MormonMike

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Guys, how does one go about " gel-coating " a kit. How is it done?

blikseme300

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Gel-coating is done in the mold before the glass is laid up.

TGDF

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[quote]ORIGINAL: blikseme300

Gel-coating is done in the mold before the glass is laid up.

[/qtuote]

But what is Gel=Coat? What is its makeup? What is its purpose? Is it just another epoxy? One or two parts? Is it primarily there to protect the epoxy from UV?

I haven't looked REAL hard, but I have been reading all I can about epoxy and I don't find much info about Gel-Coat. Not even in the descriptions of Gel-Coat products in catalogs.

Why Gel=Coat and not just a really good paint?

Mike James

Usually, when people use the term "Gel Coat", they're talking about a polyester-based product, which is indeed a coating to add hardness to a mold surface, (like we use "tooling resin" or "surfacing resin" in the epoxy world) or gel-coat can also be applied in the molds first, before a layup, to "gel coat" the parts themselves. When used in that application, it has the effect of almost guaranteeing a smooth exterior surface, free from print-through, albeit at the expense of some added weight.

Most any composite manufacturer will have information about this on their site. For example, look at http://www.fibreglast.com

TGDF

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Thanks Mike. I was aware of fibreglast.com. I'd been through their product offerings but surprisingly I missed how extensive their free literature section is. Spent quite a bit of time there this weekend. But they too are more how to than why. For instance they have gel-coat, but tout their Duratec primer, just an acrylic lacquer thinned paint, though it costs twice as much as gel-coat, as superior to gel-coat.

I'm still looking on Gel-Coat though. The info at fibreglast.com has mostly been process technique. 'How to.' I'm still looking for the 'why we use this' info. That is easy to find in the infancy of an industry, but harder to find in a more mature environment. Everyone has already made their decisions. I'm looking for stuff like the fundamental epoxy chemical info at http://www.epoxyproducts.com/chemistry.html#part1

The Swiss site recently mentioned in another thread of this forum (titled 'A really great composite site' I think)
http://www.swiss-composite.ch/scs4/h....shtml?lang=en reeeeaally is the most informative so far. Its got more product and info at that one site that almost all the other sites I've seen put together. Unfortunately, while it has a British English link, most of the pages are only in German or French. Its possible to use AltaVista.com to view the site translated automatically into English, but any of the PDF pages (which are numerous) must be individually cut and pasted into the translator. Even then, the language is so terse and colloquial and the articles so concise, it is difficult to understand the translation. Much of it is worth the try,however. There is one article which, I believe, tells how to build a plug-in monocoque wing with a spar using 4 different materials each only in its own strength/weight physical location. In other words, the spar caps are one material, the spar between the caps another and the extension of the spar beyond the caps is two more.

jetflyer

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Terry,

Try calling up a few of the companies like fiberglast and talk with their technicians. They can often give you good advice. I've done that on a few products. And they were right on.

JR Gautreaux

TGDF

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You know, I'm going to do that. Someone mentioned that in another thread (perhaps it was you). I've been hesitant to do that because I hate to waste someone's time when my question is still too broad and unfocused. I feel like I'm just asking for someone to tell me to go read a book.

But I think I have my questions sharpened enough now. If I do it and learn something, I'll post it.

Just finished my vacuum pump assy. Basically a piece of foam core glassed on both sides for a base, a pump from one of those freezer bag sealer kitchen appliance thingees and a manifold. The manifold is a 'T' shape. the upright is PVC with a vacuum gage stuck in the blind end. The pump side of the crossbar has a valve to close off the workpiece and gage so I can shut off the pump and still watch the quality of the vacuum. Just beyond that valve is a small 't' with another valve to open the system in the unlikely event the vacuum sticks everything so tight I can't open the system and I don't want to rip the bag. Should have put this valve in the blind end with the gage. As it is, I've no way to get condensation out of the upright of the 'T'. Don't think that's much worry, but I'd change it if I do it again.

I sort of threw this together. I tried vacuum bagging a few pieces with a shop vac just to keep the edges of the fabric laid down tight. I roll out my fabric pretty dry and I'd been having a problem with about 5% of my edges pulling away from the underlying layer of whatever. My fabric is completely wet with resin, I just drizel it on real stingy or sometimes even take a wet piece of fabric, fold it together with a dry piece and wring them out like a piece of laundry to get a minimum coat of resin on the glass. Anyway, for what it was worth, the shop vac did a passable job. But I had no way of knowing what the value of the vacuum was.

Its kind of hilarious, but the pump from the kitchen appliance thingee actually draws 20+ in Hg. I haven't bagged anything yet. Just put my finger over the inlet of the manifold so far. And I don't feel like holding it there long enough to make it bleed. The manifold's volume is about a pint of air and the pump draws that all the way down in about 10 seconds. The way the pump is wired it appears to have at least 2 small devices to protect against overheating. Doesn't look like that will be any worry for well sealed work pieces. I piddled around with the thing for about 10 minutes and the motor winding plates didn't even get warm. The little house I built over the pump to direct airflow seems unnecessary. Except for the pipe & valves for the manifold all of this is stuff I just pulled out of my junk pile. I can reuse the manifold with a new vacuum source.

Looks like I might be in business here. Very small business anyway. About 2-3 meters worth of business. Sorry about the quality of the pix. Cheap camera, poor light.

jetflyer

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Terry,

Look like it will work quite well. Post your results after you've done a vacuum piece.

JR Gautreaux

TGDF

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Just needs one on those sea-saw well head pumps and I coudda struck oil!!

I'll be doing a few parts this week. If I can finish the forms. Let you know. I hope the pump lasts more than 10 minutes.

Thanks.

TGDF

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I talked to a FibreGlast tech just now.

He didn't give me a hard and fast rule on when to use Gel-Coat vs paint/primer. Seems to be sort of a sliding scale. We only talked about coating the work, either in the mold or after cure. No discussion of coating the mold (as the mold surface). What I got for sure was:

1. Gel-Coat is better sprayed in the mold rather than sprayed on a finished part. The gel-coat surface pulls up to a sort of orange peel, dimpled surface effect which requires more, and more difficult finishing than paint/primer. If you need to finish the surface of the part after it is pulled from the mold, then paint/primer is likely more appropriate.

2. Sprayed in the mold and only allowed to tack up for 1/2-4 hours before the glass layup, Gel-coat will give the better adhesion of a primary (chemical) bond rather than the secondary (mechanical) bond of paint.

3. No.2 not withstanding, if you do your homework on the paint to make sure it is compatible with Gel-Coat, there's no reason you can't paint a design or logo in the mold and then spray a layer of gelcoat over (behind??!!) the design before laying up the glass fabric.

I should have asked more about the durability of Gel-Coat vs paint although that too is probably a sliding scale. Judging by the products offered it depends on how much you want to spend and what type of paint, polyeu, epoxy you want to put the elbow grease into.

Discussing layers in a mold gets to be like talking about going back in time and killing your grandfather. If you kill your grandfather, your father will not be born after he dies, before you are (were) born.