Painting MDF

[JamesAsus]

Hi all,

I live in a 3 year old new build house.

Just been sanding my skirting boards and inside door frame in the bathroom, went a bit rough on the edges and the paint has come completely off. It did not look like wood so I asked a decorators advice and he was shocked id sanded it down as its cardboard and the paint will just soak in and crack when I come to paint it again.

I did not know they made frames out of cardboard, whats best to repaint it? He said acrylic paint is best but expensive?

Also something id like to query, he is doing some glosswork in my extension and he said all he will do it wipe the surfaces down and repaint over and itll be good......I thought you always had to sand down? We got him via recommendation and his other work looks good

 

[misterhelpful]

The sharp edges on timber, especially MDF, look good but are a decorator's nightmare. It's all very well when you have factory primed materials because you can just apply your topcoat directly to the material without sanding but, when it comes to redecorating, you should always sand glossy surfaces lightly with medium-fine sandpaper/pads, just to provide a key for the new paint. This is trickier with MDF than other timbers because, as you have found out, the paint will sand away easily from those sharp edges. I always use fine nylon sanding pads for MDF mouldings, which remove the sheen without causing too much damage, but I can still get those bare edges here and there. Any bare timber/MDF must be primed and undercoated before applying your topcoat/s unless you are using satin to finish, where primer is sufficient.
I would make sure that your decorator is guaranteeing that your new paint won't peel or flake when you need to wash it, or if it gets bumped, before allowing him/her to just repaint. If you can scrape your fingernail firmly over any existing paint without it peeling, it is well adhered. This should be the same when the new stuff has cured but allow a month before trying it, as modern oil based paints take longer to cure. Using water based trim paints on top of unsanded paint is a nightmare in waiting!

 

[Diyisfun]

If the old gloss paint is in good order, he will need to lightly abrade the surface to get a good result.
As for painting on cardboard are sure its not mdf, you can get buy mdf primer.

 

[Chud]

... and he said all he will do it wipe the surfaces down and repaint over and itll be good......I thought you always had to sand down? We got him via recommendation and his other work looks good

I've heard the phrase 'wipe down' used to mean very lightly sand the surface to key it to accept new paint - best to confirm that's what he means - If he's got good recommendations it sounds like he knows what he's doing so I wouldn't worry too much!

 

[JamesAsus]

thanks guys.

Its tricky getting all the shine off without taking the edges off , so I'm best using a mdf primer? is that the same as acrylic primer? And then can I use the normal paint on top which was going to be satinwood as I don't want oil based as the room has no window and has poor ventilation.

Also he said what he would do is clean all the glosswork down then just use a kitchen scouring pad before applying the new gloss, does this sound ok?

Also the area that's being glossed doesent get a great deal of natural light, it gets some but not loads, hence going yellow to start with, he was on about using oil based gloss again and said it wont go yellow, the only reason it went yellow to start with is because in new builds they use cheap watered down gloss?

 

[misterhelpful]

The first reason it goes yellow is through lack of natural light (this is why you get yellower areas of skirting behind furniture, etc). The second reason will be because of the new VOC regs from 2010 - these made all paint companies change their formulae, resulting in poorer quality oil based paints which became renowned for yellowing extremely rapidly. Formulations have improved recently, but many are still poor as companies are trying to move more towards water based paints.

This is where the issue of sanding before applying an acrylic/water based on top of oil based paint is essential. Whilst the paint will probably take without any immediate issues, it won't stand up to any bumps, knocks or heavy wear, and will peel/scrape away.

Acrylic primer or MDF primer will be fine on the bare areas.

EDIT:
The kitchen scourer is something along the lines of the nylon sanding pads I mentioned but won't provide enough of a key for the new paint to adhere.

 

[JamesAsus]

Hmmm, guess i need to find a new painter who will sand it properly and use acrylic, i hate looking for the best person for the job, he seemed to be a be a bit of a perfectionist which i liked and has been reccomended but i dnt want to re-do it in a year

 

[misterhelpful]

Off topic, but just wondering: Is your username anything to do with computers, because my Asus laptop is being a right PITA at the moment?

 

[JamesAsus]

Off topic, but just wondering: Is your username anything to do with computers, because my Asus laptop is being a right PITA at the moment?

I have an asus but i dont know a lot about them tbh lol

 

[JamesAsus]

Looked at the gloss work of one of my friends who has had him do the work. Apparently his gloss was a year old and the painter just painted straight on top and it appears to be fine, why would this be?

Mine is 3 1/2 years old so a lot more aged.

 

[misterhelpful]

He probably prepped it better than he suggested doing for you, just got lucky or maybe used oil on oil / oil on water / water on water, which will adhere much better than water on oil with a little less prep, although you'd still be lucky if not prepped properly.

 

[misterhelpful]

To be fair, it's hard to know what his prep is going to be and we can only go by what you say. I can't condemn another decorator just by reading a few online messages, and if you and others think his work looks good and are happy, it would be unfair for me or anyone to cause doubts for you. Maybe he just doesn't go too much into the depth of his prep work with customers but, from what you said earlier, it sounded like he was cutting corners.

 

[JamesAsus]

Ive just found a ronseal white gloss oil based which has a 10 year stay white guarantee.

He was planning on doing oil and oil but definately said just a scourer and then paint it

 

[JamesAsus]

With regards to painting the mdf, is it ok to use acrylic primer on both the bare bits and sanded down paints that are still white with paint? Itll be hard to contain it to the bare bits

Ive bought a acrylic primer undercoat, and a water based gloss to go on the top?

 

[Chri5]

Maybe he thinks the surface is decent, and it a de nib and use this sort of thing.

http://multimedia.3m.com/mws/media/...ng-systems-for-paint-preparation-brochure.pdf

I used some on a barge board recently and they were really good.