How To Paint Over Water Stains – A Full Guide

Updated Mar 13, 2024 | Posted Feb 21, 2024 | Product Advice, Professional insight | 0 comments

Sadly, water stains are one of those problems which crop up in many people’s lives; burst pipes, faulty plumbing joints, cracked water cylinders, forgetful relatives leaving taps running, flood damage, leaking roofs… for all the good things water does for us, it can also be extremely damaging when it turns up in the wrong place.

Even after the cause has been solved, and the initial mess has been cleared up, the problem isn’t over.  Water almost always leaves behind unsightly tea-coloured stains wherever it goes; painting over water stains is easy enough, but is not as simple as just giving them a onceover with some cheap emulsion.

 

What are Water Stains and How Do They Occur?

 

When a water leak – or moment of bath-filling forgetfulness – occurs, water will follow easiest path (where there is the least resistance) downwards due to gravity. Where there is no easy route for it to follow, it starts to collect and form pools, until enough water has collected to either spill over any obstruction and find a new route, or to soak through plaster or plasterboard.

Once the original problem (leak, over-filled bath or whatever) has been solved and the area has dried out, the familiar tea-coloured water stains remain, marking the places where water collected and then soaked through plaster and/or plasterboard.

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There is some debate as to why the stains are always the colour that they are; some people feel that it is due to chemicals in hot water systems (but that doesn’t explain why the stains would be the same colour if caused by someone forgetting to turn off a tap).

Some believe that the water picks up tannins from structural timber (roof beams, studwork etc) that it has soaked through, while others feel that the water picks up ingredients from within the plaster as it soaks through.

The most commonly held opinion these days is that it is caused by ingredients (surfactants) in the existing paint which break down after prolonged contact with water.  Whatever the reason for the colour, nobody wants unsightly water stains on their walls and ceilings, so we need a fool-proof method for painting over the water stains that ensures they won’t simply reappear a few weeks later.

water stains covering a ceiling

Prepping a Water Stain Ready to Paint

 

The first thing to do is to ensure that the original source of the problem is resolved.  There’s no point trying to paint over the water stain – even if you do follow the correct procedure – if the water leak (or whatever the original cause was) is still there.

Find the source of the water, make sure any leaks are properly sorted out, and leave the area to dry out thoroughly. If you’re not certain it has dried out properly, you can buy portable moisture meters online by clicking here to check.

Do not paint over water stains until the material you are painting is properly dry!  Putting a dehumidifier in the room can help to speed up the drying process.  Once the area is properly dry, give it a thorough wash with a mild detergent solution to remove any dirt and grime that the water may have picked up along its route to your ceiling and/or walls.

Sometimes when an area has been damp for a while, mould can begin to grow, especially if ventilation/air circulation isn’t great. It’s important that mould is treated properly before you start painting – you can read how to do this here.

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What if Your Plaster is Damaged?

 

Sometimes, as well as causing a water stain, the water has caused some of the existing paint to flake, or to turn powdery.  If this is the case, scrape away any loose material, and then apply a coat of Zinsser Peel Stop – this “glues down” the edges of the flaky paint.  Once the Peel Stop has dried, skim over the area with a fine coat of a suitable filler (see here for some recommendations) to make it smooth.

Once the filler is fully cured, sand it perfectly smooths and apply another coat of Peel Stop to the whole area to be on the safe side.  Once this is dry, you are then ready to proceed to the next step – you may have covered some of the water stain with filler, this doesn’t matter.  Even if the stain bleeds through the filler, the next stage of the process will block your water stain and prevent it from coming through to ruin your finished look.

 

Blocking a Water Stain

 

This step is really simple and will also block any stains left behind if you have treated mould in the area, as well as sorting out your water stain.  This is where the magic happens – if you miss this step out, your water stain will in all probability simply bleed back through your nice new emulsion paint, and you’ll be back to square one.

All you really need to do to ensure your water stain is confined to history is to treat the area with a coat of a good quality stain-blocking paint.  If the stain is particularly bad, you may need two or even three coats, but in most situations, I find two is the maximum needed.  There are loads of good stain blocks around these days; some handy (but more expensive) ones in aerosols, and others in regular tins.

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The Best Paint to Block a Water Stain

 

If budgets are tight, or you’re worried about overspray onto adjacent walls, tiles or whatever, use the old-fashioned paint brush method rather than an aerosol!  There is plenty of choice of what to use; probably the most tried-and-tested product, and for years the favoured option for professional decorators (partly because there weren’t that many other options available!) is Zinsser B-I-N primer (or Smith & Rodger’s “Blockade”, or Fiddes “Full Stop”, which are similar products).

This is a magic little product which every professional decorator carries somewhere in his or her van, and it has a multitude of uses – one thing it’s particularly good at is blocking stains.

So, a quick coat of BIN, wait for it to dry (make a cuppa!), and then you’re ready to paint over with your emulsion.  BIN dries to a creamy “off-white” (see photo), so you will always need to paint over it.

Zinsser BIN Primer - a good paint for blocking water stains
stain block covering a water stain

Three Top Tips When Using Zinsser BIN:

 

  • When you buy a tin of BIN, buy a bottle of meths at the same time – it’s the best thing for cleaning out your brush afterwards (white spirit won’t work with BIN)
  • Stir the product really thoroughly every time you open the tin. Giving it a quick shake isn’t enough – the solids in the paint tend to sink to the bottom of the tin and form a sticky mass – you need to stir thoroughly to make sure these are properly mixed in the paint to get the best result.
  • Don’t be surprised if, when you emulsion your ceiling (or wall or whatever), the areas that you treated with BIN take longer to dry. Paint dries by both evaporation and absorption, and BIN forms a barrier which stops the stain bleeding through, but also reduces the ability of the plaster to absorb moisture from the paint. Just wait until your first coat of emulsion is thoroughly dry all over before applying a second.

 

If you can’t get hold of B-I-N, there are plenty of other good stain block paints around that are just as good at blocking a water stain; some are oil-based, some (including Zinsser’s new Aqua B-I-N) are water-based, and some are effectively stain-block and emulsion all in one.  To read more about the best stain block paints available, click here.

 

Painting Over Water Stains

 

Once you’ve applied a coat or two of your stain block of choice, it’s time to paint over where the stain was. Choose an emulsion that is suitable for the area you are painting:

 

 

Use a good quality brush, such as Axus Décor Silk Touch Ultra, or ProDec Ice Fusion, and a decent roller such as Hamilton Perfection, and away you go – that unsightly water stain will soon be a distant memory.  Two coats of emulsion are usually sufficient; just remember to allow the specified amount of time between coats, and don’t be surprised if the areas that you stain-blocked take longer to dry – this is perfectly normal, and due to the stain block having effectively sealed the surface.

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Final Thoughts

 

Water can be a bit scary in terms of the amount of damage it can do, but once the underlying problem is sorted out and the area is allowed to dry out thoroughly, painting over the resultant stain is relatively straightforward. Just you follow the simple steps outlined above.

 

How to Paint Over Water Stains by Robin Gofton – Wokingham Decorating Services 

For Decorators Forum UK

Updated Mar 13, 2024 | Posted Feb 21, 2024 | 0 comments

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