Trouble with spraying epoxy

[Munkul]

I could do with some advice...

I've sprayed a lot of different paints including 2k, but never epoxy primer. I've switched to it for faster and more reliable curing especially in the winter.

Using Hempel Hemadur 45143 as primer on metal. Through a HVLP gravity gun with a 2.0 fluid tip.

First shot - mixed up with a little thinners, maybe 2-3%. Quite stiff but didn't look overly thick. Anyway it barely sprayed at all and absolutely didn't atomize.

Remixed with another 3% thinners, it was better but still not atomizing properly. Used it anyway.

Mixed 2nd cup, this time with a good 12-15% thinners. This time it sprayed ok, but i could tell it was creating too much mist, like there was too much thinner.

Anyway, it seems that the paint is simply no good for gravity air spray. Is this true of all high build epoxy primers?

Would I be better off with a pressure pot spray gun with a standard nozzle?

Its a shame because if it would spray nicely, it looks like it'll be far better than the standard phosphate primers I usually use.

 

[julianf]

I spray the lechler one all the time, with a gravity cup.

I use about 5g of thinner per 130g of catalysed product.

1.4 tip, and whatever pressure gets it to spray nicely. Datasheet says 2 - 2.5 bar. I reckon I'm at the top end of that.

I spray in a heated garage.

 

[carbon]

I've switched to it for faster and more reliable curing especially in the winter.

Epoxy primer doesn’t give you that compared to standard 2k primer, what epoxy primer gives you is a lot more durable primer that adheres to different substrates without the need to use an etch primer for example with aluminium. Using epoxy primer also means if required the part can be left without the need to add a top coat as epoxy doesn’t absorb moisture like other systems.

The tds should give you the correct information regarding the recommended quantity of thinner required and hopefully a viscosity time to aid with achieving consistent results.

Anyway, it seems that the paint is simply no good for gravity air spray. Is this true of all high build epoxy primers?

Again this information will be in the tds with recommended nozzle sizes and air pressures.

I’ve never had issues spraying epoxy primers with a gravity spraygun following the information in the tds

 

[Brad93]

put the paint in warm
water beforehand

 

[Munkul]

The tds should give you the correct information regarding the recommended quantity of thinner required and hopefully a viscosity time to aid with achieving consistent results.

Again this information will be in the tds with recommended nozzle sizes and air pressures.

I’ve never had issues spraying epoxy primers with a gravity spraygun following the information in the tds

not super helpful unfortunately because the TDS is all about airless spray which is totally different.
Up to 5% thinners is recommended, which ties in with my results - overthinned isn't great.

I'll try warming it up next time it was around 10 deg C which I would have thought was OK.

Maybe this stuff is just extra viscous - it does say that in the datasheet, but in some cases viscosity doesn't correlate to ease of spraying, eg - the topcoat I use is almost like plastering mud, but it sprays fantastically.

HEMPADUR 45141/45143 being a high viscosity material, may require special measures to be taken at application

Maybe I've picked the wrong product.

What lechler alternatives? It was 50:50 for me between the hempel stuff and jotun penguard...

 

[Munkul]

I've just re-read the TDS. It says

Mixing ratio Base 45148 : Curing Agent 97430
(3 : 1 by volume)

The volume supplied was 3.35 litres paint, 1.65 litres hardener, to make up 5 litres total.
This suggested 2:1 by volume which is what I mixed it to...

So... what gives? Perhaps 3:1 would have been better to spray with?

 

[carbon]

In the manufacturers information for this product it only recommends airless spraying or brush application. If your are trying to use a hvlp spraygun you are possibly using the wrong product.

Looking at the data sheet there isn’t any values given for viscosity. You could try thinning it to about 18s with a viscosity cup and try that as a starting point and adjust the thinner quantity if that doesn’t work well.

 

[Munkul]

In the manufacturers information for this product it only recommends airless spraying or brush application. If your are trying to use a hvlp spraygun you are possibly using the wrong product.

Yes that was my thought... I'm asking on here to confirm.
I've sprayed loads of paint with the same gun which wasn't recommended for spray... doesn't mean it's not possible usually if its too thick it just doesn't flow very fast, but atomizes well enough. This stuff flowed fast enough but didn't atomize.

Looking at the data sheet there isn’t any values given for viscosity. You could try thinning it to about 18s with a viscosity cup and try that as a starting point and adjust the thinner quantity if that doesn’t work well.

Interesting... I've never used a viscosity cup before.
I've always thought it's an unnecessary step, because I can check it with my gun and user experience from the first trigger pull. It doesn't spray well when it's thick, and it's overthinned when it's at correct viscosity.
Maybe I'm wrong.


One thought I did have was using my other gun with standard high pressure air nozzle, only has a 1.8 fluid tip but the pressure might atomize the paint better than the HVLP nozzle.

Basically, I'm asking, is it my paint that's thicker than most epoxies, or is it the HVLP gun that's unsuitable?

 

[Morris]

I spray the lechler one all the time, with a gravity cup.

I use about 5g of thinner per 130g of catalysed product.

