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undercoat emulsion on walls ?

Listed under abranet, Blog, Mirka, paint, Painting Posted Feb 05 2012

Do I need to undercoat emulsion on walls that have been previously painted and are in good condition. Even with a big colour change, a first coat of undercoat is for the most part, a strange concept, but sadly it is a question that is gaining traction.

I was asked by a Swedish client just today about undercoat for walls. Where has the icon for head-scratching gone?

There are occasions where this undercoat idea might apply, (see at the end) but for most standard redecorating work, preparation plus 2 coats of emulsion works just fine. If you need 3 coats due to lack of opacity, there is certainly no requirement to make the first of those 3 coats a wall primer – ordinarily.

It turns out that this idea of a first coat of primer (undercoat emulsion on walls) seems to be a Farrow and Ball thing. They specify a wall primer coat before applying 2 coats of Estate emulsion – period. F&B say it is to ensure maximum coverage. Well, maybe if the Estate emulsion paint had better opacity, they wouldn’t need to throw this red herring into the works.

So, ordinarily, if the walls are in good condition, but need a makeover, keep it simple. These days, no more than two coats of a premium acrylic paint usually suffice. I don’t use it, but premium vinyl matt paint is also usually plenty good enough to achieve a solid new colour.

Changing red walls to white.. No need to undercoat emulsion on walls , but you should be prepared to cut in the edges 3 times, and apply at least 2, possibly 3 coats overall, depending on your brush, technique, surface and paint. But don’t think you need to buy in a special tin of primer for the first coat. If you are going white, a good white emulsion is fine from start to finish. Thin the first coat say 15% and subsequent coats 10%. “Matt” generally offers better coverage than “vinyl matt” or higher sheen wall paint.

Paint a chrome yellow acrylic wall paint over a different colour. In this extreme case, you might be best advised to apply an obliterating coat of white acrylic emulsion first, then 2 coats of yellow. (Yellow pigment for paint is notoriously weedy, and for some reason, blues especially are a pain to cover with straight yellow.) Using white first will save a little bit on cost of materials. But again, a special wall primer over solid previously emulsion painted walls is absolutely not required in normal circumstances.

Undercoat before painting walls with emulsion

There are circumstances where you “undercoat” before emulsioning, but it isn’t an undercoat, it is primer or sealer coat.

If the wall you are painting is flaking or patchy. In this case, you have to consider preparing, filling and sealing (aka undercoating) the surfaces prior to painting. The sealer will bind down or even out the porosity of the prepared surface. If that is the case, I can think of a long list of problem solving paints and primers to turn to first. A high opacity obliterating wall primer is not the solution.

For a really top class finish To achieve a level of finish that has to look good under halogen light inspection, you can really up your game with a first coat of Zinsser Bullseye, or other “problem solving” primer. You are not solving any surface issues, but the primer. This gives a really solid base for 2 top coats of emulsion. But this standard of finish is far removed from everyday good quality decorating requirements. ie it is one to for discerning clients who want something really special and accordingly it is a premium priced specification. .

Even with a basic spec of 2 good coats of emulsion, the better painters out there raise the bar, by thoroughly sanding ALL of the walls before the first coat. To go to another level, for a super finish, sand again with 220 grade abranet before the top coat of emulsion. Sounds like a lot of extra faff, until you have a Mirka CEROS sander, Abranet and a Wooster dust eater in your hands.

For US paint coverage, take a look at Jack Pauhl’s tests on bare drywall. No problems with 2-coat coverage with BEHR Premium Plus Flat Enamel by the look of it.

If you are in the UK there is no need to feel left out of the American party. We could get 2 coat coverage of strong colours over bare Toupret TX120 skim filler with Mythic (American brand) paints. Benjamin Moore paints boast exceptionally good coverage too.

The main thing to remember is that material costs are no more than 20% of the cost of a job if employing a professional. But cheap or inappropriate materials or daft specifications requiring to undercoat emulsion on walls can add a lot of extra labour costs, or waste your time if doing it yourself.

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15 comments to “undercoat emulsion on walls ?”

  1. Ann

    I have a house built 1750 and prior to painting I prepared the pre painted walls by washing well. I painted the walls with an expensive period paint and now some months down the line I find the paint is cracking and lifting in places when the loose paint is removed it reveals smooth plaster I feel sdo I need to remove ALL the paint in the room even the ‘sound’ walls ? If all paint is removed by sanding which I dread due to the mess it creates and asthma what is the first thing I should put on wall prior to repainting with emulsion ? And what is the white ‘bloom, on two of the walls ?

  2. Andy Crichton

    Thanks for posting about your current project. It is a tricky one to advise precisely, without seeing the property, but first things first;

    When you wet your finger and pass it over the plaster where the paint has lifted completely, does it leave a chalky mark? If so, which in a 1750’s house is the likely outcome, that would be the remnants of a distemper which prevents conventional modern paints from adhering. And that would explain why the subsequent coats came off in sheets.

    I suspect the top coats of new period paint dried and affected the surface tension of the paint underneath, and this lead to cracking down the road? And the peeling off, see first reference to chalky substrate.

    You might be able to remove all the paint with a long handled razor style scraper, careful not to gouge the plaster though. And large scale sanding, we highly recommend a dustless sanding kit, Mirka CEROS with Abranet or Festools sanders with Abranet connected to a vacuum.

    Once prepared, you could look at the Classidur range which is used in old churches and historical buildings.

    The white bloom could be efflorescence, which is the salts in the substrate coming through and drying on the surface. So if you washed the walls , maybe that sparked it off? That should just vacuum off as a dry powder, don’t wet it.

