Fiberglass on XPS Foam - Polycrylic or Epoxy? (for RC planes)

Skip to results and summary: 5:13
I'm a newbie when it comes to fiberglass, so please leave comments!
**Correction: Minwax Polycrylic is actually acrylic-based, not a true polyurethane or urethane.
**4-29-18 Updates:
-After about 40 flights, both the epoxy and the Polycrylic fiberglass-covered areas on my DIY Specter V3 plane are sticking and strengthening well. The only downside I see is that neither covering stuck well to the lightweight spackle I used to fill imperfections.
-Denatured alcohol does not dissolve XPS foam (extruded polystyrene). Several things will dissolve it, however (acetone, benzene, CA glue, etc), but not denatured alcohol. I think confusion about this is the source of some dislikes on this video, and that's fine.
*end of updates*
I'm building my first hot-wire cut RC plane out of XPS foam (Owens Corning FOAMULAR 150) and comparing how well this foam covers with 3/4 ounce fiberglass using Minwax Polycrylic or Z-Poxy brand epoxy finishing resin. I compare adhesion, puncture resistance, and rigidity. I find that both of these are useful adhesives with different strengths!
Thanks to NoddRC for making a similar video using DTFB: • Nodd RC - 039 - Polycr...
And thanks to the AMA for this fiberglass and Z-Poxy tutorial: • Fiberglassing Tutorial... . This is where I learned to mix the two Z-poxy parts together and split it with denatured alcohol.

[@winsor68]

I find foam more challenging then balsa building....but that is why I find it fascinating. Even when we only had balsa I was experimenting with composites.

[@hifinsword]

Thanks for the informative video. Based on your results I think I will use the epoxy/alcohol FG on the bottom of my wings for the rigidity and the MinWax PU FG on the top of the wing and fuselage.

[@smileyhomeimprovementsjohn6165]

If you could install a couple of pieces of hard wood strips along the core wing, and then fiber glass with minwax. Those wood strips will give a great strength to the wings.

[@mostlyharmlessrc3920]

I have done that to wings and it works well - I agree! In a later video, I added wood to this wing to stiffen it. Cheers

[@MarcChristensen]

One thing to note is that polyurethanes don’t cure in 12-14 hours completely. They can become somewhat hard so that they can be handled but true curing will take a week to a month. A better comparison might be a polycrylic covered wing that has cured for several weeks to an epoxy wing that has cured for 24-48 hours.

[@mostlyharmlessrc3920]

That's a very good point - thanks for that. I may have gotten quite different results after full curing time.

[@marward]

Outstanding video! This is a real service to the hobby. Much appreciated.

[@flyinflea]

This is a great video MH, you present it really well and it's full of useful info. I've said it before but i love the direction that you're taking your model builds in, you're really testing those materials and techniques before choosing the ones for the job! Looking forward to seeing some more of that plane mate! Big thumbs up!!

[@mostlyharmlessrc3920]

Thanks for totally getting the purpose of this video! I'm excited to move into a new phase of building - now I just have to get more efficient at it (I'm slow)... Going to respond to your email and send you some progress pics soon. She's coming along. :)

[@markfannin3975]

Outstanding video. I had no idea polycrylic performed so well. Please consider more build & technique videos for us newbies. Especially foam cutting equipment and techniques. New subscriber here!

[@mostlyharmlessrc3920]

Thanks for the great comment! I've been on a break from RC for a while but I like your idea for a new video!

[@pushpasrivastava915]

Wow dude! I don't think a video could had been any better! Can't believe don't even have 500 subscribes.you really deserve more!

[@mostlyharmlessrc3920]

Thanks man - very generous! This is my only really popular vid though :)

[@YknotLearnall]

You should try Zpoxy as a first layer to gain rigidity. Then a layer of poly over top to give puncture resistance. The same is best when using fiberglass and carbon fiber. Carbon fiber the inside layer, fiberglass the outside layer.

[@mostlyharmlessrc3920]

Great ideas - thanks!

[@AndrewNewton]

Brilliant investigation, thanks so much.

[@mostlyharmlessrc3920]

Thanks Andrew! If you can't find the exact video you're looking for, make it yourself. :)

[@rlake349]

One thing to remember is polycrylic and polyurethanes do not achieve maximum hardness until after 30 or 40 days. I do appreciate your extensive testing though.

