Epoxy thinning-Calling Ace, jwrass and...

[Cato]

-any other professionals or experienced epoxy users.

I use 5-minute Z-Poxy by Pacer when called for. It works well. However, many times I want to 'paint' a thin stripe or small bead in a confined area and get the usual strings or misplaced blobs. Very frustrating.

The instructions on the bottles say 'Remove excess immediately with denatured alcohol'.

My question is ; can it be thinned when mixed to get a more workable consistency? If so, denatured alcohol or some other chemical? Bond strength (if thinning effects that) is seldom an issue in these small areas. Nor cure time if thinning effects that too. I know heat (from a heat gun) might thin it but I imagine it would 'kick' it faster than 5 minutes.

Advice greatly appreciated.

[Ace-Garageguy]

Acetone is really usually the preferred "thinner" for epoxy (but in any real-world application, where the design-strength of the epoxy is important, thinning is verboten). I haven't tried denatured alcohol to thin or clean up any of the epoxies I use, but acetone should do the trick. I'd recommend testing both, as there are thousands of "epoxy" formulations, and not everything works with everything. And yes, heat will most likely kick it much faster.

Not the question you asked, but I HAVE used acetone to "thin" polyester resins in non-critical layups, mostly when the material was past its use-by date, or I just needed really quick wet-out.

Again, test before you commit to using the stuff on anything at all important. And remember...it doesn't take much acetone at all.

And thin it AFTER mixing, so you know what your percentages of A and B are.

[Snake45]

many times I want to 'paint' a thin stripe or small bead in a confined area and get the usual strings or misplaced blobs. Very frustrating.

For jobs such as this, I've often used carpenter's glue. It's like Elmer's but it's yellow, it sticks better, dries harder, and is sandable. It goes right into small areas and excess wipes away with a wet finger. It might work for some of the kind of jobs you're talking about.

[jwrass]

Cato,

From my point of view and experience there is not a glue, epoxy, resin, body filler, spot putty etc that can't be thinned, I do some consulting work for Rust-Olem on their HVAC equipment for their R&D division in Kenosha ,Wi

I have seen them mix small batches in the lab for testing and large batches in the plaint for production of thousands of gallons for resale. The basis formula for paint is resin, pigments and thinner or (reducer) after they mix the material for a period of time they check the viscosity with a zahn cup ( you can look it up on the internet) the cup in cylindrical in shape with a domed bottom with and hole in it. the top of the cup is open and they have a hand much like a ladle. To check the viscosity you dip the cup in the paint and when you pull it out of the paint you start to time( I use a stop watch) how long it takes for the cup to empty. the time it takes to empty the zahn cup would be the measured viscosity. if the viscosity is to thick they add reducer if It's to thin the add more resin and pigment. It's a simple process really, when the paint is to thick you just add more reducer, When it's to thin it's a bit more tricky because you have to add more resin and pigment and you need the color to come out perfect so when the consumer from coast use multiple cans of say sunshine yellow they all match. The mixtures of the paint are all computer controlled as to how much material you have to add (if any) to get the proper color and viscosity.

I know this chatter on paint my be a bit confusing because you asked about thinning epoxy, however I thought I would give you some insight viscosity and how they all relate.

It has been my experience that most resin base materials can be thinned down. The only question that is unanswered is what material to I use to thin it and to keep it's intended integrity.

First approach I would take is to call customer service and tell them about your problem and ask what they recommend, I call tech support from time to time and I have to say that 95% of the people know their product and steer you In the right direction.

As for fiberglass work I use acetone as that is the recommended product for that type of resin and it works great!

I will echo Aces comments on that not all resins are the same chemical make up. You may have to try several types of solvent to get the results you desire. You may have to SWAG it with a drop of this and a drop of that to get the results you desire. If I were me my first choice for a epoxy would be Acetone, then Lacquer thinner as they are pretty hot solvents. Denatured alcohol is pretty weak compared to the two I mentioned. I use denatured alcohol to remove little mistakes and finger prints on pinstriping jobs and I never have had that solvent attack the under lying paint.

