Foam preparation and filler for composite layups - need help

Brian Jackson

Platinum Member
Joined
Jul 17, 2004
Messages
3,524
Location
Hamburg, New Jersey USA
Aircraft
GyroBee Variant - Under Construction
Greetings all.

Been out of the loop for a little while but making progress on the gyro. I am preparing for (finally!) the layup work and foam sculpting of the carbon fiber items. I am a newbie at composite construction so am asking the experts here. The first question is: What kind of filler material is generally used on the foam itself that is sandable in order to achieve a smooth surface suitable for wet layup? It will be vacuum bagged. One of the items is compound curved so the hotwire will not be used, and must be shaped by hand, which will leave some irregularities that I am hoping to use this filler product I'm asking about and sand to final smooth shape. Any suggestions or recommendations would be greatly appreciated. Thank you in advance.

Brian
 
Hi Brian

Off the top of my head... Warning...

  1. Foam is hard to sand smooth.
  2. We use DOW High load 60, which can be sanded smooth enough for primer. IIRC it's construction insulation. Sandwich them together with glue to the rough shape and apply pressure on the stack as they come in sheets. I try and look for the longest curve on the design and lay the stack either horizontal or vertical so there are fewer joints to fill in with sandable primer.
  3. You hotwire cut to rough shape as close as you dare, with your skill level, and then use a file.
  4. We do not try and get putty to stick on the foam. Make a major mistake and we cut that part out.
  5. After file sand with 40, 80, 120 grit. Sand as smooth as you can with 120 grit.
  6. Next, go to the paint store and ask for a sandable high filler primer. Can't recall the name. So take a piece of Dow High load 60 and ask them to test it or if they know what will not melt it. That's what I had to do last time.
  7. Then you spray paint it with the primer starting with all of the seams/joints 1st, over and over again sanding them with 180 until you can not see them anymore.
  8. Then primer the entire body and sand with 180, 220.
  9. Then you apply the fiberglass over the plug and vacuum bag it.
  10. If it needs automotive putty we apply it to the fiberglass. We never have to do this.
  11. You sand the fiberglass with 180, 220.
  12. Then you spray the fiberglass with sandable primer.
  13. Then sand again with 220, then 320 between coats if you apply more than one.
  14. Then paint it with black paint.
  15. Then sand it with 320, 400, 600 grit.
  16. Polish.
  17. It's a plug.
 
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PS:
Being a builder = you can make a vacuum pump using a regurgitator compressor.
That's how we used to do it way back when. See YouTube for how.

Vacuum bagging uses tons of air pressure to make the fiberglass or carbon fiber smooth as glass.
If the plug is smooth there will be little sanding required and have used non-sandable primer and just 600 grit and polish. But you have to be a great painter.
 
Basically everything John said and to add when you get to the point of a lining you can safely apply to the foam to finish off for final sanding.
It goes on easy, self levels, cures in the sunlight so no need to wait hours for it to cure and is completely safe on any foam. Amazing product.

All the body work for the gyro pictured was done with their products.

View attachment 1148291View attachment 1148292View attachment 1148293
You can tell I'm old school. Thanks, I'm going to have to try this product, it would fill in all the joints/seams and less sanding.
 
Using Zerovoc

  1. We use DOW High load 60, which can be sanded smooth enough for primer. IIRC it's construction insulation. Sandwich them together with glue to the rough shape and apply pressure on the stack as they come in sheets. I try and look for the longest curve on the design and lay the stack either horizontal or vertical so there are fewer joints to fill in.
  2. You hotwire cut to rough shape as close as you dare, with your skill level, and then use a file.
  3. After file; sand with 40, 80, 120 grit. Sand as smooth as you can with 120 grit.
  4. Apply Zerovoc as per instructions and sand with 180.
  5. Then primer the entire body and sand with 180, 220.
  6. Then you apply the fiberglass over the plug and vacuum bag it.
  7. If it needs automotive putty we apply it to the fiberglass. We never have to do this.
  8. You sand the fiberglass with 180, 220.
  9. Then you spray the fiberglass with sandable primer.
  10. Then sand again with 220, then 320 between coats if you apply more than one.
  11. Then paint it with black paint.
  12. Then sand it with 320, 400, 600 grit.
  13. Polish.
  14. It's a plug.
 
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One more PS you can make finished structural parts out of this by laminating thin layers of metal between some of the Dow 60 sheets.
Made parts for boats this way too not just plugs/molds.
 
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Wow. Great information. I will digest this eagerly. Thank you all very kindly. Wait, digesting this stuff probably isn't good for you.
 
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