How to help avoid summer jointing problems

Hot dry summer weather can adversely affect the performance of plasterboard jointing compounds. USG Boral’s Category Manager for Compounds, Tim Harrington, explains why and offers some solutions. 

Many parts of Australia experience extremely hot and dry spells during the summer months. Indeed, this past winter proved unseasonably hot and dry in Queensland and parts of NSW too!

In such conditions, jointing compounds naturally lose moisture in less time than in cooler or moister conditions. Unless the right jointing compounds are used, this can result in joint cracking, or joint tape and cornices failing to properly adhere and potentially coming away.

WHY DO WEATHER CONDITIONS MATTER?

Plaster-based compounds which set chemically typically come in a range of setting times. For example, USG Boral BaseCote™ sets in 45, 60 or 90 minutes – with the gypsum in each product designed to ‘activate’ accordingly. Most professional plasters prefer the longer setting products as they give them longer time to work, and less frequent mixing.

However these setting times are based on moderate temperatures and humidity levels. Once the compounds are mixed with water and trowelled on the wall, water is lost in three ways:

1. Evaporation into the atmosphere
2. Absorption by the porous plasterboard surface
3. The water and plaster undergo a chemical reaction known as hydration to form fully set, hard gypsum

In hot dry conditions, water will evaporate or be absorbed more quickly – which may not leave enough water (or enough time) for the hydration stage of the process. Premature dry-out can result in weak and powdery joints and poor tape or cornice bond.

PRODUCT ALTERNATIVES TO HELP AVOID JOINT FAILURE

When conditions are expected to be hot, dry or windy, you have three different options for jointing compounds:

1. Choose compounds specifically formulated for faster setting – such as BaseCote™ 45 and Cornice Adhesive 45 – as they reduce exposure to extreme drying conditions.
2. If you must use BaseCote™ 60 or 90 or Cornice Adhesive 60, allow them to stand for 30 minutes after mixing so that they set soon after application.
3. Go for a ready-mixed jointing compound such as RediBase™, SHEETROCK® Taping Joint Compound, All Purpose Premix or Total Joint Finish.

Ready-mixed compounds are air-drying, so are especially suitable in hot and dry environments. Because they’re ready-to-go, they save time on a project and are economical to use.

OTHER TIPS AND TRICKS FOR SUMMER PLASTERING

Choosing the right compound is important – but here are some other ways to minimise the risk of joint cracking when the summer heats up:

• Close all windows and doors to avoid drafts
• Wet down surfaces just before trowelling
• Avoid the hottest part of the day when applying tape
• Make sure you provide ample compound under the tape; if using mechanical tapers such as banjo boxes, avoid excessive pressure or runny mixes
• Apply an immediate skim coat over the tape

Obviously, the use of compound retarders is not recommended, as the longer the set the more time for water loss.