Water based spray painting

[Dengue]

I wish to spray paint MDF with a water based primer. I need to do this from time to time.

I have never used a spray gun outfit before. I have a small compressor ( 2hp), and can borrow a bigger one no problem, and I have a 30 yr old nice spray gun that can be used for automotive finish that has never been used, and a cheap one that comes with the compressor.

Can anyone please advise the type of spray gun, and the type of paint that I need for this application? eg will normal water based primer be OK to spray?

I am particularly interested in how to clean the guns after spraying

[WillyInBris]

Sorry cant be much help with air spraying I use a wagner airless spraygun ($99) for most of the stuff I do it allows me o put on a good thick coat not sure if you can do that with a spraygun it may just leech.

Learning to use a spraygun is the hard part short sweeping motions that's the way I do it, I dont aim for high quality :p I just do as much as I am happy with.

What I normally do is the following (this is for plywood):
First undercoat spray as thick as the gun will let me.
Sand
2nd undercoat once again thick as the gun will let me.
Sand
Then The gloss coat, it seems to work well for me and keeps the wife happy.

Go get some sheets MDF and have a spray play its the only way to learn then you will find out what your finish will be like, you may be best to hand paint the undercoats with say a roller give it a good sand (prep is always key) then shoot your gloss.

With the right amount of prep you could even get away with a roller I have in years passed.

Good links well worth the read:

Is sanding sealer waterproof? (http://www.woodworkforums.com/f9/sanding-sealer-waterproof-76886/#post784968)

Painting MDF to a glossy finish (http://www.woodworkforums.com/f9/painting-mdf-glossy-finish-101943/)

MDF Sealing, Priming and Painting - Advise Please (http://www.woodworkforums.com/f11/mdf-sealing-priming-painting-advise-please-105362/)

[WillyInBris]

Good links well worth the read:

Is sanding sealer waterproof? (http://www.woodworkforums.com/f9/sanding-sealer-waterproof-76886/#post784968)

Painting MDF to a glossy finish (http://www.woodworkforums.com/f9/painting-mdf-glossy-finish-101943/)

MDF Sealing, Priming and Painting - Advise Please (http://www.woodworkforums.com/f11/mdf-sealing-priming-painting-advise-please-105362/)


That your quite aware of would think :p

[Dengue]

thanks WillyInBris, appreciate the advice and the links. - Yes, some are quite familiar :)

Can you please tell me what undercoat you use with the spray gun? Water based?

How do you clean the gun?

[WillyInBris]

Hi Jill, I use Turbans all purpose prep coat any good prep coat should do as long as its quick drying most will go off in 2 hours.

Its water based so all you need is water to clean up same with the water based glosses if you need to thin it down you can use water as well, but it it is to thin you could cause problems with the MDF.

Do it on a warm day so it go's off quick.

Do Some test runs first on some sample MDF dont do it on something small test it on at least a 500x500 piece and see how good you can get it and what your happy with.

Spay it, Undercoat leave it until dry
Sand it well
Spay it, Undercoat leave it until dry
Sand it, take time with this as you want your gloss to go onto as nearer perfect surface as you can get to get the best result.

Try it also with a roller as well as spraying, as with the air sprayer you may need to add water to thin the undercoat down this may damage the MDF if you thi it down too much.

I have got some really good finishes with a small roller you just need to take your time and prep is the key (sorry to harp on that point).

What are you painting anyway and what's the area I am actually going to do some test runs in a couple of weeks on making new kitchen doors that the wife wants done these will also be in MDF.

Willy

[WillyInBris]

When I clean the gun I just run water through it then disassemble it and clean it again it takes me about 5 mins.

I am not sure if you could use the spray gun for the undercoat TBH as undercoat by its nature is thick.

You need to do some test samples for yourself and make sure its going to work for you the way you want it.

[Dengue]

thanks WillyInBris, very much appreciated.

What diameter nozzle do you use for this Taubman's prep coat, and how thin do you make it?

Why did you not use Taubman's 3 in 1 sealer/primer/undercoat instead?

