
Prepping
I'm currently in the process of prepping for paint. The biggest pain in the ass is the cowl. I like fiberglass work and became frustrated with the cowl early. It requires a ton of fill to fill all the voids cause by inadequate resin layups.
Sand with coarse grit paper, clean with acetone. Shoot 3 heavy coats of Feather Fill primer. After cure, wet sand down to smooth with 320 paper. Any visible pinholes can be filled by "finger painting," primer into them.
The metal was cleaned with a degreaser then acetone. Next a DA sander with maroon Scotchbrite pad was used to scuff the metal.
When the painting is going happen I'm going to use a self etching primer on the metal followed by the a light coat of the paint primer.
I'm going to use a base coat/clear coat system, Dupont paint.
So far I have approximately 350 hours of prep work in prepping for paint. I'm a going a little overboard but I only plan to do this once!!! I estimate another 50 hours of prep.
I'm currently in the process of prepping for paint. The biggest pain in the ass is the cowl. I like fiberglass work and became frustrated with the cowl early. It requires a ton of fill to fill all the voids cause by inadequate resin layups.
Sand with coarse grit paper, clean with acetone. Shoot 3 heavy coats of Feather Fill primer. After cure, wet sand down to smooth with 320 paper. Any visible pinholes can be filled by "finger painting," primer into them.
The metal was cleaned with a degreaser then acetone. Next a DA sander with maroon Scotchbrite pad was used to scuff the metal.
When the painting is going happen I'm going to use a self etching primer on the metal followed by the a light coat of the paint primer.
I'm going to use a base coat/clear coat system, Dupont paint.
So far I have approximately 350 hours of prep work in prepping for paint. I'm a going a little overboard but I only plan to do this once!!! I estimate another 50 hours of prep.
Best advice is pick your paint system and then "follow" their instructions for substrate prep. And by sticking to the recommended prep, primer and topcoat, you are assured of complete compatibility.
I have painted 3 airplanes and used both Dupont Imron and PPG Concept (on different projects) with very good results.
Also, I have had very good luck with Smooth Prime to fill pinholes. Again, follow instructions and you can do the job in one sanding pass (multiple coats of filler by roller or spray before sanding). And it is water based, therefore cleanup is a snap.
Deene
BD-4, One Design, RV8QB in progress
EAA Tech Counselor, EAA Flight Advisor
I have painted 3 airplanes and used both Dupont Imron and PPG Concept (on different projects) with very good results.
Also, I have had very good luck with Smooth Prime to fill pinholes. Again, follow instructions and you can do the job in one sanding pass (multiple coats of filler by roller or spray before sanding). And it is water based, therefore cleanup is a snap.
Deene
BD-4, One Design, RV8QB in progress
EAA Tech Counselor, EAA Flight Advisor
Finley Atherton
Well Known Member
RV7Guy said:
I used Feather Fill on a Vari-Eze I built as recommended at the time by the designer. Feather Fill will give a good surface to paint on but it does have it's problems. There are a couple of places on my Vari-Eze where the paint has lifted with an air bubble under the paint layer. Apparently this can happen with Featherfill. I have not researched the latest fillers available, but I would guess some type of epoxy based filler (Feather Fill is not epoxy based) would be the best over fiberglass parts.
Finley Atherton
9A Canopy
RV7Guy
Well Known Member
Contamination
Sounds as if there was some underlying contamination. I sanded all of the glass with 150 grit then cleaned extensively with acetone to remove any release agent or other contaminates. Everything looks good.
The paint primer (like K36) sprayed nicely and sanded out great.
Finley Atherton said:
Sounds as if there was some underlying contamination. I sanded all of the glass with 150 grit then cleaned extensively with acetone to remove any release agent or other contaminates. Everything looks good.
The paint primer (like K36) sprayed nicely and sanded out great.
aadamson
Well Known Member
Fillers
The problem with fillers that are *not* epoxy is that most "shrink" with time or worse (bondo for example, especially glazing putty), will absorb moisture. Neither are good for laminates.
If you really want to fill pinholes and do it the easiest way. There are 2 approaches.
a) take a dry mix of micro and epoxy and "trowel" it on with a wide sheetrock mud blade, using your hand with all the fingers on the back and your thumbs on the front, at a 20-30 degree angle and with lots of pressure to squeeze out the airbubbles. When cured, sand to contour
b) if already really smooth, but only need to fill a few weave holes or pin holes, use regular epoxy and put it on with a squeegy, pulling most of it off. The epoxy will fill the pin holes, where a putty will just fill over them. It might take a couple of passes to get the pin holes all filled, but it's pretty easy with taking almost all the epoxy off when you do it.
