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Micro Consistency

TASEsq

Well Known Member
Patron
Hi!

I am almost ready to make the "seam" along the edge of my elevator tip fairings.

Steps so far:
- bonded alu strips inside for the rivets to bear against
- a gross shaping to help make it look right
- the "joggle" edges have been sanded back
- the edge of the elevators have been taped up with packing tape, then a single layer of electrical tape (to help achieve a consistent gap), and finally
- the whole gel coat has been sanded with 80 grit.

I am ready to mix some micro to spread over the whole thing in order to both finish the edge to a consistent gap, and also fill any exposed weave and pinholes that have shown up from sanding.

Q: what sort of consistency am i looking for in the micro to achieve this? I assume it needs to be kind of loose so that it flows into the holes? Or do i make it thicker to help make the edge against the elevator skin, and push it with a card (hotel card etc) into the holes in the fibres?

Do you think i need to use flox or a couple layers of cloth at the front to make the large gap where the counterbalance skin is curved and the tip is not?

I appreciate any advice that is available - this is my absolute first go at fibreglassing! (actually enjoying it so far - it seems mistakes are easy to fix).

Here are some overview photos of the left tip:
un0I2djIn5A-ly-NtHkys9YsbOgsbaKsaMZBrXRr6SPAlT1z4B6KgqiHZP_mvPBunuR5_yEkgNrK1aMrORtSdP1yAGEaOrG8LLqvzujS0ayrOkLGVrSsdQU5xh2n3DfLTBMizOQiPi95DKkPVIy_S9XgwebOPFPU-bpEN2mIDAZDP6lENNvHmPrekNQut1NbBTingU4teGMF1MPiPk_LRE9jgKNCoX9-FLM95ujqD0WdLhWbVmUVz8qsDKAny9bqvQjZvj5Mi0KrtQWFUJ4Gw5g0wp6nlecsGZyEx8pCNm821sWPruzhQ3tkrtqI1NVxGUWB9n1uajGrN8Am5ICp4HudqJ1FeMI0N1axNaF28P4XgyS-O6dbDuRfn2I2AuExRg9Bzqrhi24EIlDVNfGBSJOWt7afIeIT4bU_qlMqxfz4syaWJa25N0fUBV_Rnmdtte9DpZtfhzZqcPPjSaZ_BSABABlMHD9RsOS50m3P-NCJzOUuRt-VW2y-Dk5qhef2QpQe9GHoDb9pkSeKPkuvZ_Df4hpMTfpxOJWoESyeehjzg2CcSP_WkNdLO61MjGOBAxI4qgROF-BF1-sFS9BH43GomZxRta5M6H0RtHJOcJG8gnBBr8qQV0n31ptEGu5lCBIkxKDi1SewILiIXGccvHD4K0ty0TdFuFvdrxWIEQ6rxHg-VyG88TgnMAv-drcQZ5Sg7p_czaUpVeS_9VEMhPo3bvSenIDKLwZaLCfE3iwCBw9X=w800-no

https://photos.app.goo.gl/cezWUr3jQQtdrCK89

R__P6iGJ6j-d-uaiD-5a39IgA5YUIypeMpINdOgG4E72WHoP4ZcvuP9sAa2qZoXZ_eGz-5xyE4hcqj8o43D55wy8PwQuETecL0-xiZJCUimkrfe4aiP-1KssrFoQ2WStprcUtBrK-dd4oMcrIXGrwsdTp81awN5J2puJIYvHi5s66r-d9z_TyJdzxL9OsDuYmUVHXZaJiZJpc85st_r4xzdM-rBJg0zrcC35DumG2ZNJyUWsM5BYkwYctQ3aI8s8q5zZO66hoiRThW_dIE4BNUZ89UCvig2wXcnA89pGa2wdf8zrlfhe8R3ZBPdlR0Fw-ecEk5w00ZNSLGSNYfCT2RGzyhBHhY9YXNp2W7nmttvJHeS5dK-9F3OIIyNQDJmEE8EymtCTKocsyZUMsY2ioZ8naOs3r_TiSocypN4VTOe1qaBe7MGwrqzXA5VKiSrVJ0Uu9LAJbV2uc2dcoit6hdCEpO-OzPmFbDQZc4csG3O5o9oSma6XazP_mnUYj58T_ZUHTSvpUMIqMP6zicU0zWeHIPusWjKI7hAd-8eQ_1qz58gtWt1piLPIFzjjprSuNMmuZd2l_N6zwDoI7-McbdnnAsH5cRcY9qNaAUWaIdSm1RWR2G4yy7dz2849GJ3ZN55UwG0GoLVZ5PIZyVFkS_iZoP86R8ex5V4kT9_eE1Sd5UGxToqKH2qaJbccXzrIO55B6MZoxtCarP_SXA4C28NvZaK7aIsRcmjx-Gh9O-KrK999=w800-no

