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Epoxy on Inside of Cowl?

Bugsy

Bugsy

Well Known Member
Did you leave the cowling inside as is or did you put a thinned coat of epoxy in order to keep it clean. As rough and porous as it is, it sure does seem like it will collect oil and dirt over time.
 
Paul,

I put a few coatings of epoxy mixed with acetone.

Once that was hard I covered the inside of the lower cowling with aluminum "contact paper" to protect it from the heat.
 
thinning epoxy

I'm real reluctant to thin any resin with acetone. I think you are asking for trouble. no matter what vans says. just my opinion. I like what dan did. thanks for the idea I'm gonna steal it lol.;)
Erik
 
I put a coat of thinned epoxy, spray-painted some white high-temp paint, then another coat of thinned epoxy. Cleans up real nicely if needed. I also put some thin Al tape in areas near heat sources (could see where this was needed when the epoxy started turning a bit brownish).

greg
 
Erik Westlund said:
I'm real reluctant to thin any resin with acetone. I think you are asking for trouble. no matter what vans says. just my opinion. I like what dan did. thanks for the idea I'm gonna steal it lol.;)
Erik
Click to expand...

Erik,

Why do you think that is an issue? We are not talking about structural issues here.

Also, what did Dan do?
 
Bugsy said:
Did you leave the cowling inside as is or did you put a thinned coat of epoxy in order to keep it clean. As rough and porous as it is, it sure does seem like it will collect oil and dirt over time.
Click to expand...
The inside of the cowl should be sealed. For the most part, over a period of time I brushed on epoxy that was left over from other jobs. Not only does this seal the inside of the cowl making wiping away grease and grime easier, but even more importantly, gives heat foil a much improved surface to better adhere to.

2q9dlso.jpg
 
This particular Dan doesn't much like ad-hoc chemistry in the field.

Here's the question. Is there some good reason to thin it?
 
DanH said:
This particular Dan doesn't much like ad-hoc chemistry in the field.

Here's the question. Is there some good reason to thin it?
Click to expand...
The thinned epoxy runs into the pin holes better, that's all. No real reason.

The odd part was that it took a long time to harden but in checking with a Chemist friend that I used to work with, he looked up the chemical makeup and give it his blessing.

Once it hardens you can't tell any difference between this epoxy and any other. That said, I wouldn't use it any place you need structural strength.

BTW, for those reading this, the reason to coat the inside of the cowl are to fill those pin holes and keep the oil that will drip on the cowling from seeping into the porous cowling.
 
I also coated once with thinned epoxy, then painted with high heat paint and then coated that with more thinned epoxy.

Looks good and is tough but time will tell if it will work long term.

I painted it just to cover up that darn pink inside.

What was Van's thinking with that pink?????
 
Wet Micro?

I'm still new to working with composites, so pardon me if this is an ignorant question. Couldnt you use a 'wet' micro resin to get the same result as thinning it with Acetone? Not sure which way is better, but I just took the SportAir composites class and our instructor said the same thing...to never thin resin with Acetone. Maybe he was talking specifically about structural applications?
 
N941WR said:
The thinned epoxy runs into the pin holes better, that's all. No real reason. the odd part was that it took a long time to harden but in checking with a Chemist friend that I used to work with, he looked up the chemical makeup and give it his blessing. Once it hardens you can't tell any difference between this epoxy and any other. That said, I wouldn't use it any place you need structural strength.
Click to expand...

Having experimented with application methods and viscosity, I'm not so sure we ever really get anything deep into a pinhole. For the most part we just seal over them. Anything inside the pinhole is a bonus, and I'm pretty sure you need mechanical action (brushing or pressure) to do it. If low viscosity alone was enough to fill a pinhole, you could do it with a wet coat of paint or primer/sealer.

Several potential troubles with thinning. One, you could easily get two different results with two different epoxy formulations. Although the basic chemical building blocks are the same, actual formulations vary in details.

Two, the solvent can have an unexpected effect on the substrate. For example, consider a "pinhole" which extends through the glass/epoxy layup and opens into a foam core.

