Saying hi and asking for help (moulding / gel coat)

Hey guys my names Jo and wanted to join this forum for some advice on moulding.

Ive made moulds to mould various products to sell and am wondering how long it should take for gel coat to cure so that when i wax it and use the mould that they will not cure togeather?

Thanks for the help guys

 

Follow the mold gel coat manufacturers directions re times. Same for the wax or whatever release agent.

If you follow the directions, it the manufacturers problem, if you deviate its yours.

While mold gel coat is mold gel coat there are differences between different brands, manufacturers, and there may be some variations in timing due to temps and humidity.

Steve

 

Hey steve

Thanks for the response. I completely agree with following the manufactures guidlines but where i buy my gel coat from is a company that decants their product into its own branded tins and mixes different colours, This therfore leaves me with no spec sheet and drying times etc

i was told that at a rough guide line that most gel coats will fully cure in about 2 weeks and then would be safe to mould from just using wax, any time before that then it would be wise to use PVA as a barrier?

any input is always welcome so thanks

 

I usually do a test on the prepped mold surface with the production Gelcoat that we would be using.

 

And you can boost up the curing time with heat if you are in a hurry. Some 60 to 70 deg Celsius not more.. better to make a test first to be sure of the gel coat you are using..

 

Thanks guys,

if i do a test and see, how would i know if it was fully cured, are there any tell tell signs... for example last week my moulds were slightly tacky on the surface and now they don't feel tacky.

I had to move them into my house as my workshop is far too cold for anything to cure quickly.

these are only thin layers of gel coat just so i have a contrasting colour to spray my production gel coat onto

Thanks

 

It is not only the gelcoat you have to worry about but the whole mold as well. The mold must be fully cured otherwise no amount of waxing will prevent the newly laid up part from from cross linking with the partially cured mold.

If you are making mold out of poly, baking it as suggested by Teddy or putting it out in the sun for one to two days. When you no longer smell the styrene and when the surface of the mold is dry to the touch, that is the time to do a patch test.

 

Thanks Rx

The problem i have is i live in England and we have no sun. I was thinking about making a smallish oven in my workshop out of MDF to put my molds in. They are only about 4 foot by 3 foot tops so would not have to be too big.

when you say a patch test do you mean just fibre glass a small patch onto the new mould after waxing to see if it sticks?

thanks guys

 

Yes, just a small part just to make sure the mold is really cured. If after several test on different molds and you feel confident that your curing process is good enough, you can eliminate the patch test.

 

Ah cool stuff sounds like a good plan. would you go with a small patch of resin say an inch square to test if it sticks or go the whole way and spray a patch of gel coat and then a resin and mat?

Thanks

 

You are too stingy. Maybe a foot square and better at the deepest part of the mold where it tends to undercure because of trapped styrene. One or two layers will do. No need for gelcoat.

During the curing stage, you will notice the strong smell of styrene. Keep your shop well ventilated and worry about your neighbors.

 

haha stingy true... just the bigger i do the more i have to get out if i balls it up haha....

been waxing the moulds all day to prep them for tomorrow.. using miguieres mirror glaze wax and says to do 5 coats with breaks on 30 in-between coats so been doing that ready for tomorrow.

yer got to love the smell of styrene haha.. luckily i have no neighbours

Thanks

 

Mirror glaze will do. Just stay away from silicone wax. It is a no no in the composite world.

 

You are new to composites manufacturing so I will give you some valuable advice. But first let me tell you a story that actually happened.

Our plant is located in an industrial area. A polyester composite was manufacturing commercial parts about a block away. It burned down completely. They decided to move beside our place. It was brand new, modern but one day it burned down completely. They moved to an old building at the back of our plant to continue operation. It was razed to the ground again.

Lightning strikes thrice. And always, it was during breaktime when nobody is working that the fire starts.

However our building never had a fire during its entire years of operation.

Styrene, acetone, and all the resin is very volatile. Styrene is heavier than air and sinks to the bottom. Our plant is criscrossed with canals for the heavy styrene to sink into and is extracted outside by a huge fan.

Keep your extractor fan as close to the ground as much as possible. That is where the styrene sinks. Fresh air vent from the top of the ceiling.

Never mix cobalt and MEKP together. A vial has the explosive power of a dynamite.

Never leave a hot batch of resin in the shop during breaks. It has a tendency to self ignite due to thermal runaway aggravated by a narrow mixing container.

Always extract air when doing deep molds. Styrene collects in the bottom. Once, a worker plugged an electric fan to blow air out of a hull being laid up and there was spontaneous combustion merely from the spark in plugging the fan.

Another time, we were working in a small shop, a lighted cigarrete butt manage to blow away towards our resin stock and there was spontaneous combustion.

So take extra precaution, it is not as safe as you think.

 

jesus!...I did not think it was that explosive, i new that all the chemicals were bad and will take extra care now.

I think im lucky that my moulds are small and shallow in comparison to that of a boat mould but will take extra care.

Thanks for the valuable advice