And yes it did damage the paint on the plug.
a few things:
when first waxing the plug. do one coat at a time and buff, wait 20 minutes then do another coat and so on until you have a minimum of 5 coats of wax and on such a large part as a bonnet I would say do at least 7 coats of wax because you could easily miss a spot on a few of the coats. If it takes overnight to complete waxing, just cover the bonnet with a plastic sheet to keep dust away.
About the pva, as long as your rag was very clean ( preferably white so the dye in the cloth doesn’t react to it) and you let the pva dry for at least one hour before spreading your gel coat.
Trick… on a bonnet… use gravity to gel coat since you don’t have a spray gun/dump gun for gel coat. spill a bunch of gel coat on the center of the hood and tilt the hood so it runs and covers the entire bonnet. this way no possibilities of breaking thru the pva or leaving brush strokes behind. you can use a brush but try to use it to just guide the gel coat puddle where it needs to go. A gel coat thickness gauge is handy and they cost around $4 for one. 15 to 25 mils is the thickness you want to aim for across the entire bonnet. Just check it in like 6 places and it’s good.
I would aim for the higher end of that scale because then you have room to sand out flaws in the gel coat later on.
Ok, now let that gel coat “B stage” so it is cured enough that you can touch it with your finger and it doesn’t come off on your finger but it is still tacky to the touch. That is the perfect time to start laying down your reinforcement fiberglass and resin. Just do one layer of csm or glass at a time because you have a large part there. also more than 2 layers could cause problems from all the heat reaction of the polyester resin/mekp mix. You could probably use just 1% of mekp to have a longer pot life of the resin and more working time. It will still cure just takes a bit longer.
Also make flanges on your plug even if you think you don’t need them;) 
john, when you brush the gelcoat on a surface, it’s possible that you might have brushed it on too thin. Do you have an air line? if you do, you should at least make your own spray gun (although a spray gun is very cheap nowadays). If you dont have an air line, there are spray bottles that uses compresses gas that you can use. The gas wont last long, but just giving you some options out there.
If you still want to brush it on, you can do it in layers after each layer has somewhat dry, but this is hard to do if you dont know what you’re doing. You can have your surface ‘gator’ like what you had already.
So, i think you should stick to using a spray gun. Btw, you should shoot for 15mils, or 20mils for toolings.
however well you waxed it doesnt matter. if the paint reacts with the polyester, it will react. there are two solutions: use more layers of pva, your 1 layer was too thin. OR, like i did on the rear spoiler, use epoxy tooling gelcoat (surface coat) but that is very expensive, and would require you to keep using epoxy for the rest of the mold, etc… cost would go very high.
so, spray several coats of pva until you can judge it will make a surface that will protect your plug surface from the evil polyester. If you know how to handle pva, the results are mighty fine :rolleyes:
Don’t use PVA, and spray the gelcoat. Or at least brush the gelcoat on about twice as thick as the first time.
I guess i have to agree with TET, no pva this time. you will have a nicer finish on the mold surface by not using pva.
well, the paint is gonna react with the polyester again…
he has a good point there. I don’t use polyester gel coat much so i forgot that it could react with a freshly painted surface.
So what would you guys suggest he coats the plug with this time?
from all the previous statements and pieces of advise, i take it the best bet would be to:
- sand to smooth finish again!!!
- Wax 7 layers drying 30minutes between each coat
- build up layers of pva, around 4 layers to ensure paint doesnt react with the polyester
-add layer of gelcoat, just gonna pour it own the plug and move it around with the brush, leave to cure to tacky stage(where no resin sticks to hand) - Add layer of tissue matting, is this required???
- Add first layer of CSM 300GRAM with polyester resin
-leave for how long before doing next layers? I ma going for about 10 layers of csm as the 1 where i used csm before was with 4 layers and was very flimsy, plus csm is cheap!!
I found a good technique for releasing difficult parts of the mold was to hit it with hammer, is this bad or is it ok as long as you dont hit too hard and break the mold!!
Thanks John
I would place my money on John using Cellulose or Synthetic paint on the last plug and whatever he has used hasn’t hardened sufficiently hence the reaction. John?
You should use 2 pack and let it harden fully in the sun before doing anything with it.
Also follow Agas earlier tip (posted twice) where he recommended a test sample before going any further.
if i use enough pva it shouldnt matter about the reaction with the paint should it as it will create a boundary between the two?
Am i right?
Thanks John
You could also paint your part with something like duratec grey primer which is designed for this purpose.Polishes up to a mirror finish ideal for taking a mold from.I then use a semi permanent release like loktite frekote 770nc and I have never had any problems with a reaction between part and tooling gel.Parts practically fall out of the mold.