Hi, I hired someone semi-skilled (first mistake, I guess) to apply new grout (concrete/sand mix) in between the slate on my outside patio, since the old materials were loose and missing. He finished a few weeks ago, but left a concrete film over most of the slate. He said to let it dry a few weeks and then to power wash the concrete clean. Well I have tried to power wash it, but the concrete is too thick in most areas for the power washer to remove. Any suggestions on how to remove the concrete so I can see the slate again? Thank you.
Jake Johnson
Removing excess concrete from stone
-
84-1093879891
If this is genuine slate, as we in Britain and Ireland think of slate, ie; a fine-grained rock with plate-like mica and chlorite crystals in parallel orientation formed by low grade metamorphic action on mudstones or siltstones (is my 4 years spent studying geology beginning to show??), then you should be able to clean off the cement film using an acid-based cleaner. In Europe we call it Hydrochloric acid, but in your country, for some strange reason, it's known as Muriatic acid. We can buy it at molar concentrations designed to be used for cleaning cement - we call it "Brick Cleaning Acid". I don't know if there's a similar product in the States.
However, if you actually mean a slate-like stone, than may be a mudstone, sandstone, gritstone or similar, then you need to be very, very careful using an acid cleaner, as it may react adversely with any iron content on the rock. Best to test a discreet corner first - leave it 24 hours to see if there's any reaction before treating the rest of the pavement.
However, if you actually mean a slate-like stone, than may be a mudstone, sandstone, gritstone or similar, then you need to be very, very careful using an acid cleaner, as it may react adversely with any iron content on the rock. Best to test a discreet corner first - leave it 24 hours to see if there's any reaction before treating the rest of the pavement.
-
Jake Johnson
- Posts: 2
- Joined: Tue Jun 22, 2004 1:48 am