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

Some chemicals are very very bad,I prefer to buy my resins neat so that entailed keeping cobalt and DMA in the building which lived in a seperate cabinet on the far wall,the DMA just came with a Large Skull and crossbones as a hint !now overseas back the 90's this came to Kuwait from Saudi Arabia marked as "Clear Cobalt" on a large plastic bottle LOL evidently they had a comedian on staff.

 

LOL. They are so used to seeing "clear" because their diesel fuel there is as clear as water. Colorless.

 

managed to fook this up

so im not sure where im going wrong here and i am new to this so please go easy on me Lol.

i had originally made white moulds of these wheel arches and then realized it would be really hard to tell if i had a good coat of white gel in the mould when i made a set, As the mould would be white as well, So i sprayed over my white moulds with grey gel coat to make them easier to use like so.



so spent all day waxing them getting them ready to do a test patch today, made a test patch by once again waxing the mould and then laying a strip of mat and resin on that. waited till it dried and pulled it out.

EXCEPT!!!

This happend



i put the piece back in so you could see what i had done



Ive now got the other 3 moulds sitting here and i am tempted to spray them with PVA and then mould my pieces. I wont do that if when i go to use them without PVA that this happens again?

please help me out of this hole as im sick of screwing these up in the learning process

 

hey,

Little bit stuck as to what to do now, all 3 remaining moulds have all had a spray of gel coat on them when they were made as i had to do some filling and sanding to make sure the moulds where smooth..... can you not spray gel coat on? will it never stick?...

im stuck as i have another mould i am making and ive had to fill a fair few bits on it to make it smooth and the right shape. Im now worried as if i spray this one with gel coat like i did that other mould that it will just peel off.

here is the next mould.




and here is the other one after ive been swearing at it and picking at it with my finger



Thanks guys

 

Your mold is f****d up. It seems you test piece stuck to the gray gel coat of your mold. It appears your gray gel coat did not cure properly. Try to save the mold by baking it again and do the routine wax procedure. As an insurance use PVA. You intend to do short run anyway, not commercial.

Here is where you made the mistake. When you pulled out the white gel coated mold, It should have been ok if cured properly. But when you resprayed it with gray gelcoat, that is when the problem started.

Gel coat cures properly when air inhibited (not exposed to air, air contains moisture) The white gel coat has cured properly because it is in contact with the male mold preventing exposure to air.

When you decided to re spray it with gray gel coat, you are trying to bond a new layer to and already cured layer. Bond will be weak especially if you did not grit sand the surface.

Second, you should have added "wax solution" (about 10% by volume) to the gray gel coat. The wax solution will float to the surface during curing, forming a barrier between the gelcoat and the air. That is why your gray gelcoat did not cure properly. It will remain tacky for many months because the surface did not cure. It absorved some moisture in the air during the cure stage.

Caution. You should add wax solution only to the last layer if you do not want it to be tacky. If you are going to bond or glue anything to the inner surface, DO NOT USE ANY WAX SOLUTION. Let it remain tacky.

It's a beginners mistake. Try again.

 

Thanks again for a good reply. so it seems any idiot can make a mould (me) but getting it to work takes alot of skill.

what would you suggest i do with the 3 moulds that are sitting here that have had the same treatment with the grey gel coat be it that the mould was white before or that i have repaired bits and sprayed again with the gel coat.

I mean can i run them if i use pva a couple of times do you think they will cure better and i can then use them after that or is this something that will have fooked the moulds up unless i take back those layers.

Ive ordered some wax now to add my gel coat, if i was to spray a layer of gel coat with the wax in it now onto these moulds would it cure better?

so my opions are:

1 Do i use pva and use the moulds in the hope it will cure it properly?

2 Do i spray over these moulds with the new gel coat plus wax

3 do i Cry and restart the moulds but striping them back and then spraying them with gel coat plus wax

Thanks

 

Try to use the mold with gray gelcoat and use PVA. If unsuccesful, make another set.

You cannot redo the mold at this time as it is already saturated with wax. You will just be repeating your mistake.

 

so hopefully fingers crossed if i run a couple with pva that then they will be cured enough to be used, if not i will have to strip them down and re spray them with gel coat plus wax?

Thanks

 

so just to clarify for my stupidness.. if i mould them with pva then there is a chance that the heat from the fibre glassing will fully cure the sprayed on gel coat and i still may be able to use the moulds without pva?

Or


not matter what i do because i sprayed the gel coat on to other gel coat without wax it will never stick to that bottom layer and without pva the mould will pull off the gel coat?


sorry im being slow i just wanna try everything to save these moulds before having to start again.


Thanks guys

 

Whatever suits you best. If you have a white mold, why don't you make the part in gray, or black? It is a car part anyway and will be painted.

 

It's just easyier to paint if the part is White.

Pva on and then gel coat and I've mat and resined it so only time will tell. So do you think these mould will never cure though?

Thanks

 

hey guys.

Just to let you know hot its gone today.

This is what the mould looked like when i pulled out the piece i made so it was still in tack and had not pealed the gel coat off



this was what the piece looked like with the pva layer still aplied.



and after the pva was taken off



there were a few air bubbles in the resin stage which means that cocked up the gelcoat. I bought some thinner mating so i can use that first.

when i pulled it out it was very stiff to pull out the mould and still did not pull the gelcoat off. Do you think after another pull from the mould it might be ok to try without the pva ?

Thanks guys

 

Sorry was busy. If you are satisfied with minor cosmetic problem, you can continue with the rehabilitated mold. Continue the wax and PVA routine until you break in the mold. 4 to 5 tries before you give up on PVA.

Good piece for a first timer.

 

Hey

I was thinking that if i sanded out the messed up mould down to the original white gel coat and then sprayed over that with the gray gel coat but this time mixed with the wax i have just received.

When i mix the wax( 10% of the overall gel coat) how will i know if it has worked?

i am thinking of making a small oven type thing in my workshop where i can put like 2 of these wheel arches in and then heat it up to speed things up.

what sort of temp should i be getting it to for it to help and should i not exceed any temp?

Thanks