Three, solvent evaporation cools the surface, which can promote blush and probably amine deposit.

And as you noted, cure is delayed. I think we wait around quite enough.

That said, homebuilders have been doing it for years....to each his own.
 
Brian, you must of filled out your order form incorrectly.

Brantel said:
I also coated once with thinned epoxy, then painted with high heat paint and then coated that with more thinned epoxy.

Looks good and is tough but time will tell if it will work long term.

I painted it just to cover up that darn pink inside.

What was Van's thinking with that pink?????
Click to expand...

You need to check the 'boy' not the 'girl' check box.:p

Kent
 
RV7Ron said:
Couldnt you use a 'wet' micro resin to get the same result as thinning it with Acetone?
Click to expand...

Microbubbles are added to mixed resin/hardener for low mass bulk. In general, sanded micro needs a seal coat just like bare glass layups. It often shows pits and pinholes in its sanded surface because of air entrained during the mixing process.
 
I agree with Dan. In order to seal the pinholes, I would squeegee on a coat of pure epoxy, wait for it to tack and repeat, say 3-5 times. You can easily work the corners with the right size squeegee.

my 2c

Ryan
 
DanH said:
This particular Dan doesn't much like ad-hoc chemistry in the field.

Here's the question. Is there some good reason to thin it?
Click to expand...

Only that it provides a very thin sealer coating with very little added weight. I know it is not that big of a difference but weight is weight.

It also is much less work to brush it out (can be done very quickly) and have it fill all of the pores of the cowl.

I have cowls that have been in service for over a thousand hours and 8 years that were done with thinned epoxy. It is still holding up great.

Disclaimer...I do not recommend, and would never myself use, any chemical to thin epoxy when doing any glass lay-up that would be considered structural.
 
DanH said:
This particular Dan doesn't much like ad-hoc chemistry in the field.

Here's the question. Is there some good reason to thin it?
Click to expand...

Doesn't it depend on the epoxy and the thinner?

West is already fairly thin; others (ZPoxy) are a fair bit thicker. I don't think I've ever thinned out the West stuff; I've thinned out others numerous times.

Acetone is oft mentioned as a thinner but has obvious bad effects on foam etc. Isopropyl alcohol works really well, and has been used for decades by boat & model builders. I've found this to work really well for putting on the final sealing "shell" coat.
 
thinning resin

I don't like to thin resin with acetone for a couple of reasons. it wasn't made to be used in that way first off, and I have heard of people doing that and ending up with a gooey mess on their hands. not fun to clean up! I also dont think its needed in the first place. I filled all the pinholes on the top of our cowl with a blend of epoxy filler and epoxy resin (system three silvertip laminating resin and system three silvertip quikfair). In our shop if someone got caught thinning resin with acetone they probably would be sent home for the day without pay. :eek:
-Erik-
 
Thanks

Thanks Guys, great discussion.

Guy/Tom, where did you get the high temp paint from?
 
If you want easier spreading, another way to skin that cat is heat.

You brush on a coat of un thinned resin, and hit it with a hair dryer, it will flow out pretty well, a little squeegee work will spread it evenly.
 
Mike S said:
If you want easier spreading, another way to skin that cat is heat. You brush on a coat of un thinned resin, and hit it with a hair dryer, it will flow out pretty well, a little squeegee work will spread it evenly.
Click to expand...

....plus the heat expands the air in the voids. When it cools it pulls some resin into the voids.

These got a single brushed coat of epoxy, a light scuff when cured, then epoxy primer and a cross coat of two-part single stage.

 
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DanH said:
....plus the heat expands the air in the voids. When it cools it pulls some resin into the voids.

These got a single brushed coat of epoxy, a light scuff when cured, then epoxy primer and a cross coat of two-part single stage.

Click to expand...


Darn it Dan! Every time I look at your work it's one more blow to my self esteem! I think you need to keep photos of your work to yourself. ;) (Really just kidding, but once again--that's stunning).
 
