How to get mortar off off flagstone?

4 Comments on “How to get mortar off off flagstone?

  1. use a wire brush and a lot of water.

  2. The best way is to do it immediately before it dries with water. Failing that mechanical means are best. Stiff bristle brush (not wire can cause rust stains) chiseling off any chunks. After that your down to acid burning off the left over mortar stains. Always start with a weak dilution as the acid can be bad for the stones and increase the concentration by trial and error. There are many types of acid people use including hydroflouric, hydroclouric and muriatic. The best thing to do is go to your local masonry supply store and ask for a product designed for just such a purpose. Not home depot and the like but the place that contractors go to buy the bricks they’ll be able to give you the right stuff. Read the label its not to be fooled around with!

    Here’s an article you might find handy about cleaning methods.

  3. I agree with the mason about using a steel brush and going to a masonry supply store. However, be careful about using any type of acid. I’ve seen many times where the acid will burn the stone.

    There are products made by Prosoco that are a lot safer than acid. We use a product called 600 Detergent and it does a great job. You can go to their website to find the right product for you and see where to buy it.

    Great luck with your project and feel free to ask me any other questions about flagstone.

  4. It’s relatively easy to clean off excess mortar within twenty four hours, before it has had time to set up very much, using nothing more than water and a stiff nylon brush. A wire brush might scuff up the stone too much, leaving a much cleaner-looking spot.

    Mortar does not dry it cures. I am surprised a mason would use a term like dries. Mortar should be kept wet, as a matter of fact, for three days to a week after it is applied. This allows it to cure and become harder. Mortar achieves about 80% of its maximum strength after three days; if it dries out the curing process is killed.

    After twenty four hours the mortar is quite stiff, fairly hard, but it does not really have much strength at this point, so it is relatively easy to douse it with water and rub it off with a stiff nylon brush.