https://photos.app.goo.gl/tfECVnSU6SLjf8bk9

and here is one showing the sanded back edge ready to take some micro to help make a nice edge:
ASQ8MvTnmODrt_2lE-QRPIXio_98NvcQDMbB1MaKCQPEEf94x32cjj2lI-QFnfa2dCDypqMOex3YV5eKMveSaFxbM8PtM3JhjKU0PYFZJA5boEqHhaHe-di5Mg30irEvX-HI4TGnJi0Vv1amzr0GpVh31-nJ3Bl9KtpmSuEDXeXkJjZMIK-lbdxKkNGmMbeciBz5xHqduT68ndqzkG04L39U3zLGaPU56sxaTr9GjFFcd1DbEm0fjN7jT28Jcn0JSjiU5uBlUyBDMZizrheHlegCwR3swBLzzdHxtN1own8MLqvPjTU9m9RDj1YqNH4lB2w3TjXsYHBUD1TdiOv3cCznyDhKk5hxmY9qSNvGKbSEqD30Ks_i6hrMIgoK27-4QPJGrT8-uNSNIE3Fc2Hhrb0PHphd4NzeHg13SlQds4qINVod0VJ3V9D6mUxACdq4C3JDrP5mhdX12L7QoemyV8WXSe760bynVZiMciqDxIw2RSy44yKbkOfOTMWJOiwitiWj8QLbbwijmq_niJdprxIgndVF0IobABd9aaj8OytrWuGRc1r4_jD6TaBx68LXn2XB1U9o-RvWewDouWhKSP1HepfkINODGoWmDJsIDimQqry5wSJlNHQt49pRi8CwdPE-ZZp2-xitvs7n-XXo_UtVl0qbaDTicA8n7SUqIWBwapRKwP6oZ0-0HgmxuCe6ykaLQs0vkMOhh8tvsIG--G_qWgTJMtopbKgmbC2WBwogEYl0=w800-no

https://photos.app.goo.gl/H7vVxc1Qo5ty8Yfe8
 
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Trent, I'm not sure sure what you're trying to do here, so this is general in nature...

Microballoons can be combined with mixed epoxy in any proportion. There is no right or wrong, only a consistency which gets the job done.

Generally, we use the maximum possible proportion of microballoons ("dry micro") when correcting surface profile. As a practical matter, it's the stiffest mix which will still spread smoothly. There are two primary reasons to use a stiff, dry mix; the finished product will be lighter, and it will be easier to sand.

I might use a medium mix if I was wiping micro into small holes, divots, and or scratches in a foam form. The key here is that it wipes in easily.

The best known use for wet micro is filling the pores in foam prior to adding an overlying fabric, wet-on-wet. The high proportion of epoxy allows the mix to flow into the voids in the foam.

As the mix proportion tips toward more epoxy and less microballoon, the cured product will be heavier and harder to sand, but somewhat tougher.

Micro is not a pinhole filler. Holes, divots and scratches, yes. Developing a surface profile , yes. But not pinholes. In fact, when sanded, micro is a collection of very tiny pinholes; sanding cuts open all the hollow bubbles on the surface. They are nowhere near as large as the typical pinholes in fabric layup surfaces, but they are there. Spray a coat of primer, and unsealed micro will be immediately obvious.

Many builders use polyester resin based commercial body fillers on emp tips. It's not quite as tough, nor as adhesive, but it works. In addition to, or replacing microballoons, commercial body fillers may contain talc, ground styrene plastic, and a variety of other fillers, each mix tailored to a desired consistency and sanding density. Less hollow micro and more solid powder results in a more closed surface after sanding.
 
Good big picture from Dan as usual.

A few specifics for judging the cup mix, when mixing with a popsicle stick, the mix will stick to the stick, as the stick is withdrawn from the mix it will:

1. Stretch a little then bead on the tip and begin to slowly smooth and drip off the stick in 10-15 seconds.
2. Stretch a little more, then slowly bead on the cup side and likely not move on the stick. May smooth out, but won't creep off vertical surfaces.
3. Stretch and leave a relatively sharp point on the cup and stick, there is no movement of either.
4. the stick stays inclined in the cup mix. or can pick up the cup with the stick and it won't drop off.

These are 4 points on an infinite scale. Temperature will affect them vs ratios. I like something with a little smoothing action but not a fluid so it will support shear on the vertical. A tiny bit of cabosil goes a long way to shifting to stiffer near the end of a mix.

Get some dixie water cups and mix 5 grams of resin at a time to experiment a little. Some black pigment can be added (sparingly) to create a gray color that is easy (er) to see when sanding.