WOW

Hey Dan, mine doesnt look like that???

Actually i did this job today, same process as top side of cowl. Blow off all really well with airgun, just mix up west, no fillers, pour some on, use a piece of soundrproofing rubber/foam taped on the end of a plastic scraper. Squeegee it all over, let it tack up and squeegee it all the opposite way. Very very thin. Let it dry and lightly sand in the next day or two and possibly one more coat if I can still find some pinholes. Works great, both pieces took maybe 1 hour today and maybe 2 more hours to do again and sand. No big deal at all. Now, apparently I must sand it all down and use a 7 app paint job to catch up to Dan. Man thats purdy, not sure the outside paint will look that nice. :eek:
 
when good resin goes bad

ok not to sound like a broken record. but heres an example of what i've seen with bad epoxy and why it scares the **** out of me to thin resin with Atone.
so the story goes, a few years ago our company wanted to design a new resin. we had a chemist working on the recipe for at least a year. and finally came up with a suitable resin. it was going to be stronger, faster, better than before. then we tested it trying to simulate all the kinds of varables we would see in the field. weather temp ect. we tested for at least 6 months. and it worked great. so we started making boats with it. they were great. lighter than previouslly, stiffer, the surface looked better. all the things we and our customers could ask for. then a year or two later the boats came in looking like this. yikes!
http://
20h2hy8.jpg
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the paint was just falling off in places, and where it was coming off there was like this brown guck coming out of the laminate. the laminate is still as strong as it was the day it left the shop. but we still have to eat the boats obviously. and we still haven't found a way to nuetralize the laminate so that we can repair the paint and resell them as used boats. so there they sit. now I know this isn't the same thing as thinning resin with acetone. that being said after seeing stuff like this it makes me not want to monkey with the properties of the resin. just my 2c.
and by the way once again beautiful work Dan H.
Happy Building
Erik
 
I dry brushed leftover epoxy

in my cowling while working on wing tips, tail tips, etc. Seemed like a good use of the leftover 1/2 oz that I always ended up with. No color. 60 hours so far, and no problems. Thin aluminum tape from Home Depot works great to protect the inside from particularly hot areas...;)
 
I used Fiberfrax and then covered it with the aluminum sheet that you can buy from VANS. It servers as a good heat protector and also cleans very easy and probably weight less then paint and epoxy. I have applied it only to the bottom cowl and it says a whole lot cooler then my upper cowl and it weight very little.
Here is some info about Fiberfrax http://www.aircraftspruce.com/catalog/appages/fiberfrax.php

Mehrdad RV-7A
 
Heat is the Heat

Mike S, got it right.

I tried a small section with thinned epoxy and another with normal west systems and some heat. When you apply a little heat it flows like a son of a heat gun. So much that I'll have to be carefull of drips.

I used west systems, slow hardner and I store the epoxy in the frig so it was cold to start with.

Tonight the rest of the cowl gets the heat. I'll have to be real careful of drips if I use heat on the top surfaces.

Thanks Fellas
 
Bugsy said:
.... west systems, slow hardner and I store the epoxy in the frig so it was cold to start with.
Click to expand...

Paul, no need for the fridge...just makes it hard to dispense and stir, and cold epoxy will condense moisture like any cold object.
 
Getting back to your original question....

Bugsy said:
Did you leave the cowling inside as is or did you put a thinned coat of epoxy in order to keep it clean. As rough and porous as it is, it sure does seem like it will collect oil and dirt over time.
Click to expand...

I left mine unsealed with the exception of the area that I applied the metal taped heat shield as it would not stick to the raw unfinished cowl.
Most of the dirt, grease, and oil wipes off readily with a mild solvent.
I admire the attention to detail and fine craftsmanship that some put into their projects. I am sure a sealed cowling is better and worth the slight amount of extra weight, it just was not worth the extra time for me.
 
Just prime it!

It doesn't need any special sealing or voodoo. Just a coat of primer to hide the hideous pink!:D
 
DanH said:
....plus the heat expands the air in the voids. When it cools it pulls some resin into the voids.

