undercoat

[ray316]

What do you think about using emulsion as a undercoat, will it be ok.Also opinions on water based satinwood does it cover well or do you need two coats with this, to me it seems putting emulsion on.

 

[Nestor_Kelebay]

Any paint can be used as it's own primer if adhesion is not a concern.

It just means you'll use more of the expensive paint than the cheaper primer if you're painting over an absorbant substrate like bare plaster or plasterboard, tho.

 

[Zampa]

Emulsion is fine on bare plaster as a mist coat...but never on bsare wood or metal...it will work for a while but will break down in the end.

For wood I, and a lot of other decorator use thinned out oil based undercoat..it dries fairly quick and doesnt raise the grain of the wood too much.
Another good one is smooth masonry paint..its full of acrylic resin which adheres to wood very well.

 

[ray316]

zampa what l mean is will any emulsion paint be ok as a undercoat on say already painted wood skirting boards before putting a top coat on. B ecause alot of low odour paints eg. satinwood are waterbased arn't they.

 

[Nestor_Kelebay]

I'm thinking it would be best if you were to tell us exactly what you're wanting to paint over with that emulsion, and what you're planning on painting over that emulsion with. That is, is the surface you're planning to paint already painted, and if so what kind of paint and how glossy is it? And, what kind of paint are you wanting to paint over the emulsion when dry?

You see, you normally only PRIME over bare surfaces, like bare wood, bare plaster, bare concrete, bare metal, etc.

You normally PAINT over PAINT.

About the only time I could see where you'd want to prime over paint is if you wanted to paint over an oil based paint with an emulsion. In that case it would be a good idea to primer over the oil based paint with an oil based primer, and then apply the emulsion over the dry primer.

Another time might be if you wanted to change the color of a wall to blood red or canary yellow. Both of those color pigments have poor hide, and so it would make sense to use a coat or two of primer to make the wall white first, and then paint over the white wall with the poorly hiding paint. That way, even if you didn't get complete hide of the underlying white, it would look better than if you didn't get complete hide of the underlying green or blue or brown or other color.

So, pardon me for answering your question with a question, but I'm wondering if you couldn't save a step here by simply roughening the paint you want to paint over with some sandpaper, and then painting over it with the paint you intend to use. That way, you wouldn't even need to undercoat first.

But, I'm not confident that I'm understanding the question completely...

 

[Zampa]

Oh no..totally different Ray...let me deal with the first question...

No...definatly not..really..you should never use emulsion as an undercoat over previously painted gloss or satin finish.

Not all water based paints are the same..basically the typical make up of emulsion is powder (the pigment) and a binder/medium which hold the pigment together..otherwise it would just rub off as soon as you touched it..

The binder for emulsion does not have very good adhesion qualities when it comes to other surfaces.

You can however buy water based uncoat...the binder/medium for that is made up of Acrylic resin which has very good adhesion properties.

Or use masonry paint if you have any laying around..thats full of acrylic resin too...maybe more than waterbased (acrylic) primer undercoat

There are two reasons you undercoat...one to provide a suitable surface for the gloss (by keying on to the original paint and having the right surface to take the gloss) and two...to obliterate the colour underneath..but even if your putting the same colour back on..uncoating is still crutial otherwise the gloss will peel off easily

Using emulsion really isnt a good idea...do a test piece wait for it to dry then try and pick it off with your nail...it wil come off easily.

 

[ray316]

cheers zampa for that info, so what you're saying then is if l put gloss on top of a emulsion undercoat it would chip easily, like you say emulsion undercoat would come off easily.

 

[Zampa]

yep

 

[papergirl]

Zampa

Iv been having a read of your advice on this matter as i need to undercoat previously glossed wooden panels and finnish of with matt emulsion. If I use an acrylic primer/undercoat the emulsion should not chip of easy should it. Also on another subject I need to remove polystine tiles of bedroom ceiling and wallpaper. now iv been informed by the customer that the ceiling under tiles has been painted over with lime. What is a good sealer to use, could I use PVA

 

[Zampa]

Hello paper girl...on the first one...yep, acrylic primer undercoat will be fine...just give the panels a light rub over first tp remove any nibs and help provide a key for the acrylic.

