Kitchen paint: Zinsser undercoat before acrylic eggshell?

Currently the walls were painted with Dulux kitchen paint (never again), about 6 years ago and needs a good scrub and rinse with sugar soap. The room gets fairly humid and quite a lot of steam on the walls even when I cook, even with windows and doors open. This has caused a couple of very small peeling patches but luckily I've never had mould. The

The local trade centre is recommending a coat of Zinsser followed by two coats of Johnstone's trade acrylic eggshell. I'm fine with the eggshell, but is the Zinsser really needed? I've read a lot of threads and never seen it suggested. I do need to undercoat as the walls are deep blue but don't want to waste money on Zinsser or more importantly, use it if it is not a good idea. It does need some kind of light undercoat as currently it is deep blue.

It's difficult to say. If the old paint is peeling then it will take your new paint with it. If you clean down the old paint really well then you'll probably get by with just the eggshell. If you have lots of time then probably better with an oil undercoat, but you have to leave it for a week before you can top coat it.

It was peeling in one or two small localized areas, maybe 5x5 cm and I have cut those out and sealed the plaster again. The remainder of the paintwork seems sound It is pretty grubby and will need a fairly laborious scrub with the sugar soap. Time is no issue, but will it not be fairly difficult to use a water based paint over an oil undercoat?

The Zinsser route sounds a bit dramatic for this situation, if there is only some small localised flaking/peeling which has been addressed, but maybe they were suggesting it as a bridge coat so that you wouldn't have any issues with the acrylic eggshell adhering to the kitchen paint??
I would clean the surface thoroughly and repair any blemishes before giving the walls a good rub down with 120 grit sandpaper, cleaning off the dust and proceeding with the eggshell. This is a lot cheaper than the Zinsser route, but should effectively give you the same end product unless, as joe-90 says, your existing paint is peeling.

Water based paints work fine of oil undercoat as long as it is well dried out, or the solvent will make it waterproof. That's why I mentioned time as an issue.

misterhelpful said:

The Zinsser route sounds a bit dramatic for this situation, if there is only some small localised flaking/peeling which has been addressed, but maybe they were suggesting it as a bridge coat so that you wouldn't have any issues with the acrylic eggshell adhering to the kitchen paint??

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That must be the reason as I didn't discuss the existing wall with them, they just said they recommend Zinsser followed by acrylic eggshell. I didn't think to ask if they meant water based or oil based though as I have only used 1-2-3 before and assumed they meant at the time.