How Weather and Humidity Influence the Outcome of a Plastering Job

Why does one plaster repair last years and another fail after weeks?

Weather is far more important when it comes to plastering than most people realise. Whether you’re skimming walls in summer or finishing a room in winter…The ambient temperature/humidity will determine whether the finish will last for years or fail within weeks.

Here’s the kicker:

Approximately 80% of plastering defects are caused by inadequate drying conditions. Which is crazy considering homeowners completely overlook that.

Learn how weather affects your plaster …and what you can do about it.

What’s inside this guide:

1. Why Weather Matters For Plastering

2. How Humidity Affects Skimming Walls

3. The Best Temperature Range For Plastering

4. Seasonal Plastering Challenges

5. Tips To Control The Environment

Why Weather Matters For Plastering

Plaster doesn’t just “dry”… It cures.

Essentially, there is a chemical reaction occurring within the wall as moisture is slowly evaporating from it. So when the weather disrupts this balance, you get cracks/brittle patches or mould growth weeks later.

Plaster is a wet material that needs optimal conditions to set hard. Too hot and it will dry too fast and crack. Too cold and it will not set. Too humid and it seals in moisture causing poor adhesion to the wall behind.

The really frustrating part is that poor conditions aren’t always immediate. You can go in day one with a clean room and start failing half a year later.

Here’s the truth:

No plasterer in the country can work well in poor conditions. That’s why many qualified plastering contractors will postpone the job or install heaters/extractors when the weather is bad before skimming ceilings. Trying to tough it out is a risky move that seldom works — even if you have nailed the technique behind the trowel.

How Humidity Affects Skimming Walls

This is where things get interesting…

Humidity. That’s plaster’s worst enemy. If you’re skimming in humid conditions moisture can’t escape from the plaster thick enough — and fast enough — which means:

• Soft, weak finishes

• Patchy drying

• Mould growth

• Paint peeling later

Industry experts state that drying time for fresh plaster can be twice as long if the relative humidity is above 70%. In the UK we have such difficult conditions as our indoor humidity remains between 50-70% for majority of the year.

Low humidity, on the other hand, dries things too fast. This causes a different issue. The outside dries while the inside is still moist. You end up with a dry skin on top of wet plaster. It seems to look ok for a couple days… and then the cracks show.

The sweet spot? Around 40-60% relative humidity.

The Best Temperature Range For Plastering

Temperature is just as critical as humidity.

Plaster has to be laid (and dried) at between 15-25°С. Outside of those temperatures creates issues.

Here’s why:

• Below 5°C: Plaster simply won’t set properly

• 5°C to 15°C: Drying slows down massively

• 15°C to 25°C: Ideal range for skimming walls

• Above 25°C: Risk of flash drying and cracking

Studies have proven that correct temperature can reduce drying times by 40%. That’s a huge improvement when you’re on a tight deadline.

Tip: Avoid directing heat at new plaster. It’s number one reason why cracks happen. Use indirect heat rather – central heating on a low/medium setting.

Seasonal Plastering Challenges

Each season comes with its own headaches…

Winter Plastering

Winter is plaster’s hardest season. Chill temperatures make drying painfully slow. Add in dry-wall-induced humidity indoors with heaters blowing and windows closed.

In winter you should:

• Keep room temperature above 15°C

• Use a dehumidifier to control moisture

• Allow extra drying time before painting

• Avoid plastering if temperatures drop below 5°C

Summer Plastering

Summer sounds ideal but it comes with risks. The biggest one? Flash drying.

If you skim walls in blistering heat, the outer layer dries faster than the deeper layer. It forms a brittle adhesive and cracking lines will appear after weeks. You can prevent this by closing blinds and maintaining a cool room.

Spring & Autumn

It’s Goldilocks plastering weather. Not too hot. Not too cold. Not too humid. If you’ve got the opportunity to time your plastering, aim to do it these months.

Tips To Control The Environment

The weather can’t be changed… But the room can.

Here’s what professionals do to manage conditions:

• Dehumidifiers: Pull excess moisture out of the air during damp weather

• Heaters: Maintain steady temperature in cold rooms (never direct heat on plaster)

• Fans: Keep gentle airflow moving without blasting the surface

• Hygrometers: Cheap devices that track humidity in real time

• Ventilation: Open windows only when outdoor humidity is lower than indoor

Statistics from industry reviews indicate that drying problems can occur on in excess of 65% of plastering jobs. The majority of these are preventable with adequate ventilation.

TIP! Avoid opening windows when rain is predicted. Keep windows closed during rain storms to prevent too much humidity inside.

How To Know If Conditions Are Right

Before any plastering job, run through this quick checklist:

1. Is the room between 15-25°C?

2. Is the humidity between 40-60%?

3. Is there gentle airflow (no strong draughts)?

4. Are the walls free of damp patches?

5. Is the weather forecast stable for the next 7 days?

If the answer is “yes” to all five… You’re good to go.

Otherwise—if not— pause. Move the furniture. Hire someone who knows how to handle difficult environments.

Bringing It All Together

Weather and humidity make or break a plastering job.

Done right and you end up with smooth durable walls that can last decades. Done wrong and you get cracks, mould, and an expensive redo within months. The margin for success or failure can be just a few degrees or a few percent.

To quickly recap:

• Aim for 15-25°C room temperature

• Keep humidity between 40-60%

• Avoid extremes — too hot, too cold, or too damp

• Use dehumidifiers, hygrometers, and gentle ventilation

• Plan plastering for spring or autumn if possible

Wall Skimming isn’t simply a skill. Conditions have to be just right to achieve a perfect finish. Respect the weather, work with it and the plaster will thank you by looking just as good in 10 years time as it did straight off the trowel.