    If you have any other questions, probably best to post it on the forum where you will get answers from wiser folk than me. Heritage decorating forum You can post photos quite easily if that helps )an icon in the top bar, or attachment option at the bottom of the post. cheers

  3. Janet Mahony

    I have newly plastered walls. I will be using little green intelligent sand stone. Do I need a primer what is best way to pre pare walls? Using intelligent eggshell in shirting. On doors. What is best way to prepare? . Thank you

  4. Andy Crichton

    Hi Janet, this is the info on painting new plaster https://traditionalpainter.com/how-to-paint-plaster-walls-with-emulsion

    There is a wealth of info for all aspects of preparation here This is for wooden glazed doors previously painted with oil paint https://traditionalpainter.com/restoring-a-glass-panel-door-part-2

  5. Caroline Deane


  6. Andy Crichton

    If you have pigment streaks, that points to incorrectly mixed paint. If the imperfections are lumpy paint, that shouldn’t happen either! Take the paint back to the store. To remedy the issue, you would need to sand the wall area back flat. (A scraper will probably be a quick first step to remove the worst of the imperfections, and reduce the sanding needed.)

    You may have indentations in the final sanded surface, so fill them with a fine filler and when dry, sand flush.

    The Abranet sanding kit is a good bet for this type of remedial work, 80 to 120 grade for the heavy sanding and 180 or 240 for perfecting the filler. It should not require more than 2 coats to leave your walls looking as full and even as you would expect.

  7. Geoffrey Robertson

    We have been having a back and forth argument about the pros and cons of various paint type that may be appropriate for a communal hallway that has a daido some three feet off the ground. The thinking expressed is to paint an oil based paint below the daido and an emulsion above. Can you please throw some light on what is regarded as best practice that could be applied in a small block of six flats without it looking like some large “communal” building. Many thanks in advance…

  8. Andy Crichton

    Dividing a wall area up with a rail and different colours top and bottom would reduce the overall scale of the walls to the eye. A (slightly) stronger colour below will act as an anchor.

    For durability, the Little Greene Intelligent emulsion performs better than most.

    A satin Polyvine decorator varnish over the top of the paint below the dado would add some extra protection. If you apply the satin varnish and it looks too “communal”, your ticket out is secure – apply 2 coats of Polyvine dead flat varnish over the top. These varnish products are water based and quick drying. They are cured within a week, so warn folks not to touch the new paint in that time.

    You have to assume that walls in a communal area will mark, knocked by bags etc, so you will have to factor in some periodic (gentle) wiping down, even if you used an indestructible laminate.

  9. Agnes

    Hi, information online is very confusing. Most of sources suggest undercoating but do not specify what type of undercoat to use for emulsion prepainted walls. When you check undercoats of different brands, all of them are for wood or metal, none specifically for previously emulsion painted walls. But there are many tips online saying that if you rub an emulsion painted wall or rub it with wet fingers, or apply a sellotape and paint comes off, then undercoating is a must. Again, no information which undercoat is the best in such matters.
    In my case, living room walls are prepainted with some matt emulsion, I do not know the brand, light yellow colour. If rubbed, cleaned with a wet tissue or sellotape applied, paint comes off. Otherwise, walls are in a good condition and clean (they were painted 2 y. ago). I want to repaint them myself with Dulux Endurance Matt (White Cotton). Is any undercoat needed, please? If yes, would that be acrylic undercoat then? To cover light yellow and to make sure that new paint sticks to the previous one and does not come off. I read about Zinsser Bull Eye 1-2-3 primer-sealer and, though not sure it is suitable in my case, I like the fact that it says no sanding needed.
    I would appreciate your help. Please recommend me some exact undercoat available in the UK. Thank you very much.

  10. Andy Crichton

    Look at adding Owatrol E-B to the first coat of emulsion, follow the instructions. This will act as a combined binder coat and first coat of emulsion. Do not add E-B to the second coat.

    This article covers most eventualities for emulsioning walls.

    To be safe with 2 coats straight on bare or chalky surfaces, add Owatrol Emulsa-Bond to the first coat only, to create a very high adhesion, penetrated coat, and then apply the topcoat as usual, diluted a little with water or Floetrol.

    Does that help?

  11. Guy Bitter

    About 12 years ago I put emulsion on an existing layer of paint (or emulsion) without sealant or undercoat. The emulsion has now developed a dozen nests of blisters and is pealing off the wall, and I intend to re-emulsion it.
    Which steps do you recommend I take to ensure that there will be no repetition of the current situation?

  12. David Sandall

    I have just had our dormer ceiling re-borded and plastered and walls skimmed. I allowed them to dry I then mist coated them, then after 24 hours started to paint them I now have an even finish. After many hours of reading I’m confused as to do I rub down and start again or use something like Zinsser 123 as a primer then repaint what should I do

  13. Andy Crichton

    If the paint looks good with mist coat and two full coats, mission accomplished? If you were repainting a poor finish and wanted to get a fuller finish, you could sand and consider the Zinsser 123 as a full basecoat.

  14. Andria

    I am painting my hall walls and ceiling light grey, I would like the loft hatch the same colour, it is white satin now, can I paint over it with emulsion? Does it need undercoat,

  15. Andy Crichton

    Give the existing satin paint a really good sanding, 180 grade paper so it is dull. Remove dust and 2 coats of a premium emulsion. You don’t say what paint you are using, go for something like Intelligent matt. Cheaper brands, the issue down the road would be finger marks.

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