[munruben]

Airless spray is the best way to apply acrylics and plastic water based paints. Air spray with a compressor is not really suited to this type of material although it can be done the finish you achieve will not be the greatest. Water based materials do not atmomze very well with air spraying.
Is there a reason you don't want to use oil based paints, which are suited perfectly to spraying with a compressor. You have no problem here with atomization of the material and the finish is far superior to that of plastic or acrylic paints applied in this way. Oil based paints lend themselves very well to being sanded to a beautiful even surface and provide an excellent surface for a top, gloss coat.

If you are determined to use a water base paint then I would sport the $100 or so and buy an airless spraygun.

[WillyInBris]

Because the all purpose Prep coat came cheap real cheap, Free 120lt of it :wink: still have 20lt to go left over from a job.

The 3in1 should be fine but I would still do a number of coats and sanding between coats to make sure its perfect.

Nozzle is .8mm on my little wagner air sprayers are made for fine spray from what I understand whereas airless is made to put down larger volumes of paint

How much to water it down? well that depends on a lot of things the environment can make a difference I always say less is best and this is the reason why you need to trial it first and need to play a fair amount before you get into it.

What may work for you may not work me in different environments.

You will only learn by trying it.

[Dengue]

Is there a reason you don't want to use oil based paints, which are suited perfectly to spraying with a compressor.

hi munruben, general conscenus in the attached threads by WillyInBrisbane above, and my bad experiences, indicate that oil based paints do not go particularly well on raw MDF, hence the preference for water based primer / sealer/ undercoats.

I want to paint the MDF inserts on my table saw, and also the MDF on a large toy shelf ( 1800 x 1200x 350)

So I am looking at a water based primer/undercoat, followed by an enamel based top coat ( or 2 or 3) which I find are more hard wearing than the water based top coats

[WillyInBris]

Should work fine jill keep us updated how it turns out pics are always good :D.

[fletty]

Hi Jill and Happy New Year to all.....
I have just finished some MDF bathroom cupboard doors and I'm very happy with the result. I have an Earlex HVLP spraygun with which, so far, I have only sprayed water based paints.
For the MDF I worked spakfiller into the sawn edges and sanded back. I first sprayed water based white undercoat thinned with about 10% water and, after a few hours, I brushed it over with a fine synthetic sanding pad. I then sprayed water based white gloss acrylic thinned about 25% with water and found that one coat was sufficient. The finish is very good and matches the moulded acrylic basin and vanity immediately below it.
I'm a happy little fletty......

[Dengue]

Thanks for this posting, fletty, it is really encouraging. And a happy 2010 to you too :)

I had a look for your spray gun - is this it (http://www.earlex.co.uk/html/hvlp_html/hv5000.htm)? Where did you get yours? What size nozzle diameter does it come with?

I am wondering how the spak filler would go on the saw edges of plywood, instead of timber edging. Any suggestions?

[fletty]

thanx Jill,
Mine is the (much cheaper) Earlex 3900, same principles but more plastic parts. I dont know how well spakfiller would work on the larger voids on the sawn edges of plywood but, as my very late grandfather used to say .... it's a big hole that a pound of putty wont fill!

fletty

PS, I got mine from Carbatek

[Dengue]

thanks for this information fletty. I will be in Carbatec later this month on a visit to Brisbane, so will check out the Earlex units.

I have just gone out and edged a test peice of ply with a few 2 x6mm holes in the edges with Polyfilla that I had recently used to repair dings and holes in a gyprock wall. Will sand it tomorrow morning and paint it with waterbased paint

It seemed to fill the ply holes OK, but my main concern was the strength of it, and how well it would take to the punishment of being on a kids toy shelf unit.

Sound like Polyfilla might be just the thing for the side edging on the top shelf which sits on the vertical sides of the shelf carcass and is quite visible. Or perhaps I should go for some type of plastic wood filler?

PS Just found a Polyfilla RTU Timber (http://www.polyfilla.com.au/content_120.htm)product that will fill in the edges nicely. Looks like it is water soluble and it can be sanded and planed

[Dengue]

fine synthetic sanding pad

what are these, please fletty? Green scouring pads?

[fletty]

Yes, they look like scouring pads, made (I think) by 3M, available from Bunnings and are colour coded for grit. I think I used grey.
I use them in preference to steel wool as tiny pieces come off the steel wool and these pieces eventually show in water based finishes as rust marks.
fletty

[Dengue]

thanks for this fletty, I shall wander in tomorrow and have a look around