[@mostlyharmlessrc3920]

This is useful information - I appreciate it! I think there's at least as much information in the comments now as in the video. :)

[@ZombiemodzFPV]

you saved me a lot of time in homework..... Thank you!

[@mostlyharmlessrc3920]

That's exactly what I was hoping for with this video! Thanks for sharing and good luck.

[@Migueldeservantes]

Really nice video specially at the beginning where you start with daydreaming about building, but never the less very informative, keeping in mind that I never use nothing else but epoxy "West Systems" usually my planes last until I get bored with them and back in the box they go, fiberglass covering extends the life of and RC Model 100 fold! I even wast trying to find a good home for my older model of X8 Skywalker, but no one seems to be interested.. but the reason it actually lasted that long was because of the Fiberglass.. Thanks for posting.

[@mostlyharmlessrc3920]

Thanks for the great comment and information Miguel. I didn't know you were already doing this on your planes - they look great and are a lot stronger for it I'd guess! I have heard good things about the west systems stuff so I'll check it out. Cheers man

[@Migueldeservantes]

Try to get a few books on Fiberglass laying "Preferably for airframe work" West systems are among the best on the planet when it come to quality & Strength, but it is heavier than most out there so you have to learn to be super Scrooge McDuck, I mean you have to lay it almost dry then give it the bare minimum, because the possibilities of using vacuum on a peace of foam means that chances of distortion are really high.., I have a FX-61 that crashed at 83 degrees full throat, and the wings survived unscabbed.. so yeah that stuff is really good! Thanks for the prompt response, good luck with your project.

[@dennisyoung4631]

The “thin” fiberglass is easy to cover molds…. Never used glass this thin, though - 2-3 oz cloth seems to work decently, in past projects.

[@eckiger_luki6424]

can you please make a video on hotwiring the airfoil ? there are tutorials but no really good ones you have big wings and they are perfect

[@mostlyharmlessrc3920]

Thanks for the kind comment but I'm not able to post anything at the moment. I just followed the advice of Andrew Newton and others. See this video to get you started: kzbin.info/www/bejne/gHq1q4SFaatrmc0

[@bullitanaconda]

Hi Great video I love your way to approach thinks we would've got along very well in the shop. Before watching this video I did a test similar to yours to choose between three fibreglassing techniques, The first technique was with the polycrylic the second technique was with zepoxy resin diluted with denatured alcohol and a third technique was zipoxy resin without diluting The Zepoxy without diluting is stronger than the other two techniques but it demands alot more attention when applying. I also did a few resistant tests similar to yours I never thought of the puncture test it's a great idea to test that. One extra test that I did is a sending test which I thought it would be important to know which technique would protect better in case of a belly landing onto A concrete runway. again the zepoxy without diluting is the more resistant so I was debating what technique to use because really refer the polycrylic because it's so easy to apply and then I said to myself how much strength finish do a plane really needs? if I think about it most of ARF models are covered with monocote and they hold up together pretty good so I guess the polycrylic is strong enough to cover any size model. But when I do apply polyacrylic I do at least 3 to 4 coats for better strength as opposed to zipoxy only one coat and it's still not that heavy because 60% of the polycrylic just evaporates. Keep up the good work

[@mostlyharmlessrc3920]

Thanks for the excellent comment! I have yet to try full-strength epoxy as a coating, for fear of the heat produced by curing and the extra weight. I have no doubt that full-strength epoxy is stronger than a thinned mixture, though! I also agree that polycrylic/polyurethane is the better choice in most cases - especially since you can just add another coat of it over your paint whenever you need to (I've done this on the Specter V3). Good luck man

[@JamesDoylesGarage]

Watch this friends. Best home SCIENTIFIC facts and comparison. Well done. Thank you.

[@mostlyharmlessrc3920]

Haha! Thanks James. I am a science guy by training, but this was just a comparison based on my own curiosity 😎

[@DaveFer]

Hey, thanks for this great video. I may be about to do the same type of layup on a model boat. Would love to see you actually do a wing. I'm dying to learn how contours and overlaps are handled.

[@mostlyharmlessrc3920]

Thanks for the comment! You may get your wish soon. :) I'm cutting new wings for a fast plank design now and was thinking I'd post it.

