Ben H Posted December 27, 2015 Share Posted December 27, 2015 I put to following on my build thread of my extra 330, but I thought it might be of interest as a hints and tips for the use of epoxy as a fuel proofing treatment to firewalls and bulkheads. I was removing the engine again to fuel proof the bulkhead and firewall. I use 30minute epoxy for this, but NOT THINNED as many seem to do. There's a reason for this rebellion from what seems to be the norm. I come from a marine engineering background and would consider myself to have a reasonable working knowledge of epoxy systems. When we use epoxy as a surface treatment we want to lower viscosity so it's easy to apply a thin layer to avoid excess weight and waste and to get an even finish. There are two ways to reduce viscosity in epoxy resin, one is heat, the other is the use of solvents. Solvents such as denatured alcohol (methylated spirit to us in the uk), acetone and thinners does reduce viscosity, but significantly reduces strength, takes a long time to dry, and importantly for fuel proofing MAKES IT POROUS... Yes, not good for sealing a surface! What happens is that the surface starts to cure first, leaving unevaporated solvent beneath the surface, as this escapes it blows holes in the part cured surface leaving a porous surface that would actually wick spilt fuel into the wood core! Not good! Heat on the other hand, reduces viscosity with no chemical change to the mixture, no detrimental effect on strength or proofing ability. Heat your resin and hardener bottles in water from the hot tap, about 60 degrees is good, for 5 mins before you mix it, you might have to change the water after a couple minutes to keep it warm. Mix it quickly in a pre warmed bowl or container. Have a hair dryer at hand, and a brush for application. Pre warm the wood with the hair dryer and keep it warm as you brush on the epoxy mix, you'll find it will flow almost like water as it is warmed with the hair dryer on the timber. Don't warm the mixed epoxy in the mixing pot, as it will accelerate curing, just warm it as its applied to the wood. The working time will be reduced but you'll still have a good 10-15 minutes before it starts to turn, so don't mix too much at a time. A small amount of epoxy goes a very long way here, so don't mix too much! It'll be touch dry in 30mins and properly hard in 24h. Here is a link to some evidence to support this from West Epoxy Systems, leaders in epoxy resin.. http://www.westsystem.com//ss/assets/Uploads/ThinningEpoxy.pdf If anybody has any contradicting information or evidence related to this, I'd be fascinated to hear about it... Quote Link to comment Share on other sites More sharing options...
Former Member Posted December 27, 2015 Share Posted December 27, 2015 [This posting has been removed] Quote Link to comment Share on other sites More sharing options...
PatMc Posted December 27, 2015 Share Posted December 27, 2015 Posted by Percy Verance on 27/12/2015 21:03:12: I put my epoxy bottles in the microwave for 20 seconds Ben. Works a treat.......... I knew someone who used to do that with Humbrol enamal paint, instead of using any type of thinners, when he wanted to spray. It worked well for him. Quote Link to comment Share on other sites More sharing options...
Ben H Posted December 27, 2015 Author Share Posted December 27, 2015 Posted by Percy Verance on 27/12/2015 21:03:12: I put my epoxy bottles in the microwave for 20 seconds Ben. Works a treat.......... Good Idea Percy, that would save some time waiting for hot water to warm the bottles Quote Link to comment Share on other sites More sharing options...
Craig Carr Posted December 27, 2015 Share Posted December 27, 2015 Hello Ben, I have always used epoxy skinning resin mixed straight from the bottles for fuel proofing. no need to heat them up or anything. Just mix and apply straight on with a brush, you'll still get nice thin layers Craig Edited By Craig Carr on 27/12/2015 22:26:03 Quote Link to comment Share on other sites More sharing options...
Geoff S Posted December 27, 2015 Share Posted December 27, 2015 That's really interesting and, as you obviously have experience using West epoxy which I first came across when building dinghies, you're probably right. However, when I needed something to thin epoxy a few years ago I got a 5 litre can of acetone through a friend of mine who knew the owner of a firm making glass fibre canoes in Stanley near Ilkeston in Derbyshire. Presumably they used the acetone for something but what? Would there be another use for it in glass fibre moulding? Geoff Quote Link to comment Share on other sites More sharing options...
