Painting MDF

[Nerine]

I have put two coats of Zinsser 123 Primer on MDF doors, followed by two coats of Crown Satin white non drip water based paint. Its not covered well and is patchy, some bits shiny, some matt.

I have also done some MDF shelves with the Zinsser, followed by 2 coats of Dulux oil based coloured satin and they look great.
So the problem seems to be with the water based top coat. I don't want to use oil based white as it will yellow, neither do I want to sand off the whole lot and start again :-/
Should I have done more sanding between coats or will that make no difference? Is it the paint and is there a water based one I can use?

 

[sparkwright]

You could try going over what you have done with an oil-based undercoat in a similar colour to the emulsion.

When the undercoat looks 'solid', apply the emulsion.

 

[Nerine]

Thanks, I assume you mean when the undercoat is thoroughly dry?

 

[sparkwright]

I do yes.

 

[opps]

I spent many years painting (raw) MDF cabinets (bookcases, wardrobes, etc).

I used the Leyland Trade waterbased undercoat/primer for no reason other than the fact that when it raised the grain (which all waterbased paints do) it was easy to sand flat. I then applied oil based eggshell over the top.

Only on one occasion did a client specify a waterbased finish (fired earth). I used oil based primer but had to wait days for it to cure before applying the waterbased eggshell. If you apply the WB finish too soon you will get fisheyes.

I would never recommend water based primers followed by water based finishes on MDF. At some point you need to use a paint that really does seal the MDF- that can be oil based, shellac based or 2 pack.

TLR

Follow Sparkright's sound advice.

 

[gc1967]

[URL=http://www.georgecoullpaintinganddecorating.co.uk] Mdf should always be treated at some stage with oil based paint to seal it before you put on dreadful water based paint, this myth about gloss yellowing I dont buy it, I have been a painter and decorator for 33 years, if you prepare the woodwork correctly and use high quality trade paint and not shed crap it stays white. I went back to a clients house I had worked for before, I did a room 5 years ago finished in crown trade gloss and I had a quick look in the room and that was nearly as white as the day I put it on, daylight, smokers, heat all contribute to oil based yellowing, plus for water based low odour and dries quick, and bodge it and scarper can use it and get a job finished in a day, the day oil based paint is discontinued I will be quitting decorating.[/URL]

 

[opps]

I did a room 5 years ago finished in crown trade gloss and I had a quick look in the room and that was nearly as white as the day I put it on, daylight, smokers, heat all contribute to oil based yellowing

Between 2010 and 2012 oil based paints did yellow extremely quickly until the paint industry got their post 2010 VOC compliant paint formulations right.

I purchased a tin of oil based Dulux Trade eggshell on the second of January 2010. Applied a coat over WB primed MDF. Turned up the next day to apply the second coat and it was still tacky. From that day onwards, I add terebene (an additive that I had never used before).

I hated the way that the 2010 oil based paints flowed and did consider packing in cabinet painting. I soon discovered that adding extra owatrol and white spirit helped.

Regarding gloss- here in west London, bar exterior woodwork, hardly anyone has gloss. 95% of the interior woodwork I paint is eggshell.