[@aerofpv2109]

Great technical DIY info. Very detailed and I must admit ... great hot wire cutting. Those wings looked perfect.

[@mostlyharmlessrc3920]

Thanks Aero! This hot wire cut wing has some imperfections where the wire wandered a little, but I filled these with lightweight spackle and sanded it flat. This wing is now fully fiberglassed and ready for paint. Thanks for the great comments as always man!

[@aerofpv2109]

I guess someday when I find the time I too shall DIY an airplane. Currently I have a 4 year old boy whom requires most of my energy ☺ Have a great Sunday my friend.

[@mostlyharmlessrc3920]

This kind of DIY building takes A LOT longer than FT or EA foam board methods, so expect my new plane production rate to go down! My wife and I don't have kids, but I work a lot and have other hobbies, so I understand time shortages. Maybe your little boy can have a cameo appearance in a video at some point. :) Have a great Sunday as well mate!

[@aerofpv2109]

That's a great idea .. the cameo ☺

[@YourAverageJoe1000]

Great video! Did you notice a difference in curing time for Z-Poxy and Alcohol versus pure Z-Poxy? Did it cure faster, slower, or not really make a difference?

[@mostlyharmlessrc3920]

Thanks! Sorry for the slow response. Adding alcohol reduced the curing time of Z-poxy a little, but I always left it to dry overnight. Good luck to you

[@nakul3424]

Thank you sooooo much, going to glass my jet first time and this was really helpful, bang on comparison, just what i was looking for and full of information. cheers!

[@mostlyharmlessrc3920]

You're so welcome! Thanks for the generous comment.

[@haideriraq1950]

Hi .. where did you get that fiberglass cloth?

[@Nicksbf109]

You answered my question z poxy is best suited for wings and poly is good for body

[@mostlyharmlessrc3920]

Glad you found it useful!

[@jimmytiler5522]

I cover all my foamy's with pantyhose and wall paper paste.Strength and paintable surface.just like back in the days of the 50"s and 60"s.

[@mostlyharmlessrc3920]

I have heard of using pantyhose but wallpaper paste is a new one on me! I may try that. I can picture the benefits of both - thanks for the useful comment. :)

[@jimmytiler5522]

Yeah when I use to roll my own rocket tubes for black powder rockets everyone used mixtures of PVA . I saw the paste on menards one day got the idea tried it now everyone who makes tubes for fireworks all use it.The strength is unsurpassed.Dont buy the liquid buy only yhe paste cheap and goes a long way. The panty hose were substitute for silk in the ole days.

[@justinw1765]

Thinning out epoxy with alcohol or any solvent, weakens it some. Thinning it by heat/warmth is the best method.

[@mostlyharmlessrc3920]

Thanks for the comment. I’m sure you’re right that thinned epoxy is a little weaker. Do you use a heat gun to “thin”? Thanks 👍🏻

[@justinw1765]

@@mostlyharmlessrc3920 I suppose you could use a heat gun, but that might be too intense for it. I just mix it in a glass jar, and put that jar in a container holding hot'ish water. You don't want to warm it up too much, just enough to thin it. Hope this helps

[@aliberkozderya3112]

Excellent video, much thanks for sharing

[@carlreeves9762]

Why not try uv resin, it started making surfboards.

[@mostlyharmlessrc3920]

I have never used it- good idea!

[@FarmerFpv]

Awesome content 👍 subscribed. I use to glass my gws planes with that same cloth and minwax to keep it light.

[@mostlyharmlessrc3920]

Thanks very much! People either love or hate this video 👍🏼

[@FarmerFpv]

@@mostlyharmlessrc3920 only worry about the positive folks. Welcome

[@EnglishTurbines]

Great Video, be interested to see that wing done in the water based varnish?....and glass cloth....I think it will be fine, avoiding the epoxy altogether is good if you can because of cost. The wated based poly is going to be far easier to use as well. Have you also considered using glass tissue..?...Not as strong, but lighter for sure....A local Uni did a UAV using this method and blue foam, it worked very well.....A coat of spray paint and your done..lol....Nice Video, thanks.

