Making a mold

If I were to build a cedar strip hull, sheathed and well encapsulated in glass, then built a mold off this "plug" how would I prevent all the release agent on the hull/plug from wreaking havoc with my paint job on the wood hull when it is finished off?

Paint doesn't like release agent? Are there certain products that would work? Certain techniques (i.e., how to insure all the release agent is removed!?)

Cheers,
Clint

 

Clinton,

You have not described the type of "paint" you finish the hull in, but if you use two pack polyurethanes such as Awl craft or Sterling you can simply wax the surface and the mould will release. Remember the mould will be the same quality as the paint so spend a lot of time making the plug perfect and then finishing it perfect.

The waxing process is quite intensive and it is done over and over again. It is not a simple wax on wipe off job. Only do two coats a day.

If you use auto type waxes like Maguires, then you do it at least 5 to 6 times, each time doing a very thorough wax job. You will notice after about 3 goes that the surface is starting to look quite smooth and shiny, certainly do it 5 times minimum.

 

and use only silicon free wax. We usually put 7 - 9 coats down on the plug before taking the mold and never had problems with the release. I get the best results with a water soluble polish.

 

Thanks Wynand, yes that is VERY impportant.....NO SILICON, anywhere.

 

Thanks for the tip - is that because the silicon stuffs up further paintwork?

Whats the main reason for avoiding the silicone waxes ?

Cheers

 

Silicone based wax's will cause fish eyes in the gel and then when you refinish it will happen again and again.
If it is a new mould you can also for insurance use PVA release agent.

 

Clinton, is this mold to be used for infusion? If so, remember to add trim flanges to it for your plumbing and bag attachments.

-jim lee

 

Guys, Thanks. I intend to use a 2-part paint, usually I roll and tip but wish to get good at spraying, which would be better for a plug, I assume. So, this is the sort of paint job that I don't want to redo for many years, right, due to the build up of wax on the outside? -- I wish to try to use the plug as my own boat and finish it off next to the eventual composite hull.

THANKS FOR THAT REMINDER JIM! Would it be best to add the trim flanges to the plug and laminate the mold over that so it's one continuous piece? In tat case I'll figure out a way to do it...plank past the sheer a little bit, add the trim tabs, glass the plug, pull off the mold, and cut the flanges off the plug when I cut the sheer.

I started another post to get people's thoughts on doing my design in composite. Thanks.

Cheers,
Clint

 

If I understand what you are asking, you should be able to finish your woodstrip hull/plug with the paint you want before you make the mold, then wax/ release agent over that so after you pull the mold off you don't have to do anything to the plug/hull to finish it as it will already be finished.

Ideally you shouldn't have to do anything, hopefully no more than a light buffing to the mold once you pull it off the plug. It is mucho grande easier to fair a 'positive' plug/hull to perfection than a 'negative' female mold, so you want your plug/hull to be as perfect as you want your finished product from the mold to be. So, paint and finish your wood hull to perfection, wax and release coat it and make your mold on that.

It kind of depends on the whole scheme of things, but flanges don't necessarily have to be a 'construction' on the plug, in that all they have to do is to be able to be carefully laminated against. They don't always have to be screwed and braced, if taping or gluing will work. If you can get tooling gelcoat and 1 light layer of mat on them without them moving/flexing too much, you are pretty much OK. Every layer of glass will make them stronger.