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Setting compounds require water to set hard. This chemical setting occurs after the specified time for a compound (i.e. a 90 minute set product, actually starts to set after 90 minutes). If the water content in the compound is lost or greatly reduced before the setting process starts, e.g. the compound has dried before it sets, then the chemical setting process can not occur and cure the compound to achieve its required strength and adhesion. The symptoms of this are the compound will be soft, have little or no mechanical strength and adhesion, and the tape may bubble, crack or even fall out. Setting compounds must not dry out before their specified set time. Learn More
Water, wet compound, air and surface temperature above 10°C should be maintained until the compound is completely dry. Structures may require heating to achieve this temperature. Use of a 1 x 2KW fan heater per 50m2 of floor space in a house is usually sufficient. Do not raise temperature above 18degrees celsius as other issues may arise. During winter months or under cold damp conditions, drying rates can be improved using more but thinner coats of compound. Setting compounds dry quicker and are better suited in colder conditions as a first and second coat.
HOT TIP
In winter there is increased risk of shrinkage during these colder months. If the air drying compound is not dry, it has not stopped shrinking.
Some air drying compounds are promoted as a total system, including the taping coat. These systems are common overseas in warm climates or houses that are heated during construction once closed in. Warm air allows the thick taping coat of the air drying compound to dry (and shrink) in a reasonable time.
In New Zealand however, for at least 6 months of the year, the temperature is too low to enable a commercially acceptable time frame for drying of a thick coat of air drying compound. Added to this, for cost reasons, most houses are not heated in winter during the finishing phases of construction.
It is unwise to use air drying compounds as a system, unless you are certain that each separate coat will dry, so that shrinkage is eliminated.
This cannot be achieved in winter without heating the building being stopped. Doing this would eliminate most of the subsequent issues seen by both the stopping and painting industry, provided the workmanship by both parties is up to scratch.
If the individual coats of a joint are not 100% dry prior to the next coat being placed, delayed shrinkage, caused by the moisture eventually drying out in warmer weather, will create hollow joints, shadow lines on joints, tram lines either side of the tape, etc.
A thin coat of air drying compound on top of a plaster based coat will dry quicker than a thick coat. And because it’s thin, it will shrink less in relation to the entire joint. This system generally works, however will also benefit if the house is heated.
In conclusion: think about the implications for total air drying systems before using them. They have their place in heated premises or in warm / hot climates. They should not be used as a total system in a building that is being stopped in winter without heating.
Setting compounds usually shrink back to a degree to ensure the joint tape is pulled back into the joint as it sets. Once set, the joint will continue to shrink at a much reduced rate as the compound dries, and stop shrinking when dry. Painting a joint that has not dried properly can delay shrinkage by several weeks or even months resulting in delayed shrinkage.
When bedding in paper lined metal trims such as the GIB® GoldlineTM products or metal trims such as the GIB® Rondo® angles or the GIB Slimline angles, setting compound should be used. Stronger and more reliable adhesion will be achieved when using a setting compound.
Back-blocking plasterboard joints eliminate movement in the joint and thus greatly reducing the possibility of cracking, and popping and peaking in the joint area, if done correctly. Refer to the GIB® Site Guide where back-blocking is required. The back block must cover most of the joint, and must be stuck down properly. Use GIB Tradeset® , GIB MaxSet® or GIB-Cove® Bond as the bonding agent, and ensure it has been put on at least 3 mm thick. Compounds must not be applied if they have started to set, or are thickening up. |
GIB Plus 4® is the recommended compound for skim coating. Use Victor® Multi Plus for skim coating or screeding/rendering a solid plastering over a masonry surface, (i.e. brick, block and tilt slab and in an interior environment). Victor® Multi Plus can be mixed with sand and applied up to 10 mm thick in one application. An unblended coat is usually applied as the finishing coat. This plaster compound differs from jointing compounds in that water can be applied during the setting stage to allow polishing of the compound to a very smooth "glass" finish. Trade level skills are required to achieve a flat polished surface with this product. For application details refer GIB® Site Guide. Victor® Multi Plus is available in a 90 minute set time and 20 kg bags.