Gel Coat as final finish?

[jodava]

Before I offer my thoughts on this, I probably know what everybody is going

to be thinking....is he crazy? Maybe. Of all the reading I've done, I've never read

anything about anybody using gel coat as a final finish. Many years ago I used

to work with gel coats and resins as I owned and operated a small marine repair

yard and did quite a bit of prototyping for some boat manufacturers and was

involved in other projects building plugs and molds. For those who have never

done this kind of work before, or who have limited knowledge and or experience,

the process of using gel coat may seem like a long and arduous process compared

to filling, priming and painting, which seems to be the only type of finish I've

read about.

My question is how does gel coat wear on an aircraft insofar as stress

cracks and wear in general? I know that on a boat the cracks will, eventually

almost inevitably appear around the hardware attachment points such as chain plates,

cleats and winches. Anybody have any comments or experience with kit planes that

have gel coat as a final finish or what they've done themselves? My personal

preference is gel coat, as I don't think you can beat the depth and luster once

sanded and polished out.. I know that gel coats have improved tremendously from what

I used years ago, so the gloss should be very satisfactory, but certainly not as great

as Imron or any other paint.The weight of gel coat and Imron are close. Gel coat weighs

about one and a half to two pounds more per gallon, varying with color.

When sprayed properly, the first coat of gel coat can fill almost all pin holes

and fill the weave in most places enough to be blocked and sanded to a flat or fair

finish. Spray a second coat, then sand and polish. Sanding gel coat isn't too bad if it's

sanded within the first couple of days after spraying as it is rather soft within that

timeframe. It's a lot work I know, and is probably more work than filling, priming and

painting, but again, that's my preference.

If anybody has done this, and can testify to the longevity, I'd appreciate it.

Everybody have a good day.....

[Edge 513]

Just to say that, with how well the present epoxy finishing works, there is no need to, and reason to, use the weight of a gelcoat finish. [Of course I am thinking of the old applications I was exposed to when spraying gelcoat into molds during boat hull construction. It got pretty thick in there.] I hadn't even thought of using something other than the plans finishing system, since we are building things that fly vs things that float. Gelcoat was MUCH heavier than paint back in my day.

Maybe you should produce a test bed for yourself and satisfy your curiosity.

We obviously don't want any more weight than is absolutely necessary.

It means you cant have as much fool or baggage onboard....

...and since I need the capacity for both I am using the West system.

[brainfart]

> Just to say that, with how well the present epoxy finishing works, there is no

> need to, and reason to, use the weight of a gelcoat finish.

 

Tell that to the glider crowd. Most of them use white gel coat.

[Lynn Erickson]

> Just to say that, with how well the present epoxy finishing works, there is no

> need to, and reason to, use the weight of a gelcoat finish.

 

Tell that to the glider crowd. Most of them use white gel coat.

gel coat is heaver. it weighs more then paint. gel coat is resin with pigment in it. when applied all the weight of the resin and pigment are there on the part that it coated. paint contains solvents that evaporate when it dries, there for you can not compare the weight of it in the can as a liquid. Gel coat will never give you as good looking a finish as paint.

[rickh]

My question is how does gel coat wear on an aircraft insofar as stress cracks and wear in general?

If the boats I've seen are any indication, I suspect your plane will have spiderwebs in no time. I think the glass/foam/glass sandwich flexes a bit more than a boat.

 

Is a gelcoat UV proof? Need to protect the underlying foam.

 

Weight factor, especially on the ailerons and elevators!

 

Can gelcoat be had in an epoxy formulation (I don't know)? Polyester over epoxy doesn't exactly 'mix'.

 

Rick

[Big Steve]

You build fiberglass boats with gelcoat and really thick matt and fiberglass buildups. You build airplanes with very light epoxy and micro which 90% gets sanded off. You put paint on airplanes because they need to be light to cary the fools Edge was talking about. Build on STeve

[brainfart]

A gelcoat sprayed into a mold isn't any heavier than all that epoxy coating/micro stuff, I'm tempted to say the opposite is true. Most gliders from the past and many today use gelcoat, and cracking and durability aren't any concerns. Neither is excessive weight. Using gelcoat is also a big timesaver when laminating in a mould, compared to all the endless sanding, microing etc. required when working without a mould.

 

> Is a gelcoat UV proof?

 

Yes of course.

 

> Can gelcoat be had in an epoxy formulation (I don't know)?

 

Yes, epoxy gelcoats are available.

 

> Gel coat will never give you as good looking a finish as paint.

 

Sorry, but that's just not true.

[argoldman]

A gelcoat sprayed into a mold isn't any heavier than all that epoxy coating/micro stuff, I'm tempted to say the opposite is true. Most gliders from the past and many today use gelcoat, and cracking and durability aren't any concerns. Neither is excessive weight. Using gelcoat is also a big timesaver when laminating in a mould, compared to all the endless sanding, microing etc. required when working without a mould.

 

> Is a gelcoat UV proof?

 

Yes of course.

 

> Can gelcoat be had in an epoxy formulation (I don't know)?

 

Yes, epoxy gelcoats are available.

 

> Gel coat will never give you as good looking a finish as paint.

 

Sorry, but that's just not true.

Gelcoat would be a great thing for aircraft externals (assuming the above is correct) if only were it not for the fact that we epoxy "things" to the outside as the buildup progresses. Thus we have to fill and recoat.

 

The process involved in making the aerocanard parts is, rather than using Gel-coat, to spray the waxed mold with epoxy primer, let it cure slightly and then lay up the glass. This gives a great thin finish of primer which can easily be sanded off for further bonding or be somewhat roughened for final finishing.

[rviglierchio]

I've been on a lot of 15 year old sailboats where the gel coat was shot and we polished our butts off to try and get a shine. Have seen several 15 year old canards with great looking old paint jobs......

[brainfart]

I've seen many gliders and also regular motorized planes with gelcoats that weren't terribly cracked, since plane surfaces usually don't have many sharp bends and corners and attached clamps.

When I took fuselage repair classes we worked on damaged wings of crashed certificated planes (dunno which type) which had gelcoats. We intentionally made holes into the wings, damaged the trailing edge etc. and then repaired that damage, including the application of gelcoat and sanding and buffing as the last step. I might even have some pictures somewhere to prove it.

 

Here for example is the maintainance handbook for a motorized glider, unfortunately it is in German:

http://www.stemme.de/man/s10v/whb/a4010120_13a.pdf

 

You don't need to understand German though, just do a search for gelcoat in that document and you'll find the phrase "UP Gelcoat" mentioned several times. UP gelcoat of course means unsaturated polyester gelcoat.

 

Here is a thread about repairing or painting older gelcoated gliders:

http://www.gliderforum.com/thread-view.asp?posts=18&threadid=319

 

I'm not insisting on gelcoat being a better or the perfect surface for an airplane, but it is indeed being used on many planes.