making a mold question

[stephendehong]

We are making a 39feet motor boat mold, and just extracted the hull mold and start the deck plug, but the hull mold is not shining,even we polish that with wax, when look at the mold surface, a lot of small scratchs on the mold gelcoat, maybe that's the reason it's not shining,and we made a small piece on the mold, and extract that for testing, it's also a lot of scratchs on that, and not shining, so what can we do to repair that?
Our making prograss is:
1.Make the plug with wood
2.laminate fiberglass on the wood3
3.Apply putty
4.Sanding
5. Spray gelcoat on the putty
6. Water-sanding the gelcoat
7.Apply wax
8.Spray Mold gelcoat
9.laminate fiberglass
10.put the reinforce
11.extract the mold

[Thin water]

The scratches are in your mold because they were in your plug. You need to sand the mold with 320 grit paper until the scratches are gone then sand with 400, 600, 800 grit intil it is smooth then re polish it.

Make your new plug the same way, no scratches. It must be glass smooth or every part you make will look bad.

I have made 7-8 molds so I am learning also. Above based on my limited mold making experience.

JIM

[tja]

Hello, When you prepare a plug you want to wet sand to as fine of grit as posible say 1000 grit. Then use an electric buffer and compound to a high gloss. If the plug isn't shinny then the mold won't be shiney. If you want to fix the mold that you already have made i would start with no coarser then 600 grit and then sand with 1000 grit and buff to shine. As far as the part you already have made do the same with 600 and 1000 then buff. Hope this helps. Tom.

[stephendehong]

thanks for your help, right now I have re spray the gelcoat on the mold, because our gelcoat on the mold is too thin, so i have to spray another layer before we re sand that, when we re wet sand that on the new gelcoat, shall we start at 320 grit or 600 grit?

[Thin water]

It depends on how smooth it is and how long you feel like sanding. If you start with to fine of a sandpaper you are just waisting a bunch of labor. If you start with 320 or 400 then go to 600 800 100 etc each finer grit removes any scratches left by the last. I make knives like this. I start with 400 and go finer and finer all the way to 10,000 grit that is used to polish lenses. When I am done it is as smooth and reflective as any mirror.

Make sure you get all of the wax off before you put on the new gel coat.

[tja]

Are you sure that the gelcoat is too thin. Tooling is tranparent and may look thin when it may be ok. Regelcoating would be my last resort as it is quite a job. There are products from Advance coatings that will work easier then using tooling gel. Try sanding and buff before regelcoating. I aiways take the conservative approuch. Good luck. Tom.