Etch Primer "Cobwebs"!

Lindsay G
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Joined: Thu Aug 07, 2008 2:16 am

Etch Primer "Cobwebs"!

Postby Lindsay G » Tue Nov 30, 2021 3:23 pm

Having got a number of plastic and resin bodied wagons sprayed, detailed, decal-ed and weathered, I thought I'd move on to several metal and whitemetal bodied wagons. Out for the first time came the etch primer (Precision two pack PQ31), and thinned down per Ian Rathbone with 2 parts PQ32 and 1 part cellulose thinner. Tried it on a test area and got lots of what looked like cobwebs blowing about the place, tried without the cellulose thinner but same result.

Cobwebs.jpg

Could try fiddling with the pressure (20psi used without probs previously) and other slants - but could the Best Before End 2019 be the problem?!

Lindsay
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Daddyman
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Re: Etch Primer "Cobwebs"!

Postby Daddyman » Tue Nov 30, 2021 3:44 pm

Lindsay G wrote: could the Best Before End 2019 be the problem?!


I would say so, yes, as I've used Ian's recipe many times without this happening. This assumes you were absolutely accurate with measurements, and the temperature was OK. When you say "try with 20 psi", as opposed to what? That cobwebbing might occur with very low pressures too.

John Palmer
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Joined: Fri Jul 15, 2011 11:09 pm

Re: Etch Primer "Cobwebs"!

Postby John Palmer » Tue Nov 30, 2021 4:13 pm

I feel for you, Lindsay, having myself encountered exactly the same problem with the Phoenix self-etch primer. I got much better results by increasing the proportion of thinner from a 1 : 1 (manufacturer recommendation) to a 2 : 1 ratio, though without the addition of any cellulose thinners, as illustrated here: https://www.scalefour.org/forum/viewtopic.php?f=95&t=5905&p=65908#p65899, but I have subsequently found this primer to be hyper-sensitive to cobwebbing, and haven't come up with a reliable solution.

Certainly the age of the product could be a contributory factor, but I originally encountered this problem with both parts of the product well within their manufacturer's specified lifespan, so it is clear to me that age is not the only reason for such cobweb effects.

It would be good to get to the bottom of what the cause of this phenomenon is, particularly since advice on appropriate remedies can be completely contradictory. For example, https://itstillruns.com/paint-gun-cob-webbing-stringy-7637309.html says: "A low spraying pressure stops paint from atomizing correctly and results in thin strands of material being forced through the air cap of the spray gun", but if you then take a look at https://www.carcolourservices.co.uk/cobwebbing/ you'll see the following recommended solution: "Reduce air pressure and/or viscosity until cobwebbing disappears."

Is this a case of this particular primer being unduly sensitive so far as correct air pressure for spraying is concerned? If so, how does one arrive at the optimum pressure?

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John Bateson
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Re: Etch Primer "Cobwebs"!

Postby John Bateson » Tue Nov 30, 2021 4:13 pm

Quite a few years ago now I tried using this stuff with their recommended thinner but found the cobweb issue as well. Also it seems to block everything up and solidify very quickly.
Moved to Upol from Halfords and haven't looked back.
John
Slaving away still on GCR stuff ...

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Tim V
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Re: Etch Primer "Cobwebs"!

Postby Tim V » Tue Nov 30, 2021 5:12 pm

Agree with John.

I use Upol, never looked back. Problem with low volume sales like modeller's paints is they just aren't very good.
Tim V
(Not all railways in Somerset went to Dorset)

Daddyman
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Re: Etch Primer "Cobwebs"!

Postby Daddyman » Tue Nov 30, 2021 5:14 pm

John Palmer wrote: I got much better results by increasing the proportion of thinner from a 1 : 1 (manufacturer recommendation) to a 2 : 1 ratio, though without the addition of any cellulose thinners, as illustrated here: https://www.scalefour.org/forum/viewtopic.php?f=95&t=5905&p=65908#p65899, but I have subsequently found this primer to be hyper-sensitive to cobwebbing, and haven't come up with a reliable solution.

Ian Rathbone discovered this years ago, hence the recommendation to increase thinners:paint ratio to 3:1.
John Bateson wrote: Quite a few years ago now I tried using this stuff with their recommended thinner but found the cobweb issue as well. Also it seems to block everything up and solidify very quickly.

You don't say what ratio you were thinning at.

I've found this a completely trouble-free primer when mixed as per Ian's instructions.


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