These got a single brushed coat of epoxy, a light scuff when cured, then epoxy primer and a cross coat of two-part single stage.
Click to expand...

(Hijacking thread)

Dan, do you mind sharing which primer and which two-part single stage? My application is slightly different (one-piece glass canopy skirt) but I'm at the point where I need to do the same thing. Yep, I've searched; it seems like PPG K36 or K38 is popular, but not much information beyond that. Thanks!
 
rvbuilder2002 said:
Disclaimer...I do not recommend, and would never myself use, any chemical to thin epoxy when doing any glass lay-up that would be considered structural.
Click to expand...

Doesn't apply here, but West Systems says thinning their resin with 5% of a volatile solvent decreases its compressive strength by 35%. Thinning at 10% results in epoxy that is flexible when cured.
 
Lars said:
(Hijacking thread) Dan, do you mind sharing which primer and which two-part single stage?
Click to expand...

Lars, there are many good choices. I prefer major players; PPG, Sherwin Williams, Akzo Nobel, etc. I don't mix and match brands; again no ad-hoc chemistry.

This airplane is all PPG, so DPLF epoxy primer is first. K36 primer-surfacer is next if you need bulk surface fill for blocking. If you don't need the fill, go directly to topcoat. The topcoat white in the cowl photo is PPG's cheap Shopline two-part single stage. The outside will get a two-stage base/clear, but that's only because I'm crazy.

"Two-part" means A+B, paint and hardener. "Single stage" means no clear coat; the color coat is the final finish.

The other majors all have similar products. About the best reason to pick one over the other is your local paint shop, who probably handles just one of the lines. If they're friendly and helpful and painting is new to you, use their line and ask a lot of questions while you're handing over money ;)
 
DanH said:
Lars, there are many good choices. I prefer major players; PPG, Sherwin Williams, Akzo Nobel, etc. I don't mix and match brands; again no ad-hoc chemistry.

This airplane is all PPG, so DPLF epoxy primer is first. K36 primer-surfacer is next if you need bulk surface fill for blocking. If you don't need the fill, go directly to topcoat. The topcoat white in the cowl photo is PPG's cheap Shopline two-part single stage. The outside will get a two-stage base/clear, but that's only because I'm crazy.

"Two-part" means A+B, paint and hardener. "Single stage" means no clear coat; the color coat is the final finish.

The other majors all have similar products. About the best reason to pick one over the other is your local paint shop, who probably handles just one of the lines. If they're friendly and helpful and painting is new to you, use their line and ask a lot of questions while you're handing over money ;)
Click to expand...

Thanks, Dan. I share your view of ad hoc chemistry, having personally witnessed the results in another life, developing stuff to go in the ocean.

PPG is the brand of choice at our local source. Product availability is somewhat limited here in Yolo County, CA due to environmental concerns. We are in a "non-attainment" area in terms of air quality, which automatically restricts what can be sold, even in consumer quantities. Fortunately the PPG products mentioned are on the "good" list.

You are using DPLF before any high build primer- I presume that the DPLF does a better job of bonding to the West epoxy (like everyone else, that's what I used for my layups) than would K36 alone?

I've shot a few things, mostly old trucks, but it's been a loooong time. And yep, mine will get clear too- what can I say?
 
Lars said:
You are using DPLF before any high build primer- I presume that the DPLF does a better job of bonding to the West epoxy (like everyone else, that's what I used for my layups) than would K36 alone?
Click to expand...

Correct. My first major glass project (late 80's) started peeling several years later. Actually peel isn't the right word, more like the fill and paint coats separated from the underlying glasswork, in particular in concave body curves. Opening the areas found nothing unusual, just clean, dry separation. Back then I was very busy with a new business and had turned the fill/paint steps over to a body shop. They sprayed a primer/surfacer (K100 as I recall) direct to glass, followed by single stage color.

So, I'm sensitive to the issue. I had a talk with a PPG factory rep during his visit to my local paint shop. He said the best way to ensure maximum adhesion to a glass/epoxy substrate was to spray a coat of DPLF and follow with the K36 "as soon as you can clean up and reload the gun".

