Vacuum Bagged M1 mold

[Kazzer]

I've been fiddling around with GRP for a while and my skills are gradually improving, but not perfect. My last mold had many small bubbles in the gel, and I thought I had it perfected, but no!

So, I've decided to try the Freeman method of vacuum bagging! I bought a vacuum pump and a small supply of materials from Freeman.

I am using woven cloth in 1" 3" 6" and 12" widths, and my usual epoxy.
First, I waxed the mold a couple more times, then applied three coats of PVA, thinned with Iso-propol (sp??) Alcohol. It lays down a thinner layer more evenly, and dries quicker. I use a $12 Harborfreight gun.

I bought a 500' roll of 5mm plastic sheet formed into a tube. (It's for making bags) Laid flat it is 18" across, so has a 26" circumference.
Freeman supplied me with breather cloth which looks like lightly compressed felt, and some plastic sheet with thousands of holes in it, called a bleeder.


Here you can see the bag and the airline going to the compressor. I sealed the end of the bag by folding over the edge placing some paper over it, and ironing it with a clothes iron.




Here's my clean table where I cut up the cloth etc.



Here, once I had the mold in the bag, I placed some caulk inside the open end, squished it together, then folded it over a couple of times. Finally, used tape to secure it and clamped it between two pieces of wood.




The ironed end.


The procedure is:-
1. Wax molds
2. PVA molds
3. Paint a thick coat of resin over the mold.
4. Lay in the pre-cut fiberglass cloth
5. Lay in the bleed film
6.Lay in two layers of breather cloth. As the resin soaks through the bleeder cloth, the breather cloth soaks up the excess (hopefully)
7. Apply another layer of bleeder cloth. To allow air to pass through.
8. Apply one layer of breather cloth.
9. Bung it in the bag and start up the pump.

I'll go look at it later today, to see what sort of a pickle I've gotten into.

[Subculture]

I find trying mix a decent gelcoat with epoxy resin a bit hit and miss. If you make it thin it runs off and pools up, and if you thicken it further it doesn't tend to coat as nicely as a polyester gelcoat.

For the delphin hull, as it has no moulded in detail I didn't bother with gelcoat, and just went straight in with the cloth and resin, which produced a light and strong hull. Had a couple of minor bubbles to fill afterwards, which I just touched in with colloidal silica filled epoxy.

If I mould any more boats in epoxy, and I require moulded in detail, which tends to dictate a gelcoat, I think I may purchase some ready blended epoxy gelcoat.

[Kazzer]

I pulled the conglomeration apart to find numerous successes and a couple of failures.

Firstly, No bubbles in the gel coat. (Well, I had two small ones) Major big deal!! Success!
The finish was smooth and needed little work.
Overall the resin and fiberglass was even. Resin had oozed through the bleeder film perfectly

Much better result, and well worth the extra work. Actually, I thought this was quicker and easier than a normal layup method.

The bad things -

I had rucks in the bleeder film and this allowed the resin to build up, making the inside of the product look unsightly.
The edges of parts of the mold where sharp corners were, left much to be desired. The vacuum was unable to pull the glass cloth into these areas.

So, my next plan is to make up a small batch of resin with gel/cabosil, retard the cure slightly with a splash of lacquer thinner and also keeping it cool, and applying this as a paste to all these bad areas. Then I'll be coating the entire area with a good coat of 2:1 resin.

Plan # 2 will be attempted tomorrow. I have a good feeling about this.

[Kazzer]

I find trying mix a decent gelcoat with epoxy resin a bit hit and miss. If you make it thin it runs off and pools up, and if you thicken it further it doesn't tend to coat as nicely as a polyester gelcoat.

So many epoxies around, all with different viscosity. I only use one epoxy, and so that is not a variable. I only use Cabosil to thicken it, so my only concern is temperature and the amount of Cabosil. As long as I am applying a layer of this in a THIN cross section, I can add lacquer thinner to further retard the cure, but this is no good in a chunk, as it will take ages for the lacquer to evaporate.

At room temperature, my mix is fairly viscous, but it is ideal for filling up thicker areas. I guess the thing you have to remember with this is the exotherm, or heat. If the cross section is thick, the resin will set quicker. However, there is a point where the resin will become more liquid as it creates exotherm, then it will quickly start to thicken and harden, unless you get it spread out on a a mold, which will cool it off.

I've been ****ing with this stuff for 30 years and i can still screw it up~!