Gelcoat application

[jiggerpro]

I did cover a male plug with VE tooling gelcoat recently and I hope everything went along nicely ( I have not popped out the mold yet), I did it with a brushing quality gelcoat and did it by brush hopefully, successfully, but this was a relatively small part, my concerns are that the brush application was not at all easy to get the gelcoat nice and even and while I understand that being against the plug the brush marks are irrelevant, I do not think I would be a good idea to do the same on a bigger piece ( a boat hull mould) because not only it was quite difficult to achieve a relatively good lay up, I would say that a "quite uniform" thickness is almost impossible to guarantee by brush application.

So as I see it, and particularly when gelcoating to get a boat hull from the mould, It seems to me that spraying is "the more guaranteed" way if a uniform thickness is wanted.

For my initial low volume production I do not think a costly airless system is a good way ( not to mention some other theoretical disadvantages those systems might have ) , so I am leaning towards a pressure pot to feed a spray gun and in regards to this some doubts arise: for a start in the disposable cup type spray guns they reccomend noozles with quite large orifices around 4 - 5 millimeters while ( even in the same vendors web pages) they reccomend HVLP spray guns with 2.5 mm nozzle diameters so I am quite confused about what should I buy and would like to hear your best advises in regards to the exposed doubts and questions

[waikikin]

Jiggerpro, A "polycon" cup gun is a very reliable & easy to clean item, they have a large orifice & simply clean with a cup of acetone & pipe cleaner between pots, using a 2.5mm gravity or hvlp gun althogh possible is heaps slower with out thinning & clean up is a pain- you nearly need 2 guns & an assistant on multi pot shots. do some practice shots onto melamine sheet to tune your technique on the trigger & lapping your spray pattern & gun angle, here's a random vid of a random dude using one. http://www.youtube.com/watch?v=NkSco...eature=related Usually I advance the spray pattern with the gun angled slightly back towards whats already coated, tag the edges of your work to represent gelcoat laydown for pot volume per M2 & lap the pattern as you go, it aint rocket science but not far off . All the best from Jeff.

PS: heres some other random dudes rolling gelcoat, http://www.youtube.com/watch?v=PLBE9...eature=related apparently you can flame up your cheroot in the background, much less than recomended esp when spraying!!!!

[jiggerpro]

Hi Waikikin, I have nothing against realiable and easy to clean, but can those spray guns be connected to a pressure pot ?? because as my pieces might be quite big, those cups would be empty very fast so I would have to make too many mixes, I am talking about gelcoating a 10 meter boat hull mould which I believe could take around 50 kg of gelcoat to achieve the desired thickness of 800 microns (0.8 mm).
If those guns accept being connected to a pressure pot, I could, If working fast diminish the number of mixings and clean ups

[waikikin]

Thats the price you pay for simplicity, some organisation in having the pots lined up & some loss of about 125gms hanging in the pot, I wouldn't like to have 10 kg of gelcoat sitting in a pressure pot already catalysed unless the system offered mixes down the line I'd sneek up on that. The Polycon gun I use can take up to 2 kg per pot but I only ever put in 1.6-1.7kg 'cos I be weak of arm & that does a nice amount & nothing goes hard in a pipe before your done

[jiggerpro]

For sure you are right, some gelcoat and catalyzer can stand measured but not mixed ready to mix and spray, so everything can go quite fast, I will almost sure follow your advise, and talking about advises, for spraying large pieces fast, which size of nozzle do you think is best ??

[Herman]

Whatever you do, check your work with a wet film thickness. If you do not have one, ask your supplier, or let me know, and I will send you one. (or more)

[waikikin]

Originally Posted by jiggerpro

For sure you are right, some gelcoat and catalyzer can stand measured but not mixed ready to mix and spray, so everything can go quite fast, I will almost sure follow your advise, and talking about advises, for spraying large pieces fast, which size of nozzle do you think is best ??

My Polycon gun came with a tip about 6mm, I never actually measured it & only use it for gelcoat, I got other guns for other stuff. The polycon gun uses plastic pots with plastic lids with a tip hole & vent hole in the lid- change over is quick with a quick wash between in the fluid passage which is only maybe 1.5 inch long & strait. At the end peel off all the lids so the leftovers cure nice & pop out easy. regards from jeff.

[jiggerpro]

Hi Herman, I already have some wet film gauges, but when applying by brush is not at all easy to get a relatively even surface and thickness.

In a mold, not subject to flexing and quite rigid, I suppose is not so important, but in a hull ..........