As in any body work, be sure to put on enough material so no original surface is left after sanding.
 
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I know this sounds confusing but.

I was taught to apply raw epoxy to the fiberglass part before adding/applying micro. The "dry" micro isn't wet enough to soak into the glass structure by itself. Wet micro will be wet enough. The key here is you want bonding to occur.
I will sometimes drill small holes like 1/16" to help with bonding as it is getting covered/filled anyway.
Once you get close, I switch to fine/finishing automotive bondo, because it is easier to sand in very thin layers and feathers out smoother than micro.
 
+1 for Bob's Epoxy priming comment

Regardless of the coarseness of the surface (raw glass or not) I prime with epoxy then stir micro in the balance of the resin. This is especially relevant to "dry micro" application when there is not a surplus of mobile resin in the mix.
PS, I also find dry mico does not spread well ( re Dan's comments), so I lay a piece of poly film over the rough deposit and shape it nicely with my hand, credit card, roller or what evever works. Leave it til cured and it looks pretty good for minimal sanding.
 
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IF priming the sanded surface with neat mixed epoxy, use a small piece of cotton rag and rub it on to the surface, so there is no wet liquid, just damp. Wet epoxy guarantees dry micro won't spread well, and worse, when sanded after cure, the neat epoxy will form a hard ring around the micro due to being harder to cut.
 
Trent,
If I may give you some insight from my poor choice of micro balloon use.
I used fiberglass tape and then some mb for this same area to fill that same gap between the fiberglass and elevator. Since I have been flying for six years now I have paint chips in that area. When I fly through heavy rain I get new chips there. My though is that the mb are too soft. This is not a great area for MB. Yes they make sanding much much easier but you need more strength there.
I will be using chopped fiberglass and some Cabosil in that spot.
Filling pinholes is a different matter.
 
What DanH said. The only thing I would add is that on the leading edge, the micro is going to want to drain out. I would cover the micro on the leading edge with peel ply to keep that from happening. If you choose to do that, put the micro on a little thick so that there are no low spots in the micro which would have to be filled later. You will find that any low spots in the micro will leave a ring of pure epoxy around the perimeter like a coral reef around an island. When you fill and sand that area, the left over ring of epoxy is harder and you can never sand it flat.

So my advice in general is to put the micro on too thick and plan on sanding it back down flush.
 
Flox, Duct Tape, and the Cory Bird Method

Having built an entire airplane using this method, I have a few points that may help:

If you have an edge you care about staying sharp despite being impacted, use flox (flocked cotton mixed with epoxy) to fill it, not micro. If I was doing this, I'd put a small gap between the fiberglass tip and the aluminum, maybe 1/16-1/8". Then when you are ready, mix up flox pretty wet and squeeze it into the gap with an old credit card (don't turn in your hotel keys, they make great epoxy squeegees.) The gap makes it so the flox will conform and stick in there. Be aware that flox and micro sand VERY differently, so you may want to make that flox edge first, let it cure, sand it, then proceed with micro for everything else.

Using electrical tape like you have will create a nice even line, but actually duct tape is better at breaking free from the part after the epoxy cures. Cheap duct tape works ok, but I generally buy my duct tape by weight. The best I have found is the Gorilla brand.

Brushing raw or neat epoxy on the surface before dry micro is a good idea to get it to adhere, especially if you are using very dry micro, but follow DanH's advice and do it VERY lightly. I typically put it on with a cheap bristle brush that I trim down so the bristles are only ~1" long so they are stiffer. This will force the epoxy into the weave better. Then wipe as much off as you possibly can. Use the credit card followed by a dry brush. It should just be shiny when you're done, with no epoy pooling anywhere.

Finally, when you have micro'ed, sanded to fair, guide coated, sanded it actually fair, and think you are done, then follow the Cory Bird Method. Fellow EZ builder Wayne Hicks has a great explanation of it on his website here:
http://www.ez.org/pages/waynehicks/chapter_25_skimcoating.htm

and Quickie builder Sam Hoskins has a great video of the technique here:
https://youtu.be/43K1qwoHbnc

Good luck. It isn't hard, it just takes some practice. And sanding. Lots and lots of sanding.
 
Trent,
If I may give you some insight from my poor choice of micro balloon use.
I used fiberglass tape and then some mb for this same area to fill that same gap between the fiberglass and elevator. Since I have been flying for six years now I have paint chips in that area. When I fly through heavy rain I get new chips there. My though is that the mb are too soft.

I dunno Mark. Whole lot of airplanes out there with micro in various leading edge surfaces, including mine.

Here's an exercise I often invite new users to try. Mix some epoxy, and split it up among 4 small cups. Mix dry micro in one, wet micro in the next, flox in the third, and enough cabo to thicken the neat epoxy in the fourth. After mixing, just dump them out in four separate piles on plastic sheet, and allow then to cure a week at 70F.

