Aerosol Spray Paint on Wood

[Teejay]

I've made a wooden lid out of 18mm moisture resistant MDF.

It has been painted with multiple layers of Plastikote aerosol primer and sanded so it's perfectly smooth.

I've moved on to Plastikote aerosol satin wood paint and I want the finish to be perfect like on a car. I've used multiple coats and it's looking patchy. I tried up and down, side to side from one end to the other. I also experimented with slightly different thickness layers.

There were a few areas that weren't flat so I used 320 and 360 grit wet sandpaper to sort it out but there are light scratch marks (nothing more than surface deep). When I sanded it, there were clumps of paint being picked up from light wet sanding.

The paint is still flat but patchy.

Can I sand or should I not do that? Why is it patchy and how can I get that perfect finish that is totally flat like on a car? I've used about three cans of satin wood on it already (it's about 1m X 0.40m).

Any experts out there?

 

[Droogs]

if you want a car like finish then you have to go trough the prep that would be used for a car. This is how I paint especially with aerosol:
first surface prep
1: sand the surface with a ROS starting with 240g moving up to 320
2: Totally clean the surface first with lint free cloth with a little acetone and then with a tac-rag
3. then put on a skim coat of Isopon P38 then repeat 1 and 2
4. spray a mist coat of red primer and then sand as lightly as possible
5. check for low spots and repeat 3 and 4 until happy that the surface is level (use a bright light at low angle to show imperfections
6. When happy lightly build up a primer coat. Better to put on 3/4 mist coats and build up than 1/2 heavier coats
allow to dry and cure if in an unheated wksp then leave at leat 48 hours
7. cut back the primer with 320 until smooth and even
8. clean off with a fresh tac rag
9. apply first coat of 2pack base coat (the paint in the colour you want) - check again for flatness of surface
10 cut back with 320 and clean again and then apply next coat. keep doing this until you have 3 to 4 good coats
11. leave to dry and CURE
12 de-nib with 400 and clean off with fresh tac rag
13 apply top coat lacquer in exactly the same way as the base coat. lots of thin layers. I normally end up with about 10 coats of lacquer and the finish will be glass smooth and nice and deep shine.
14. leave to dry and cure and then polish up lightly

the below post has links to photos of my results
post1267978.html#p1267978

hth

 

[rafezetter]

There is the possibilty that you are spraying in temperatures colder than recommended, this can also result in a patchy finish - I can't remember for the life of me what it's called, but does have a specific name, this patchiness.

I've had it myself when spraying larger areas, only thing you can really do is lightly sand that layer and hit the whole thing again - but do it after having warmed up the item indoors overnight, and kept the can of paint indoors as well to warm that up too, and bring the item back inside the house afterwards.

 

[Teejay]

Thanks for your replies. I think it could have been temperature related.

Just out of interest, how do the pre-painted skirting boards you can buy in Wickes get done in the factory? It can't take anywhere near as long as this nor require sanding. I'd be happy with that standard finish.

 

[Teejay]

I've sanded back using 320 and 600 grit wet and dry paper in water and this is what I have at the moment:

It needs more paint now.

I still want to know how Wickes paint their pre-finished skirting board.

 

[Droogs]

600g may make the surface too slick for the next coat to key properly depending on the paint you are using

 

[Rich C]

Thanks for your replies. I think it could have been temperature related.

Just out of interest, how do the pre-painted skirting boards you can buy in Wickes get done in the factory? It can't take anywhere near as long as this nor require sanding. I'd be happy with that standard finish.

Machine sprayed with expensive airbrushes essentially. Much like cars. The factory finish is very hard to match by hand because it's so tightly controlled.

 

[AES]

+1 for all the above comments and how-tos. Unfortunately I can't see the finish all that well in your pic Teejay (apart from anything else my screen is a bit grubby at the mo!), but it COULD be that your paint is "blushing". You can get that effect with any sprayed paint, but fast-drying cellulose is particularly prone to this, though with cellulose, the "blushes" often appear to have a slightly white-ish tinge. The cause is ambient (room) temp too low, and usually, ALSO, humidity too high. The only way to get rid of it (after warming & drying the room) is to lightly sand it off the job (not too fine an abrasive as Droogs says) and then spray again.

