Internal Linings – Compounds, Jointing & Finishing

Edward (Ted) Gale is a chemist and material scientist working as a Senior Technical Officer at CSR Gyprock’s Wetherill Park Research and Development / Technical centre.

Ted’s been in the Gyprock business for more than 30 years and has an extraordinary storehouse of knowledge on compounds and jointing systems.*

Building Knowledge asked Ted to shed some light on the pitfalls of choosing the wrong jointing compound or system for internal linings.

Firstly, what is the basic difference between ‘dry setting-type’ and ‘premixed drying-type’ jointing compounds?

“A dry setting-type jointing compound (Gyprock Base Coat) sets through a chemical reaction and is available in different setting times from 20 minutes to 90 minutes,” Ted says. “The advantage of using this type of compound is that it dries quickly, has low shrinkage, resists cracking and can be coated-over the same day once setting is complete.

“Unlike a setting-type compound, a premixed drying-type jointing compound (All-Purpose/Topping compounds) dries by evaporation of water and is available in large plastic buckets. An advantage of this type of compound is that it is available pre-mixed, ready-to-use and can be pretty easily sanded once it is completely dried.”

 

What’s the key difference between fibreglass and paper jointing tapes and how do we avoid cracks appearing in new walls of our commercial office or home interiors?

“Paper tape joints are usually stronger than fibreglass mesh (Easy-Tape) joints. Easy-Tape joints are prone to cracking if not back-blocked. When bedding paper tape, you need to ensure adequate thickness of joint cement under the tape. Ideally, minimum thickness should be 1mm. Misaligned joints can cause jointing problems including, poor tape adhesion, cracking and peaking, so the basis for perfectly smooth joints will be accurately aligned boards; it really boils down to accuracy of the frame.”

And after we’ve learned about jointing compounds and jointing tapes varieties, then what’s the best way to achieve full properties of base coat?

“In hot, dry conditions, base coats shouldn’t be applied immediately after mixing with water, wait perhaps 5 minutes but ensure you do it within 30 minutes of the commencement of setting – otherwise, they are at risk of drying out without setting and remaining soft and poorly bonded to the tape.

“Also, setting retarders should not be added to base coats or cornice cements because they increase the risk of drying without setting. Joint compound additives such as ‘No Pock’ should not be used because they negatively affect tape adhesion and joint strength properties of base coat.

“When using premixed drying-type compounds, it’s important to ensure that each coat is fully dry before applying the next coat. Wet-on-wet application of drying-type compound can cause poor tape adhesion and excessive or delayed shrinkage problems.”

More important Ted Gale tips include:

Cornice Fixing

Cornice cements 45 and 60 are designed for fixing plasterboard cornices to plasterboard walls and ceilings. Masonry adhesive should be used for fixing plaster cornices and plasterboard cornices to masonry.

Painting plasterboard

Low-sheen paint applied over unsealed joints can develop a higher gloss level than the same paint applied on Gyprock. A three-coat paint system which includes a good quality sealer is required to ensure a good quality, sheen-free finish.

Mould-resistant paint should be used in locations with high humidity or where there is condensation of water such as veranda ceilings. Otherwise, mould growth tends to occur on the paint over jointed areas.

*Thanks also to Adnan Javed, Technical Officer | CSR Lightweight Systems for his contribution to this article.


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