Construction Technology of Weather-resistant Silicone Sealant

1. Introduction

1. The following construction steps are the basic requirements for applying construction sealants. Strictly following these construction steps can ensure that the sealant has good performance, which is also a necessary condition for obtaining quality assurance. Because construction silicone adhesives are used in many different environments, this construction step cannot be used as a quality assurance document covering everything.

2. Scope of application

It is suitable for the construction silicone sealant series products produced by our company.

3. Construction environment

The sealant should be constructed in a clean environment with a temperature of 4-40 ° C and a relative humidity of 35% -75%. Ambient temperature is too low will reduce the adhesion of the sealant, because the surface wettability of the sealant is reduced, and frost and ice may form on the low-temperature substrate, affecting the adhesion of the sealant. Therefore, the safe use temperature of the sealant should be greater than 5 ℃. High ambient temperature also has an adverse effect on the sealant. On the surface of the building with excessively high ambient temperature and direct sunlight, the actual temperature of the substrate surface may be higher than the ambient temperature Much higher. Due to the influence of high temperature, the sag resistance of the sealant will be poor, because the time for chemical conversion will be faster, the use time and the trimming time will be shortened, and at the same time it is easy to generate bubbles. If the relative humidity is too low, the sealant will slow down. The excessively high relative temperature may form a film of condensed water on the surface of the substrate, affecting the adhesion between the sealant and the substrate, and may also cause the sealant to form bubbles. .

On-site adhesion testing must be performed to ensure good adhesion of the glue and verify any recommendations regarding glue. (See the chapter on quality management)

There are five basic requirements for the correct interface surface cleaning and glue application:

1. The interface surface must be clean, dry, free from dust pollution and free from freezing.

2. If primer is required, the primer must be applied to a clean surface.

3. If necessary, use backing materials or release tape.

4. Fill the gap of the interface with glue when applying glue.

5. The leveling work is to ensure that the glue has the correct shape and can completely contact the substrate.

2.Surface treatment of the substrate and the application of silicone

1. Material cleaning steps

This chapter discusses cleaning solvents and basic cleaning steps for porous / non-porous materials. The adhesion between the sealant and the substrate depends on whether the substrate surface is clean. The user should contact the supplier of the substrate to ensure that this cleaning step and the selected cleaning solvent are compatible with the substrate.

A) Use of organic solvents

Not every solvent can effectively remove every contaminant. Some solvents will seriously damage a certain material, please follow the solvent manufacturer’s safe use recommendations and local or national solvent use regulations.

note:

Isopropyl alcohol may not effectively remove contaminants on polyester dust coating materials. Xylene is recommended to clean this material.

B) Non-porous materials

Before applying glue, the surface of the non-porous material must be cleaned with a solvent. The choice of solvent depends on the contaminant and the substrate. Non-oily dust and dirt can be removed with 50% water and 50% isopropyl alcohol. Oily dirt and film should be removed with a degreasing solvent such as xylene.

C) porous material

Building materials such as cement boards, concrete, granite, limestone, other stone materials or cementitious materials, and substrates that can absorb liquids are considered porous materials.

For some new porous materials, dusting may be sufficient. Depending on the surface treatment, the surface of the porous material needs to be abraded to clean, some to be cleaned with a solvent, and some to both. The float and dust on the cement board must be cleaned. Fine silicon dust, water repellent and other surface treatment residues on the surface of the cement substrate, protective coatings and old sealants all affect the adhesion of the adhesive. In order to ensure good adhesion, the above surface residues, coatings and old sealant residues must be removed by grinding. Abrasive cleaning methods include grinding, sawing, washing with sand or water, mechanical grinding or a combination of the above methods. Use wire brush, vacuum cleaner and compressed air without oil to remove dust and loose particles on the surface. Once the surface is clean and dry, the glue can be applied. If the surface is dirty, it must be cleaned with a solvent using the “two rag cleaning method” (described in detail later). Some porous materials will absorb solvents or primers during the cleaning process, and must be allowed to evaporate before applying glue.

Please note that the recommendations discussed above regarding the removal of old sealants, surface cleaning, interface cleaning, and sealant are not suitable for repairing organic sealants and interfaces or other potentially risky substances containing PCBS substances . If you know or suspect that the existing sealant may contain PCBS or other dangerous and toxic substances, please contact a professional agency for disposal.

D) “Two rags” cleaning method

Use clean, soft, absorbent and non-linting cloth. This cleaning step involves first wiping with a cloth with solvent and then wiping with a second clean cloth.

(1) Thoroughly remove loose residues on the surface of the substrate.

(2) Pour a solvent of suitable purity on the cloth. Organic solvents are best packed in squeeze-resistant solvent-resistant plastic bottles. Never immerse the cloth directly in a container containing solvent

Here, because the dust on the cloth contaminates the solvent.

(3) Wipe the surface vigorously, check the rag to confirm whether the surface dirt is absorbed. Take turns to clean the cloth with a clean place until no dirt is absorbed on the cloth.

(4) Immediately afterwards, use another completely clean dry cloth to wipe off the solvent and residue on the substrate. Before evaporation, the organic solvent must be dried with a dry cloth, otherwise it will fall

Low cleaning effect. Some materials may have a little residual solvent on the surface or climatic conditions. If you encounter this situation, you must wait for the surface substrate to dry before installing the backing material and small circle

Stick and sealant.

E) Winter / Summer solvent selection

Isopropyl alcohol can be dissolved in water, so it is very suitable for use in winter, it can effectively remove condensate and frost on the surface of the substrate. Toluene and xylene are insoluble in water, so it is more suitable

Use in summer.

2. Primer

If primer is required, the construction method is the same as above.