Ben H Posted December 27, 2015 Author Share Posted December 27, 2015 Hi Craig, skinning resin does brush nicely if you have some, but it's expensive and I usually have plenty of 30min lying about... Geoff, fiberglass is made of polyester resin not epoxy, so acetone is often used but usually for cleaning and prepping purposes Quote Link to comment Share on other sites More sharing options...
Jon H Posted December 27, 2015 Share Posted December 27, 2015 I have always thinned the epoxy I use for glasscloth over wings/fuz etc but not for anything else. I have never had any issues with the resin used on the wings as the thinners evaporates long before the epoxy dries, especially when I give it blast of heat with a heatgun on low after I brush it on. If however I leave some in the pot it sets very rubbery as the thinners is trapped as ben suggests. I don't know why you would thin epoxy for firewalls or anything structural, that makes no sense to me Quote Link to comment Share on other sites More sharing options...
Former Member Posted December 27, 2015 Share Posted December 27, 2015 [This posting has been removed] Quote Link to comment Share on other sites More sharing options...
Jon H Posted December 27, 2015 Share Posted December 27, 2015 Fair comment, I tend to use naturally thinner finishing resin in that situation but I have been known to thin resin further if I have a fine stress crack to deal with or I want to get resin into the grain, but again I tend to thin it with some epoxy thinner which evaporates so fast when applied thinly that it makes no odds. I have also sprayed thinned epoxy with great success and this is now how I tend to fuel proof tank bays on artf models. Works a treat, just make sure you are quick getting it out of the airbrush though. Quote Link to comment Share on other sites More sharing options...
PatMc Posted December 28, 2015 Share Posted December 28, 2015 Posted by Ben Holt 1 on 27/12/2015 22:39:04: Geoff, fiberglass is made of polyester resin not epoxy, so acetone is often used but usually for cleaning and prepping purposes Ben, surely fibreglass is the dry material that's bound together by the resin be it polyester or epoxy ? I've used both types of resin with FG many times. PS I agree that acetone is best used only for cleaning purposes. Edited By PatMc on 28/12/2015 00:15:14 Quote Link to comment Share on other sites More sharing options...
Geoff S Posted December 28, 2015 Share Posted December 28, 2015 Posted by Ben Holt 1 on 27/12/2015 22:39:04: Hi Craig, skinning resin does brush nicely if you have some, but it's expensive and I usually have plenty of 30min lying about... Geoff, fiberglass is made of polyester resin not epoxy, so acetone is often used but usually for cleaning and prepping purposes Ah yes, that makes sense. However, as Pat says, fibreglass can be used to reinforce both polyester and epoxy resins. Apparently the canoes were pretty classy ones used for competition so they could have been either polyester (cheap) or epoxy (expensive). Geoff Quote Link to comment Share on other sites More sharing options...
Ben H Posted December 28, 2015 Author Share Posted December 28, 2015 Posted by Geoff Sleath on 28/12/2015 00:29:41: Posted by Ben Holt 1 on 27/12/2015 22:39:04: Hi Craig, skinning resin does brush nicely if you have some, but it's expensive and I usually have plenty of 30min lying about... Geoff, fiberglass is made of polyester resin not epoxy, so acetone is often used but usually for cleaning and prepping purposes Ah yes, that makes sense. However, as Pat says, fibreglass can be used to reinforce both polyester and epoxy resins. Apparently the canoes were pretty classy ones used for competition so they could have been either polyester (cheap) or epoxy (expensive). Geoff Your quite right Geoff (and Pat), fiberglass is the matting that binds the resin together. I was generalising because you were talking about canoes by saying it would be polyester resin rather than epoxy. Epoxy can of course be used with glass mat, carbon mat, Kevlar etc, for a higher strength lay up than polyester. Whether epoxy of polyester, acetone would be used for prepping the surface and cleaning rather than to thin the mix. Quote Link to comment Share on other sites More sharing options...