[@mostlyharmlessrc3920]

Thanks for the info! I have not seen or ever used glass tissue, but it sounds like I should try it. I am new to these methods and generally agree that polyurethane is easier and cheaper than epoxy! The uav made by your local school sounds interesting.

[@EnglishTurbines]

Yes, glass tissue is quite common. Since the fibres are short and random, the strength is fairly uniform in all directions. It will be lighter, but not as strong as the cloth. It does work, and you can sand it afterwards. I think you can get it from Car body repair shops etc.

[@scottdunlap4109]

Did you get bubbles with no precoat?

[@mostlyharmlessrc3920]

No I didn't, and I've used this method on three planes now. I think this is because I thinned the epoxy and also try to keep the fiberglass cloth flat and taught. Good luck.

[@ryanstreuli8667]

Have you considered using a composite material to cover the xps and leaving a hole to use a material like gasoline or acetone to melt the XPS inside? I feel like that would make a similar structure to the full composite airframes without all the work

[@patrolmars3371]

I know and old comment but will weighing h in anyway. 1. The method is valid for creating a fiberglass shell but it has the downside of nasty dirty solvent with styrene melted in in it. 2. The foam adds tremendous amount of rigidity, the shell needs to be significantly thicker to be as strong as glass over foam. Most true light weight composites use foam cores to give thickness to structures with little added weight - usually stronger than XPS which is not good for shear forces. But Burt Rutan designed real aircraft to be built by glassing over XPS and hundreds if not thousands were made. Foam is structural part in those too, not just a DIY friendly material for shaping.

[@Chris-vc1dh]

But fiberglass will not melt foam?

[@mostlyharmlessrc3920]

Fiberglass can be attached to foam with slow-curing epoxies like the one I used (Z-poxy) without damaging the foam at all. A few epoxies are not safe to use on foam, though, and some create a lot of heat as they cure. I recommend trying your epoxy on some scrap foam first to make sure it will work. Good luck.

[@tvideo1189]

Minwax Polycrilic is NOT a water based polyurethane. It is solely an acrylic product. No urethane in it at all.

[@mostlyharmlessrc3920]

Thanks for the correction. I'm pretty sure you're 100% correct. Urethane takes much longer to dry than polycrylic and is probably more durable. I'll put this info in the description.

[@tvideo1189]

@@mostlyharmlessrc3920 No worries. People all over sites like RCGroups, RC Universe and WattFlyer make the same mistake calling Polycrilic "WBPU".

[@Dg-zj6jo]

can you use carbon fiber mstting on foam planes

[@mostlyharmlessrc3920]

Yes I think you can. Most weights of carbon cloth are heavier than I'd want to use on a small plane, though. Kevlar cloth is also an option - have a look at the "Think Flight" channel for videos about this method.

[@thomasdaniel2022]

Thanks for the video🙂

[@veganautfpv1237]

Like the Old Chub in the background!

[@mostlyharmlessrc3920]

You weren't supposed to notice that. ;) Better builds come from better beer!

[@robertchapman7773]

Did you conduct a baseline test on untreated foam to get a % of improvement ?

[@mostlyharmlessrc3920]

@@robertchapman7773 Hi there- yes I did with the weights and puncture test (see tables near the end), but unfortunately not with the bend break part.

[@michaelrempel9025]

I am thinking of covering a foamie I bought. I was wondering what you do for hinges in those? The existing setup is just bendable foam, no hinge. Thanks for this video again. I was wondering exactly the same questions you answered.

[@mostlyharmlessrc3920]

Thanks for the great comment! Yes, you can cover a foamie using either method here, but I think I'd go with polycrylic in that case. You can buy plastic hinges from an online store for your control surfaces or just use heavy duty packing or extreme (reinforced) tape. Tape hinges are surprisingly strong. Good luck 👍🏼

[@thenatedog]

Had to come back and watch this again. So did you use this on the specter v3? That paint job looked amazing. I have designed up a "plank" style 50" slope soarer i am going to hot cut. I think i will do this on it. Keep up the cool videos man!

[@mostlyharmlessrc3920]

Just an update on the Specter V3 - I found a couple of small bubbles under the glass on the underside of the wing. The wing glass was put on with epoxy and the fuse glass with polyurethane. Ergo, it looks so far like I maybe should have glassed the whole plane in polyurethane! It's lighter, less toxic, and is adhering better after a few flights. Add more sparring to your wing if you do this, I'd say.

