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Surface Preparation - To Over-Coat or Not to Over-Coat

By Jack Josephsen

There’s a job coming up with an existing floor coating and the client would prefer to over-coat rather than remove to save money. What do you do?

There’s no right or wrong answer to the question, just risks you need to weigh up in deciding to over-coat or not.

The over-coat risk checklist

Here's the checklist I use when deciding to over-coat:

  1. Do you know what the existing coating is? Is it a two-pack or single-pack coating? If you put a little bit of solvent on it does it bubble or wrinkle? If it doesn’t handle solvent well then it’s probably a single-pack coating, which means you shouldn’t waste your time over-coating with the much stronger two-pack.

  2. Is the existing floor coating stuck down well or flaky? If it’s flaky then remove it. Over-coating a flaky coating could end up with both peeling off.

  3. Is the existing coating stained, meaning that contamination has absorbed into the coating? This is not a good sign and if the stain is oil based then I’d remove the existing film or to eliminate the risk of coating delamination.

  4. Is the existing coating bonded well, but badly worn? This is one of those 50/50 scenarios where some will err on the side of caution and just remove it while others will over-coat.

  5. Is the new floor coating subject to harsh conditions, either through chemical exposure or temperature fluctuations? If so then I’d want to ensure it had the best possible chance of withstanding the conditions by bonding it directly to the substrate.

  6. Does the new coating wet out the existing coating? For example, if you do a small test patch does the coating flow nicely, or does it crawl and cause surface defects? Obviously this sort of incompatibility means the existing coating would need to be removed.

  7. If it’s a large project and you’re completely unsure on over-coating, can you do a small trial? That is, apply the coating as you intend to on a larger scale to see if it all works.

  8. A practical consideration is: can you even remove the existing coating within the shutdown period? Not every coating grinds off easily and this may override all other considerations.

A flaking floor in a garage that would need to be removed rather than over-coated.

Involve the client

If you choose to over-coat at the end of the day, be sure to educate the client on what you are doing and any risks that might be involved. Be open and honest, so they can participate in the decision-making process. I’d much prefer the client tell me they’re prepared to take the risk than wear all the responsibility myself. Overall, if there’s too much doubt around over-coating then you’re much better off to remove the existing floor coating regardless of what the client says. If you lose the job because you’re now too expensive then so be it. You never make money when you have to re-do a job anyway!

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