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  #1  
Old 04-03-2012, 03:30 PM
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Default Epoxy dripping into underside of layup

I'm back to building after rotator cuff surgery and started on the F-28 bulkhead this weekend. After glassing one side, I flipped it over to do the other side and saw that the epoxy that had dripped onto the table during the first layup had "wicked" between the underside of the bulkhead and the table. I had dried puddled epoxy in several place on the underside. I sanded most of it off, but was wondering if anyone else had this problem and what they did about it.
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  #2  
Old 04-03-2012, 03:55 PM
aviator_edb aviator_edb is offline
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Default Re: Epoxy dripping into underside of layup

Ed,
I tried a couple of different things.

I put wide painters tape around the underside borders and raised the piece off the table with a piece of plywood. There was still some wicking but no big puddles. I ended up with a several hard 'drips' of epoxy most of which are on the tape. Some epoxy still wicked uner the tape but to a much lesser extent.

A couple of caveats. The tape can be a pain to remove around the drips. Remove carefully.

Second. Make sure you support the piece if you raise it so it doesn't warp while you're squeeging. I cut 1/2" plywood rectangles roughly 4-5" smaller than the piece I'm working on.
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  #3  
Old 04-03-2012, 05:11 PM
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Default Re: Epoxy dripping into underside of layup

i made my layups over sized then used the router to cut to size.
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Old 04-03-2012, 05:28 PM
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Default Re: Epoxy dripping into underside of layup

I did many of these flat 2 sided layups on 4 ml clear plastic. Once one side was done (still wet) I'd put plastic on the top, squeege, turn the whole thing over, remove the plastic from the bottom, add micro, layup, squeege, add new plastic on top, squeege again then lay weights on it. When it cures you have a cured layup both sides.
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Old 04-03-2012, 06:40 PM
ZG4Me ZG4Me is offline
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Default Re: Epoxy dripping into underside of layup

Several times.
After the first few I watched close for any drip onto the table surface and promptly wiped it up with a damp rag. Damp with denatured alcohol in the gallon cans.

When doing a single sided layup it may help if you stop just shy of the edges, both slurry and epoxy, and let the epoxy "wick" to the edge of the glass as you scissor trim the overhang to 1/4". Once trimmed, stipple/brush a little more epoxy on if needed. Look for drips on the table again You'll get the slurry to the edge w/o drooling on the table with practice.

If double sided layup, do the first side, peel ply it, flip it over onto smooth/uncreased poly, slurry/glass/peel-ply the second side. Add some poly, a full width board and add some weight until cured. Peel-ply may be optional in some locations (like the center), but it gives a uniform appearance to the cured part. Straight poly will work as a non stick release if you want a glossy finish that mirrors every wrinkle in the poly.

Working on a sheet of poly will keep the drips off the table, but does nothing to keeping them off the back side. a clean table is REAL nice, so use poly regardless. You'll get in the habit of setting your epoxy cup and brush (and squeege, and snips, and...) on a blank section of the poly 'table cloth', and your coffee mug on the table itself. Other way around works too, but you'll eventually run out of coffee mugs.

Buy paper towels in bulk, nitrile gloves too. I've gone through at least 48 rolls, and 450 gloves, and I'm ~3/4 done with my plane.

Rick
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Old 04-03-2012, 07:36 PM
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Default Re: Epoxy dripping into underside of layup

I hardshelled both sides first then did my layup (after sanding.) The hardshelling minimizes the weight gain that accompanies raw epoxy on unfilled (slurried/hardshelled) foam.
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Old 04-04-2012, 12:55 PM
argoldman argoldman is offline
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Default Re: Epoxy dripping into underside of layup

Quote:
Originally Posted by TMann View Post
I hardshelled both sides first then did my layup (after sanding.) The hardshelling minimizes the weight gain that accompanies raw epoxy on unfilled (slurried/hardshelled) foam.

T,

I'm confused.

What kind of weight saving from the raw epoxy. My recollection is that with fabric over foam (and a little epoxy to boot) the first thing you do is to (1)mix up a slurry of micro, the thickness to depend on the type of foam you are doing your layup upon, (2)Squeegee it into the foam, (3)remove the excess (4) lay glass upon it (5) allow excess epoxy to "wick" (or ACS) its way into the cloth and then add more epoxy for the final layup.

The purpose of the initial micro slurry is to prevent pure epoxy from filling the unfilled foam ad to give a relatively smooth, light bonding surface. The chosen consistency of the micro slurry is thicker with foam that has rough surface ie. Styrofoam and thin or none for smooth pvc or whatever.

