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nissan
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Discussion Starter #1
Ok so im spray painting my car, atm doing my engine bay. Every so oftern my gun shots what comes out like sand paper has happened to me in both my undercoat and my colour but only every so oftern cant work out why. Im using a hichem gun 40psi and a 2mm nozzel.
 

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nissan
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More info mate. What sort of paint? What ratio are you thinning it?
 

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Discussion Starter #3
undercoat is motospray acrylic, mix thinner 1.5 to motospray 1, top coat is dupont acrylic laqure, thining it 1:1 with high gloss thinners.
 

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ok mate its very difficult to tell without looking at it but it sounds like it is going on too dry.

I am not sure what ratio dupont acrylic should be but when I was in the trade the acrylic laquers I used were more like 1.5-2 parts thinners to 1 paint.

And I used to spray at around 80 or more psi. Maybe some pictures would help?

You can try adjusting your fluid to air ratio.

Sorry I am not much help but that gives you a few things to look at. It could also be the paint under it 'frying up' and making it look like its going on dry and leaving a sand paper effect. Is it happening in the same spots or a random thing?
 

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Discussion Starter #5
ok yea i thought maybe i needed to add more thinner its my first time using a gun. Engine bay is a ***** to paint pannels are so much eaiser. Cheers
 

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Ok so im spray painting my car, atm doing my engine bay. Every so oftern my gun shots what comes out like sand paper has happened to me in both my undercoat and my colour but only every so oftern cant work out why. Im using a hichem gun 40psi and a 2mm nozzel.
That sounds to me like your not straining your paint and every so often a big batch of half dried out paint is spitting out your gun. This can be caused by not cleaning out your gun properly from the last time you used it, not stirring the paint properly ( eg chunks of pigment), hard paint around the lid falling in your gun when pouring or as mentioned above your not thinning your paint correctly.

Generally though if you haven't thinned your paint correctly it will come out dry all the time so I think if you strained your paint with either some proper paint strainers or some cheap stockings (not fishnets:grin:) it should solve your problem.

Cheers ****.
 

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nissan
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Discussion Starter #7
should i be cleaning my gun bettwen coats this seems to be when im getting it?
 

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nissan patrol
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should i be cleaning my gun bettwen coats this seems to be when im getting it?
Can you post up a pic mate? That will give us a better idea on what the drama is. The sand paper look does sound like the paints to thick but it generally happens all the time not just sometimes.

How long are you leaving between coats because if your leaving it a while yes it will clog up your gun but you should never leave it anymore then 10 minutes anyway. If the paint it sitting a while then you may find the paint is going off and requires more thinner but again you should never leave it that long between coats.

I haven't used acrylic for 15 years so your pushing my memory with your problems.:grin:

Cheers ****.
 

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Discussion Starter #9
sorry have already sanded all the dodgeness out and started refitting engine if it happenes while im doing my pannels later on ill take a pic nd post.
Cheers.
 

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GU8 CRD
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One word you said tells me your problem. ACRYLIC!!! Hate the stuff. 2Pac all the way. :)
Yeah acrylic has to be buffed although PPG comes out pretty good off the gun if you hit it right. I'm not a painter by any stretch, but I've shot a bit of acrylic. Sandpaper effect is definitely going on too dry. The 2 mm tip is too big for acrylic (that is a spray putty / primer size). Should be about 1.4 to 1.7.

The short story is that the paint is drying before it can flow out. Possible causes are incorrect air pressure / paint flow, incorrect thinning ratio, incorrect thinners or too hot a surface causing the paint to flash off too fast. Basically every possible thing lol. Of course, being in NQ we have to keep an eye on the humidity as well as if its too high this causes drama.

Because it is intermittent it might point to varying air pressures, especially if your air compressor is a bit dodgy or underrated or the temp of the substrate is varying (i.e. bits out in the sun). If chunks of paint are building up around the nozzle of the gun, this is a sure sign that something aint right with the setup or the paint.

In my (limited) experience I find that you usually need to thin the paint down a tad more then the directions on the can say.
 

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Just thinking outside the square for a bit.

But having painted a few engine bays in my time you can get over spray that ends up looking like sand paper. As you paint one side of the engine bay then move to the other side the over spray bounces all over the place and dries out and then settles on the still wet surfaces.

Is it a gravity feed or suction gun?

Also look very closely around the needle and you will see an outer ring that holds the needle. Then between the outer piece there will be a gap. Needs to be 100% clean. Paint will build up here and cause no end of problems. Easy to fix just undo and clean out.

Also make sure everything is centred properly too.

Cheers

Justin
 
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