3. Installation of backed small round bar

A) Design considerations for mobile interfaces

When designing a mobile interface, the following points must be noted:

(1) It is recommended that the interface width is at least 6mm; the wider interface and the narrower interface can withstand larger displacement capabilities.

(2) Three-sided adhesion will limit the original displacement ability of the interface. You can use a small round bar or anti-adhesive tape to avoid it. If the three-sided adhesion occurs, the sealant can withstand the displacement.

The amount does not exceed 15%.

(3) Thinner glue can bear greater displacement capacity than thicker glue. When the shape of the interface is hourglass, it can exert the best displacement performance.

(4) When the width of the sealant is larger than 25mm, the depth should be controlled to about 2mm. There is no need to allow the sealant to be applied more than 12mm deep.

B) Interface displacement during glue curing

 one-component sealant needs to react with moisture in the surrounding air to cure. Changes in the interface during the curing of the glue can lead to an unsightly appearance (shrinkage of the interface). At the same time, because the adhesive properties of the adhesive will not be formed until the adhesive is cured, there is a potential for loss of adhesion. The loss of adhesion due to interface displacement during the curing of the glue can be minimized using a primer, and the primer can reduce the time required for adhesive curing.

The following suggestions help reduce the deformation of the glue surface.

(1) Use open-cell polyurethane round rods.

(2) Try to apply glue in the evening, because the surface temperature of the substrate is not high at this time, and the temperature difference changes little.

(3) The glue is not more than 6mm thick.

The above suggestions help reduce the surface shrinkage, but may not completely eliminate it. In fact, this kind of problem of deformation of the appearance of the glue caused by the displacement of the interface during the curing of the glue,

All sealants can happen.

4. Steps for applying sealant

The applied sealant must be filled into the entire interface and firmly adhere to the surface of the substrate that needs to be in contact with the glue. If the sealant cannot completely fill the interface, there can be no good adhesion, and the performance of the glue will be weakened. In order to get good adhesion, the glue needs to have a clean, dry, frost-free surface. Although silica gel has a wide range of construction temperature, it can be easily applied, but the actual construction temperature will be limited by whether the interface surface is frosted. When the temperature is lower than 5 ℃, the cleaning solvent on the frosted surface is the most Good choice of water

Soluble solvents such as IPA.

The sealant should follow the following steps:

(1) Use masking tape to prevent excess silicone from polluting the surrounding surfaces of the interface.

(2) Use a glue gun or glue machine to continuously glue the rubber. Apply appropriate pressure to fill the entire gap in the joint.

5. Leveling of sealant

(1) Before the skin of the glue is skinned (usually within about 10-20 minutes), level it up. Leveling can make the glue squeeze to fill the gaps and make the surface smooth and smooth. Do not use liquids such as water, soapy water and alcohol to help leveling. These substances may interfere with the curing and adhesion of the glue and cause appearance problems.

(2) Remove the masking strip before cementing. (Within about 15 minutes after leveling)

6. Adopt silicone construction sealant to replace the failed organic sealant

Over time, the organic weathering glue must be repaired or removed and reapplied. Due to the aging and deterioration of organic rubber, it is necessary to repair it. When the sealant fails, it is best to identify the cause of its failure and apply a better quality sealant to replace the old failed adhesive.

To repair the failed organic glue interface, please follow the steps below:

(1) Cut the glue as close as possible to the surface of the material.

(2) Remove the debris in the interface to a depth sufficient to place the new sealant and backing rod. There are several methods for removing, such as: brushing with a steel wire brush (using a motor or manual), abrasion, cutting or cleaning with solvent .

(3) Use oil-free and water-free compressed air (6. 0kg / ㎡) to blow off dust, loose substrate particles and other impurities. Sometimes a steel brush must be used for secondary brushing and high-pressure air blowing to ensure the cleanliness of the interface. The residue of the backing material originally left in the interface should also be cleaned up.

(4) After cleaning, the interface must be completely dry, dust-free and frost-free before applying glue.

(5) Attach masking tape.

(6) If you need to use primer, please apply primer before applying glue according to the method described above.

(7) Install the backing material to control the sealant to reach the designed depth.

(8) Continuously apply Ding sealant and fill it with the interface.

(9) Use a blunt, dry appliance to level the interface to make it slightly concave. The leveling work should be carried out immediately after the glue is applied, and the masking tape should be removed.

(10) Prepare small samples at the scene and check the adhesion effect of the glue after 7-21 days.

7. Removal and replacement of old silicone glue

A properly designed and applied silicone glue interface can last at least 20 years without any repairs. In some cases, when the interface is mechanically damaged or otherwise needs to be repaired

Please follow the steps below:

Assess the cause of interface failure:

(1) If the glue is cured normally and the weather resistance and waterproof performance are good, but the appearance is uneven due to incorrect leveling, then the surface of the sealant should be cleaned with a solvent and then repaired with new glue.

a) Use xylene and toluene to remove impurities and completely evaporate the solvent.

b) Cover the masking tape again.

c) Apply a thin layer of glue to cover the old glue.

d) Dry the surface.

e) Remove the masking tape.

(2) If the surface of the glue is cracked, or the above-mentioned shielding remedy does not improve the appearance of the interface. At this time, it is necessary to cut off the old glue and apply new glue.

a) Remove the old glue. If the old glue still has excellent adhesion to the substrate, the old glue can be kept no more than 2mm thick.

b) If the adhesion between the old glue and the substrate is poor, the old glue must be completely removed and the substrate must be cleaned again. (For example: cleaning with xylene, using appropriate primer, etc.)

c) Apply masking tape

d) Re-gluing (If re-gluing and tapping are not performed on the same day, cleaning work must be performed before re-gluing. If the substrate surface is cleaned with toluene / xylene)

e) Leveling interface

f) Remove masking tape

g) Check the adhesion of the glue after 7 days.