But there's other VERY important points when using aerosols with ANY type paints:

Absolute constant pressure within the can, AND absolute consistency of mix. This is achieved by:

1. Rattle the can continuously for a MINIMUM of 2 minutes (time it!);
2. Drop the complete can top down (with the nozzle removed) into a bucket of hot ("ouch", but not boiling) water and only remove when the can feels nicely warm all over;
3. Repeat 1 above;
4. Refit the nozzle, hold the can inverted, and spray a short burst until the colour comes out (onto a piece of paper, scrap, w.h.y);
5. Use one of those plastic "trigger thingies" you see in DIY stores;
6. From your pix and description it seem like you've got the actual spraying down technique pat (spray parallel to the surface; start spraying before the pattern reaches the job and keep spraying until after the job);
7. When finished, invert the can and spray against scrap until no colour comes out of the nozzle;
8. Remove the nozzle and store in a jar with the appropriate thinners;
9. Store the can inverted with the outer cap in place (assuming there's some colour left in the tin).

Same procedure applies if spraying clear lacquer.

If the above sound a bit of a rigmarole, it is, BUT it guarantees perfect results. IME, aerosols (basically a pretty crude "instrument") can, using the above procedure, produce finishes equal to professional guns and airbrushes (on smaller jobs like your box lid, but NOT on wardrobe doors of course)!

HTH

 

[Teejay]

Thanks for your reply. Would you recommend any compound as part of the painting/polishing stage? If so, what should I get?

 

[AES]

@ Teejay:

I'm not sure what you mean by the "painting/polishing" stage, sorry if I'm thick!

IF after rubbing the existing paint down (with about 400 grit, as Droogs suggested above) you have a nice glossy surface with an even colour coating, then - subject to the paint you've used and your technique - then "polishing" shouldn't be necessary unless you want a really HIGH gloss. If you do, then you'll have to wait a LONG time for the paint to be to be really hard - I'd suggest at least a whole week. You could then apply something like metal polish (Brasso in liquid form I'd guess, or perhaps wadding-type polish, like Duraglit - if either of those products are still available in UK - dunno. Rub that stuff into the whole box lid, then buff up with a really soft clean cloth.

But assuming that you started off with a gloss paint in the first place, and assuming you've got no defects such orange peel (too much paint) or "spackle" (nozzle too far away, so that the paint droplets were drying before they landed on the job), then I doubt that polishing is necessary,

HTH, and hope I've understood the Q.

 

[rafezetter]

Thanks for your replies. I think it could have been temperature related.

Just out of interest, how do the pre-painted skirting boards you can buy in Wickes get done in the factory? It can't take anywhere near as long as this nor require sanding. I'd be happy with that standard finish.

Have you ever fun your fingers along the moulded sections of those? I have, quite recently - I think the texture is around 120 grit maybe a bit coarser like 100 grit.

Truly awful, rough as an armadillos backside - no self respecting painter would just paint over them "as is".

 

[rafezetter]

Thanks for your replies. I think it could have been temperature related.

Just out of interest, how do the pre-painted skirting boards you can buy in Wickes get done in the factory? It can't take anywhere near as long as this nor require sanding. I'd be happy with that standard finish.

Machine sprayed with expensive airbrushes essentially. Much like cars. The factory finish is very hard to match by hand because it's so tightly controlled.

REALLY? I'd love to know which Wickes branch you get your "hard to match "factory finish from....

Other factory finishes on Kitchen doors and the like sure, but the skirtingboards? No way.

 

[Rich C]

REALLY? I'd love to know which Wickes branch you get your "hard to match "factory finish from....

Other factory finishes on Kitchen doors and the like sure, but the skirtingboards? No way.

Maybe not hard to match as its just a quick run through to get a primer coat, but are you saying that wickes don't machine spray all their stuff? At their volume of sales? I hardly think they have a couple of staff out the back with an ebay spray gun.