When cured, attack the samples with pliers, cutters, whatever you wish. For sure, put on safety glasses, place the samples on concrete, and whack them with a hammer.
 
Hi all,

Thank you for all the replies! I?m a little overwhelmed and confused but let?s see if I understand this correctly!

@danh - firstly thanks for your reply and all the great info you have on this topic scattered through the site. I?ve searched and read most all of it I reckon! Second, these are gel coated (grey) vans elevator tips. The finish was really good. I?ve just fitted them and contour sanded them. I.e, where they were thicker than the aluminium they were abutting they got sanded down, or the mould lines sanded off etc). This has left some exposed glass and left them deliberately lower than the aluminium edge as per section 5.

My goal is to simply fill the gap against the aluminium edge, and fill the areas where I?ve sanded through the gel coat and into the glass.

I used the word ?Pinholes? wrongly I think.

So, from everyone?s replies and the great cozy website link (thank you!) here is my proposed process. Please correct my misunderstandings if you have the time!:

- use a ?dry coat? of micro to fill the edge against the aluminium and over any bits where the glass is exposed or where there are any large holes or scratches. (Or do I do it over the whole part??) The consistency is so that it does not run on its own and does not drip off the stick. Squeegee it on quite thick (thicker than the high spots).

-sand this back off to make the edge I want and get the contour I want using a flat sanding board and maybe 80 grit? (Or go finer for micro?)

-once sanded apply a skim coat of raw mixed epoxy, let it go tacky, then another coat.. I will use danh?s method of rolling it on with a foam roller to get the ridges to help in sanding it back off later and not going back down into the micro it glass etc.

-wet sand this with say 180 or 240 on a block?

Have I got an acceptable process do you think?

The only question I don?t get is whether flox would be better to fill the edge against the aluminium skin and also the 1/8? thick section at the front of the counterbalance arms where the skin is curved but the fg part is flat. Can I use flox to fill these edges, sand it back once cured, then micro over the rest of the part as above? Or do the different hardnesses cause issues?

And should I remove the electrical tape and add a few thicknesses of packing tape instead? I really don?t want it to stick and I haven?t tested to see if epoxy sticks to electrical tape.

Thanks for everyone?s time. Apologies if the initial question was confusing or used the wrong terminology. (Apple?s autocorrect changes ?pinholes? to ?pringles? - a topic I do have ample experience with 🤣)
 
On your specific question on filing in the gap between the fiberglass tips and the aluminum skin, this is what I do:
- Fill in the gap with micro
- Sand the micro flush
- Apply a single bid of medium glass over the gap
- Skim coat of micro over the glass after it sets
- Prep for paint

Do not fill up a gap with just mico or flox and expect the paint not to crack - it will. This is why the glass is needed.

Do not glass over a gap, fill it with micro and sand flush first. If you glass over a gap then you just need to fill it with micro later after it sags into the gap - and now you recreate the paint cracking issue.

Note - same process for finishing windows on the RV-10.

Carl
 
On your specific question on filing in the gap between the fiberglass tips and the aluminum skin, this is what I do:
- Fill in the gap with micro
- Sand the micro flush
- Apply a single bid of medium glass over the gap

Hi Carl,

Thank you. Won?t this however make the fairing sit above the aluminium? And when you try and sand it flush you will just sand back into the glass? Keep in mind I am not glassing the tip onto the elevator - I just want a nice clean even gap. I.e. I?m not putting micro across the gap between the tip and the elevator to make the seam disappear. I could imagine if you did this it would certainly crack without glass support.
 
Do not fill up a gap with just mico or flox and expect the paint not to crack - it will. This is why the glass is needed.

Probably true if the tip is simply riveted into place per plans.

Try bonding the glass flange into the aluminum with Hysol 9430 or similar, riveting while wet, prior to fill.

900 hours and counting, just micro, no cracks.
 
Would West System G-Flex qualify as "similar"?

Not really. The addition of G-flex would be better than rivets alone. However, the goal is to minimize relative movement between the aluminum and the glass tip. The specification of interest is tensile modulus, in effect a measure of how much a material will stretch under load. Tensile modulus for G-Flex is given as 1.44E+05 psi (144,000), vs 380,000 psi for the 9430, so the Hysol product is more than twice as stiff.
 
Also, for the newer tips with gray gelcoat, it would be a good idea to remove the gelcoat from the mating flange surfaces before bonding. Otherwise, you're transferring loads through resin which is much less stiff than the glass.

I cut mine back using 240 grit on a long sanding block, cleaned up the fiddly bits with a dremel, then bonded the mating surfaces with 3M EC-2216 while installing the rivets.
 
bonded the mating surfaces with 3M EC-2216 while installing the rivets.

