Fiberglassing- a discussion

[Tom M.]

 Jack kindly asked me the other day to attend your next pilot's meeting and give a little presentation about glassing- I've done a few models but am certainly no expert but seeing as I can't make the meeting I'm happy to share what I know here (such that it is). I hope that anyone with an interest in the subject will chime in with their own knowledge or questions.
  I guess the first thing to decide is what to use as resin- epoxy or WBPU (water based polyurethane). Due to it's strong odour and brittle nature, polyester resin (the kind CTC sells) isn't usually considered as ideal for our purposes so we won't. Compared to WBPU, epoxy will provide a substantially stronger finish, both in impact resistance and stiffness, but at the cost of more weight and a lot more work. My first Sabre was done with WBPU, the current one with epoxy, and the latter is a few ounces heavier, so it's not a huge penalty. As for the effort required, if choosing epoxy stock up on good quality elbow grease as it sands hard, but I supposer that characteristic is a good thing, or so I tell myself. WBPU will provide an equally nice finish for paint, so if that's all you're after have at it. The great thing here is that there's no reason to just go with one or the other- both resins get along fine and adhere to each other so you could happily do areas you feel require more strength with epoxy and finish the other areas with the water-based stuff. More on how to achieve a clean transition later...
Were I doing a flying boat hull, as are Robert and Bruce with their incredible projects, epoxy will certainly provide the strength and waterproofing needed- after all, some of the world's fastest and most beautiful wooden boats are glassed with epoxy.
  As for what kind of epoxy to use, I would highly recommend West System products. These guys (the Gougeon brothers) pioneered the formulation and use of modern epoxies for use in everything from wooden hydroplanes to aerobatic aircraft wing spars to wind turbine blades. Considered the industry standard, West epoxy isn't outasight expensive either, compared on an ounce by ounce basis with the usual hobby stuff, and it work's so much better- follow the directions (and a myriad of information is available about the product) and you won't go wrong. Available at any marine store or Lee Valley.
  All that said, Z-poxy seems to be popular as well, though my LHS says it can't be imported into Canada (as a "hazardous substance) so if that's the case then would seem to be a non-starter. I don't think it offers the choice of hardeners to suit working times or shop temps that West does, anyhow.  As when using any chemical product, observe the recommended healthy and safety practices.
As regards WBPU, I think any good quality one will work well- I just picked up a quart of Varathane "Professional"  at Home Depot and it seems fine. Deluxe Materials has a product called Eze-Kote but it looks, smells and acts like ordinary WBPU, though they present it as revolutionary (and expensive). If it walks like a duck... 
  I glassed a few parts for my CF-18 last week-end  (using epoxy) and will show you some pics and talk about the process next post. 
  Tom

[Papa]

Thank you Tom, looking forward to your input.

Jack.

[sihinch]

This is going to be great. Thanks Tom!

[Wingnutz]

Tom, thanks for taking the time to share some of the magic which creates Muir Masterpieces! I have lots of questions for you but I'll wait until your curriculum touches on them...the timing for your thread couldn't be better with me rushing into a foam scratch build and not knowing half what I need to know to finish!

[Tom M.]

