DOWSIL™ Silicone Sealants – Frequently Asked Questions

Here are answers to some of the most frequently asked questions we have received about DOWSIL™ and XIAMETER™ silicone sealants. Please note that as the conditions and methods of use of our products are beyond our control, this information should not be used as a substitute for customer testing to ensure that the products are safe and effective. should not be used as a substitute for customer testing to ensure that the products are safe, effective and fully satisfactory for the intended end use. intended end use

What methods can be used to promote membership?

 

Cleaning: Use of appropriate solvent and wiping with two wipes is recommended.
Chemical methods: Primers
Surface energy modification: Corona discharge treatment, plasma treatment, flame treatment
Physical methods: Abrasion on some surfaces (roughening of the surface to increase the adhesion surface)

 

How should the primer be applied?

 

Dow offers a special primer that should be applied in a very thin layer or one coat to promote maximum adhesion. Open the container and pour a small amount onto a clean, lint-free wipe and wipe over the surface to be treated. Allow the primer to dry and react on the surface for 30 minutes. If a white powder forms, it should be wiped off with a clean, dry, lint-free cloth.
A properly applied primer should form a clear (single layer) coat on the surface without any excess. Remember that this one-coat primer will react and form a bond with the surface. Allow the primer to dry and cure for 60-90 minutes before applying the sealant. Always read the product instructions for more details and always reseal the container when not in use to ensure continued quality.

 

Can the primer be used instead of cleaning the substrate?

 

No, the surface must always be properly cleaned, regardless of the use of a primer.

 

The distributed primary seems cloudy and white, is there a problem?

 

Yes, if it is cloudy, it should be thrown away. Open containers will eventually react with moisture in the air and become cloudy.
Always use a fresh, clear primer.

 

How do you prepare the substrate surfaces before applying the sealant (or primer)?

 

Most substrate surfaces should be cleaned using the recommended two-wipe solvent cleaning method to achieve a clean, oil-free and dry surface. For difficult to bond surfaces, adhesion can be improved by using a primer. Some surfaces may need to be abraded to remove embedded dirt, but take care not to damage the surface. Check with the substrate supplier.

Is the use of a puttying tool recommended?

 

Yes, the use of a tool is always recommended to coat or wet the surface of the substrate, which is necessary to promote maximum adhesion. The usual procedure is to properly fill the joint and then apply the sealant dry by pressing and pulling a round-tipped spatula across the sealant surface. This step forces the sealant into the joint surfaces and helps eliminate air pockets or voids at the bond line. Some use a rubber glove and work the joint with their finger. Others use tongue depressors or similar tools.

 

What is a formed-in-place gasket (FIPG)?

 

FIPG materials are applied to a surface and assembled to the corresponding part while the sealant is still wet. After a sufficient curing period, the sealant relies on the adhesion of the material to both parts of the assembly to ensure a seal.

 

Can DOWSIL™ silicone sealants/adhesives be used underwater?

 

We do not recommend our silicone sealants/adhesives for continuous use under water.

 

Do our sealants adhere to bondable plastics such as polyethylene, polypropylene, urethane, acrylic or PTFE?

 

Usually, no, silicone sealants do not adhere to these substrates. However, the use of one or more adhesion enhancing techniques: chemical treatment, surface roughening, etc. may help. Always bear in mind that even if they do not have great adhesive strength on these substrates, the adhesion may be sufficient for a particular application. Test the silicone sealant in your application before using it.

 

Do silicones break down under UV light and ozone?

 

Silicones in general show high UV and ozone stability.

 

Will silicone sealants affect the surfaces to be painted?

 

If possible, you should always prepaint the surface before applying a silicone sealant. Painting problems can occur if there is direct contact with the silicone. Use our DOWSIL™ OS-2 Silicone Cleaner and Solvent to clean up any uncured residue and test with paint to verify effectiveness. Most paints will not generally adhere to silicone sealants/adhesives, so it is recommended to avoid contact with the surfaces to be painted.

 

Would you recommend DOWSIL™ 732 multipurpose filler or any other acetoxy curing filler for use with concrete?

 

No because the curing of DOWSIL™ 732 Multi-Purpose Sealant induces the release of acetic acid (low pH) and masonry applications are basic (high pH). The acid/base reaction forms salts, which will prevent adhesion between DOWSIL™ 732 Multi-Purpose Sealant and concrete.

 

Is there a sealant that can withstand higher temperatures than normal silicones?

 

DOWSIL™ 732 Multipurpose Sealant can tolerate intermittent temperatures up to 200°C. DOWSIL™ 736 Heat Resistant Sealant tolerates intermittent temperatures up to 300°C.

 

How can I remove a hardened sealant?

 

Cured silicone can be removed from a surface with a sharp blade if the cured silicone is accessible. If it is difficult to cut, solvents can be used that will soften the cured sealant and make it easier to cut.
Solvents that can soften cured silicone would be isopropanol (IPA), toluene, xylene, naphtha or mineral spirits. DOWSIL™ OS fluids can also be used to help soften cured silicone and/or remove silicone residue after it has been mechanically removed from a surface. DOWSIL™ OS fluids will generally be a lower VOC option than standard solvents as well.

How long do silicone sealants last outdoors?

 

Will they become fragile?
In general, silicone sealants remain flexible and retain their performance properties (durometer, tensile, elongation and modulus) when applied in accordance with Dow’s general requirements.

 

Can cured silicone sealants be yellowed?

 

Most do not yellow. Some oxime sealants, which contain amines, do yellow and should not be used in areas where yellowing will be visible. Sometimes other sealants can be discoloured by the hard coatings used on plastics. Some rubbers contain plasticisers which can leach out and discolour adjacent light coloured sealants.

 

Can sealants be used after their use-by date?

 

We do not recommend using our products beyond their useful life.

 

Can your sealants be diluted for spraying or dipping?

 

In general, you can dilute sealants with DOWSIL™ OS fluids or naptha. DOWSIL™ 236 Dispersion is a dispersed sealant.

Can silicone sealants be exposed to aggressive chemicals?

 

Total immersion with aggressive chemicals such as strong acids, bases, solvents and fuels is not recommended for most silicone sealants.
However, splash contact is generally tolerated, even with aggressive chemicals. Again, test for appropriate performance in your application. Try DOWSIL™ 730 FS solvent resistant sealant for most applications. Be sure to test it for suitability in your application.

More info
Would you like more information on the entire Dowsil product range? Contact our technical department by telephone on 04 26 680 680 or fill in our contact form. Download our documentation dedicated to electronic protection:
PDF
Documentation
Silicone sealant selection guide (french version)
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