Foam preparation and filler for composite layups - need help

Brian Jackson

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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
 

All_In

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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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All_In

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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.
 

All_In

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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.
 

All_In

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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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All_In

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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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Brian Jackson

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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.
 

giro5

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jm-urbani

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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,

all is explained there :


they show all the mixes needed

Directly on the foam you need to spread a running mix of glass microballloons powder and epoxy resin, it will be lighter then spreading pure resin on the sanded foam ( the foam will "drink" less)

they also show all the other techniques , I have used all those techniques and it has been a great help

if you need I have a bunch of pictures I can send you ( privately of course)

see ya
 

jm-urbani

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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?

Brian
Brian,

you must not prepare the foam with any filler/resin that you would spread on the foam and then let cure , then sand and put the carbon or glass layers on it ..

you have to simply cut your foam well enough so that your surface is acceptable to strafify directly on the foam without preparation

with a bit of trainning it will be a piece of cake provided you have the right hot wire temperature ( very important) ,

to get the rigth temperature you need : 24 volts supply and a basic motor controller (20 quids) with a pod you will adjust tol send more or less electrons in the wire,

just take a large piece of foam and put the hot wire cold on the foam and progressively increase the wire temp turning the pot until the hot wire starts cutting under it's own weight (it is shown on the video linked in my previous post)

the wire must not smoke, neither it must resist and the wire must always be well tensed.

with training and good temperature you should obtain a good surface with no waves ,

there you will spread your running epoxy.resin/microballoon powder mix on the foam ( look at the techniques in the video) and directly lay you first layer of carbon on the foam, and then on layer of glass rowing fiber glass, and the last layer of fiber glass ( 200 g per square meter for carbon and fiber glass)

3 layers are OK of for Fairings IMHO, but maybe here again should I have asked a structural engineer before puttin only 3 layers ...

after this you put your bag on and vacum, or you can squeegee the excess of resin using a small squeegee made out of foam ( see the video)

whether you use vacum or simply squeegee, once all is cured your surface won't be perfect and you will have to put on filler and sand

there you must not all costs use car fillers ... never ( they are horribly heavy)

you will have to mix epoxy resin and glass microbaloons powder (or phénolic microballoon powder)

both are really light, the glass microballon powder mix is way more difficult to sand ..

generally speaking you have to self-train to use the filler on any surface ( a piece of wood for example), in order to use as less as possible ... and hence reduce you sanding/refilling/sanding/refilling time ...

took me days ... to remove the excess ...

if you need I can send you pictures on my process.... which will show you all the errors you must not commit ... I have many ... just tell me

also train to use ths bloddy epoxy resin before attempting any serious work

when you buy it check the expirery date on it ( they are alway trying to sell out nof date resins to private clients) , don't buy old resin it does not cure properly and the resistance of the part will be reduced.

the buy a scale that don't switch off automatically ! or only after 30 minutes coz there is nothing worst then seeing you scale switching off while you are pouring the resin ..(if it happens you must bin everything coz you must be very accurate in the mix proportions)

put the resin, carbon, fiberglass, carbon, microballoons, indoors at room temperature (22° C at least) for 12 hours before using them (it takes ages for the resin to rise to the good temperature really), and of course work at room tempreature.

make a test of your resin before making your parts .. ( the day before) so that you are sure that everything is ok ...

and be very patient , it takes hours to cure, and when it seems cures the part have no resistance before 2 days ....

don't mix too much resin at the same time because it cures faster in the pot when your mix volume is big ( make 300 g max)

buy tons of rubber gloves and change it as soon as you get resin on it (to avoid fibers to stick on your gloves) ... it is not ecological but keep in mind that you will make only on fairing and only one rudder in many years .. so the better you do it the less parts you will bin hence the less polluting it will be

etc etc
 
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