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Michael’s Mythbuster: Beware! The wrong pre-cleaner can affect silicone adhesion

Wednesday, 29 March 2017

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When preparing a surface for silicone work, the products you use for pre-cleaning can do more harm than good.

The adhesion of silicone on different substrates can vary greatly, and while the correct silicone should be the primary consideration – correct cleaning is vital to ensure your surface is in optimum condition to support silicone adhesion and final finishing.

Methylated spirits is the most common culprit! Methylated spirits will assist in the removal dirt grease and other contaminates from the surface, however in its process of breaking down these properties it leaves a residue on the surface which affects silicone adhesion.

Dow Corning guidelines recommend the use of solvents such as white spirits as a final clean to remove any by-products of previous cleaning agents on all substrates to ensure no contamination is present before commencing silicone works. See our range of white spirits here.

In most cases this will be sufficient to achieve a chemical bond and good adhesion. However, on some surfaces and structural joints (including single and two part silicones) the use of Dow Corning 1200 OS primer is a must – available here. The GCS team are always happy to provide more advice depending on your needs, contact us to discuss.

General recommendations are:

For non-porous surfaces such as glass and coated aluminium:

- Solvent wipe the joint surfaces using a non-oily solvent such as methyl ethyl ketone, white spirits or isoprop on a clean white lint-free cloth to remove any oils and contaminants.

- Immediately wipe with a second dry cloth to remove any traces of solvent and contamination.

For porous surfaces such as concrete:

- Wire brush or abrade the surfaces to remove loose debris, old paint and other contaminants.

- Remove dust with an oil-free compressed air blast and/or high pressure water blast.

- Allow to dry before sealing. If necessary solvent wash and allow to dry.

Priming:

A DOW CORNING® primer may be needed for optimum adhesion to some substrates based on testing conducted by the end user. Information on Dow Corning Primers is available on request from Dow Corning.

(Source: Dow Corning)

Remember - Primers aren’t cleaners and cleaners aren’t primers. There is a difference!

Do you want more tips like this? Express your interest in our training workshops on silicones and sealants by contacting us.

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