Trouble spraying Jotun Hardtop

[rcx132]

Not having too much luck spraying Jotun Hardtop AX (similar to XP). Last time I got solvent pop but only a couple of parts ending up with paint running.

This time I'm using a 2.5mm tip spray gun. I don't know if I will get solvent pop as it hasn't dried yet, but more than half the parts I sprayed ending up with paint running, even though I was being extra careful. Seems there is just a very narrow gap between the painting being under applied, where the droplets don't fuse together into a smooth surface, and where it's over applied and runs.

I'm using 10% thinner and a 2.5mm gun. I think last time I used 10% and then 5% with a 1.8mm gun.

Was thinking tomorrow to try 0% thinner with the 2.5mm gun.

On the good side, my "new" (used) 18 CFM compressor is keeping up fine with my mask and spray gun.

 

[ajlelectronics]

Suction or gravity? 2.5mm is a bit large for either but especially gravity. Instead of going up in nozzle size, try heating your paint to 30C or so before spraying.

 

[rcx132]

Suction or gravity? 2.5mm is a bit large for either but especially gravity. Instead of going up in nozzle size, try heating your paint to 30C or so before spraying.

Gravity. Oh, I thought 2.5mm for such thick paint would be good. But yeah, that's what's changed since last time. Maybe save the 2.5mm gun for the epoxy primer.

 

[ajlelectronics]

I use a 1.4 for epoxy primer, changed from a 1.8 on the advice of my paint and equipment supplier. Reduces overspray and gives a nicer finish, especially when you keep the paint temperature up.

 

[rcx132]

I use a 1.4 for epoxy primer, changed from a 1.8 on the advice of my paint and equipment supplier. Reduces overspray and gives a nicer finish, especially when you keep the paint temperature up.

Ok, so what determines the tip size to use? I thought that thicker paint needs bigger tip and epoxy primer is as thick as it gets!

 

[I'm getting on a bit]

Ok, so what determines the tip size to use? I thought that thicker paint needs bigger tip and epoxy primer is as thick as it gets!

True

Are you holding the gun too far away?

 

[richie00boy]

What epoxy are you using? Epoxy mastic is the thickest and may justify a 2.5mm tip. But most other epoxies would be good with 1.8mm.

As for the top coat 2.5mm is too big and could give the symptoms you are experiencing.

 

[rcx132]

What epoxy are you using? Epoxy mastic is the thickest and may justify a 2.5mm tip. But most other epoxies would be good with 1.8mm.

As for the top coat 2.5mm is too big and could give the symptoms you are experiencing.

I've been using Jotun Jotamastic 87, that sprays on beautifully.
The top coat is Jotun Hardtop, so sounds like I've been using too big a gun.

Which gun to try for the topcoat then? I have 1.3, 1.4, and 1.8 mm tips in addition to the 1.8mm.

 

[richie00boy]

1.4mm should be ok with 10 percent thinners.

 

[fizzy]

They only seem to recommend an industrial airless spray or brush for epoxy paints. Nice to know you can spray it conventionally.

 

[rcx132]

Followed your advice, today I used a 1.4mm tip and no thinner, it's a totally different experience, far more forgiving, getting much better finish. It's still more difficult to apply than the Jotamastic primer though, so doing awkward shaped parts I end up either under applying or overapplying and seems there's nothing that can be done about it. But for the main parts that are exposed to the elements, e.g. suspension parts, I'm getting good full coverage.

Thanks for the tips, you have solved my problems! Where would I be without this forum! My wife keeps asking what I'm doing on here all the time, I try to explain!

 

[ajlelectronics]

Did you warm the paint?

 

[rcx132]

Did you warm the paint?

I didn't warm it, couldn't think of an easy way to do it.

 

[RaceDiagnostics]

Put it in buckets of hot water.

 

[fizzy]

Put it in buckets of hot water.

Then the epoxy goes exothermic and sets before you can use it!
I normally put epoxy cans in cold water to give a longer working time - but then again I am brushing it.

 

[RaceDiagnostics]

Then the epoxy goes exothermic and sets before you can use it!
I normally put epoxy cans in cold water to give a longer working time - but then again I am brushing it.

So your answer on how to warm the paint is to put it in cold water, clever!

 

[fizzy]

So your answer on how to warm the paint is to put it in cold water, clever!

I was commenting on why epoxy should not be warmed!

 

[richie00boy]

Glad it worked out.
For the issues you are having with awkward shaped parts, try a 1.0mm hvlp mini gun. About 12 quid on eBay. The chrome ones I prefer as some of the coloured ones are simply painted...

 

[ajlelectronics]

Then the epoxy goes exothermic and sets before you can use it!
I normally put epoxy cans in cold water to give a longer working time - but then again I am brushing it.

No it doesn't. At room temperature, Lechler has a pot life of four or five hours, I have even found liquid residue in pots the morning after spraying. Heating the mixed paint to arround 30C in washing up bowls of water will still give plenty of pot life, certainly enough to get 600ml on the panel. It's not as if you are going to warm the paint then go and have a siesta is it?

 

[fizzy]

No it doesn't. At room temperature, Lechler has a pot life of four or five hours, I have even found liquid residue in pots the morning after spraying. Heating the mixed paint to arround 30C in washing up bowls of water will still give plenty of pot life, certainly enough to get 600ml on the panel. It's not as if you are going to warm the paint then go and have a siesta is it?

Who knows?

I see what you mean though - I was thinking of painting my trailer which will be more like the Forth Bridge! On a small panel it doesn't matter.