Play around with some scrapes before you commit to your model, As you add thinner go slow a drop at a time, it's allot easier to add a bit more thinner that to try to hurry to add a bit of A&B because you have little time before it kicks if you choose the mix it all at one time method

The one thing I would do different than Ace is I would thin part A and B in separate containers and get them to be of equal consistency. Then I would mix the two together A&B this gives you longer working time. as you not trying to add this or that as the epoxy is starting to cure. Once A meets B it's game on!!!!! the chemical reaction has begun and your time is limited. Either method is fine and will work The method I describe gives you a longer work time and could save you the hassle of trying to add this or that because you over reduced

I hope this helps!!! Good luck & cheers Jimmy "RASS"

[Cato]

Great to have industry pros on the site that share. Excellent advice, tech explanations and tips. I will test all of them as I want a solid, 'go to' system every time I need epoxy. And I will test the Carpenter Glue as well-never thought of that.

Many thanks to all of you.

[Ace-Garageguy]

The one thing I would do different than Ace is I would thin part A and B in separate containers and get them to be of equal consistency. Then I would mix the two together A&B this gives you longer working time. as you not trying to add this or that as the epoxy is starting to cure. Once A meets B it's game on!!!!! the chemical reaction has begun and your time is limited. Either method is fine and will work The method I describe gives you a longer work time and could save you the hassle of trying to add this or that because you over reduced

Let me elaborate on my reasoning and experience.

All the epoxies I'm familiar with are high-performance aviation and industrial products. They HAVE to be mixed on a gram-scale, and accuracy HAS to be maintained to 1/2 of 1% by weight, part A to part B. If I mix an aircraft epoxy incorrectly on a wing spar repair and it fails, people die. This pretty well precludes sloshing some "thinner" into a container until it feels right, and mixing two components together in kinda similar amounts. And the printed Product Data that we keep on file (with which I must comply EXACTLY according to FAA regs, and not a conversation with some tech rep on the phone who MAY know what he's talking about...and I've encountered plenty over the years who had no clue) are very specific as to the handling of these materials. Thinning is forbidden on most of them. And it's these resins, once they've gone out of date and are illegal to use on aircraft, that I use in model building. I ALWAYS mix on a gram scale, and I never thin them. If they've deteriorated to the point they NEED thinning, they won't work properly and should be discarded.

Epoxies cure by cross-linking of the molecules in the resin and hardener (unlike polyester resins, the commonly used "fiberglass resins" which CAN be thinned in moderation with acetone, or styrene monomer in some cases) and if they're to perform anywhere near their maximum design strength, the ratios of resin-to-hardener (A to B ) must be maintained accurately, and why I suggested thinning AFTER you get your mixing ratios as close to equal as you think you want them. Adding odd amounts of "thinner" into un-weighed tiny amounts of A and B parts before mixing is a guarantee of bond failure at some time.

This is why I personally have no use for 5-minute products that mix a little of this and a little of that, and whose strengths vary all over the board as a result...from never hardening properly to being so brittle as to be useless. I like to know every time what I'm getting, so I use better materials...and stronger materials almost always give you plenty of working time because THE STRONGER AN EPOXY IS, THE LONGER IT TAKES TO CURE. My primary resin system takes a full 24 hours to fully cure, and gives over an hour of working time at 75degF.

To summarize, try to mix your materials as accurately as possible, and TEST FIRST, thoroughly, if you want consistent results you can always count on. Obviously you don't need aviation-quality bonds, but you DO need methods that are repeatable and reliable.

EDIT: I DO use 5-minute epoxies sometimes in aviation work, but only as temporary fixturing material that will be removed completely in the final repair area. Their rapid set-up does make them useful to hold something in place while a proper lamination is performed on the other side of a join or repair...but they MUST be removed and not laminated over on structural work.

EDIT 2: The kind of fiberglass work I do with models demands absolutely predictable results every time. In this shot, I'm laying up an epoxy / fiberglass track-nose in a polyester / fiberglass mold I also made from my own master. The cloth shown here is only .009" thick, and two layers (laminated with MGS 285 resin) are all that are necessary to produce almost-scale-thickness parts that are vastly stronger than any styrene or resin could possibly be.

This is a finished layup before trimming.

This shot of the track-nose layup gives a good idea of the thickness of the completed parts. The black stuff is residual primer I've been sanding away to compensate for a less-than-perfect mold surface. This was also early in the experiments that have led to getting consistent results with these materials on models.