 

[Teejay]

This is what I was referring to: https://www.wickes.co.uk/Wickes-Bullnos ... 5/p/133616

It's very nicely finished. Not just primer.

 

[rafezetter]

@ Teejay:

I'm not sure what you mean by the "painting/polishing" stage, sorry if I'm thick!

IF after rubbing the existing paint down (with about 400 grit, as Droogs suggested above) you have a nice glossy surface with an even colour coating, then - subject to the paint you've used and your technique - then "polishing" shouldn't be necessary unless you want a really HIGH gloss. If you do, then you'll have to wait a LONG time for the paint to be to be really hard - I'd suggest at least a whole week. You could then apply something like metal polish (Brasso in liquid form I'd guess, or perhaps wadding-type polish, like Duraglit - if either of those products are still available in UK - dunno. Rub that stuff into the whole box lid, then buff up with a really soft clean cloth.

They do still exist, but that's a bad idea in his situation, at least any form of liquid polishing compound - the paint is still not uniformly FLAT - there are clearly still divots and unfilled sections which will hold onto the polishing compound and leave unsightly traces.

TeeJay I have to ask, just how far do you want to take this?

If you are after an almost flawless gloss finish, you've got some work ahead of you - which I can outline if you desire.

If not, and you can live with it "as is" then go up from the 600 to 1200 and LIGHTLY go over the item again wetsanding (lots of water, assuming all the sides of the MDF are now watertight), with barely any pressure at all, just to reduce the 600grit marks.

DO NOT use your fingers for this, it's very hard to get an even finish this way - get a sanding block, preferably cork, but otherwise an old one of those sponge sanding blocks will do (the ones with the grit on) and wrap the 1200 on that.

Wipe it back with alcohol, see how you feel, if you want a tiny bit more shine, repeat with 2,000 grit.

I'm now going to grab some brasso and see how it reacts to being used on an aerosol "high build" sprayed finish.

Never crossed my mind to try it.

Edit - when I said Brasso, I meant the wadding type not the liquid compound. Well it seems to have made very little difference, there is a slight increase in shine from a satin finish, but not much and for a project of any size, would be pretty labour intensive. It's proven very hard to photograph as I don't have any indirect light to get a decent closeup.

Teejay - if you do decide to use a polishing compound of some type like brasso liquid or autosol (t-cut is too abrasive, clue is in the name) make sure you apply and remove it with a very soft cloth like a microfibre, then clean afterwards seveal times with alcohol (meths) or white spirit to remove the traces left in the "grain" of the paint.

If you're not used to it, don't be tempted to buy a lambswool polishing pad or sponge for an angle grinder as they take practise and will only take a second to cut right through the paint if you've only got a few layers of paint sprayed on - as in less than 10.

Let us know how you get on.

 

[rafezetter]

This is what I was referring to: https://www.wickes.co.uk/Wickes-Bullnos ... 5/p/133319

It's very nicely finished.

No it isn't. The flat face is, sure, because it's flat and the flat face of MDF has never been an issue for painting or spraying.

The MOULDED sections of those - the roundovers, ogees and whatnot, those sections have been cut INTO the fibres of the MDF and expose the inner fluffiness just the same as the sides.

Rich C - yes of course they spray, but again as above, I've fitted a fair few metres (quite a few) of MDF Ogee skirting and architraves, with doing just shy of 70 metres not two weeks ago. the moulded sections on all of them were rough, needing at least 2 passes using 120 grit with a primer in between.

No idea what the primer is that they use, but when sanded it leaves an unpleasant smell, and it clearly raises the grain.

Am I being overly fussy? No idea, but afterwards the moulding feel the same as the flat bits, which will also mean less dust accumulation, and gloss paint won't look like it's been applied and then sprinkled with salt, which is how it would otherwise look.

The SIDES of MDF have always been an issue for people to contend with to get a reasonable finish, with some people (myself included) going to quite extensive lengths to get a "flawless" high gloss finish.

 

[Teejay]

Thanks for your replies.

Can I use cellulose thinners to clean the primed surface prior to painting?

I used Zinsser Ultimate Performance BIN.