  Thanks guys, I'm happy to share.
The above photo shows the stuff laid out for a glassing session, though I forgot the roll of paper towels. Nitrile gloves are more chemically resistant than latex and tougher so preferable, and the alcohol is just for clean up. If you're using WBPU I wouldn't worry about the gloves. A very important point to reduce the frustration level when cutting glass cloth - a good, sharp pair of scissors! The ones shown are Fisker's from CTC and work well. Remember- good scissors.
As for cloth, 3/4 oz. (per sq. yd.) seems to be the standard for models in the, roughly speaking, 5 to 10 lb. range, and then heavier (1 1/2 to 2 oz.) for the big birds. Not to say that a smaller model won't benefit from heavier cloth in stressed areas (i.e. wingroots) or 2 layers of light cloth, for that matter. (These can be applied during the same session, incidentally- epoxy cures due to a chemical (exothermic)  reaction so thickness doesn't matter. WBPU relies on evaporation so 2 layers will cure more slowly.
I've used Hobbico (Top-Flite/Great Planes?), Hangar 9 and Hobby King cloth and though much cheaper the HK stuff isn't nearly as nice to use though I suppose the end result is similar. (See the photo of the newly opened HK cloth with all the nasty strands already waving around from careless cutting.) It's worth the extra maybe $15 for good cloth to do a plane, I reckon. If buying HK cloth, 18 gm/sq. mtr. is equivalent to 3/4 oz., 48 gm. to 2 oz.
  Parchment paper is a wonderful thing and is not only good for cooking chicken wings but also as a surface to lay your freshly glassed parts on wirh no worries of permanent sticking- cured epoxy (or WBPU) will stick a little but the paper will cleanly peel away. I wanted to do both sides of the tails and rudders last week-end so this was the ticket- do one side, flip them over and do the other, then leaving the parts in place until mostly cured. This last is important because (still) wet cloth WILL pull away from the part if it's moved at this point and make a mess. Let it be. But I'm getting ahead of myself...
  So having cut out your pieces of cloth (with your sharp scissors), leaving maybe 2" all around your (prepared) project, position and smooth it out. I'm not going to get into surface preparation at this point but realize that any real defects on the surface will still be there later, so do the best you can. You needn't sand to 400 grit, however- 120/180 is fine and will give the resin some "tooth" to bond to.  Incidentally, any rough skin or ragged fingernails will snag the cloth when you handle it so take a minute to sand your fingers beforehand.
  Mix up your epoxy of choice (or open the can of WBPU) and stir either longer than you think you have to. I apply either resin using the 4" foam rollers shown- it's funny that this method of applying resin isn't mentioned very often in forum discussions etc. but I've found it's the only way, really. Foam or bristle brushes are usually used and then excess resin is removed with a credit card or kitchen or toilet paper is laid on the surface to absorb it. Messy and needless. Use a small brush to deposit some resin centrally on your work to "locate" the cloth and then dip the roller in the tray containing the resin (of course the roller is on a handle ) Don't actually roll it in the tray at this point; just a little resin is needed. Gently dab on the resin and then gently roll in one direction only, towards the edges of your work. Lift off the roller at the end of the stroke (like an airplane taking off)- this will minimize the cloth lifting as you lifrt the roller. Continue adding small amounts of resin to the roller and applying it to the cloth. You'll find that, as a greater surface area of cloth is stuck down with resin, rolling can be done with more vigour and less worry of lifting the cloth. We want enough resin to saturate the cloth but not so much as to float it or appear glossy. This may all sound difficult but it isn't and the roller will give great control- adding a little more resin to dry areas or rolling out overly wet areas is no problem. Work under the best lighting you can manage so those wet or dry areas can be seen. Rolling from the center of rhe work to the outsides works best, pushing the cloth and removing wrinkles as you go. If you do get a pesky wrinkle that can't be gently corrected by your gloved fingers or snipped with scissors don't sweat it and just roll 'er down- it'll just need a little extra sanding later. Don't pull hard on the cloth or you'll get a nasty run in the weave.
  I'd hoped to get farther along tonight but gotta go- 'till next time. 
Tom

[Andy Hoffer]

Hi Tom:

Excellent dissertation on glassing!

Any thoughts on East System vs West System epoxy?

Tx

Andy

[sihinch]

Tom

When using a roller on a foam plane, with the moulded details and panel lines etc, do you have to do anything special or different to get the cloth to follow the contours of the detail?

Put another way, how do you get the cloth in to the nooks and crannies with a roller?

Thanks
S

[Wingnutz]

Tom,
What a wealth of information you've given us already! Thanks.
I found your brief discussion of the strengths and weaknesses of WBPU and epoxy a good start to helping me choose a resin for my scratch built Piaggio. 
I'm concerned about AUW of the finished Piaggio model as the wings are really small and I don't have the magic airfoil or the intricate flap system Piaggio uses on the full sizer. To keep the weight down as much as possible, I'm thinking WBPU on/in 3/4 oz cloth for most of the fuse(white EPS wafers between balsa formers) and 3/4 oz cloth/epoxy around the wing saddle, the centre of the wing and the small section of the fuse which connects the tail feathers to the rest of the fuse.
Any advice about that general plan would be appreciated.
Are you heating the workshop in this cold?

[Tom M.]

Hi Tom:

Excellent dissertation on glassing!

Any thoughts on East System vs West System epoxy?

Tx

Andy

  How's it going Andy? I've heard of East epoxy but have no experience with it, so did a little search at work today:
http://www.oneoceankayaks.com/Epoxresl.htm
From reading these test results East looks like a good, and less expensive alternative to West System- name's kind of a rip-off, though.
  Tom

[Tom M.]

Tom

When using a roller on a foam plane, with the moulded details and panel lines etc, do you have to do anything special or different to get the cloth to follow the contours of the detail?

