Gel Coat reactions

Cool. So how come i only ever get a reaction when I sprayed onto the original pieces So the original wheel arches. When I spray onto Pva it never reacts. It's very odd.

Thanks

 

That could well make your wax the issue

 

Polycon guns are way cheaper than a metered gelcoat spray system & may be good for your application http://www.kcmouldings.co.uk/polyconspray.htm heres a supplier in UK. Regards from Jeff.

 

Thanks for a good response. I was thinking it may be the wax bit I've tried 2 different types and had the same problem so either it's my application of the wax or the thinners reacting. No idea

Thanks guys

 

Sorry you need to review some of the info you just posted .
Its .4 to .5 mils , not 4 to 5 thats almost 1/4 inch !!
if you use 20% thinning be it styrene or acetone you are a nut case !!

Styrene yellows the gel coat over time and if you use acetone and spray 90% of what you put in Evaporates so like i have for the lasy 25 years acetone is my choice every time and always will be . Also if you want to thin it just warm it up . a little warmth does wonders plus a little acetone .
To clean wax off a mould we use styrene ! so if you load you gel coat and its a slow gel time what is happening to the wax you have on you mould ??
If you use acetone it evaporates very quickly and by the time the gel as gone off a good percentage has gone so how can it dull the mould , over the years we have exsperianced the complete oposite . Moulds stay shiney for longer and require less frequant waxing

 

You're thinking mm-millimeters. Mils are thousandths of an inch, of which I thought you needed about 15 mils or so to prevent alligatoring of the gel coat. That's why I could never get brushing it on to work as the thickness had such a huge variation.

Cup guns are cheap, I guess.

http://www.fibreglast.com/product/Gel_Coat_Cup_Gun_00120_A/Supplies_Tools_Spray_Guns_Equipment



Although this thing is only $150.

http://stores.infinityfrp.com/-strse-123/spray-gun,-gel-coat/Detail.bok

 

so you think i should thin down the gel coat with "Acetone"?.... ive tried to clean my mould out with acetone and its goes all sticky?

i made a piece with brushing the gel coat on and used about triple what i normal would have to spray it on... Now i know that its not as thick obviously but for my application which is purely aesthetic it seems to be fine... all i want to do is stop it reacting onto a piece because at the moment im still breaking in the moulds with pva. When i switch to not using pva this is where i may start having these problems.

I did a small test on 2 pieces of plastic, 1 i had waxed and then sprayed with gel coat and the other i had not waxed and then sprayed. The waxed one did react and the other did not.. ive switched wax since then and not had the chance to try.

Thanks

 

A mil is a thousand of an inch. = 0.001".

I did not say the mold will get dull. It is the gel coat on the part that will get dull.

And I did not say thin 20%. I said not more than 20%. Are you nuts?

 

Why not asking the supplier for a datasheet, and follow their instructions?

Gelcoat is available in brush and spray quality. The rheology of spray gelcoat is much different. (thin through the nozzle, and thick on the mould).

Also keep within the recommended wet film thickness, usually between 0,4 and 0,6mm.

If you need to thin the gelcoat for whatever reason, first try styrene, but keep in mind that pigment loading drops, and so does resin content.
Another route is acetone. Make sure you spray from a distance, so (most of the) acetone can evaporate while flying to the mould.

 

Here is something from the net.

"Do not thin your gelcoat with acetone, MEK or lacquer thinner. Thinning with these materials can lead to an un-curable application that will aligator on the next shoot,"

 

You might also let the wax air out for a few hours before applying gelcoat.

 

There are consequences with every type of thinner used to reduce gel coat.

If these things helped to make the product "better" (spray, flow and level) and had no detrimental side affects they would be used in the original formulation.

The problem is that almost every product added to gel coat will compromise the performance, whether the trade off of easier spraying is worth the loss of performance is up the person doing the job.

Acetone will inhibit the cure, if all or most of it flashes off during the spray process its not as much of a problem, but frequently (more often than not) acetone will stay trapped in the film and reduce the physical properties of the gel coat.

Styrene will not inhibit the cure, but will reduce the water, weather and crack resistance of the gel coat.

Other thinners (solvents) will have similar combinations of issues.

Small amounts of these thinners don't typically have a noticeable affect, but if we say its OK to add 3% it turns rapidly into 30% on the shop floor.

As for the fisheyes experienced by the original poster, the combination of wax and acetone are creating the problem, a different wax may solve the problem, but the better answer is to eliminate the acetone.

The dump gun discussed will spray gel coat OK, the problem is they require a high CFM compressor, larger than most DYI’ers have on hand, so while they are low in cost and fairly easy to use, buying a new compressor to use one can be expensive.

In the UK you should easily be able to buy brushable gel coat, in fact it should be the normal product for sale there. I can easily brush gel coat on small parts to the correct thickness and with very little practice you shouldn’t have any problems either. This should speed things up and reduce your costs.

 

Thanks for all the replys and i can see there are a vast amount of different ideas in this thread which is only to be expected with so many people doing the same good job just differently.


"Ondarvr" you are of course right with the adding of any after market products there will always be downfalls. I have not cleaned the mould with acetone since the first time i did it as this made the wax go all sticky which was very anoying lol.

because you guys are in the industry when you say "cheap" it has a different meaning to my cheap a cheap gun for you guys is around $150 ish dollars or £100 pounds for me a cheap gun is £25 from scerwfix .

I am only trying to start out making small parts to get money and if this proves profitable then i can afford to start using better quality everything to achieve top results.

At the moment this is the level of quality i am achieving with using pva on my mould surface spraying on a thin coat of white gel coat (which has a small amount of thinners) and then fibre glasing it.


I do have a big enough compressor to run any tool or spray gun so that would not be a problem but you must understand that i am working on a budget which most of you would laugh at untill i can make some money.

in regards to the "Fisheye reaction" this is what has proved me the most problems as if it turns out to the the acetone this is what i clean my gun with and most of my parts.. i will eliminate it and see if i can get past this reaction.. im not sure if "migueries mirror glaze wax" is the problem but that is the second wax ive tried.

 

When we say acetone is the problem, we don't mean acetone causes fisheyes in the same way silicone or other contaminates do. The reason for fisheyes with acetone is because it reduces the viscosity of the gel coat (which is what you want it to do) and this is what makes the gel coat more susceptible to fisheyes.

The wax forms a barrier on the surface and depending on several things, including type of wax, application method, removal method, type of cloth used, ambient conditions, etc, the surface of the mold may still have some excess wax on it which can lead to fisheyes. So the combination of acetone and wax may be the issue, and the correct use of each product could eliminate it.

Other products like silicone or oil can cause fisheyes that can be a nightmare, so remove any silicone spray type products from your shop and never spray silicone anywhere near the mold or on any equipment.

 

Ah wicked. That has cleared alot of my questions up. Really really helpful. Thanks