Advice Needed on Primer and Undercoat

Joined
25 Sep 2011
Messages
71
Reaction score
1
Location
Yorkshire
Country
United Kingdom
Hi all,

I am decorating a bedroom and I need to paint some old alcove built in wardrobes, which have old paint on, some unpainted skirting, a bare timber sill and some MDF shelves that have recently been built. I am going to finish the MDF shelves, skirting and sill off in white oil based satinwood and the wardrobe I am going to get colour mixed in an oil based eggshell. However, I am not sure what to do about primers and undercoats (not used them before to be honest).

I know Crown and others do specific MDF primer, I presume I can put oil based eggshell on top? Do I have to use an undercoat after the primer?

Its all so expensive so I was wondering would I be able to buy a primer and undercoat in one for wood, and use it on the bare timber, painted timber and also the MDF, or does MDF need a special primer? Any help appreciated. Someone said to be careful with MDF cos its carcenogenci, so dont know if that means using only a specific primer.

Thanks,
 
Sponsored Links
Joined
21 Sep 2011
Messages
4,540
Reaction score
1,041
Country
United Kingdom
Most water based primers will work on MDF but it is better to get one that is specified for it cannot see any reason not to use it on normal timber too. Most primers today are water based and will take oil based top coat OK.
A good (but expensive) primer/sealer is Zinsser Bullseye 123 it will stick to almost anything even plastic.
MDF is suspected of being carcinogenic (causing cancer) but the risk is from the dust created when cutting or sanding not a panel fixed in place and undisturbed. It is very fine like talcum powder, better to avoid power tools unless you have good dust extraction.
 
Joined
25 Sep 2011
Messages
71
Reaction score
1
Location
Yorkshire
Country
United Kingdom
Most water based primers will work on MDF but it is better to get one that is specified for it cannot see any reason not to use it on normal timber too. Most primers today are water based and will take oil based top coat OK.
A good (but expensive) primer/sealer is Zinsser Bullseye 123 it will stick to almost anything even plastic.
MDF is suspected of being carcinogenic (causing cancer) but the risk is from the dust created when cutting or sanding not a panel fixed in place and undisturbed. It is very fine like talcum powder, better to avoid power tools unless you have good dust extraction.


Thank you for your help - appreciated. I will get an MDF primer and use it also on timber skirting and sill. One other question, do I need to use undercoat on the skirting and sill, in between using primer and an oil based satinwood? From what I have read, after putting primer on MDF I can go straight on top with the oil based top coat, without an undercoat, can I do same with normal timber skirting and sill?

Bit concerned about sanding the MDF edges down, I can use a mask but have a young family in the house. Thought about just smoothing the edge over with some woodfiller and then painting... any thoughts?

Thank you.
 
D

Doggit

The primer just seals the wood, and although you can get primer and undercoat in one nowadays, you still need to put on two coats. You need to prime, then undercoat, and then topcoat twice with a light sanding between all coats. And if you're using an oil based topcoat, then you're supposed to be able to use water or oil based undercoats, but it's best to go like for like.
 
Joined
25 Sep 2011
Messages
71
Reaction score
1
Location
Yorkshire
Country
United Kingdom
All the primers for MDF I have seen are water-based. So I am not sure I have any other option. So I guess I could use MDF primer on both the MDF and timber, then undercoat the timber, then two oil based topcoats on both...?
 
D

Doggit

You've got it, but I'd just do 2 coats of a combined primer undercoat, and then the oil based topcoat.
 
Sponsored Links
Joined
25 Sep 2011
Messages
71
Reaction score
1
Location
Yorkshire
Country
United Kingdom
You've got it, but I'd just do 2 coats of a combined primer undercoat, and then the oil based topcoat.

I dont think you can get any MDF primer that has undercoat in it as well. My options seem to be:

A) Use MDF Primer just for the MDF, then 2 coats of oil based eggshell. Then use a Primer and Undercoat in 1 for the timber, then 2 coats eggshell
or
B) Use the MDF primer on both MDF and timber, then apply some separate undercoat to the timber, then eggshell on both.
or
C) I've read that you can use Bullseye 123 Primer on MDF and timber, and that no undercoat is needed with it even on the timber. If this is true and others think it is good, then this would be the simplest and cheapest method. It seems pretty cheap compared to MDF primers, Standard primers and undercoats etc.

Any thoughts on these options?
 
D

Doggit

The Bullseye 123 is a primer and stain blocker, and whist I've never used it, I think it'll still need an undercoat, and you seemed hell bent on not using an undercoat; as I've said before, I'd use an acrylic primer undercoat for both the mdf and the wood, and then use whichever topcoat you want after that. But it's up to you.
 
Joined
25 Sep 2011
Messages
71
Reaction score
1
Location
Yorkshire
Country
United Kingdom
The Bullseye 123 is a primer and stain blocker, and whist I've never used it, I think it'll still need an undercoat, and you seemed hell bent on not using an undercoat; as I've said before, I'd use an acrylic primer undercoat for both the mdf and the wood, and then use whichever topcoat you want after that. But it's up to you.

Thank you, im happy to use undercoat, I am just confused because some people say it is not needed on MDF, only primer and topcoat is. Likewise, some people say that you need a specific MDF primer for MDF, and none of those branded as MDF primers claim to be undercoat also!
 
D

Doggit

Fair enough, but I've never managed to get away without some sort of an undercoat, no matter what the info says. You can use water acrylic undercoats on oil based paints, but not the other way round. And whilst the manufacturers will say use a specialist primer on mdf, (which may well have an undercoat in it) you can actually just use emulsion to seal it, so I'm not convinced on some of the "supposed" methods they suggest.
 
Joined
21 Sep 2011
Messages
4,540
Reaction score
1,041
Country
United Kingdom
The results from using a proper undercoat will be better, undercoat is usually thicker than primer so has a "filling" effect over slight imperfections can be rubbed down lightly without breaking through to the wood and give a better depth of colour to the topcoat. That's why I tend to avoid solely using combined primer undercoat on it's own unless time is very tight.

As for MDF safety, hard to say I guess with it and other modern materials like glass-fibre only time will tell.
Myself I tend to hand sand outdoors if possible using slow smooth strokes to avoid spreading it too much. In-doors I do the same and catch the dust on a dust sheet that can be washed. If you wanted you could lay damp newspaper under the work and fold up and dispose of it that way. I don't freak too much about, it just common sense really.

Most fine dusts are dangerous if inhaled, plaster, filler, lime, I understand that some hard wood dusts are toxic to a degree. At least any left around will be caught in the vacuum cleaner and these days more and more have HEPA filtration that will cope with most dusts (not asbestos though) I would just keep the kids away and make sure you clean up well, but in the end it is down to your personal decision really. I doubt anyone on here is an expert we can really only give a personal opinion.
 
Sponsored Links
Top