[@thenatedog]

Did you put spars in the wings? I usually put 4-6mm fiberglass kite rods on top and bottom right at cg. I am going to try the polycrylic way for sure. I really dont like working with epoxy. Going do it like a surfboard. One coat of 3/4 fiberglass. Paint job. Second coat of 3/4 fiberglass.

[@mostlyharmlessrc3920]

Excellent! Yes, see 0:32 in the specter v3 vid - you can make out spar channels I cut into the underside of the wing, covered in filler. I used 3 CF strips and one 5mm carbon tube. Fiberglass rods sound cheaper and easier to use. I would honestly do 3/4 ounce glass and poly, then another coat of poly, sand lightly, then paint and paint again. This is what I did on the fuse of the v3 and it seems bullet proof. I also did one final coat of poly over the paint on the underside of the fuse too, so maybe the order doesn't matter! The polycrylic comes in gloss or matte finish too, so you can make it as shiny as my wing if you want.

[@HowToDIYRc]

usefull vid must find some of your kind of foam my pink foam always started to melt because of the reaction heat

[@mostlyharmlessrc3920]

Thanks for the comment man! The z-poxy finishing resin doesn't make a lot of heat while curing in my experience. It's a little different from regular (especially the fast acting) epoxy.

[@HowToDIYRc]

Thx for the info mate

[@dudebroski9460]

This didnt waste my time at all. Great video! What would one coat poly and one coat z do on a panel?

[@mostlyharmlessrc3920]

Dude Broski Thanks! I'm really not sure - I don't know if the two would get along. My guess is it would be okay as long as the first layer dried completely. Let me know if you try it 👍🏼

[@darkknight90964]

Can you use an oil base polyurethane on fibreglass to cover XPS foam ? Does it works? As the water base polycrylic ??

[@mostlyharmlessrc3920]

Thanks for the question. I think oil-based polyurethanes have a good chance of melting (dissolving) XPS foam. What I used in this video (polycrylic) is not a polyurethane. It’s worth trying this on a small scrap of material. Good luck to you.

[@warbuzzard7167]

So, this was awesome. Thank you.

[@mostlyharmlessrc3920]

Thanks for the great comment! Hope the information is useful to you.

[@thenatedog]

awesome info man!

[@mostlyharmlessrc3920]

Thanks Nathan! Like I said to Andrew, I couldn't find this information anywhere so I had to generate it.

[@rcpilot4970]

Hi, what fibreglass cloth do you use? Thanks.

[@mostlyharmlessrc3920]

Roger Waters Have a look at 1:56. It's 3/4 ounce glass cloth from Hobbico. This material is available from quite a few hobby sources though. Good luck!

[@Dana-ov7fo]

Please make more videos

[@sparrow082]

Yep, yep, yep, yep, yep, and yes I just cut my first wing today. Lol.

[@mostlyharmlessrc3920]

Adam Sparrow Lol! Thanks for commenting and congrats on your wing!

[@asifheliRC]

Suscribed nice content.

[@mostlyharmlessrc3920]

Thanks and thanks!

[@earlallen6628]

What Resin do you yous

[@mostlyharmlessrc3920]

Hi there, I used Z-Poxy finishing resin.

[@ianhennus1518]

Hi, doesn't the alcohol disolve / deform the foam??

[@mostlyharmlessrc3920]

ian hennus Hi there! No, I didn't see any deformation of the foam due to alcohol. Perhaps that's the reason people are disliking this video? I used this alcohol/epoxy technique on a large wing and had no issues. Thanks for the comment.

[@ianhennus1518]

ok, thanks! I will give this method a try.

[@dhymers]

Will this work with EPO foamies ?

[@mostlyharmlessrc3920]

Dave Hymers Yes, both of these techniques will work fine on EPO, though I recommend skipping the thinning with alcohol step if you use epoxy. Good luck and thanks for commenting 👍🏼

[@JoesRCCorner]

Thats a great video. I have been building planes using the WB-Poly for some time. No I am not using it for strength. I use it to bind the balsa sheeting prior to painting. Check out my video on fiberglassing my Super Chipmunk.

[@mostlyharmlessrc3920]

Thanks for the comment and the good idea! I'll take a look...