Makes sense. Epoxy primers are all about surface adhesion. As for the subsequent coat, the product literature is specific; DPLF is to be recoated before it can fully crosslink, 7 days maximum. You may add 1/2 part reducer or not; without it there isn't a solvent flash time concern prior to recoat.....nor a VOC issue in your regulated area.

BTW, DPLF has a choice of catalyst, 410 or 402. 401 requires a 30 minute induction time prior to spray. Several bulk users in my area use DPLF in their paint process for new aluminum, and they order 401 catalyst. I figure if they are willing to wait on induction time in a production paint process, they have a tested reason. 401 is also specified in the DPLF data sheet for applications over difficult materials like E-coat, rigid plastics and SMC. No downside in my home shop, so I'm using 401. Mix first, spend the 30 minutes on booth and part prep.
 
Contego.jpg
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In case of an aircraft fire, keep your temperatures low until you can safely land!

DESCRIPTION

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AREAS of PROTECTION

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METHOD

When activated by heat or flame, a dense carbon char is formed separating and shielding the substrate from heat while off gassing displaces oxygen from the treated surface; thus eliminating two of the three components needed for combustion.

HOW TO USE

Simply prepare the surface of the firewall or etc. just like you would before you paint anything. Clean the surface. If the surface is smooth, etch it so paint will adhere to it. Spray the Contego on. Paint until you get approximately a 21mil thickness (0.021 inch). Let dry.

CONTEGO Fire Protection - One Quart, Cont-Q., $29.95
+ $12.00 for shipment WITHIN the continental USA ONLY

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DanH said:
Correct. My first major glass project (late 80's) started peeling several years later. Actually peel isn't the right word, more like the fill and paint coats separated from the underlying glasswork, in particular in concave body curves. Opening the areas found nothing unusual, just clean, dry separation. Back then I was very busy with a new business and had turned the fill/paint steps over to a body shop. They sprayed a primer/surfacer (K100 as I recall) direct to glass, followed by single stage color.

So, I'm sensitive to the issue. I had a talk with a PPG factory rep during his visit to my local paint shop. He said the best way to ensure maximum adhesion to a glass/epoxy substrate was to spray a coat of DPLF and follow with the K36 "as soon as you can clean up and reload the gun".

Makes sense. Epoxy primers are all about surface adhesion. As for the subsequent coat, the product literature is specific; DPLF is to be recoated before it can fully crosslink, 7 days maximum. You may add 1/2 part reducer or not; without it there isn't a solvent flash time concern prior to recoat.....nor a VOC issue in your regulated area.

BTW, DPLF has a choice of catalyst, 410 or 402. 401 requires a 30 minute induction time prior to spray. Several bulk users in my area use DPLF in their paint process for new aluminum, and they order 401 catalyst. I figure if they are willing to wait on induction time in a production paint process, they have a tested reason. 401 is also specified in the DPLF data sheet for applications over difficult materials like E-coat, rigid plastics and SMC. No downside in my home shop, so I'm using 401. Mix first, spend the 30 minutes on booth and part prep.
Click to expand...

Thanks for the additional tips!
 
Not crazy (necessarily)

DanH said:
The outside will get a two-stage base/clear, but that's only because I'm crazy.
Click to expand...

Dan,
After painting the '9 with a single stage (DCC) and the '8 with base/clear, I believe I'd do the base/clear any day. Its a bit more expensive but I think its easier to achieve really good results. Plus I really like the look!
 
Doing my annual, and now after 160 hours, I decide I need to put some of the Cowl Heat Protector that Van's sells inside my cowling. There are a couple of areas where exhaust heat is affecting the glass. Of course, in my haste toward the end of a three year build, I did not do any prep to the inside of the cowl. My engine runs pretty clean, but like any, there is some oil residue, and the adhesive won't even come close to sticking to the cleanest areas, let alone those affected portions.

