Zinnser 123 over oil based trim - undercoat also required?

[Kaymo]

Hi,
Recently sprayed upstairs trim/doors etc in my house with Wagner W950 HVLP, using Leyland fast drying satin, straight onto previous white paint. It was thoroughly keyed and cleaned, but while it worked well and gave a great finish in the bedrooms, the paint on the doors and trim in the upstairs hall didn't adhere well and was peeling in places.

Reading up online, I suspect this was due to the previous paint, probably being oil based, and the water based satin not adhering to it, and not wanting to repeat this experience in the downstairs I am planning to spray a coat of Zinnser 123 on the trim first, to provide adhesion.

Having never used this before, my questions are:
1. Is one coat of Zinsser normally enough?
2. Do I need a separate undercoat before the top coat, or will the 123 serve this purpose?

Many thanks.

 

[Kaymo]

Any thoughts?

To summarise my question, can Zinnser 123 serve as an undercoat, or is an undercoat needed between this and the top coat?

Thanks.

 

[Kaymo]

I think I may have managed to answer my own question, but putting what I found below so that others who come to this thread in future will get the info. More than happy to hear from anyone if my impression below is not accurate.

My confusion on this came from the fact that the Zinnser data sheets only refer to it as a primer, which is similar to the OP in the thread I just found below. However, 123 is clearly a bit more than a cheap primer that you might use to seal bare wood. Strangely, the Australian 123 documents that I stumbled onto call it an undercoat/primer, while the UK one only says primer. It can also apparently be tinted, which again I would presume means the intention to use as an undercoat. Looking at reviews its also clear that some people who use it a lot are using it as primer and undercoat.

https://www.diynot.com/diy/threads/zinsser-primers-do-i-also-need-undercoat.507341/

In the thread above there is a bit of discussion of where an undercoat might add benefit, but I think for me because I am not covering up a non white or non paint surface, I am just looking to get adhesion between the oil based finish and top coat of the same colour, I would think it would be fine without an extra undercoat.

So, unless someone of experience advises me otherwise, my plan would be spray one coat of 123 for adhesion, then 2-3 coats of Leyland WB Satin for a finish.

 

[DiyNutJob]

I used 1 2 3 primer with brush on cured oil paint, and it was fine. I would have preferred International water primer, but the brand disappeared. I haven't worked out what under coat does and not currently using it. For exterior hard to access areas, I use 10 year oil paint x 3 coats on 2 coats of premium water primer. For easy access locations, I would be happy to cut some corners.

 

[Kaymo]

Thanks Diynutjob. My understanding is that traditionally primer is for bare surfaces, to seal or soak in, while undercoat is for surfaces that have already been primed or painted. I believe that the composition of undercoat can help with opacity (for example when changing colour) and hiding imperfections.

However, there are a lot of products on the market now that call themselves primer/undercoat, and from what I read some pro painters would dispute whether these products can actually do both jobs. Zinnser 123 does seem to be a bit more than just a primer, or undercoat, and is marketed as a sealer/stain remover.

Personally I don't think I have ever used undercoat, but in the limited painting that I have done (other than walls/ceilings) I am usually painting over with the same colour.

Outside, and everywhere really, I tend to use water based paints now. I get that Oil based is likely to last longer, but i've also heard that (the modern versions) oil paint yellows with age.

 

[DiyNutJob]

Oil paint doesn't yellow if it's sun washed. There are claims for 15 year water paints. But, I'll rather not risk it. I am happier risking for 8 year dulux weathershield at great cost.

 

[Wayners]

I use Zinsser BIN rattle cans or foam roller and brush to apply a can of BIN as rock solid.
Then over with water-based gloss.

Other way is abrade. Use gloss off or sugar soap and get the water based undercoat on.

I'd recommend using a spray primer. I'll look it up now. Hang on.
Edit
WP136 primer may spray well as thin.
Spray only.

Some don't believe the marketing of adhesion primers. Paints will stick well if surface is prepared well. Adding water will affect the primer adhesion if you add loads

 

[Kaymo]

Thanks for the response Waynes

I use Zinsser BIN rattle cans or foam roller and brush to apply a can of BIN as rock solid.

I had went for the 123 as water based, thought it might be less toxic than BIN. Will be wearing a mask, but spraying in a fairly confined hallway.

WP136 primer may spray well as thin.
Spray only.

Good tip. I looked this up but seems hard to get, online order and doesn't say anything about adhesion.

Some don't believe the marketing of adhesion primers. Paints will stick well if surface is prepared well. Adding water will affect the primer adhesion if you add loads

I probably wouldn't have believed the hype either, but I prepared the trim fully sanded down and cleaned, more thoroughly than I usually would in this case. I normally use tape to edge because my cutting in is poor, but even yellow frog tape was pulling paint off in large amounts. On a door I know that I skimped on, the paint was falling off, but the rest of the wood was well prepped and adhesion was really poor, just bumping against it was taking it off. Apart from the door that I had to repaint, i've just about gotten away with it upstairs, but I don't think it will last as long as normal. A bit of research online showed that this can happen sometimes when trying to paint over oil based paint with water based paint. It might be that I have just been unlucky with the type of gloss used previously upstairs in my house - I have painted over oil based paint with water based before and not had this problem.

The article below was an interesting test, where the guy used a number of so called adhesion primers over an oil based paint, without sanding, and all of them, including the 123, stuck well.
https://www.thedecoratorsforum.com/the-best-adhesion-primer-on-the-market/

I've already bought the 123, so I am going to try spraying a coat of this, then do the scrape test the guy in the above link did, and take it from there.

 

[Wayners]

Just remember the primer you are using has a 7 dry cure time. People that use on vinyl kitchen doors have to wait before top coating.
I liked spraying otex akva.

Paint manufacturers don't like this scratch test.

 

[Kaymo]

Just remember the primer you are using has a 7 dry cure time. People that use on vinyl kitchen doors have to wait before top coating.
I liked spraying otex akva.

Paint manufacturers don't like this scratch test.

Good point. Not a good idea to scratch before cure!

Actually, I tried a spoon on the existing coating and it scratched off, and it has never been a problem, so maybe this is too severe a test, or maybe I have too sharp a spoon!!