Paint surfaces exposed to high humidity with Zinsser

Updated May 2, 2024 | Posted Sep 29, 2017 | Professional insight, Product Advice | 0 comments

If you need to paint surfaces exposed with high humidity, then there are a few things to consider. Normal emulsion will not withstand these conditions for any length of time. If you use the wrong paint, then mould, peeling, and staining would soon show.

You might be painting a bathroom, shower room, swimming pool, even a busy kitchen. Don’t worry though, it isn’t more difficult than painting a bedroom or a lounge. It just takes a slightly different approach. I’m going to explain all you need to know in this blog.


What you need to paint surfaces exposed with high humidity


I’ll list the materials you will need to carry out this type of work here. These are trade products, which you can buy from any trade counter. However, unless you qualify for a trade discount, it’s usually cheaper to buy them online. The two trade websites that we use are The Paint shed, which you can visit online by clicking here, or Decorating Centre Online, which you can visit online by clicking here.


  • Zinsser Mould Killer
  • Sandpaper
  • Filler, caulk etc
  • Zinsser Bullseye 1-2-3 Primer Sealer
  • Zinsser Perma-White Interio


1. Surface Preparation


All surfaces must be clean, dry and free from anything that will interfere with the adhesion of the materials you’re working with. Remove loose material by scraping or brushing with a stiff bristle brush to a sound edge. Prior to painting, the moisture content should not exceed 12%. All visible signs of mould growth needs to be treated with an agent like Zinsser Mould Killer to kill the spores.

Ensure everything is stable and dust free as part of your prep. It doesn’t matter whether you’re working over bare plaster or a previously painted surface, the prep needs to be right. After all, you’re asking the paint to stand up to a challenging environment, so getting the prep right is essential.


2. Cracks and Surface Defects


Fill any cracks and small surface defects with a suitable filler as appropriate in accordance with the manufacturer’s instructions. Allow to dry. Rub down with a fine grade abrasive paper. Remove all dust. This is common practice with any decorating and will help you achieve that perfect, blemish free finish.

If the surface you’re working on is previously painted, then the filling should be done now. If you’re working on bare plaster, then your filing should be carried out after you apply a coat of primer (as explained in the next section). Click here if you need a guide on the best filler to use.


3. Priming


The product I’m going to recommend for painting surfaces with high humidity is Zinsser Perm White.  The adhesion of Perma White is great on its own, but you will still need to prime when painting over bare surfaces like plaster or wood.

Previously painted surfaces don’t need to be primed unless they are chalky, porous, or you’re going for a big colour change. The finish product has great opacity unless you’re using white. So, if you’re going from a colour to white, then you’ll save yourself some time by using a white primer first to blank out the colour.

The recommended primer is a product called Zinsser Bullseye 123. This acts as a stabiliser, aids adhesion and blocks stains.


4. Decoration


Decorate with two full coats of Perma-White® Interior Matt, Satin or Semi-Gloss in accordance with the manufacturer’s instructions. Allow a minimum drying time of 2 hours between coats in normal drying conditions. Zinsser Perma White is a specialist product, designed to perform well on surfaces exposed to high humidity. It is available online in white, and a range of colours.

You’ll find Zinsser Perma White easy to use and leaves a great finish. But more importantly, it stands up to humidity better than anything else I’ve tried. I’ve seen it in action; I painted the changing rooms of a swimming pool about 8 years ago. Before I painted it, the client struggled with mould growth and peeling paint. He was getting it painted every year with durable matt emulsion or acrylic eggshell, but the problem kept coming back.

His issues were caused by high humidity and products that struggled to cope. I painted it, following the exact process explained on this guide. I repainted it a couple of years ago, but that was only because my client wanted a colour change. The actual decorating still looked mint after 6 years. Zinsser stood up to the humidity where other products failed.




How to decrease humidity in a house?

There are a few ways to decrease the humidity in a house. Ventilation is key, particularly in a kitchen or bathroom. Just keep the air moving and allow humidity to escape the house. A dehumidifier will also help. Oh, and avoid drying clothes in the house if you can.


How to solve condensation on walls?

Ventilation is the biggest factor. Open a window, install an airbrick, use an extraction fan, etc. The other thing you could do is use Thermoline (thermal lining paper), or thermal paint. Water condenses on the coldest surface in a room, so if you insulate the walls, you reduce condensation. However, this doesn’t address the issue of humidity.


Can condensation get behind paint?

Yes, if you use paint that isn’t waterproof like normal matt, contract matt, vinyl matt etc, then condensation will penetrate. Instead, you should opt for a durable product, especially in humid areas.


Does a cold house cause condensation?

Poor ventilation and cold surfaces causes condensation, but the cold certainly adds to the problem. Heating your house will help dry it out providing humidity isn’t too high.


Final Thoughts


I told you it isn’t difficult to paint surfaces with high humidity. It’s just about getting your prep right and then using the correct products. Providing you carry out these steps, painted areas will last.

Your humid rooms will then be resistant to mould growth, staining, and other associated problems.

This blog was written by Mike Cupit, a Professional Decorator of over 20 years and owner of Decorators Forum UK.

Updated May 2, 2024 | Posted Sep 29, 2017 | 0 comments

About the Author

About the Author

Mike Cupit has been in the decorating industry since 2002 and has mostly worked as a Trade Decorator in the domestic sector (peoples’ homes). Self-proclaimed “product geek”, Mike has a passion for paint and decorating tools. Mike now spends most of his time testing paint products and tools, comparing them to similar products on the market, and blogging about the industry in general.


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