First, thanks everyone for a whole pile of good advice.
As you will see from the pics in the last thread, the boat has quite a lot of tumblehome so getting it out of any kind of mould is a problem.
I propose to lay it up without the bow and stern transoms and to cut it in two down the centreline while it is still green. Once it is off the mould, lay up the transoms, trim to exact faired shape and epoxide/carbon tape the whole thing together.
In the past (on full size boats) I have generally used PVA release agent applied carefully. Come release time, prize the gunwale away from the mould in a couple of places, and pour some water into the gap. Go to the pub and come back. Hopefully the boat is floating in half a gallon of water. If persuasion is needed (it usually is) a small hole or so in the bottom and a compressed air line generally does the trick - and gives you time for another visit to the pub!
All this seems a bit like overkill for a 12", rather wobbly moulding. Any comments?
Angus - The sort of thin lay-up you should be gunning for with your Footy project will be flexible enough to pop from the mold, even with the tumblehome, provided that you don’t make the bow and transom at the same time. Leave them open so you can flex the sides, and add the transom and work on the bow later.
As for mold releases, it all depends. You need to match the mold release to the resin system that you plan to use. Pva is not universal, and your method of application will effect your results. Remember, with thin lay-ups whatever is on the surface of your mold (or plug) will telegraph through. A smooth mold with a brushed on layer of PVA will show the brushed on pattern. If you use PVA its better to spray it on with an airbrush.
If you use epoxy (I use WEST SYSTEM), which you should, you should use several coats (6 minimum for the first time, 2 or 3 thereafter) of wax release followed by an aerosol release agent made specifically for epoxies. The wax should be formulated for use with epoxy as well, but in a pinch you can use bowling alley type wax. Do not use wax for cars! It contains teflon and several other liquifying additives that retard the cure of epoxies.
The best advise I can give you is to contact the manufacturer of your resin system, describe your project and get their recommendations.
Niel, I use Mcgurie’s mold release wax, it works great. I have never had any brush marks in the PVA? if spraying the PVA use high air pressure. I have been doing fibber glass for about 40 years, started out with polyester and went to epoxy, and yes West System is the best. I wax the mold 4 times, then PVA, then spray epoxy primer, then lay the glass. this comes out of the mold with no pin holes. I use air to blow it out of the mold most of the time.
The mold release wax that I use is from TR Industries in California. They make two grades, basic and regular. Basic is for mold making and for the first couple of castings from a new mold. The regular grade is for subsequent castings. They also make a superb sealer-hand glaze.
For hulls from a female mold I use the TR wax by itself, the number of coats depends on how broken-in the mold is or how old the mold is (although I do not do production runs of my hulls so most of my molds are retired before they become too degraded).
I use the wax in combination with Mann Ease-Release (which comes in a spray can) for female hulls over male plugs and for casting my fittings in carbon fiber/epoxy. Spray releases like Mann’s products come formulated for use with different resins. I started using them while doing a casting job in urethanes. There several other companies like Smooth-on and Poly-ease that make comparable products for epoxies, and while they can be expensive a little goes a long way and they yield a great surface. Just be sure not to load the stuff on, a dusting is all thats necessary.
I do not use an epoxy primer coat or primer and paint on my r/c boats. All that stuff does is add weight in my opinion. My boats are made using an outer layer of sheathing fiberglass and either carbon fiber, kevlar or spectra, or some combination thereof. An M class hull comes out of the mold between 7 and 8 ounces (in sheathing glass and two layers of spectra).
I use West System Pro Set 125 post-cured to around 160 degrees as my epoxy casting system. I use West System 105 for assembly and general gluing purposes because it seems to stick better to the cured Pro Set than Pro Set itself.
So there you have it, these materials have worked for me over the past 15 years of small boat building very reliably. If you want to go high tech, all these materials are out there on the web.
How dificult would it be to split your mould into halves or front & back? It would make the extraction easier, but only you’d know if it would be practical.