Whether it's hot, wet or cold outside, weather affects the performance and working qualities of drywall joint compounds. Different types of weather create different job site issues that need to be addressed.

Table 1:
Hot, dry weather hastens drying. Wet weather slows drying and may trap the unwary that rely on appearances to judge joint dryness. Cold weather slows mixing and risks the hazard of freezing. Any of these conditions can result in costly and serious problems unless preventive measures are taken.

When weather is hot and dry

• Close doors and windows to eliminate drafts. Then raise the humidity level by placing open cans of water about the job.

• Work shorter joint lengths in order to finish each section before the compound becomes unworkably dry.

• Don't add excess water to compound to extend its working time. This practice increases shrinkage.

• Keep inner walls of buckets and other containers, above the compound level, wiped clean to prevent crusting. Dislodged pieces of crusted compound will contaminate the fresh mix.

• Don't allow extremely rapid air movements over wet joints-especially if a thin-consistency mix is applied. This combination is a major cause of fissure, check and edge cracking.

• Use 20, 45 or 90 minute setting times of setting-type or lightweight setting-type joint compound. Shorter hardening times help minimize the effects of too-fast drying conditions.

• Don't allow compounds to lie exposed to full sunlight for extended periods. Such exposure may be harmful, particularly to topping compounds.

• Use setting-type or lightweight setting-type joint compounds or taping or all-purpose ready-mixed joint compounds for embedding tape. All of these compounds have a high resistance to edge cracking caused by hot, dry weather.

• Don't store ready-mixed compounds outdoors. Optimal performance is ensured by providing covered storage for these materials.

When weather is wet and humid

• Allow each coat of compound to dry thoroughly before applying subsequent coats.

• Don't rely on visual inspection to check joint dryness.

• Choose setting-type or lightweight setting-type joint compounds-especially during cold, wet weather. Their rates of hardening are virtually unaffected by high or fluctuating humidity.

• Don't store tape and powder compounds in damp areas. The working qualities of both are seriously affected by dampness. In addition, joint tape has an affinity for moisture, and damp tape is a major cause of center humping and edge wrinkling.

When winter winds blow

• Provide heat and maintain a minimum of 55 degrees F (13 degrees C) throughout gypsum panel erection, taping, finishing and until the final decoration dries. Avoid temperature fluctuations of more than 15 degrees F (8 degrees C). Use central heating plants wherever possible-unvented temporary heaters may produce staining fumes.

• Protect ready-mixed joint compounds from freezing. If freezing occurs, thaw the compound at room temperature. Never force thawing. Thoroughly remix any thawed compound without adding water.

• Raise the temperature of powder compounds to 70 degrees F (21 degrees C) prior to mixing by storing them in a warm area and use warm water for the finest results.

• Do use setting-type or lightweight setting-type joint compounds for an extra margin of safety if a minimum 55 degree F (13 degree C) temperature cannot be maintained after application. These quick-hardening formulations work well under such weather conditions, which cause failures with conventional joint compounds.

• Open windows slightly in various locations to provide ventilation. Uneven drying can cause bond failure and delayed shrinkage.

• Don't allow any compound to freeze on the wall. The materials lose bond strength after freezing and must be replaced.

• Plan work to allow sufficient drying time between coats and before decorating begins. Under adverse weather conditions, more than 48-hours drying time may be needed between coats. Finishing over basecoats whose surfaces appear dry but are wet underneath, is the principal cause of delayed shrinkage and joint discoloration.

• Don't add water just to speed mixing. Excess water causes "sloughing off" as the mix stands in the pail and excessive shrinkage when used.

When finishing exterior ceiling joints

Setting-type or lightweight setting-type joint compounds also can be used in treating joints in exterior gypsum ceiling panel construction, provided the following painting recommendation is followed: After the joint is treated and dried, apply one coat of a good-quality oil- or alkyd-based exterior primer and, after drying, cover with at least one coat of good-quality alkyd or latex exterior paint.

• Insist that exterior gypsum ceiling board be used where there will be indirect exposure to the weather, such as in canopies, carports, on the soffit side of eaves, etc. Its special core and paper resist sagging. And the eased edges contribute to stronger, more ridge-free joints and smoother ceilings.

• Prefill exterior ceiling board joints with setting-type or lightweight setting-type joint compound-the compound specifically formulated for both interior and exterior use.

• Reinforce exterior joints with joint tape.

• Use setting-type or lightweight setting-type joint compound for fill and finish coats-for filling and finishing exterior corners and for spotting nail or screw heads.

• Don't mix more setting-type or lightweight setting-type joint compound than can be used before hardening.

• Don't mix and apply unless weather forecasts promise temperatures above 45 degrees F (7 degrees C) until the compound is thoroughly dry.

• Don't apply if high wind and impending rain threaten to wet the compound before it hardens.

How to get the best results inside and outside,

in all weather

• Rotate stocks of joint compounds on a first-in, first-out stock rotation basis.

• Keep tools and mixing containers clean at all times. Always use clean water for mixing.

• Add powder compounds to water when mixing-not water to powder. And sift compounds while pouring.

• Apply compounds of heavy consistency over nail and screw heads.

• Apply three coats for the finest results.

• Apply relatively thin coats in angles to prevent corner cracking.

• Minimize fill coat craters by applying the finish coat with firm pressure and with the tool held at a 45-degree angle.

• Fill open joints (1/4-inch or wider) and allow them to dry in case of conventional compounds, or harden in the case of setting-type or lightweight joint compounds before proceeding with regular joint-finishing operations.

• Choose setting-type or lightweight setting-type joint compounds when time is short and job schedules are critical.

• Thoroughly smooth each coat of conventional weight setting-type joint compound before hardening occurs, as sanding is difficult. These compounds may be used as the final coat but they must be dry before priming with the first coat.

• Apply a thinned cover coat of tile adhesive to the exposed core of cutouts in water-resistant gypsum panels.

• Use #120 grit or finer sandpaper (#200 grit or finer mesh cloth) when sanding conventional all-purpose joint compounds.

• Use #150 grit or finer sandpaper (#220 grit abrasive mesh cloth) when sanding topping or lightweight all purpose joint compounds.

• Remove all sanding dust from surfaces prior to decorating.

• Avoid roughening the surface paper of drywall panels when sanding. This raises the nap of the paper and can cause joint and fastener area outline through the final decoration.

• Improve fastener and joint area concealment. When gypsum panel walls and ceilings will be subjected to severe artificial or natural side lighting, apply a high-quality, high-solids, undiluted, latex flat wall paint prior to painting, texturing or wallpapering.

• Don't use conventional drying-type joint compounds under bathroom wall tile construction.

• Don't expect "all-purpose" type compounds to possess all the superior characteristics of compounds designed for specific purposes.

• Don't combine powder and ready-mixed compounds.

• Don't apply excess knife pressure when spotting nail heads. This practice scoops compound out of the dimpled area surrounding the fastener.

• Don't allow painters to begin work before joints are thoroughly dry and surfaces are free of dust. Painting over wet joints is a major cause of joint discoloration.

• Don't build high crowns over joints. This practice produces shadow areas, encouraging ridging.

• Don't use drill-type mixers with speed higher than 650 rpm. Excessive mixing speed whips air into compounds and accelerates hardening action of setting-type joint compounds.

• Don't overthin compounds with water. Excess water doesn't speed mixing-it can cause delayed shrinkage and bond failures. One exception to the rule is that setting-type joint compound tolerates excess water since it does not materially affect hardening rates.