Spraying Gel Coat

[factory47]

Having an odd problem, i have tried to spray Hi-Bond white gelcoat multiple times with the same problem. the gun spits like the material is unreduced. i have tried it unreduced and reduced with styrene and still had no luck.

[Herman]

Without me being an expert on machines, I still would suggest a bit more info would be nice.

-White gelcoat, which type? Is it brush or spray quality?
-Which gun
-Which nozzle size?
-What pressure?

[factory47]

yes, sorry about the lack of detail
it was Hi-Bond White with Wax it said it can be sprayed
i was using ES G860 with a 2.5mm nozzle
i tried everything from 30psi to 70psi, with the same outcome
i had also tried my Iwata spray gun with a 1.8mm and had the same outcome across all psi ranges
Hi-Bond does not have a product information page to say exactly how to use there product, i was going off of the info on the side of the can

[gonzo]

Use Duratec clear additive. It is 100% solids.

[factory47]

Wouldn't that thicken the mixture?

[gonzo]

No, it is a clear liquid. When it cures it is 100% solids. That means it is not a solvent that will leave pores when it evaporates.

[factory47]

thank you! i will try that!

[13AL]

If he ads a clear, will he have to put down more material due to transparency?

[ondarvr]

Duratec is a good product to make it spray and flow better, but you reduce the water and UV resistance, plus the already mentioned hide when using it.


Actual spitting is normally seen on siphon feed guns when there is a very small air leak, not on gravity feed guns unless the gel coat is very (very) thick. So are you seeing spitting, or sort of a poor fan with large droplets that don't level and flow resulting in a rough surface?


How big of an area are you trying to spray?

[gonzo]

I have heard people claiming there is less water and UV resistance, but have seen no evidence. I talked to the engineer at Duratec and he has not seen any degradation in performance either.

[ondarvr]

If the resin used in the clear made gel coat better, or had no affect other than making it spray better, then it would be used more often. This type of resin does not have the same water resistance as a good marine gel coat and it also yellows when exposed to UV light.

Short term you may not see any issues and you may not see the yellowing depending on the color unless you’re doing a repair on an item refinished with it, or have done a repair with it and it has aged.

Gel coats rely almost 100% on pigments for UV resistance, so by adding anything you are reducing the pigment loading. In the lab we can detect the difference in even as little as a 2% reduction in pigment loading, so when you add Duratec clear in the amounts they recommend it can have big affect on weathering.

[gonzo]

It does make the gelcoat better, in repairs. On a mold, you want the resin to stay sticky so the laminate bonds to it. They are two completely different applications. It does make the gelcoat better and it is used in repairs for that reason. Do you have any data or is it just speculation? What lab do you work at?

[ondarvr]

You say it makes it better, in what way besides reducing the backside tack and improved leveling.

I say besides these, because they only concern the person doing the repair, not the outcome of the final product. Yes you can possibly speed the process of doing the repair and make it easier on the person doing the work, but it doesn't improve the final product, it can actually reduce the quality of it.

[gonzo]

Ease of use is not the only concern of an ethical workman. I have not seen any evidence of degradation from using Duratec in the last seven years. All I hear are speculation and opinions. If any lab has results that contradict the chemical engineer from Duratec and my personal experience using the product, I would like to see it.

[ondarvr]

As the largest gel coat company in the world we've done decades of testing on almost every combination of ingredients you can imagine. After doing these tests we make recommendations on the best products and techniques to use in building and repairing all products made with them, not just marine products. Plus we try to formulate our products to yield the best results.

I will have some panels made with the clear and do new testing, then post the results. This will take some time because I'll need to get the clear, make the panels then do the testing, just the testing typically takes a few months. So don't expect results in the next few weeks.

I did forget to add one of the other things that Duratec clear will do, the re-spray will normally have a higher gloss than it would without the clear. This is because pigments and fillers don't buff to a high gloss, so the less of these you have and the more resin there is in the mix, the higher the gloss can be.