For more info, google chapter 25 of the cozy, varieze, etc manuals and peoples reponses. There are some very good, and pretty easy ways to finish FG with one pass if done right.
I should know, I'm usually up to my armpits in it every day
The problem with fillers that are *not* epoxy is that most "shrink" with time or worse (bondo for example, especially glazing putty), will absorb moisture. Neither are good for laminates.
If you really want to fill pinholes and do it the easiest way. There are 2 approaches.
a) take a dry mix of micro and epoxy and "trowel" it on with a wide sheetrock mud blade, using your hand with all the fingers on the back and your thumbs on the front, at a 20-30 degree angle and with lots of pressure to squeeze out the airbubbles. When cured, sand to contour
b) if already really smooth, but only need to fill a few weave holes or pin holes, use regular epoxy and put it on with a squeegy, pulling most of it off. The epoxy will fill the pin holes, where a putty will just fill over them. It might take a couple of passes to get the pin holes all filled, but it's pretty easy with taking almost all the epoxy off when you do it.
For more info, google chapter 25 of the cozy, varieze, etc manuals and peoples reponses. There are some very good, and pretty easy ways to finish FG with one pass if done right.
I should know, I'm usually up to my armpits in it every day
Finley Atherton
Well Known Member
Finishing Fiberglass & Feather Fill
IMHO there are better products than Feather Fill. For one perspective on finishing fiberglass parts go to:
http://www.maddyhome.com/canardpages/pages/waynehicks/chapter_25.htm
In the section on primers you will find the following quote ; "Stay away from polyester fillers, like Featherfill and Eliminator!" They shrink up and will start flaking off after a few years." I think this is overstating the problem, after many years my Feather Filled Vari-Eze still has all it's paint on. However, I think you would find that very few composite aircraft builders would be using Feather Fill these days.
Finley Atherton
9A
IMHO there are better products than Feather Fill. For one perspective on finishing fiberglass parts go to:
http://www.maddyhome.com/canardpages/pages/waynehicks/chapter_25.htm
In the section on primers you will find the following quote ; "Stay away from polyester fillers, like Featherfill and Eliminator!" They shrink up and will start flaking off after a few years." I think this is overstating the problem, after many years my Feather Filled Vari-Eze still has all it's paint on. However, I think you would find that very few composite aircraft builders would be using Feather Fill these days.
Finley Atherton
9A
One quick note about polyester and epoxy.
Epoxy will happily stick and cure over polyester. In fact, epoxy is PREFERRED for repairs on polyester fiberglass since it will stick better than more polyester. Polyester, on the other hand, may not even cure over epoxy. If you're lucky enough to get it to cure, you can be sure it won't stick to the epoxy worth a hoot.
I've never used FeatherFill, but if it's polyester based and you're using it over epoxy, that might be most of your problem right there.
Epoxy will happily stick and cure over polyester. In fact, epoxy is PREFERRED for repairs on polyester fiberglass since it will stick better than more polyester. Polyester, on the other hand, may not even cure over epoxy. If you're lucky enough to get it to cure, you can be sure it won't stick to the epoxy worth a hoot.
I've never used FeatherFill, but if it's polyester based and you're using it over epoxy, that might be most of your problem right there.
I'm not sure I buy all the "polyester won't stick to this or that" talk. Bondo (or similar) is used on virtually all auto body manufacture and repair. I think that bondo and polyester based surfacers adhere through a mechanical bond, so proper prep is a must, but I don't really see how the stuff would know whether it was going on over cured epoxy, steel, alum, etc.
szicree said:
Let me qualify my statements. Polyester will not cure properly over not fully cured epoxy. Epoxy can take weeks to fully cure, so if you've done a layup and then try to put a polyester product over it, it just simply will not cure properly. Even if it does cure well on properly prepared materials, polyester's bonding characteristics are pretty poor to begin with.
When doing layups with polyester, you depend on doing the various layers in a specified time period to allow the new layers to chemically bond with the layers underneath. Without this, you just simply would not have any sort of structural integrity. The only reason polyester is so widely used is that it's dirt cheap compared to epoxy.
Properly prepared, polyester gel coats work well over epoxy, but the epoxy must really be fully cured. Also, some people coat the underlying epoxy with an additional coating that enhances the adhesion. I've never done this myself so I don't know much about it, or what it's called.
Last edited:
Highflight
Well Known Member
godspeed said:
It's probably primer of some sort so that they can see what the finished areas look like.
As far as what kind of primer, if they're smart, it would be 2-part epoxy such as DP40 or the like.