Interesting. I hadn?t thought of bonding the part in addition to riveting it. Just curious as to what the advantage of this is if you are not glassing over the seam?

Also the 2216 seems like just an epoxy - why not just used west systems and some flox to thicken it up a bit? (That?s now I bonded on my metal strips for the rivers to bear against).
 
what the advantage of this is if you are not glassing over the seam?
It's been my experience that epoxy makes a terrible bond to aluminum - even if you prep the aluminum properly by sanding and etching. The Hysol or 2216 makes a much better bond but I wouldn't trust those either without riveting or some kind of mechanical attachment.
 
It's been my experience that epoxy makes a terrible bond to aluminum - even if you prep the aluminum properly by sanding and etching. The Hysol or 2216 makes a much better bond but I wouldn't trust those either without riveting or some kind of mechanical attachment.

I've heard this before but the West Systems I used bonded to sanded aluminum like a beast!
 
A source for facts on adhesives.

If you want data ( ie. Real experience on RVs), contact HFS. He uses the stuff on his airplanes and does strength testing with his own machine.
 
Need a new hammer..

As a data point here is a video showing a hammer test on 2 blobs of epoxy. The first is “dry micro” and the second is flox. The flox is definitely harder than the micro, but the micro was by no means soft. It did dent on the first hit but took a lot of force to split it in half. The flox needed a massive whack - harder than stone.

https://youtu.be/TEAzdL7PTHg

And here is what the “dry micro” consistency was like before I smeared it onto the elevator tip. This was 70g of part A, and 14g of part B, and it took 30 teaspoons of micro to get it to this consistency - was way more than I imagined. It really did have a tendency to “roll up” behind the knife, but if I kept it thick it was ok. In a few hours I will cut it back with a surform then sand tomorrow.

https://youtu.be/3wPJNiNmLyw

Here is the first tip waiting to cure:
ue5BgijZXZbbiv2fosS2uEBTy23mSR6AHRpz1sLMAAnj5CxulhBv72sPVxU_xNF-tK_NHUcMbVycqxIvSem5W6Git6JQx3o8sWgkz6H7iapBzAmpB7xJ2hmniH_M8V0F44zxVkkMpb310qvcHu4XUA761DCHWJLKzKWOd8pz9LHSJHzt28b2AXsytA5IuiFs9_YxiHIoF9qwS3195zBKzLi3BAP5PKo9DjjzPQy1e73ofP8JXcuh2vVbqNvJEn6ltf7NdTV82pWtQustgKczSDzR3B1qygciprFQdcjsNBBEGICQFQ0nzpp-Mloq5iQzAx9vBEWx0ym3WSFccx4bvhq-Mr_NvbuRJ9t1wyGQvRKhrMj-F8FJmf5G80IRVZxPGw7wXw2SVwnzTr-7D7KHIuXOtQSrNGi4a8QHDQu_xdu3gF35_PDiN_F6sOqEXC_R34tsJcyuk91DUFfppvDajZXbfiatnKfPbvyQKZ2OPzKSeObMujyfPLsIINHwmuJI04GBdf4k5r6AA5T23rXjCdg4C0oYS_tY4K0LPCu87kf7I6hopefNbhczbdMuKqgELqGbEgJvrvpQSEx8IEBi3vQtijt9BFQWt0BhznzZ0_8IkJAQJ8PECEOWyLHtPkBS9RtAnohhfczXhDubS54fC1I7vr0MQyR0DpQH34hc2-_mS9J-tnPSmsADkrjhKsYzHjQiphcwYIfKgUGbR1ZoBEym7DZIPBv4ehBBhHytOAyXKYBk=w800-no
 
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The Joys of Fiberglass

And here is what the ?dry micro? consistency was like...
Great photos! I did both my wings like that using West Systems and microballoons. I put it on thick then knocked down the high spots with a Sureform file. All the subsequent sanding and filling took two years and just about killed me, though. I had to hire some help lest I go insane.

5eUB8D.jpg


You can see one area here where I almost sanded through the glass cloth. You don't want to do that.
owdC92.jpg
 
Update

So after slathering on the "dry micro" and then taking a lot of it off again with the surform file, i have the following observations:

