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Glass fibre mould from the slender plug

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sparky961:
I performed some significant rebuilding of the coaming on my fibreglass kayak last year.  I was going to use polyester resin because it's readily available.  But after doing some tests with it, I opted for higher quality epoxy resin.  Yes, it cost more.  But it doesn't have the nasty odour typical of polyester, and cures almost transparent - unlike most polyester I've seen.  I used MAS brand after reading through many, many reviews and unscientific test comparisons of brands.  It's less expensive than the oft-touted West Systems, but many people reported obtaining very good results with it.  Though I haven't had a lot of experience with it, I was certainly not turned away from epoxy work after using it.  It actually has such low odour that I sometimes initially forgot to don my respirator - though I tried to do so religiously.

vtsteam:
Sparky, since you were adding to already cured resin, epoxy was the sensible choice. If you'd tried to use polyester, even with wax removal and abrasion, the bond would have been relatively weak by comparison.

There is a third choice, btw, vinylester resin, which has properties somewhere in between polyester and epoxy when laminating. However it has a very short shelf life, and is mainly used for specialty production moulding.

And just to add to the confusion, there are actually two kinds of finish resins commonly called "gelcoat" - the main and original type is sprayed into a female mould, and has an air inhibited cure. The second and more recent (and unfortunate) usage for the word applies to a color coat applied to the exterior of a male moulded part. And that must be an air hardening type, since it is the final finish exterior coat.

PekkaNF:
Interestingly some seemingly large shops don't know or recognize that little difference on wether their resin has wax ot not. Laminating resin seems to be elusive. But found a palce to order black ot red gelcoat for moulds.

Ordered one small sheet of 2 mm acryllic sheet to have plan "B" for the almost transparent blade.

Today I have been making more plugs...need to find out what paint to used to make the MDF plugs smooth and non porous.

Pekka

ddmckee54:
Pekka:

I stumbled across this youtube channel a couple of weeks ago. 

https://www.youtube.com/user/WJP004

Don't know if it will help or not, but he pretty much walks you through everything.  In various videos he shows all the steps, making the mold, hand laying up the part, de-molding the part, trimming the part and assembling multi-piece parts.

Hope it helps,

Don

vtsteam:

--- Quote from: PekkaNF on June 26, 2018, 12:21:58 PM ---Interestingly some seemingly large shops don't know or recognize that little difference on wether their resin has wax ot not. Laminating resin seems to be elusive. But found a palce to order black ot red gelcoat for moulds.

Ordered one small sheet of 2 mm acryllic sheet to have plan "B" for the almost transparent blade.

Today I have been making more plugs...need to find out what paint to used to make the MDF plugs smooth and non porous.

Pekka

--- End quote ---

Yes, that's often the case -- even pro's sometimes don't understand the basic reasons for what they order for supplies day-to-day -- as long as their usual method works for them. If you understand the materials, though, you can also do something different than what you're used to day-to-day.

Pekka, re finishing MDF (or wood, as I do for patterns) try hand brushing lacquer with a few spoonfulls of baby talcum powder mixed into a pint (not the cornstarch type, but the real talc type). Uhh, I mean into a half liter. You have to keep it stirred if it sits too long.

This dries very quickly and sands beautifully with fine sandpaper. MDF is quite absorbent, so it might take 3 coats, sanding between each -- but it works very quickly. Then overspray with colored lacquer (Krylon regular in rattle-cans, here in  the US is lacquer based). Two coats, then wax, or release agent (PVA is often used.

Hope that helps.

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