In high - temperature summers, the temperature often reaches above 35°C, accompanied by low humidity and strong winds. Such harsh climatic conditions pose severe challenges to dry - mixed mortars, such as tile adhesives, putties, and plastering mortars. Specifically, the water evaporation rate far exceeds the hydration rate of cement/gypsum or the film - forming rate of polymers. This causes the mortar to lose water prematurely, leading to a series of serious problems, including insufficient strength development, sanding, cracking, and a sharp shortening of the "open time" of tile adhesives.
Based on over 20 years of front - line technical and formulation research and development experience, adjusting the high - temperature formula cannot be a simple "one - size - fits - all" approach. Instead, it is necessary to comprehensively balance various aspects, including workability, water retention, strength development, and raw material costs. The following details the formula adjustment plan and construction precautions from the perspective of technicians.
I. Formula Adjustment Strategies in High - temperature Weather
The core logic of high - temperature formula adjustment is to slow down the water loss rate, replenish the surface wetting ability, and control the initial hydration heat release.
(I) Cellulose Ether (HPMC/HEMC): Balancing Water Retention and Anti - slip
In high - temperature environments, the key issue faced by cellulose ether is the gel temperature. The gel temperature of ordinary HPMC is generally around 60°C - 65°C. However, under intense sunlight exposure, the temperature of the base layer or the mortar surface can easily exceed 50°C or even higher, resulting in a sharp decline in the water retention rate of cellulose ether.
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Increasing the Gel Temperature
In summer, it is necessary to select cellulose ether varieties with a high gel temperature (＞75°C), or use a combination of modified hydroxyethyl methylcellulose ether (HEMC) and HPMC to ensure that the water - retaining performance of cellulose ether on high - temperature substrates is not compromised.
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Moderately Adjusting Viscosity and Dosage
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Affected by high temperatures, the viscosity of the mortar naturally decreases (thermal dilution effect). In tile adhesives, the proportion of low - viscosity cellulose ether can be slightly adjusted and increased (or the total dosage can be increased by 0.02% - 0.05%). This can ensure that the water - retention rate in high - temperature conditions remains above 93% while avoiding problems such as stickiness, toughness, and difficult spreading caused by high viscosity.
(II) Selection of Retarders: Precisely Controlling the Open Time
In summer, it is not advisable to blindly use a large amount of strong retarders (such as sodium gluconate), otherwise, it will cause an overly long final setting time and slow strength development in the later stage (especially after the temperature drops at night).
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For Tile Adhesives/Cement - based Mortars
Give priority to organic acid salts (such as citric acid, tartaric acid) or inorganic phosphates that have less impact on the later strength. The dosage needs to be determined through "step - by - step" laboratory tests. The goal is to control the open time so that after 15 - 20 minutes of high - temperature spreading, the tensile bond strength can still reach above 0.5 MPa.
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For Gypsum - based Putties/Plastering
In summer, the solubility of gypsum changes, and the hydration rate is extremely fast. High - efficiency gypsum retarders (such as protein - based or synthetic amino - acid - based) should be selected, and the initial setting time should be adjusted to 60 - 90 minutes. Strictly prevent "sand - turning" and secondary water - adding and mixing at the construction site.
(III) Redispersible Latex Powder and Crack Resistance Optimization
Excessive water evaporation at high temperatures can prevent polymer latex powder from fully aggregating and forming a continuous film (below its minimum film - forming temperature MFT, or unable to form a film due to lack of water).
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Balancing the Glass Transition Temperature (Tg)
In the summer formula, latex powders with a combination of high and low Tg can be appropriately introduced to ensure that before the mortar loses water rapidly, the polymer can form a continuous three - dimensional network, lock in the remaining water, and provide flexibility to counteract the thermal expansion and contraction stress.
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Anti - crack Fibers
For exterior wall putties or thin - layer mortars, 0.05% - 0.1% of short fibers (such as polypropylene fibers or wood fibers) can be appropriately added in summer. The physical network structure can be used to resist the initial plastic shrinkage cracking.
(IV) Optimization of Water - reducing Agents and Thickeners
To prevent workers from adding a large amount of water privately at the construction site due to the fast - drying mortar (which will completely destroy the water - cement ratio of cement and gypsum), a small amount of high - efficiency polycarboxylate water - reducing agent (PCE) can be introduced into the formula. This can reduce the amount of water added while ensuring that the mortar has excellent fluidity and thixotropy at a low water content, thus extending the workable time.
II. On - site Construction Precautions (Process Coordination)
Even if the formula is well - designed, if the on - site construction violates the laws of material mechanics, problems may still occur. As the saying goes, "Three - tenths of the material, seven - tenths of the construction."
(I) Management of the Base Layer''s "Water Absorption" (of Paramount Importance)
High - temperature and dry walls (such as aerated concrete, red bricks) have extremely strong water absorption. They are like dry sponges, quickly absorbing the water inside the mortar. Therefore, the base layer must be watered and moistened 1 - 2 days in advance before construction. When constructing, ensure that there is no visible water on the surface. For base layers with extremely high water absorption, an interface agent must be applied first.
(II) Prohibition of "Secondary Water - adding"
When the mortar thickens in the bucket, it is because the hydration reaction has started or the water has evaporated. At this time, it is strictly prohibited to add water and stir for use! Otherwise, it will lead to a serious imbalance in the water - cement ratio inside the mortar, and problems such as powdering and falling off will inevitably occur in the later stage. The correct approach is to stir in small amounts and multiple times and use it up within the workable time. If the mortar thickens, some fluidity can be restored by high - speed mechanical stirring, but do not add water.
(III) Avoiding High - temperature Periods and Direct Sunlight
Exterior wall construction should try to avoid the high - temperature exposure period from 11 am to 4 pm. Adopt the "sun - following direction" construction method (i.e., the construction surface is on the shady side of the building). In case of strong winds, a wind - proof net needs to be set up, because the air - drying speed has a more serious impact on the mortar than drying.
(IV) Controlling the Spreading Area
During tile adhesive construction in summer, large - area spreading at one time is strictly prohibited. It is necessary to "spread and paste as you go." Each spreading area should be controlled within 1 - 2 square meters to ensure that the tiles are pressed in and kneaded in place before the mortar surface "skins."
(V) Post - construction Curing
After the cement - based plastering mortar or tile adhesive joint filling, water spraying curing should be carried out according to the actual situation within 24 - 48 hours, especially on the exterior walls and surfaces directly exposed to sunlight, to ensure the basic humidity required for cement hydration.
The above comprehensive strategies from formula adjustment to on - site construction can help construction workers effectively address the challenges faced by dry - mixed mortars in high - temperature summers, ensuring construction quality and the smooth progress of the project.