1. The surform file is a great bit of kit. "Cheese grating" took off 80% of the extra micro and the rest was easy to sand off. In fact, i missed some places and used it after a week or so to see if it still worked on cured expoy - no problems at all.
9gIi9KqJx3MdtelXMiUJewLDTFrmPNwlCQfIQVfAb-cjU7aO0E9Pw5dxLDtfVQ8NwHj4ZltK1GSpt_wT0YU264obLorImodDlQSWCuPdlvKNL0ZcbzXUt6G_6GfeBDl79eng_ANayJbcN6ljTWVG3S7qMICt2-oQIdByFzj2B7HUlQCa6fRsxShrM_3-3rQOS3uQZQdS2tSzb1Nu3gxRRDAucrLa5MsD2gmPTdkuqFqSJ3XCAU7Ujbi-ud0mCmK1lNAMglUDpRUHgGQzKNfCqsMPIoZNvriBNYNqKGANlNjAmzml7pXqXbQL8EWO4O0nWMwpJlnTPreuQ5v62QKLSrqG_AhQningLgmlsj0iEFbVZsJegun1j4A6ZCmdQPdKiOpe43yUrhiRsrVJKy6S7arxb0uLZaNi2TgBSKAJbR86eZpB-7OSjlpDY2bmf2Nt8aXjXrves9yE0fOVUVfOaIX-cTcFTA4svjo0uQVQa-dFbgR1JBqj_PQ-ckPu6cA-49twM8DDxdEIPKpoAMPWyIIEr4_3dLzc3izRjCOsEi1oDf8ROBAKCU9ufTZsrbg1EWLet7XhH1yIbcqalLO9dD4x4Qw7tbsCLOyPN2b0DZzk5tQHRlFrDCw96eYG_5Gi4Nb4uBwVXvRZFSbwCaRgjpintpiJIzV_w9JfhHmJPqeOZ02EHFgb_5Lhsyatun99ALRZJI21xajG4_oGZYkvG__3seKD13CneF3lkOmFFZcl28DH=w800-no

https://photos.app.goo.gl/GQu4mwpBmq2qiNuM9

2. Once i started sanding, i used 80 grit on a long flat sanding block i have from my model aircraft days - this worked really well and i was able to cut the micro fast back to being flush with the aluminium skin. I was also able to contour the tip to a good shape, taking off almost all of the micro, but leaving the low spots filled. Sands a lot easier than car body filler in my opinion.

Having said this, there were a lot of holes which i would call bigger than just "pinholes" (there were a lot of those). I think the large holes were from voids when i trowelled on the micro - i am thinking it was too thick (you could definitely notice it getting thicker as i worked).

Is it better to make it a little runnier, or try a heat gun to thin it out? Would this "avoid the voids"?
Holes in the counterbalance end skin:
ky3h3gEK7LkKXYVHq-myafsbRaMXOjT3tQreMt6pBVtp9godWuZG5HNoy_pU5fSABGI3pwQ9khSVIVZetQjLTTg07_0QfeyvJIbPNe6GuVt3X-UrXYK3Q0mYxImZS0KM71f2aAGUJcwUJVvFzNtWyNqGPwfq-NmJkpwWPgK1GpzzdhiMCo8V8shesr2tLHyCZBDCCrJ2Eg60IR0YUoy6dSCFLNjkAgZ-advQE1GT-qUSMmlAMfM8EO2m-SJOIgjTbjLIHb6WP3Ia_aDvWyaNbemn3lLcUK6kqffgglrLl03iuyY3m5dgzoyZbeoxvGBWJNdWcfz6_IjVjMKnDrj092nc1GmcsUdte3MQnJTBSRgkHVwV4sguP_1Ex8qULzTkyNtgR8LDcQlMhmknlaz3faUpXtqiOiUDwb9gwV9BTa81RnEG9hkJlviVcwwpgJpl1BGuOxztnh3gIa4Q4mKrIhDLsvlVh0BDzeM-zwoDX6XQWq51vHtX2uW66LaIyCMjl4uJ9i-Fz2jp-FZVtsC4CV9o3BWl3ci_iK4v86nuZRU6keLd9p-X6dxg4SZgAftqgPqKKXdt8qpUnB_p4cS2ureDAlPuCS6JPxsxlWUm_ffnOEnnxo8iCiiyOkl6-RXbUbOUDkVAlBx_93lTa7m3MFxBS_QRI4QLB-y1BotZDbHmiCRhZSQggRNzsxib0AAT0tMyonBYDkizph0sKZkKvnfYfkINcdlyk3s5_b6B0TQe1cBY=w800-no