Engine Doctor Posted December 28, 2015 Share Posted December 28, 2015 Just my opinion but why would you want to use epoxy adhesive for fuel proofing models in the first place ? It's heavy , usually sets to a rubberry like skin and doesn't penetrate the surface well. Skinning or finishing epoxy sure ,that's a different stuff that can be brushed thinnly and soaks in reasonably well but not the adhesive type. I think using epoxy is a left over from the past when you couldn't get a proper fuel proofer suitable for models so used whatever was at hand . A propper fuel proofer like Solarlac designed for model aircraft is a far better option that can be thinned if required ,soaks into the surface so preventing fuel from soaking/wicking into the wood and at a fraction of the weight. It's also a heat sensitive resin that bonds any iron on covering film to the wood preventing fuel from creeping under it. Even the two pack type fuel proofers are far better at proofing . Edited By Engine Doctor on 28/12/2015 09:43:25 Quote Link to comment Share on other sites More sharing options...
Former Member Posted December 28, 2015 Share Posted December 28, 2015 [This posting has been removed] Quote Link to comment Share on other sites More sharing options...
Cuban8 Posted December 28, 2015 Share Posted December 28, 2015 Posted by Ben Holt 1 on 27/12/2015 22:25:04: Posted by Percy Verance on 27/12/2015 21:03:12: I put my epoxy bottles in the microwave for 20 seconds Ben. Works a treat.......... Good Idea Percy, that would save some time waiting for hot water to warm the bottles I understood that the heating effect of microwaves relied on the excitation of the water content of the item being cooked. Didn't think there's water in resin of any description............obviously something else going on. Quote Link to comment Share on other sites More sharing options...
John Lee Posted December 28, 2015 Share Posted December 28, 2015 The epoxy molecules get just as excited as water molecules! It can also be used as a last resort on old epoxy which is going crystalline in the container. I can't say I've had any problem using solvents with epoxy, I've done so for over 30 years without concern. Whilst I accept the theory in the OP, in practice it does not seem to have any notable material effect. Quote Link to comment Share on other sites More sharing options...
Don Fry Posted December 28, 2015 Share Posted December 28, 2015 You will find than thinning epoxies with propan2ol, or isopropyl alcohol, available on e bay, has no effect on tensile strength, and will evaporate off long before cure, unless you are thinning something like 5 minute epoxy. And why would you want to. Good solvent for the second coat when skinning a wing, as it flows better when applied, and is evaporated in minutes so does not run. Quote Link to comment Share on other sites More sharing options...
Ultymate Posted December 28, 2015 Share Posted December 28, 2015 Personally with large petrol models, which I've flown for many years now, I've found the engines run so clean that I've not felt the need to fuel proof at all be the model ARTF plan or kit built. Occasionally I've strengthened engine boxes with triangulated balsa but never fuel proofed a single one Quote Link to comment Share on other sites More sharing options...
Engine Doctor Posted December 28, 2015 Share Posted December 28, 2015 Posted by Percy Verance on 28/12/2015 10:18:07: ED I don't think you'd use Solarlac/Clearcoat again if you tried Poly C.............. no mixing, brushes/tools clean up with water. Superb fuel proofer. I will defo try Poly C when my Clearcoat runs out. Quote Link to comment Share on other sites More sharing options...
Former Member Posted December 28, 2015 Share Posted December 28, 2015 [This posting has been removed] Quote Link to comment Share on other sites More sharing options...
onetenor Posted December 28, 2015 Share Posted December 28, 2015 Oh dear What ever happened to the fuel proofers of yesteryear , I was away from the hobby for some yrs so have lost touch.But various makers did them and some really good HMG Joy, and a surprise one from Humbrol. While not advertised as such Humbrol Marine Varnish turned out to be Hot fuel proof and a wonderful gloss to boot.Surely in the ensuing yrs proofers have been improved even more. There were also some good American dopes as well but names escape me now. Regarding glassfibre, beit chopped strand mat woven cloths etc. Any or all of which can be used in a moulding . The whole thing being known as a Glass Reinforced Plastic moulding . ( a GRP ) trrespective of the resin used. I've not looked on t'interweb but I think there should be some good proofers about. Have a look and report back if you find any . ! or 2 part Cheers John Quote Link to comment Share on other sites More sharing options...
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.