INTRODUCTION Adhesion is a complex event. The adhesion of silicone to most substrates relies on chemical compatibility, and similar surface energies. Do not take for granted that similar coatings will behave in the same way for example different colours of P.V.F2 have varying adhesion characteristics. In addition, batch variation of coatings can have a significant effect on the adhesion achieved.Routine adhesion testing, by our laboratory will establish the various properties of different substrates.

Correct surface preparation is critical too the success of any adhesive application. The surface preparation technique used needs to take into account the specific requirements of the substrate, the contaminant and the practicality of completing the task. Unless the surface is completely clean and dry the sealant will not adhere to the substrate, and a significant reduction in the weatherproofing properties and structural performance of the sealant will occur. There are three distinct types of substrate, each of which requires specific preparation techniques.
IT IS IMPORTANT THAT WHATEVER THE SUBSTRATE TYPE ALWAYS ENSURE THE SURFACES ARE DRY AND FREE FROM EXCESSIVE MOISTURE/FROSTIICE.
Do not prepare too far in advance, as the risk of dust, moisture or other contaminants depositing on the surface between the preparation of the surface and application of the sealant.

Impervious Substrates.
Common examples of these substrates are glass, anodised aluminium, polyester powder coated aluminium, and P.v.F.2 coated aluminium. With these substrates, the objective is to remove any dirt, grease or other contaminant. Pre-test the solvent to ensure it adequately cleans the substrate, without causing surface damage. These contaminants can come from manufacturing and handling processes, i.e. cutting and handling lubricants, grease from operators' hands or as residues from the coating processes.
The technique required to clean these substrates is the two-wipe technique. The materials required are a plentiful supply of clean rags, and solvent. The clean rags can be cloth or paper; provided they are absorbent, do not leave lint and are colour fast when soaked in solvent.
The technique is to:
1. Only clean a small area at a time.
2. Pour solvent onto a new clean cloth or paper towels. Ensure the cloth or towel is lint free and not dyed. Vigorously rub the substrate with the damp cloth. If the colour is transferring from the substrate to the cloth the solvent is damaging the substrate, therefore select another solvent.
4. Wipe the solvent off before it has evaporated with a second clean dry rag.
Discard both rags.
Repeat procedure on another section.

Do not
1. Do not dip the cloth into the solvent container, as this will allow contaminants to enter the solvent container. These will later smear onto the substrate during the cleaning process.
2. Do not wait for the solvent to dry before the second wipe. The solvent dissolves the contaminants and places them in suspension, if the solvent evaporates before the substrate has been wiped the contaminants are re-deposited onto the substrate, and will not be wiped off.
3. Do not use dirty rags, these will only spread the contaminants.

Always
1. Check to ensure that the solvent will dissolve the contaminants, as not all solvents work satisfactorily with all contaminants.
Check to ensure that the solvent is compatible with the substrate, as some solvents will deteriorate substrates.
Ensure the solvent is not injurious to the health of the tradesmen, and that the correct safety procedures are used.
The solvent supplier can supply the appropriate Material Safety Data Sheet

Solvent Selection
There are three considerations when selecting a solvent. Many solvents are harmful, ensure you refer to the manufacturer's Health and Safety Data Sheet before using a solvent. One solvent does not remove all surface contaminants; several may need to be trialed before the correct one is established. Test the solvent to ensure it does not damage the substrate.
Anodised Aluminium
This material is generally a very good substrate for Silicone Sealants. The exception is when a residue remains (typically nickel salt) from the anodising process. This residue is usually water soluble, testing to the manufacturers standard adhesion test will uncover this contamination. Priming the substrate usually treats this.

Polyester Powdercoat
Again, this is usually a very good substrate for silicone sealants. The exception occurs when the surface has excessive wax on it. To remove the wax, prepare the substrate using the two-wipe process, detailed above, with a solvent such as Prepsolve, following the manufacturers safety instructions.

PvP Paint Finish
This coating is developed as a non-stick coating. Some silicone sealants adhere very well, always check the adhesion before commencing the project. Prepare the surface using the two-wipe procedure.

MillFinish Aluminium
The surface of mill finish aluminium oxidises and turns to powder. Abrade mill finish surface with a belt sander to ensure the removal of all oxidised material from the surface. Dust surfaces and degrease using solvent wipe technique described earlier in this section.
Prime aluminium with Rhodorsil P4094A, as per the technique described in the relevant paragraph, following.

Porous Substrates
The surface must be sound, dry and free of contaminants. The objective with porous substrates is to ensure the removal of all contaminants such as form oils and curing agents, loose material and laitance. The substrate must be sufficiently cured and dry before sealant application. The only truly satisfactory way to achieve this is with vigorous mechanical abrasion, with a saw cut, wire
brush or drill attachment followed by dusting with oil free compressed air.

Typical Substrates
- Concrete
- Timber
- Cement Sheet
- Brick
- Stone

DO NOT USE SOLVENTS. Solvent will only thin any oils and grease, which will be smeared over the substrate and absorbed into it.
Either result will reduce the effectiveness of the adhesion of the silicone to the substrate.

Timber
Some timbers, such as Cedar and Maranti, have very high oil contents. The oil content can cause poor adhesion.

Stone Substrates
To minimise the chance of sealant staining stone substrates we strongly recommend the completion of stain tests on the substrate.
The stain tests are to be between the recommended sealant and a sample of the actual stone batch from the project. For major projects, where quarrying of the stone is likely to occur over a lengthy period we usually repeat the tests throughout the project. This is to ensure that variations in the stone from different parts of the quarry do not exhibit different properties, which could cause problems with the project.