The HVLP ( primer ones) guns have 2.5 mm and I read that to make them work with the high viscosity of gelcoat, the gelcoat has to be reduced this causing some unwanted secondary effects so it seems that the polycon guns with nozzle orifices ranging from 4 to 7 mm are the only option ( apart from airless high pressure gear which could be a pain to buy or maintain ) so it seems that the only viable options are:

1) To become better roller or brush applicators

2) to buy a polycon gun

3) to buy a gun intended for its use for gotelé application which can have quite large nozzle orifices for example this one:

http://www.sagola.com/sagola/paginas...egrav_eng.html

But this may not work, since gotelé paint consist of some sort of spitting paint and for sure will not stand the acetone or styrene.

The safest bet seems to be the polycon gun which can carry 2,2 liters of product and which can probably be "tricked" to be fed from a pressure pot, those Polycon guns as advertised, are said to be able to project up to 3.5 kg per minute of gelcoat so they could be quite fast if needed to be

[idkfa]

I toyed with your options, ended up with a pressure pot.

Yes the polycon guns can be fed from a bucket, but still gravity. Seen one for sale too, will post link if I find it again.

Pressure fed, you could try the smallest nozzle you can find and separate air lines for gun air and gel-coat flow (<5psi), might work, still don't have a needle to regulate gel-coat flow though and will end up with a garden hose if you can't slow the flow down enough.

The smaller nozzle of a pressure pot forces the gel coat into smaller particles for a more even and controllable spray pattern and I'm able to empty the pot, 4L in a couple of minutes too.

[Herman]

Also keep in mind that for spraying gelcoat, you need a sprayable gelcoat (rheology is totally different).

Although I do not know what the Polycon gun is capable of. We only used one for spitting sand...

[ondarvr]

The Polycon guns work OK in some applications, but a 10 meter boat is a little larger than what they are designed for. A pressure pot is what you need, its much easier to control and adjust.

With a Polycon type gun you also need a very large air compressor, most small to medium size compressors can't keep up with the volume of air needed, especially on something this size.

[jiggerpro]

Hi Ondavr;
I have a quite large compressor ( screw type 15 Kw) thoroughly filtered ( the air), I consulted a spray gun manufacturer ( Aerometal ) and they suggested the use of a new gun they have for the projection of putties froma pressure pot which seems to be good for the intended purpose but I will not be buying it unless it has been proven, they sent me a PDF about it, I will see if I can find it online and post the link.

On the other hand I do not see why you say the polycon gun won´t be useful it is just a matter of making 10 mixes for every 20 kg of gelcoat ....... yes a pain in the neck but what are the other options apart from going airless, most of the HVLP guns only have a 2.5 mm of nozzle orifice and this is clearly insuficcient for the gelcoat viscosity ( if reducing is not wanted) needing 4 to 6 mm of noozle orifice, and I have not found any HVLP gun with such a noozle diameter.

[ondarvr]

You can buy any size tip you want for a good pressure pot gun, so spraying gel coat isn't an issue.

The Polycon guns are rather crude, there is no needle to shut off the flow of gel coat, all you can do is tip the gun back to stop the flow, the trigger only activates the air. On small parts this isn't too bad, but on larger parts where you are standing in or over the part, it tends to drip, and if you move wrong, it can pour out of the tip.

There is also no way control the fan other that with air pressure, the fan is round, with sort of like a splatter affect, not exactly ideal.

Can you use it....yes....is it the easiest and best spray gun for a 10m boat...no

[jiggerpro]

those are the links please Mr Ondavr and Herman take a look and let me know what you think
http://www.aerometal.es/folletos/V2014.pdf

and this:
Specially for road signs.

CHARACTERISTICS:
Air cap, nozzle and distributor made from hardened steel.
Product regulator.

Nozzles:
3 - 4 - 5 - 6 - 7 mm. (optional).

P - M - G type air caps(depending on surfaces and density of product).

Ref. Nozzle Air cap
9RUT P 3 3 mm. P
9RUT M 4 4 mm. M
9RUT M 5 5 mm. M
9RUT G 6 6 mm. G
9RUT G 7 7 mm. G

[jiggerpro]

I have not been able to find a direct link but please take a look into

http://www.aerometal.es/ingles/home.htm

then look into products and then please take a look into their " Spray Guns for Decoration and Roadway Signs GOT & RUT " and once there into their "IMPER 9 RUT" spray gun ....... so far and in theory it should be completely suitable as the fabricators say it stands all kinds of solvents ..