Put another way, how do you get the cloth in to the nooks and crannies with a roller?

Thanks
S

Hi Simon,
                 I was going to discuss that in the next "installment" so this is a timely question! I'll re-attach the photo of the flare and chaff dispenser detail on the Hornet's tail which shows how the light cloth can be coaxed into details like this. Just dab at it with a small brush (I use disposable acid swabs), adding a bit of resin to be sure it's wet. Do this before wetting out the surrounding area or the cloth may be too taut across the detail to conform into it and an attempt to force it might(will) tear the weave.
The same principle applies when doing a long joint like the one shown (now sanded and primered). I laid the dry cloth over the fuse and started by wetting out those "joints" between the fuse sides and leading edge extensions with a 1'' brush , then began using the roller. The cloth did move away a bit but I kept checking on things and I think used a credit card to press it back into the angle. Just keep in mind that enough slack in the cloth needs to be maintained to keep it where it belongs and you'll be fine. If you get an area that's "tenting" and can't be easily fixed just slice the cloth with a razor blade, wet down the edges and apply a little patch of cloth to fill the gap. Or just add more resin to the area- when sanded out later the lack of cloth won't matter, but you don't want to leave an area of tented cloth, or when sanding you'll cut through the cloth and expose the bare, soft foam underneath. Done it lots!
  Tom

[Tom M.]

Tom,
What a wealth of information you've given us already! Thanks.
I found your brief discussion of the strengths and weaknesses of WBPU and epoxy a good start to helping me choose a resin for my scratch built Piaggio. 
I'm concerned about AUW of the finished Piaggio model as the wings are really small and I don't have the magic airfoil or the intricate flap system Piaggio uses on the full sizer. To keep the weight down as much as possible, I'm thinking WBPU on/in 3/4 oz cloth for most of the fuse(white EPS wafers between balsa formers) and 3/4 oz cloth/epoxy around the wing saddle, the centre of the wing and the small section of the fuse which connects the tail feathers to the rest of the fuse.
Any advice about that general plan would be appreciated.
Are you heating the workshop in this cold?

Hiya Bill!
               I think a career in aerospace would have suited you as well as your chosen one in education- your plan sounds good! (and I've been following your build.) I'll post what I've learned about transitioning between areas in the next day or two. It's nothing difficult- basically just using masking tape to delineate the boundaries.
Regarding heating the shop- let's just say Carolyn was "surprised" by the last hydro bill, Bill. 
  Tom

[Andy Hoffer]

Hi Tom:

Excellent dissertation on glassing!

Any thoughts on East System vs West System epoxy?

Tx

Andy

  How's it going Andy? I've heard of East epoxy but have no experience with it, so did a little search at work today:
http://www.oneoceankayaks.com/Epoxresl.htm
From reading these test results East looks like a good, and less expensive alternative to West System- name's kind of a rip-off, though.
  Tom

Thanks Tom.  This article provides a lot of good insights for glassing.  I like the discussion on adjusting the viscosity to suit the intended application (wetting out and penetration of wood substrate vs filler coat).  Very neat.

Andy

[Tom M.]

To transition from one resin to another, or if doing a larger model where it's only practical to glass,say, half of the fuse at a time, simply mask your ending point off with 2 layers of masking tape, allowing for perhaps a half inch of overlap for the subsequent layer of glass that'll be applied to the adjacent area. After curing, sand the tape line until the tape can be removed and you'll have a nice sharp line to work with. Apply tape on the line (on the unglassed side) to protect the soft foam or balsa and soften the edge a bit. In the photo below I've taped the stubs of the vert. stabs as they fit tightly into sockets in the fuse so so I don't want them any larger.
If going from epoxy resin to WBPU, as Bill is planning with his Avanti, I'd suggest doing the epoxy coat first as sanding will go better with the softer material on top.
  Tom

[Andy Hoffer]

...Mix up your epoxy of choice (or open the can of WBPU) and stir either longer than you think you have to. I apply either resin using the 4" foam rollers shown- it's funny that this method of applying resin isn't mentioned very often in forum discussions etc. but I've found it's the only way, really. ....
Tom

Hi Tom: 

I assume each roller is used only for one epoxy application and then discarded, i.e. you don't bother cleaning the rollers in alcohol after use.

Have you tried grooved rollers (http://www.aircraft-spruce.com/catalog/cmpages/grooveroller3.php)?

Andy

[Papa]

Is WB PU acceptable for use with the thicker FG such as 2oz or  is Epoxy better?

Jack.