Edited September 21, 2014 by Ace-Garageguy

[Snake45]

And I will test the Carpenter Glue as well-never thought of that.

It's fun stuff to play with. It dries fairly hard and is supposed to be sandable, but I've never tried feather-edging it into styrene so I don't know if that will work or not. But I have used it as a putty of sorts sometimes, say I've glued a roll bar support on and there are gaps between the two pieces, the carpenter glue on a toothpick fills those fine and if there's any extra, it just looks like weld bead.

It can also be used as a casting resin for thin or flat-ish parts. For example, I have several P-51 Mustang (airplane) kits that have very poor landing gear doors. This is a fairly simple part and I could scratchbuild them but it has some internal structure that would take some time and effort to duplicate. I also have kits with good doors. I'm gonna make a silicone mold of the good doors, and then fill it with the yellow glue and make the parts out of that. Might take two or three thin fillings but the stuff is cheap and I got time. If it doesn't work to suit me, there's always J-B Weld.

I'm sure you'll come up with a dozen uses of your own for the stuff, once you've tried it.

[Cato]

Excellent tech discussion guys. Thanks again.

[Psychographic]

Try heating the epoxy with a hair drier after it is mixed and while it is still in your mixing vessel. Many liquid epoxies will get much less viscous with heat. IIRC correctly you have to work quickly as once it cools it will thicken up. I used this trick when building an RC boat ages ago and had great results. I don't remember what brand of epoxy I used and can't guarantee it will work with all epoxies.

[Mike Kucaba]

I've been using epoxy for years and store mine in the 'frig to lengthen it's shelf life. When I take them out I set the bottles in HOT water and it thins them out nicely. I only use 30 minute set type though. I've also noticed that this speeds up the cure considerably, can't imagine what that would do to the 5 minute set type.

BTW, I googled thinning epoxy and came up with a plethora of ways to thin the stuff.

[Cato]

Well I knew there were a few pros right here which is why I didn't search elsewhere. All the answers have been terrific with explanation and experiences. Yeah, I tried the heat gun in the past but I wasn't good enough with 5-minute to lay it out. It kicked too fast but I'm sure that's my fault.

Thanks David and Mike too.

[jwrass]

Ace,

Great information!!!!!! I know you have vast experience in the Aircraft Arena and thank you for sharing The how's, the whys, the wherefores and most importantly the safety.

There is a art and science to what you do when making repairs, their are no short cuts and you need to be a seasoned technician with years of schooling and training to qualify to do the types of repairs you do. these are not DIY projects

Their are many product and materials used in many industries that components are mixed by weight because that's how they are designed. It's just like paint problems I feel most painter problems start at the bench by not adhering to mixing ratios.

How I described the way I would mix could easily be done on a scale to get the proper proportions. I personally I would still do it the way I described as it would in fact give me a larger working window.

I have all sorts of big box epoxy brands and curing times for house hold use. I have never use any epoxies on models (just got back into modeling the first of this year after being away from it for many years) I use the stuff for nick nacks and things that get broken around the house but never have had success with any if it where strength was a factor.

I know the epoxies that are used for aircraft are of a critical nature and that best practices prevail.

With big box types of epoxy I personally don't feel it's that critical (to a degree) I would bet that I have never mixed a batch of epoxy, body filler, glazing putty to exact ratios using the ribbon method as recommended by the manufactures and I have been mixing that stuff for close to 40 years

With big box epoxies whether you add thinner before you mix A&B or after you mix A&B I really don't feel theirs a difference ( you say tomato, I say tomato, come see, com sa) your still adding a additional component to the mix which in theory does alter the base product. It's a model no one is going to die if it falls of the shelf (Hopefully)

I personally I have had great tech support (but I don't work in the aircraft business) within 2 minuets I can tell if the person I speaking with knows what they are talking about. Just like my customers I try to qualify them to meet their needs and my needs. If I feel the tech doesn't have a clue I ask for another one. I go as high on the food chain as I have to get the answers I need. If I buy their product I feel they owe me that. I'm not bashful in getting the answers I need. Having product data sheets is great and I keep binders of every product I use. I have found errors over the years in many data sheets. Nothing is exempt to error, we read about it everyday during the new cycle.