https://photos.app.goo.gl/rhucRqasNz4KMb9U7

Holes near the trailing edges of the tips
NIEVo_tdnZLBLWySIU8g_MyKgrCkT3MXAJboY8OIXYnannW1tyT7i3WDKE0Kw2e6Ic6ZNhSNNsguhoN0vL7fp_Vw3NJF6RMUaBIQEsRZXRY7ZHloOZvGWoOcwrzvNGmqBI-rErmdjmZYhHinc4MSXJcBU3J_p50MPNFIsQJl0m_Li76n0PY8tADCvGY8lKNbSmQB2gvIFBewGEiFWNCnE62R_Nu8tWqRn1Yu_1YyoldNejI_YUDQ56RiBweHoCIqNZIOS5Dodm7B4LY_u4Yk5nsJaU7kCuGBD1Iq7oK44oFuXbkDVBHCwjNTfA92ic_h4cRjVvvCYN9I4bhhS6hImrZsH-abIQgluGafEA1CSo9EPvR9uRqjvVj9BOf09T89dxFXVU7ayq0ysYMZr0rSwadMxfS8WkN54xXAAchQUrfE7w74oUMM0Bw3tWSFuFUok24xnbdnodOTZ0b9D0kMWyG3SpAG1ZvO5Ij3Z4zsGOnOrhaJDFDea-a237tzvhH-SellEW3KwQqUzhEn_5SFODteGKkdcLMTaDGc2ilTHk19Y1zgBRMhHHjopD-L1TqdW-la-u3KriyhnyM0ojzq-oidcgSw4YPnORy9QM0SRVUS78PSSDPkO54WSK9SX1wLDJ42LybgfWvw4Oqt5GjmPS0MJzBIcl8zjBDpMzl4E3Ub9oPttuvflMsxIDOrltYrdPylRpJcjZgzzLBRM8YIAZXRhDh3lLWBFHLc1Wc-QptWfQVH=w800-no

https://photos.app.goo.gl/dbkX7xMcm5xra2ze9

I think these are just normal pinholes???
ETtC8On6pdu8HkmgM3oA0RhQ19fGerx4l39T_c1Vt6g1-lGYj9yjHwdmkwRX789A96z3a1WSITAJs5PjEFDAw5ksyo-Z3q91-a51wF0S3VZOh5pnFDXjrn-MEKBV69RBTi9r8wr6NNtvOYT4j0GJ6KpHEBk32lqRX_8sNNhhf-Zdi5d72WJBbJyAXnxddG192FMV2DSEVXqdLnBuhQ_pCUJuIFjTD1YSGED5m5wwu7cRKoZ56jDdyaBqzEmq2b8iJtcSCSLpz-tFSNTBK1XQVZIlLhI1C3wZhd3Aozhio_VzX0mwNsJrAZsuYc0n-343Rs21GRJHxANWaf7tuaYQCXoN4a18GvKzSrPHqWXMqnLlpp6m2_ERr5yXKSNedfUJ4NvWOiBNzNMTKaNnJk8b8rDH8S5DHLvzDfW9NXGVa4ckF8dZQ1wBFmiD8pOTByzXi5SPC8YsV3-Bn_faJv_fpHs5jaLBlMLH7ytsmyh5lLEkre92Colq0x1qbQbuViJ_1eg51HB3zGzCikN8EbI-eeM7hmidXqiMOqF5DKLeLrii-yQRIh18EI0ZYNh7WCGu1dYQZIpqIcpud7kPIdgq7ieimIqYjuQ6YslVmKS8Rg1dvsF13k9qy8PpHhCdXHRu8fvnr2fIs-d88RWM6DC3Wuk0OaBD0DrFv62_jFtlNFeNPiggJ8zWMkd_lQ-l1ktf3vJ61DQSjgfqoCjBlwGbpEHVRU3AOagOxcPL5uMejsi77LcZ=w800-no

https://photos.app.goo.gl/94s5E5EaScN9wpKZA

What is the best way to fill the larger holes? I am aware that adding more micro is a bad idea - polyester body filler from the car shop? Will the "skim coat" of neat epoxy fill these?

3. I am not a fan of the packing tape. I had 2 layers on the skin and in some spots sanded through either the top or both layers. I used a brand name tape, not cheap stuff, but this still sands through very quickly using 60 grit. This was fine, but meant the stuff was a real pain to remove (kept splitting). I am thinking of going back to the electrical tape.

Next up is the skin coats of epoxy. I plan on the following - with the part off the aircraft:
- Bush some on so that it it all glossy.
- Leave for 30 mins
- Squeegee it all off again with a rubber squeegee
- Leave for 30 mins
- Repeat until it looks like i have built up enough resin to fill the holes that exist.
- hope. pray. et al.

