Dulux Eggshell problem (now solved) then MDF painting tips

[RobertMP]

29.11 Changed the thread title as there is some general info on MDF painting on page 2 now.

-

Bit of an essay... sorry.

I'm trying to spray a lot of MDF that I've turned into parts for refreshing our kitchen with new doors and trims as you may have seen
here in my WIP thread.

I thought I'd identified the problem I have been having with bits appearing in the finish coat of Dulux Trade Eggshell..... but now I'm not so sure.

There are some pictures in the other thread.

What happens is that the eggshell coat spontaneously develops 'dust' within a minute of being applied to the door panel - and a few 'fish eye' spots.

I spray the coat on and it is wet and even with no inclusions and as i stand there looking for problems they appear across the panel at random positions.

I've been doing some tests to try and work out what is happening and I'm getting more confused!

so far..

1, I stretched a plastic bag over a piece of chipboard so I had a guaranteed clean virgin surface and spray painted the bag with the eggshell. Perfect - no dust. no fish eyes. left it to dry - still perfect.

2, All doors etc are painted and rubbed down with a water based MDF primer made by Leyland paints. This was what I thought was the problem and reacting with the topcoat. Bought some oil based undercoat. undercoat shows only slight reaction. today I sprayed eggshell over the oil based undercoat... and got the same reaction

3, Tried spraying the paint neat but the gun won't have it. Bought some expensive high purity white spirit 'for thinning paint' (been using wickes stuff) and thinned by the minimum to get it to spray - same problem.

4, Tried wiping down with white spirit, meths, and even cellulose thinners in an effort to stop fish eyes. cellulose seems to reduce it a bit but is too aggressive on the primer.

5, tried not rubbing down an undercoated panel at all - same reaction. tried not wiping with anything on a sanded primed panel - same reaction.

6, I had a small amount of Leyland paints Eggshell so I tried that instead of the Dulux - it reacted slightly less but still reacted in the same way.

So I'm a bit lost as to what to try next. painting plastic proves the paint is clean and can stay clean. painting anything with a previous coat on it (even recoating sanded eggshell) just looks dirty.

Any suggestions gratefully recieved!

 

[Chris Knight]

Robert,
You must be very frustrated by now! I am sorry I don't have a solution for you. Normally a "dusty' finish is the result of not getting a proper wet coat on the job but you have all but eliminated this in your comments and by the results on the plastic.

I'd still be inclined to question the drying time but my first instinct would be to turn to Dulux for the answer.

Not many folk on this forum seem to use sprays so you might get a better answer elsewhere. I'd recommend a couple of American sites except that Dulux is presumably a UK brand people might not know. This is Jeff Jewitt's site/forum and he has been helpful to me in the past but I don't know how your query may be dealt with - worth a go though.
http://www.homesteadfinishing.com/phpBB2/

 

[jasonB]

How are you removing the dust from the rubbed down surfaces, a tack rag will remove far more than just wiping with a duster. If there is dust on the surface before you spray it will come to the surface as the solvent evaporates and the film becomes thinner.

Jason

 

[wizer]

Can you make your own tack cloths? It is just a rag with white spirit impregnated?

 

[jasonB]

You probably can, its stockinette but it has a more oily texture, don't know what it is.

Jason

 

[RATWOOD]

HI Robert
might sound funny but how long do you leave your extractor on before and after you finish spraying

 

[JonnyD]

I usually hoover the surface with a soft brush vacumn attachment gets it really clean.

The fish eyes you describe are usually a sign of contaminationon the surface with something such as silicone.

I use a paper disposable filter to make sure the paint is clean and free of bits. Temperature can also make a difference i try to spray at a miminmum of 15 degrees but its not always easy to get the workshop warm enough.

jon

 

[RobertMP]

In no particular order..

I have used tack rags (starchem branded) as I first thought it was dust. I've even wiped half a panel with the tack cloth and left half un wiped - no difference.

I've been filtering the paint with disposable fine filters and there is a filter on the suction tube of the gun.

The extractor stays on while I watch the spots appear. Temperature was something I wondered about. I have some heat in the workshop but obviously it all goes out the wall once I turn on the plate fan.

Dulux and Leyland eggshell paints both have the problem so it is not unique to dulux.

There is no dust on the workpiece or in the paint. 'dust' miraculously appears up through the paint - I can watch a lovely smooth wet surface turn spotty!

I could just carry on and paint everything, as if you are not looking as closely as I now am you probably wouldn't see the faults. Knowing that the paint can go on perfect (as spraying a poly bag proved) it is frustrating to have to consider something less.

Many years ago I've sprayed lots of stove enamel and I've even sprayed a car but I've not come across a mystery like this one. Spraying wood and HVLP are the new factors I don't have huge experience of. Fish eye spots that don't respond fully to thorough pre cleaning is another new one.


Thanks for the input.

 

[RobertMP]

I got an air tools kit included with the compressor I bought a year or so back. Think I'll find the included ultra low quality spray gun tomorrow and try some conventional high pressure spraying as tomorrows experiment. Not that I really expect it to prove anything....

 

[jasonB]

Another possible is that by sanding back the primer you are exposing any raised fibres which could then be swelling as the solvent soaks into them. I would suggest applying the primer to a non absorbant surface such as a scrap of MFC or laminate, rub down as per your doors then eggshell. If no problem then we can rule out the primer not being compatible with the eggshell.

