Getting cement stains off of composite decking
 

Hi, we had our chimney re-done(brick to stone), and the Mason did a beautiful job. However, he failed to properly shield our Trex composite deck so there are cement stains all over. We’ve tried various cleaners liked “wet and forget” and Valspar deck cleaner. We’ve obviously used a pressure washer too. Alas, none have worked!
Google didn’t provide any new insight so I turn to the collective mind of the forum for suggestions.
I tried to attach photo, not sure if it worked.

If it was me, I would try a wire brush and go with the grain. Unfortunately, it’s mortar. Has acids. Once you get off what you can with the brush you may test a latex exterior stain on those areas. Oh course, you match the stain to the deck.


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Found this on the web:

https://www.fiberondecking.com/blog/...osite-decking/

Also saw something about using Maria tic acid. If you have an extra piece of decking you can do a test to see if muriatic damages it.


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Mortar contains portland cement, and thus is alkaline, not acidic. So it does make sense that an acidic solution would react with it. Muriatic (hydrochloric) acid might do it, but even vinegar, a weak acetic acid solution, might work.
https://cretedefender.com/the-importance-of-ph/

Muriatic acid will definitely make it bubble and liquify. That is what the concrete companies use to clean the drums on concrete trucks. It works well and does not damage the paint on the trucks. The question is what it will do to the deck. Try it on a sample piece or the underside first.

When using it to clean I would start with a 10 parts water to 1 part muriatic acid and go from there


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