With hard shelling you do steps 1-3, let it cure then your next step is to sand the entire surface then go to step 4 (which is now step 5 after some extra work.

The hard shelling stops the ability of the glass to wick up the excess epoxy and the new bond is more mechanical than totally chemical as it would be when done directly. Furthermore, the surface of the cured hardshell is full of nuks and crannies (to use an English muffin analogy and unless you thoroughly sand the surfaces the best you can hope for is getting the nuks dull as the crannies are below the level of the nuks. To get the entire thing appropriately sanded, you have to chop off the tops of the nuks, which leaves you with only 1/2 of the benefit that you you were hoping for when did the hard shelling as there is unepoxied foam there.

Having done both, I hold with the direct method and don't think that hardshelling gives any advantage, (except psychological) and very possibly adds weight. It does, however extend building time.

Where it possibly has some merit is in the glasing of large structures (wings etc) where you can divide the process into two parts, with, of course the cost of having to sand-- time eater. To decrease the necessity to sand, you can peel ply the hard shell micro. this will give a much smoother surface and sanding is minimal (although I would recommend a light sanding)
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Old 04-04-2012, 01:14 PM
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Default Re: Epoxy dripping into underside of layup

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Originally Posted by argoldman View Post
The purpose of the initial micro slurry is to prevent pure epoxy from filling the unfilled foam ad to give a relatively smooth, light bonding surface.
yep, that's it in a nutshell. If you slurry one side and do your layup, you haven't filled the pores of the opposite side and you end up with a higher density of epoxy trying to perform that function (from any spills.)

By hardshelling, I have a consistant density to sand which becomes fairly obvious when you sand foam that has been microed together such as wing cores, canard, winglet etc. consisting of multiple pieces. When you try and sand the joints into submission (higher density cured-micro) you end up damaging the surrounding foam. If you hardshell then the density is uniform.
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Old 04-04-2012, 02:14 PM
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Default Re: Epoxy dripping into underside of layup

Quote:
By hardshelling, I have a consistant density to sand which becomes fairly obvious when you sand foam that has been microed together such as wing cores, canard, winglet etc. consisting of multiple pieces
And you do this onevery Damn piece???? Seems like a LOT of unnecessary work to save a couple ounces and watch half your micro and epoxy fall on the floor. Must not be enough sanding for you. Can you come over and help me this summer finish my plane if you like sanding that much?

Quote:
By hardshelling, I have a consistant density to sand which becomes fairly obvious when you sand foam that has been microed together such as wing cores, canard, winglet etc. consisting of multiple pieces
This works great! I did some parts with peel ply as well and made a few big panels to cut when cured like ZG and Stevo did. Two weeks ago this worked especially well. Got all my panels for seats, armrests, and rear panel done in 3 days.
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Old 04-04-2012, 02:18 PM
argoldman argoldman is offline
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Default Re: Epoxy dripping into underside of layup

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Originally Posted by TMann View Post
yep, that's it in a nutshell. If you slurry one side and do your layup, you haven't filled the pores of the opposite side and you end up with a higher density of epoxy trying to perform that function (from any spills.)
Lesee, you would rather spend all of the time and effort to hardshell to prevent some spills that with proper technique, or perhaps just some masking tape, you can completely avoid. If you do both sides of the piece at one sitting (standing) as been described before you not only avoid this but save mucho time.

With flat panels, it is soooooo much easier to do them oversize (one side or both) and then trim them with a band saw-- You can use the same band for all of your bulkheads, however after you cut glass, one time, the band is useless for aluminum.


Quote:
Originally Posted by TMann View Post
By hardshelling, I have a consistant density to sand which becomes fairly obvious when you sand foam that has been microed together such as wing cores, canard, winglet etc. consisting of multiple pieces. When you try and sand the joints into submission (higher density cured-micro) you end up damaging the surrounding foam. If you hardshell then the density is uniform.

I have to give that one to you, however if you use a sanding board with duct tape on each side of a 1" abrasive gap, you can easily hone down the micro with little damage to the foam. Additionally, when you glue together, get as much of the ooze off and put a piece of peel ply over the joint.

All of that being said, I am not against hard shelling-- have done it myself and stopped for the reasons that I have written. If you like it, do it, structurally, for our purposes, it probably makes no difference.

Of course, then again, this writer is using a Renesis engine-- so what does that say??
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