The test procedure we use is ASTM D 2203-84. The design of this test is specifically for evaluating the potential of staining between natural stone and elastomeric sealants. The development is by an independent authority and is therefore unlikely to be accused of the bias that a 9.orporate lest Method of a sealant supplier could be, and it provides quantifiable results. As well, we often use our own C.T.M., however this is only used as a back up for internal use only.

Concrete Block and Cement Sheet
Both of these materials tend to have dusty surfaces and are very porous. Take particular care to ensure that they are dry and sound.

Plastic Substrates
Solvents usually adversely effected plastics. Therefore, take care in the handling and preparation of plastic substrates, to minimise the transference of contaminants onto the plastic. If de-greasing or cleaning is required the use of a mild solution of warm water and detergent is possible, however completely rinse this off with clean warm water. An alternate procedure is to use a 50:50 blend of IPA (Iso Propyl Alcohol and Water), applied using the same technique as recommended for impervious substrates. Before using detergent or solvent on the plastic, test compatibility of solvent to the plastic to ensure it does not damage the plastic.

Desian Evaluation Service
Termicide offers a free project evaluation service. With this service we review the sealant joint details employed in working drawings, to ensure that sealants of the correct movement capability and tensile strength are specified, and that the details do not incorporate risky details, such as three sided adhesion. The other essential element to the project evaluation service is adhesion testing;
Termicide can provide these in our Quality Control Laboratory. Following the evaluation we provide written reports detailing the results of the testing a commentary on the details employed and a sealant application specification.

APPLYING THE SEALANT
Firstly, cut the nozzle to the required width, so the tip of the nozzle reaches the bottom of the joint. Insert the nozzle into the joint, so that the tip of the nozzle is 2mm from the bottom of the joint. Gun the sealant into the joint so that the sealant overflows the joint. If the joint is wide place the sealant in two passes, firstly down one side of the joint, then down the other. When applying the sealant ensure that there are no air pockets left in the sealant. The cause of these could be changes in the pressure applied to the trigger of the cartridge gun or by variations in the speed at which the gun moves along the joint. Once the sealant is applied, remove the excess sealant, tool the sealant off and remove the masking tape. Carry out these three operations before the sealant has skinned. Refer to the product data sheet for information on skinning times of the various sealants.

CURING OF SEALANTS
Silicone cures by absorbing water vapour from the atmosphere. It cures from the
outside through to the inside, therefore the deeper the joint the longer the curing time. In addition, the cure rate slows as the cured portion moves deeper into the joint. To ensure that silicone cures it must have access to atmospheric moisture. In curing silicone sealant releases a by-product as a vapour. Therefore, we recommend curing the sealant in a well-ventilated space, particularly if the silicone is an acid cure system as the acetic acid released could irritate the eyes and nose of the people in close proximity.

Figure 1 Recommended Sealant Depth to Width Ratio	Figure 2 Fill the joint from the bottom to the top

MOVEMENT OF THE SUBSTRATES
Damage to the sealant will occur if the substrates move differentially to each other while the sealant is curing. The problems that can occur are air voids in the silicone, lack of contact between the sealant and the substrate or tearing of the sealant skin. If the sealant skin tears then this tear will continue through the body of the sealant. Therefore, minimise joint movement during the cure process.

CLEAN UP
The simplest way to clean up silicone sealant is before it has cured. To do this scrape off the bulk of the excess silicone, being careful not to spread the silicone or scratch the substrate. Then use a rag moistened with methylated spirits to wipe the excess up. (Note if concemed about the methylated spirits damaging the substrate test it first on a spare piece of the substrate). If the silicone has cured, cut as much of the silicone off as possible. Then mechanically abrade the balance of the silicone off. Take great care of this method will lead to damage to the substrate.

TYPE OF CURE
During the curing process silicones release a by-product, as a vapour. When specifying a sealant take care to ensure that the by-product is compatible with the substrate. For example, acetoxy cure silicones are incompatible with coated steel.

BACKING MATERIALS
Backing materials are important to control the depth of the sealant, and to avoid three-sided adhesion. For specific details regarding the requirements for backing rods, refer to the Sealant Selection and Design of the Joint Technical Data Sheet. SEALANT MUST BE APPLIED TO THE FULL DEPTH OF THE JOINT Sealants are most effective when they have a strong adhesive bond to the edge of the joint. To achieve the best possible bond to the substrate the sealant must have adequate contact, or WETTING OUT, of the substrates. Because of the highly viscous nature of sealants if applied to a joint without a back-up material, it will tend to be extremely convex, and not have sufficient contact to the sealant wall, i.e. fig. 3. However, if a back-up material is used the sealant
will flow down to the back-up material, and then flow across to the edge of the joint. Using this method described the sealant will better wet out the substrate, therefore offering a much more effective seal. The use of backer rod assists greatly in the gauging of the correct depth of sealant.
Figure 3 the incorporation of a backing rod aids in wetting out the substrate I

ADHESION
Silicones generally have good adhesion to various substrates. Where adhesion is critical to the success of a project, Rhodia will carry out adhesion tests. We strongly recommend this service for structural applications where variations in substrates can have serious consequences.

TOOLING
Tool all sealants into place. This action forces the sealant into the joint and assists the sealant to "wet out" the sides of the joint. The tooling action should positively force the sealant into the joint; therefore, apply downward pressure to the sealant. It is not just the process of lifting excess sealant off the joint.

MASKING TAPE
To provide a neat and tidy joint, and to protect the finishes adjacent to the sealant, mask the edges of the joint. Remove the masking tape immediately after tooling the sealant. If the sealant skins before removing the masking tape, it will leave a ragged edge.

Trafficked Areas
Sealant with a higher Shore A Hardness is recommended for paved areas subjected to traffic. Shore 'A' hardness is a penetrometer test that determines the resistance of a sealant to penetration.