2 more layers of FG on Cured Polyester
 

I built a mold last night, I was up way to late so at 5am I HAD to get some shut eye. At that point I had base layer of polyester resin and two layers of resin/glass (6 oz) laid up waiting for each layer to get tacky before proceeding. So now I have a perfect mold. My FIRST one! It released and everything....But as you can guess it is too pliable. Should I scrap it or can I lay more layers on this already cured mold?

2 more layers of FG on Cured Polyester
 

Just lay up some more layers. the two that you have now are not fully cured yet. I find that it sometimes take up to 3 days to fully cure.
Scott

2 more layers of FG on Cured Polyester
 

You could be in trouble. because you used polyester for the mold you have a major potential problem staring you in the face. As the polyester cures it will shrink and/or twist. If you just add more layers to the existing half cured mold you will compound the problem.

If possible put the plug back into the mold and ensure it is all the way in. This will hold the mold shape while it cures. I do not know what you are molding or how big the mold is. I make all of my molds a minimum of 1/8" thick. The smallest molds I make are wheelpant molds, they are close to 1/8" thick. I use the fibreglass mat to build up the thickness. The resin can take up to two weeks to fully cure. During this time is when it shrinks and warps.

Good Luck

Ed S

2 more layers of FG on Cured Polyester
 

I've got to tell you Ed, I don't know where you get your polyester
resin, or what was done to it, or what ever, but i've NEVER heard
of all this shrinking and twisting you're talking about. A mold needs to be reinforced to some degree, depending on the size of
the part. Thats where all the time and money is spent. But this
shrinkage? I've seen literally thousands of boats, boat parts,
and pieces of whatever come out/off molds, and NEVER have I
seen shrinkage. You better not let that secret get out to the
boating AND full scale aircraft world, or there will be some REAL
unhappy folks, finding out their investment is "Faulty".
Over 40 years in glassing, Steve

2 more layers of FG on Cured Polyester
 

I agree with Ed. Put the mold back onto the plug, and let it continue to harden/cure. You'll probably be fine. You can also add some additional backup layers while its on the plug.

A typical mold half of a fuselage, will typically have a C-typed cross-section. The ends of the "C" shape (near where the flanges would be located) will tend to want to curve inward more, if pulled early and without enough backup structure. Twisting or warpage is certainly a possibility. Although, it most likely won't shrivel up! :p

2 more layers of FG on Cured Polyester
 

I have decided to get away from Polyester. The smell was just too much. I am going to try Epoxy. Less shrink, less stink, more stregnth from what I hear.

This is for a Vehicle. I know that polyesters use a gelcoat for the first layer, what do Epoxies use? Nothing? It will need to be primed and painted to match the vehicle.

2 more layers of FG on Cured Polyester
 

You can follow the same process for laying up the part as you did with the polyester resin part you made. Wax, PVA, etc. When done laying up the part, if you remove it too soon, it will ALSO be soft and gummy. Just let it sit in the mold for a few days, and give it time to more fully cure.

2 more layers of FG on Cured Polyester
 

You guys are full of great info!

For an automotive part, non load bearing but does need to be stiff of course, How many layers should I do?

I want to start with 2 oz for detail layer then maybe 6 oz and then 10 oz. Any suggestions? Should the mold be made even thicker than the actual parts?

2 more layers of FG on Cured Polyester
 

If we know the size of your mold/part we can offer some better help. Approximately, the length x width x depth.

Ed S

2 more layers of FG on Cured Polyester
 

Approx 10 inch wide X 22 inch long edges are about 1 inch high but not at a 90 degree angle. They are maybe at a 45 degree and rounded

Here is a pic of the mold pulled the other day

http://www.importpoweronline.com/hoodvent/moldnew1.jpg

2 more layers of FG on Cured Polyester
 

Your mold looks simple to make, first off all this talk of never seeing polyester shrink is wrong, the reason why all this shrinking and twisting is happing is you never put cloth of any type on as your first layers, the twisting is caused by the fibers running down and across the mold will cause this very thing to happen, I allways use 1/12 oz matt as my first 5 layers of lay-up, one to two at a time, then after the part has had a good time to settel down use the cloth in small squares ond lay them and like bricks, this will not let the cloth warp the molds.
Been making molds for 20 years
The proper polyester resin to use is the ISO polyester resins, these are more tooling grade, and can be used in Exotic Materials parts lay-up. Also I have been using Orange Tooling Gel-Coats for molds and they make a better surface, they dry faster and less mold defects..
Mike