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  #1  
Old 01-04-2022, 11:43 PM
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N546RV N546RV is offline
 
Join Date: Aug 2010
Location: Brookshire, TX
Posts: 1,188
Default Looking for some micro consistency feedback

Cutting to the chase, I'm finally getting my hands dirty (literally) with fiberglass work. While working on my rudder bottom, and sanding the tail light pad flat, I went too far and needed to build it back up. So I laid up a few plies, then cleaned the area up and got ready to do my first bit of micro work. I mixed to what I thought was an appropriate peanut-butter consistency, but within 15 minutes of applying it I realized I definitely left it too wet, and it wasn't staying put:



Fortunately it didn't run too much, and tonight I got that mess sanded down and looking nice. Then I got ready to build up my rudder tip a bit to match its contour to the vertical stab tip. In the intervening time, I watched the EAA composite videos, and got a useful new metric for dry micro, namely mixing it until the stuff didn't "sag" at all.

Tonight's mixture didn't run, which is good, but I found it extremely hard to work with. I never could seem to get it to lay down nicely, no matter how much careful work I did with a plastic spreader - half the time, it'd stick to the spreader and pull away from the work piece. Eventually I gave up on creating anything resembling a pleasing shape and just gooped on enough stuff that I figured I could sand this horror down to a semblance of the final shape:



What I'm wondering is whether I made this batch of micro too dry, and maybe that's why it was a real pain to spread? Or is this just me needing some better technique for spreading the stuff? Any other thoughts or advice to offer?
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  #2  
Old 01-04-2022, 11:50 PM
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wcalvert wcalvert is offline
 
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Location: Anacortes Wa
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Philip,

Micro is great for reducing the weight (density) of mixed epoxy, but Cabosil (fumed silica) is better for thickening. If you add enough micro to thicken the mix to peanut butter consistency, you'll have the lumpy mess in your photo. Try adding some micro (there are a lot of formulas out there), then ad the Cab until you get it thick enough. It should handle well and not be lumpy.

Lots of experts out there with good advice, this is what I found that works.

Cheers
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  #3  
Old 01-05-2022, 04:58 AM
Larry DeCamp Larry DeCamp is offline
 
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Location: Clinton, Indiana
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Default More options

I have dipped my glove in acetone for a lubricant and sculpted the goo to a nice finish for sanding. Another option is leave the micro wetter and apply a very thin poly film (like dry cleaning bag ) and shape as desired. The the film holds the micro in place until stable. Leave the film on until fully cured or it will adhere and screw it up.
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  #4  
Old 01-05-2022, 06:13 AM
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DanH DanH is offline
 
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Micro, cabo, and flox, your three reliable friends. Mix and match to suit the task. Add one or all to mixed epoxy in proportions based on the desired result...you know, like "salt and pepper to taste".

Microballoons, glass (white) or phenolic (red) add bulk without weight.

Cabosil (fumed silica) makes the mix thixotropic, i.e. it only flows under pressure.

Flox (typically cotton fiber) adds structural strength.

Specific to dry micro (max ratio of micro to epoxy), more dry means faster sanding and less finished weight, but too dry is hard to spread. Do what works.

Don't worry about smoothing or applying some exact right amount. Load it up with plenty of excess so only one application is required. Let it cure to something like hard cheese, then rip off all the excess with a sureform file. The come in all sizes: https://www.zoro.com/stanley-plane-p...commended=true
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  #5  
Old 01-05-2022, 09:01 AM
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wirejock wirejock is offline
 
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Default Micro

Dan's the Man!
Remember, Flox is structural. It's really hard and won't sand at the same rate as the surrounding area. If I need to build up a hole or cavity, I usually try to encapsulate it between fiberglass layers. When the layup is squeegeed, the flox speads between layers into the space. Top layer is glass and sands easily.

Im sure it's wrong, but an old auto repair trick works for me.
I use a gloved hand. Dip in water or spray the surface and lightly smooth the micro. It's very liw humidity up here so it dries very fast.
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  #6  
Old 01-05-2022, 10:36 AM
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N546RV N546RV is offline
 
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Lots of good info, and some stuff for me to try out with tonight's work session. Maybe comparing my technique to Mike Arnold's isn't the best way to start. He makes it look really easy in those videos...

I have a feeling that I'll be sanding off the bulk of the micro on that tip and covering it entirely with another layer to get the final profile, but I'm OK with that. So far I've actually been kind of enjoying sanding. It's quite satisfying to take something like that blob in the first photo and sculpt it back into a nice pleasing shape.
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  #7  
Old 01-05-2022, 10:57 AM
Zero4Zulu Zero4Zulu is offline
 
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I step outside when adding the micro balloons and Cabosil to the resin and mix it outside until the stuff isn’t floating in the air. Just keeps the stuff from floating around the shop.
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  #8  
Old 01-05-2022, 02:18 PM
PilotjohnS PilotjohnS is offline
 
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Location: Southwest
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Default Just me

First off to me it appears the lumpy micro is too dry. I find if it that dry it is hard to spread, and if I do get it spread, it has pits when sanded. I think one can heat it up with a heat gun or hair dryer and get it to spread easier if it is that lumpy. I am going to try that next time I mix it too dry.
I am working in a cold hangar and have similar problems.

I think The runny stuff is not enough micro, I like runny, but cabosil has been back ordered so I dont have it to thicken, so i have been using a dry mixture like your lumpy stuff and been dealing with trying to get it smooth. I am using 1 hour catalyst, but it takes two days to cure hard enough to sand. It is tough working glass in winter…..

Anytime I am using raw micro, I use a respirator. Also when sanding I use a respitrator and have a vacuum going to suckmup the dust. Did I mention I hate fiberglass dust….if I didnt, I hate fiberglass dust.
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WARNING! Information presented in this post is my opinion. All users of info have sole responsibility for determining accuracy or suitability for their use.

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  #9  
Old 01-05-2022, 02:45 PM
agent4573 agent4573 is offline
 
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Quote:
Originally Posted by PilotjohnS View Post
I think The runny stuff is not enough micro, I like runny, but cabosil has been back ordered so I dont have it to thicken, so i have been using a dry mixture like your lumpy stuff and been dealing with trying to get it smooth. I am using 1 hour catalyst, but it takes two days to cure hard enough to sand. It is tough working glass in winter…..
West marine has it in stock....
https://www.westmarine.com/buy/west-...1-2-oz--323618

EDIT: Cab-O-Sil is advertised as a fumed silica, the 406 is colloidal silica but they're basically the same. DanH has even stated in previous posts that 403 is equivalent to Cabosil.
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Last edited by agent4573 : 01-05-2022 at 02:57 PM.
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  #10  
Old 01-05-2022, 05:04 PM
PilotjohnS PilotjohnS is offline
 
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Location: Southwest
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Default Thanks for tip

Quote:
Originally Posted by agent4573 View Post
West marine has it in stock....
https://www.westmarine.com/buy/west-...1-2-oz--323618

EDIT: Cab-O-Sil is advertised as a fumed silica, the 406 is colloidal silica but they're basically the same. DanH has even stated in previous posts that 403 is equivalent to Cabosil.
Thanks for the tip. I will check it out!

(Wow this is expensive at West Marine)
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WARNING! Information presented in this post is my opinion. All users of info have sole responsibility for determining accuracy or suitability for their use.

Dues paid 2022, worth every penny

RV9A- Status:
98% done, 2% left to go
Structure done (less gear)
Electrical/Panel done
Firewall Forward 95% done
Fiberglass 70%
www.pilotjohnsrv9.blogspot.com

Last edited by PilotjohnS : 01-05-2022 at 05:08 PM.
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