Jason

 

[Shrubby]

Robert
Very frustrating when this happens near the end of a good project!
Jason sounds right - have you flatted back the primer too much? or need a second coat to allow for sanding to a super smoth finish.
The only thing i can add is the fan.This will pull dusty workshop air across the workpiece.I worked in a tiny place with a similar setup to yours, we sectioned off a corner with clean air drawn in through a window to supply the booth fan
Matt

 

[RobertMP]

Think I have ruled that out. It happens on the dulux undercoat and when applying a second coat over eggshell that has dried and had the nibs knocked off. new spots appear in plain previously good areas not necessarily on top of old ones.

Can't get my head round it being fine on a plastic surface and not fine on a painted one... whatever it is painted with.

Still worth double checking. I'll try a second coat of undercoat and not rub it down, even if there are any spots, before putting eggshell over it just to see if the sanding is opening pores that suck dry spots in the paint... or something. Hmm sucking the solvent out and leaving piled up paint solids does sound like a theory. Plastic is not porous :idea:

 

[jasonB]

BTW Dulux do not recommend spraying their oil based eggshell!! though that may be more a H&S issue than practical.

Jason

 

[RobertMP]

It does say health and safety as the reason on the tin. I'm wearing a carbon cartridge filter mask and cant even smell the paint plus the plate extractor is pulling it all away from me so I'm not too worried.

I've been out for a look at the few drawer faces I sprayed yesterday. Most of the 'dust' eruptions have vanished again! That was not happening when spraying onto the MDF primer so the dulux undercoat must have helped even if it did not look like it when wet.

I can still see the fish eyes but I doubt anyone else would notice them. I will experiment a bit more but it does look like I have a way forward after all.

 

[RobertMP]

Today I've sprayed a fresh coat of Dulux undercoat onto the 8 panels and trims for the first area of kitchen I want to complete.

With them done I dug out this cheapo spray gun and wished I'd cleaned it after spraying preserver on the shed with it last year :lol:

Anyway it cleaned up OK so I put some Dulux eggshell in it - poured unfiltered from the paint I had previously had in the Fuji Q3's gun. I sprayed 2 drawer faces with it. Both had previous coats of the same paint which I had rubbed down to flatten the odd spot and some prominent fish eyes.

There were no new fish eyes using the paint with the high pressure cheapo gun. I could see the slight impression of the ones I had rubbed the top off of but no new ones appeared. Now I'm not going to condemn the Fuji HVLP just on the evidence of 2 panels but it has made me think. The 'dust' after spraying has happened just the same but hopefully they will reduce with drying like I saw last time.

The Fuji was an excellent condition used unit - does anyone know if there is something inside it that could age and cause contamination of the air? looks like more testing tomorrow to try to pin down the source of the contamination. It would explain why I couldn't wipe the panel clean enough to stop it though.

 

[CNC Paul]

Robert,

It sounds like the wrong tip/nozzle size in the Fuji. Where you thinning the
Dulux in the Fuji ?


Paul

 

[RobertMP]

Yes. Thinned to about 35 seconds originally. With the new high purity white spirit I added just enough to some fresh paint to get it to spray but have not checked the viscosity on what was only the one cup full of mixture (though it is thicker).

The Fuji has the original (#4?) 1.4 nozzle kit. Guess I could invest the £40 in a 1.8 (?) set. Also wondering if the intake filter should be changed.

Thinking tomorrow I will try spraying half a panel with air only from the Fuji then spray the complete panel with paint using the high pressure gun and look for fish eyes again.

 

[RobertMP]

Well I've solved the riddle of the fish eye spots.

I have taken out the intake filter on the fuji Q3 and it was dusty. So I took off the end box assembly with the sound deadening inside and blasted everything with compressed air. Put the end back on but left the filter out.

Tried a test spray - still making fisheyes

So I unscrewed the hose connector near the gun held a bit of stocking material from a pair of the mrs old tights over the thread and screwed it back together as a inline filter. Fisheyes still happening but less than half what there was before and mostly small ones.

I did let the fuji run for a while with nothing on the hose end but either the contamination is not coming from the filter or there is so much in the system it will keep coming through.

I have a sheet of hard plastic that I can spray then wipe off and spray again for testing. Sprayed it 3 times with the fuji and 3 times got fisheyes appearing. Sprayed it twice with the el cheapo gun on my small compressor and no fisheyes at all.

I do think the 'bits' in the paint are mostly drying symptoms now and arguably fit in with the notion of 'eggshell'

Not sure now there is much to be done with the fuji apart from selling it on ebay

 

[Jake]

One differences is the higher temp of the air through the gun with the HVLP, which a paint not designed for spraying might not like.

 

[RobertMP]

I've just managed to spray a panel with the Q3 without fisheyes

I took the hose off the turbine unit and left it running while I beat the cabinet about a bit with a bit of rubber and specks landed on the white cloth I had in front of it .... then I screwed a garden hose connector on the front and attached the only bit of plastic pipe I had which is only 4ft long. So with the unit on a stool behind me i tried it out - no fisheyes and less 'dirt' than before too.

It appears resisting the temptation to throw it out the window was not such a bad idea.

I don't trust the fuji hose to be clean so I'll get a bit of garden hose for now.

Hopefully I can make some progress soon.