1. My advise to those of you at that point in the build, take the time, seal and paint the interior of your cowling and do use the aluminum heat protector.

2. Any advise (from you crafty glass people) now, how I can rectify this situation? I am concerned that adding a coat of epoxy to the cowl, despite my best effort at prepping the cowl, would now be futile, as so much oil residue is impregnated into the rough glass. I am reluctant to use an aggressive solvent and risk making what is mostly a cosmetic issue into a structural one.
 
I have used K2R Spotlifter for many years to get the oil out of glo furl powered balsa models when I needed to do a repair. Works fantastic:D

Never tried it on fiberglass, but it might be worth giving it a shot??

http://www.k2rbrands.com/

After the K2R, clean with acetone or MEK, scuff well with 60 or so grit sandpaper, another wipe with solvent, and coat with epoxy.

Another produce that may work?? I have used it to remove oil stains in car carpet with great sucess. Spot Shot. http://www.spotshot.com/

Again, never tried it on fiberglass, but who knows?? pretty heavy solvent smell to it, so could damage paint.
 
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Thanks Mike for the quick advise. Wife says we have some of that carpet cleaner at the house! Worth a try anyway. Thanks again
 
Most any solvent and some rags will do the job. Adhesive tape won't stick very well even on a new cowl as the surface is kind of rough.
 
What about that bilge paint for boats, I seen one post on here that they used it...
 
Smagnuson said:
Doing my annual, and now after 160 hours, I decide I need to put some of the Cowl Heat Protector that Van's sells inside my cowling. There are a couple of areas where exhaust heat is affecting the glass. Of course, in my haste toward the end of a three year build, I did not do any prep to the inside of the cowl. My engine runs pretty clean, but like any, there is some oil residue, and the adhesive won't even come close to sticking to the cleanest areas, let alone those affected portions.

1. My advise to those of you at that point in the build, take the time, seal and paint the interior of your cowling and do use the aluminum heat protector.

2. Any advise (from you crafty glass people) now, how I can rectify this situation? I am concerned that adding a coat of epoxy to the cowl, despite my best effort at prepping the cowl, would now be futile, as so much oil residue is impregnated into the rough glass. I am reluctant to use an aggressive solvent and risk making what is mostly a cosmetic issue into a structural one.
Click to expand...

It would be difficult to get it clean enough to make anything stick to it.

If the aluminum foil is installed before the cowl gets dirty it stays in place pretty well. Probably as well as applying it to a painted surface. The inside of the cowl is an extreme environment in terms of temperature and possible leaking oil.

FWIT Burt Rutan never advised to paint the inside of a cowl with the canards, it added weight to the airplane and violated his rule, if you throw it up and it comes down its too heavy. :)
 
Cleaning

One thing that hasn't been mentioned is cleaning. As has been noted, proper adhesion is the key no matter what you use. For this to happen it has to be clean.

The first thing I do to the cowl is use high pressure air on all surfaces of the cowl. From there, I scrub the inside of the cowl with denatured alcohol. (I have used acetone as well). Blow it out again and then scrub with soap and water with a heavy nylon brush. Hose out and let try. I also sand out any ridges, overlaps and other imperfections.

I like West Systems and use it for full scale building and my RC projects. I waste nothing!!! If I mix some for project and have any left, I brush it on the inside of the cowl. Since the cowl is at the end of the project, my cowl is almost coated just from left over epoxy.

I often thin the epoxy with a few drops of denatured alcohol. I have noticed no change in curing or hardness. It does flow nicely and doesn't take much to thin slightly.

When done, you could leave it as is or begin the finish process as others have done. FYI, very little weight is added in the process.
 
I sprayed the inside of my cowl with Epoxy primer (SPI), same as the exterior and interior. Nice and thin and works really well. It will easily handle 250* I painted an Oil pan on a small block Ford with this and it holds up really well to rock chipping and heat. I also put reflective tape anywhere I the cowl was near the exhaust.

I did this to make future repairs possible. Getting oil out of the pores is very difficult and didn't want this problem if I ever had to make repair of fabrication
 
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