Great lay ups Bill!!! quality A+++++ Just curious are the bucks original pieces or did you make them? They look great! I have done much fiberglass work in my career and have played with resin castings of late with mixed results. I'm definitely going to try your process!!! Thanks for sharing.

My greatest respects to you Bill!!! You are truly a asset to all who are on this site! jwrass

[Ace-Garageguy]

Just curious are the bucks original pieces or did you make them? They look great! I have done much fiberglass work in my career and have played with resin castings of late with mixed results. I'm definitely going to try your process!!!

I use different techniques depending on the project. The track-nose master was made like zo, from kit parts and bondo...

...fitted to the car...

Master on left, mold in center, and first pull on right. I learned from mistakes on this one, like compatibility of mold-release materials with model materials, etc. The ugly surface on the black part is because I failed to properly prepare and seal the surface of the master prior to laying up the mold.

[Len Woodruff]

Let me elaborate on my reasoning and experience.

All the epoxies I'm familiar with are high-performance aviation and industrial products. They HAVE to be mixed on a gram-scale, and accuracy HAS to be maintained to 1/2 of 1% by weight, part A to part B. If I mix an aircraft epoxy incorrectly on a wing spar repair and it fails, people die. This pretty well precludes sloshing some "thinner" into a container until it feels right, and mixing two components together in kinda similar amounts. And the printed Product Data that we keep on file (with which I must comply EXACTLY according to FAA regs, and not a conversation with some tech rep on the phone who MAY know what he's talking about...and I've encountered plenty over the years who had no clue) are very specific as to the handling of these materials. Thinning is forbidden on most of them. And it's these resins, once they've gone out of date and are illegal to use on aircraft, that I use in model building. I ALWAYS mix on a gram scale, and I never thin them. If they've deteriorated to the point they NEED thinning, they won't work properly and should be discarded.

Epoxies cure by cross-linking of the molecules in the resin and hardener (unlike polyester resins, the commonly used "fiberglass resins" which CAN be thinned in moderation with acetone, or styrene monomer in some cases) and if they're to perform anywhere near their maximum design strength, the ratios of resin-to-hardener (A to B ) must be maintained accurately, and why I suggested thinning AFTER you get your mixing ratios as close to equal as you think you want them. Adding odd amounts of "thinner" into un-weighed tiny amounts of A and B parts before mixing is a guarantee of bond failure at some time.

This is why I personally have no use for 5-minute products that mix a little of this and a little of that, and whose strengths vary all over the board as a result...from never hardening properly to being so brittle as to be useless. I like to know every time what I'm getting, so I use better materials...and stronger materials almost always give you plenty of working time because THE STRONGER AN EPOXY IS, THE LONGER IT TAKES TO CURE. My primary resin system takes a full 24 hours to fully cure, and gives over an hour of working time at 75degF.

To summarize, try to mix your materials as accurately as possible, and TEST FIRST, thoroughly, if you want consistent results you can always count on. Obviously you don't need aviation-quality bonds, but you DO need methods that are repeatable and reliable.

EDIT: I DO use 5-minute epoxies sometimes in aviation work, but only as temporary fixturing material that will be removed completely in the final repair area. Their rapid set-up does make them useful to hold something in place while a proper lamination is performed on the other side of a join or repair...but they MUST be removed and not laminated over on structural work.

EDIT 2: The kind of fiberglass work I do with models demands absolutely predictable results every time. In this shot, I'm laying up an epoxy / fiberglass track-nose in a polyester / fiberglass mold I also made from my own master. The cloth shown here is only .009" thick, and two layers (laminated with MGS 285 resin) are all that are necessary to produce almost-scale-thickness parts that are vastly stronger than any styrene or resin could possibly be.

This is a finished layup before trimming.

This shot of the track-nose layup gives a good idea of the thickness of the completed parts. The black stuff is residual primer I've been sanding away to compensate for a less-than-perfect mold surface. This was also early in the experiments that have led to getting consistent results with these materials on models.

Bill can you share the source for the resin & .009 fiberglass mat?

[jwrass]

Bill,

Thanks for the pictures and the text! Most Excellent!!!!!

I sent you a pm on Sept 12 Did you receive it? I have had some problems with pm's that's why I ask.

Jimmy "RASS"