Oh dear..lime wash or distemper...evil stuff..

No easy way with this one im affriad, you really need to wash it off as best as you can then seal it...id go for zinseer 123 or the cheaper but just as good dulux stain block...thinned our a little.

There are a few paints on the market designed to go directly over these powedery surfaces,..but im sceptical of them and id always go for a wash/scrape off.

Dont bother with PVA or exterior stabiling solution...the wont work and you could be adding to your problems.

 

[papergirl]

Hi Zampa,

Thanks for the reply, I think I will go for the Dulux stain block, will let you know how it goes, wont be untill at least a month or so though so dont hold your breath

 

[wreckedit]

I have tried some of the water based top satin top coats and I find they don't cover so well as an oil based paint. Consequently I have had to apply a second coat. I find that any paint that you have to brush out to get a finish and cover is best done with oil base. One of the worst paints I tried was a non drip water base. It would not flatten out so I stirred it to liquify it a bit and when I put it on it behaved like a very cheap emulsion. I will only use oil based paints for wood from now on.

 

[Zampa]

Yep..we still lag a long way behind most countries water water based paint technology...although it does sound like you was using a domestic product not a trade one..the latter covering better in most cases.

But you shouldnt really judge a paint on how easy you can get away with ne coat...most paints are meant to be used as part of a two coat system...

Water based non drip...that sound like a double whammy...i wouldnt fancy using that either...just goes to show though that 'thickness' doesnt count for much with paint...its know as 'false body' and paint companies employ it to help the paint go on thicker..thus giving the appearance that it covers better...it doesnt...theres only one thing that makes a paint cover better and thats pigment in its various shapes and forms.

 

[MissDIY]

I have a similar question related to what undercoat I should use…

I have stripped off the old painted wallpaper in the living room walls. Underneath there was a white paint – not sure what type – that has partially come off. The plaster is in relatively good condition apart from some small cracks that can be sorted out with Polyfilla.

What kind of undercoat should I use before painting the walls with matt emulsion paint? A guy at the local Homebase recommend Alkali Resistant Primer Sealer in off white from International, but he also said that I could use a normal white emulsion paint, if the plaster is in good condition and I want to save money. Alkali Resistant Primer Sealer is supposed to seal salts in new plaster, but surely this is a not a problem as the house is over 35 years old?

So… should I spend money on more expensive primer sealer or splash white matt emulsion all over instead? Removing the old paint first is too much work and therefore not an option…!

Reading the previous answers it looks like I’d need a different undercoat for skirting boards than for plaster walls. Is this the case? Is there not an undercoat that can be used on both plaster and wood?

 

[confidentincompetent]

I have a similar question related to what undercoat I should use…

I have stripped off the old painted wallpaper in the living room walls. Underneath there was a white paint – not sure what type – that has partially come off. The plaster is in relatively good condition apart from some small cracks that can be sorted out with Polyfilla.

What kind of undercoat should I use before painting the walls with matt emulsion paint? A guy at the local Homebase recommend Alkali Resistant Primer Sealer in off white from International, but he also said that I could use a normal white emulsion paint, if the plaster is in good condition and I want to save money. Alkali Resistant Primer Sealer is supposed to seal salts in new plaster, but surely this is a not a problem as the house is over 35 years old?

So… should I spend money on more expensive primer sealer or splash white matt emulsion all over instead? Removing the old paint first is too much work and therefore not an option…!

Reading the previous answers it looks like I’d need a different undercoat for skirting boards than for plaster walls. Is this the case? Is there not an undercoat that can be used on both plaster and wood?

Use matt emulsion on walls thinned a little to soak into the bare plaster patches (after preparing i.e. sand and clean off old paste.) alkali resisting primers only needed if plaster is bare and solvent based finish is needed.ie eggshell.

Woodwork, if your looking for a gloss finnish use a wood undercoat, acrylic primer /undercoat is good (water based/odourless). If your looking for a satinwood finnish , satinwood is self undercoating and needs just two coats of satinwood. but if strong colour change needed, or wood surface is grotty then undercoat would be good.
I've never looked at these B&Q paint everything paints