How to prevent 'orange peel' spray finish

[Dengue]

I have just sprayed some Valspar Lic40 polyurethane enamel (data sheet attached) with an electric compressor Earlex 1900 HVLP spray outfit using a 2.0mm tip, and the whole job had an orange peel finish.

I rolled on the first coat, didn't like the result, sanded it back, and then sprayed two coats 15 minutes apart as per the recommendation. This spray outfit can only change the amount of fluid, not the air

The mixture was 4:1:10% for Lic40 : hardener : thinner

Can anyone please suggest ways in which I can improve this quality of finish? smaller needle, more thinners etc?

[rustynail]

Jill, I dont know your particular outfit but there are a few tips which may help without changing the mix.
Spraying on a cold surface can cause peel. Also it is important to spray at right angles to the surface. If you drop your arm it means the bottom edge of the spray is closer, this usually shows up as stripes of peel across the work. Also laying on too thick and/or too slow can cause peel. Hope this helps.

[RETIRED]

Jill. I am assuming there are no contaminants on the surface.

Reading through the specs on the varnish your nozzle may be too large and you are applying too much. This causes the outer surface to dry too quickly particularly if it is hot.

Try very thin coats and see how that goes..

[Dengue]

thanks rusty and Ian. I have ordered a 1mm and a 1.5mm needle, will give it a go after the existing finish cures in a week or so

[GPL]

What are you spraying? Well, if you're spraying something flat 15mins intervals between coats is too long and that would be the cause of the orange peel because the paint is not flowing but then again I've never used that product so what do i know. Also that gun doesn't do you any justice either. 4:1:10 is pretty thick mix. Have you tried adding a slower drying thinners by any chance? Try adding 15 to 20% thinners to your mix. Also try spraying your first light coat leave that for 10mins then come back and spraying 2-3 coats one after another. Hope it helps. Goodluck

[soundman]

There are a couple of problems that may be compounding.

Depending on the HVLP unit, it may be heating the air stream, that may caose the finish to partly dry in the air, and warm air of the surface my be doing you no favours..

we are talking about a polyeurathane finish that may not realy be designed for spraying.....we have to be carefull with polly finishes, they don't tolerate being thinned aywhere near as much as laquers.
thin them too far and you divide the resins and film strength suffers, and they also tend to get cloudy.

laquers also dry very fast, pollys can stay wet for quite some time and if you overcoat too early they can be tretcherous as hell with runs.

you may be ablet to get away with thinning more but I would tests it first.

I would be looking at the clasic causes of orange peel.

If it is a polly designed for brushing, perhaps brushing may be the best option.

Of course if it is a two pack the hardner may be accelerating the drying and retarding flow out...is there a slow hardneer available or a retarding thinner.

The HVLP spray unit you have may be doing you no favours, it may work well for spraying water bassed acrillic paints, but as soon ast you start playing with solvent bassed products, it my not give you the controll that a compressor bassed gun would give.

you realy need the ability to manipulate air and product.

cheers