Here is an overall picutre of what it looks like. I was really happy with the hard sharp edge this process had created and a very even gap. I ended up sanding the edge very slightly lower than the skin, to allow for the thickness of the epoxy skim coats to come.
49LM_oraJcy3W52ocMlNytY4n2hys1pRlROK57Fh23wow0s09UX76kNyGcLxNUffuidmqqEVqokHEhSAS9Zj05lXvCPY7JzUbVqXpagByCGVNbxA8mvGCL_bE_a1JO43pAGjra5dWLA6ct8iyPWYMUay2zQUPz9PG2-M2RZpDP3Nxrako74steQPAmsm3Twsso_Tw9AaLsPP_2VuxLI61cfAU1fiXwtTAWkUdImUno3JZdIfqAzxaTE7XZ3RrKvpnsIAOTSV4ccv9ZEL_EVJv6IDnWAT0Smr5kAWagGsrwskxcO5ukxhcIdU2h-wCGCcMA4LgHaUozPg8_yD5yNHGvp0Es9oc-HHoY8nq2wdnhYGcXKXNPq0u_g80xTbNZYSKT-Tz4Up0pp4HTIRMGWBzRmaRjcw-XATnFWyk1ddpM2XuEAazydThkgzMK_SmfflAgovOZQjj-8ZwZZOIvkwo4xkxykihdENC3iGawSTExkmZd7rY-nsVLBMVcT4VVfp-8mIXmWOuMX527BM_DuffjXss0BFgJOEzqnkB-acnEjXbiNUIzv2s-weVzJ3t2mzRp7h4MjmH5zOouOfPZFWZjFRcP26lcy4T7xxCmS4Vlk505fIZmLcFa8UvWcVaZVNN2JkqPkRwXh_42bsutlmCVRv837ER4YOLdIMu1GVek84Hi-Rj9LY5_A3eGDjn_L2fH-tXMa1_Fnd0sxuDEBzSMxmAAbain6bG18iACVj5kkvxCD2=w800-no

https://photos.app.goo.gl/7sos9FbokpXGF5BX7

Thanks all for following - if anyone has any further advice i would really appreciate it. The shed looked like a Dean Martin song this arvo - snow everywhere.
 
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Rather than the epoxy skim coat, I would use Polyester Glazing Compound to fill those small pinholes. I think you're going to have to use some more micro to fill that large hole and deal with the resulting discontinuity. Overall, you did a good job.

P.S. I have often thought that it would be great to have a bell jar and vacuum pump to suck all the air bubbles out of the micro before application.
 
....there were a lot of holes which i would call bigger than just "pinholes" (there were a lot of those). I think the large holes were from voids when i trowelled on the micro - i am thinking it was too thick (you could definitely notice it getting thicker as i worked).
Is it better to make it a little runnier, or try a heat gun to thin it out? Would this "avoid the voids"?

The divots and pinholes are due to air entrained in the dry micro while mixing. A really dry mix will hold every bubble, while a wet mix will allow the bubbles to float to the top. I would not go wet just to reduce the number of pinholes in the finished product, as dry micro is lighter and easier to sand.

A different mixing method may entrain less air, but mostly it's something to ignore. All the little stuff will be eliminated in the sealing stage.

What is the best way to fill the larger holes? I am aware that adding more micro is a bad idea - polyester body filler from the car shop? Will the "skim coat" of neat epoxy fill these?

The big divot is a case of "whatever works"...a dab of micro or two part polyester prior to sealing being the most common. I'd simply begin the seal coat process by wiping some dry micro into the divot with no excess (surface slightly low), and skim neat epoxy over it just like the rest, no waiting.

A word about adding additional layers of micro or body filler products. The caution is about adding patches of a material with a different sanding density, as it's very hard to sand a surface optically flat when part of the surface is soft, and another part is hard. The final painted surface will be wavy, something which becomes apparent after paint. The best bodywork reflects a perfect image across a large panel...no optical distortion. It takes a lot of blocking to achieve that finish.

Doesn't mean you can't add filler. Simply avoid patchwork filler applications in areas where being visibly flat will matter. I have seen unpainted RVs where the builder tried every filler product in the body shop catalog. Sorta looked like a spotted dog in multiple shades of white and gray and red and beige. Those surfaces will be wavy when painted, but given the right color and scheme, it won't be noticeable at 10 yards. RVs are mostly made up of wavy sheet metal anyway. Next trip to OSH, go search out a past Grand Champion composite plansbuilt, and sight lengthwise down the big surfaces.

In recent years my favorite epoxy skim application method has become cheap foam rollers. First coat gets squeegeed around some to fill the holes, then rolled to even the surface. All additional coats are rolled on.
 
Thank you Dan - appreciate your prompt response!

I?ll mix up my batch of neat epoxy to do the skim coat and remove a bit and mix up some dry micro, full the super large holes then do the skim coat straight away.

So to clarify your process - you apply the epoxy with, say, a brush initially, squeegee it off, use a roller to add texture and remove the squeegee marks, then from there the additional coats are just rollered on? (Not squeegeed off again and roller for texture etc?)
 
Thanks - I?ll give that a go. Any tips on the best way not to sand through the skim layer? (Like a guide coat after the first layer etc?)
 
The foam roller leaves an even orange peel finish. Just sand until the orange peel is gone.
 
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