1.4 tip, and whatever pressure gets it to spray nicely. Datasheet says 2 - 2.5 bar. I reckon I'm at the top end of that.

I spray in a heated garage.

Pretty much how I do it except I apply local heat to the job. Paint comes off the shelf at pretty much outside temperature. Never had a problem. I use Lechler epoxy.

 

[Dcal]

You are comparing apples with pears.

The Hempe is an epoxy mastic, the Lechler is a straight epoxy primer.
The main difference is the solids content and to turn an epoxy mastic into a epoxy primer, add more thinner or just buy an epoxy primer.

I really like epoxy mastics and some spray better than others, Jotamastic 90 sprays better than 87 for example.
I use a cheap gravity gun with a 2.5 tip and need to add about 10 to 15% thinners. Heat also helps and if you heat the paint and the work piece, you can get away with less thinners at the expense of pot life and consistency as it cools down.
More thinners means thinner coats so more coats requires for the same results, but it is great stuff.

 

[DaveB]

Basically, I'm asking, is it my paint that's thicker than most epoxies, or is it the HVLP gun that's unsuitable?

I have not used that particular Hempel product, I have used 15570.

15570 has a base paint that is considerably thicker than the curing agent as the base is loaded with mica flakes.
I mixed the two base on weight rather than volume as the two parts have quite different viscosities and densities.

I've also used HB 989 and that also has a difference between base and curing agent viscosities and densities.

I only used the Hempel with brushes or rollers.
The HB sprayed very nicely.

Reading the info on the Hempel tech data sheet and the application guide I think you have the wrong product for the application method.
45143 is a cold climate version of 45141 that might spray better at current temperatures here in the UK, but still looks like a pressure spray product rather than an air spray.

 

[julianf]

You are comparing apples with pears.

The Hempe is an epoxy mastic, the Lechler is a straight epoxy primer.
The main difference is the solids content and to turn an epoxy mastic into a epoxy primer, add more thinner or just buy an epoxy primer.

I've only ever used epoxy primer and standard 2k high build. I'm unfamiliar with epoxy mastic.

I can imagine what it is, but what's it's application? I mean where would you use the thicker epoxy rather than the thinner one, and why?

My assumption is on chassis etc? In which case is it just a speed advantage over multiple coats of the thinner product?

 

[Dcal]

I've only ever used epoxy primer and standard 2k high build. I'm unfamiliar with epoxy mastic.

I can imagine what it is, but what's it's application? I mean where would you use the thicker epoxy rather than the thinner one, and why?

My assumption is on chassis etc? In which case is it just a speed advantage over multiple coats of the thinner product?

It's for industrial applications where they are painting acres of steel work and every coat takes time, think Forth Road Bridge.
It doesn't have to look good close up, but it does have to last for about 20 years in really corrosive environments before first maintenance.
Rarely is one coat sufficient even with epoxy mastics as any defect will cause a breakdown in the system, so usually a three coat system.

 

[carbon]

I've never used a viscosity cup before.

When I was at college I did a short spraying course. At the time it was cellulose based and was instructed to use a viscosity cup. As I don’t spray full time I still use one, this may be just specific to the paints I’ve used but with some of the black 2k I’ve used putting it through a viscosity cup after adding the hardener has shown that it was already thin enough and has not required any thinner.

 

[Munkul]

Thanks all for the comments. I think it sounds like I've picked a product that's a bit too thick for the job. As Dcal says, its an industrial grade paint so you can get the dry film thickness up with each coat. It's not something that's been a problem for me before, but the epoxy does behave a little differently to acrylic/oil base.

The application is for things like this, its all interior steelwork that gets a waterbased topcoat:

Acrylic primer usually works out ok, but if its not fully cured it plays havok with the WB topcoat. It's the curing that's variable, and the older the paint gets, or the colder the temp, the worse it cures.

I might try jotomastic 90 next time... or maybe just a 2k primer.

 

[Munkul]

When I was at college I did a short spraying course. At the time it was cellulose based and was instructed to use a viscosity cup. As I don’t spray full time I still use one, this may be just specific to the paints I’ve used but with some of the black 2k I’ve used putting it through a viscosity cup after adding the hardener has shown that it was already thin enough and has not required any thinner.

I did some bodywork spraying years back as well, learned off a local paint guy, and I get that if you want that beautiful liquid finish with no runs, you need the viscosity just right and I made plenty of mistakes...! Clearcoat is not so easy... maybe should have had some viscosity cups back then

The steelwork I'm doing is much more forgiving... The matte or satin topcoats can just about be thrown on with a trowel and it comes out great. The primer I usually err on the dry and orange-peely side.

 

[Dcal]

Something worth remembering with all epoxies, no matter the flavour, is they have a recoat time after which you need to abrade before applying another primer or top coat. It is normally a week or two, but once fully cured top coats won't stick well.

Another epoxy primer worth considering is Selimix 7-413.
It's an industrial coating and might be well suited for your application as you can apply a top coat wet on wet which is a real time saver.
It is however nowhere as forgiving as Jotamastic 90 for example and will run if you are not careful but it does go on nice and flat.