THE CONCRETE SURGERY
How to acid wash pattern imprinted concrete – Step by step process
Dr. Concrete, PICS UK.
29th AUGUST 2018
Wash off the Release Agent as normal, using Release Agent Wash and a water jet, until the water runs clear.
Prior to applying Acid Wash:
- Ensure the paving is TOTALLY saturated with water (no more water will soak in).
- Ensure the paving is ‘water rich’. In other words, that there are puddles of water in all the deeper parts of the pattern and texture.
- Always apply acid with an all plastic sprayer. Never use a bucket and brush / broom.
- Always apply acid carefully / sparingly / a small amount. Acid can always be reapplied; however it is not possible to mend the PIC if it is damaged by the acid.
- It does not matter if the acid is left on for one minute or one day. Once it has reacted it becomes neutral. Therefore there is no rush to wash it off.
- After applying acid, always wash off the surface with a high pressure water jet. Do not use a hosepipe as this will not be powerful enough to remove the weakened concrete surface.
- Apply acid again (and again) if /as required.
- The aim is to ensure that there is no residual RA left on the top wearing surface of the paving, as this will act as a debond and the sealer may delaminate and fail.
- The antiquing effect will remain in the deeper parts of the pattern, where there were puddles of water, as the acid will have been diluted and have little or no effect in these areas.
- If it is only necessary to apply acid once to the paving, it indicates that possibly too much acid was applied in the first instance and therefore the acid may have nearly damaged the CSH. If the acid needs to be applied 2 or 3 times, it indicates that is was applied very carefully and sparingly and it is unlikely to damage the CSH.
- Remember, if you wash off after 2 days you are more likely to damage the CSH with the water jet and / or acid. If you leave the paving for 4 or more days you will be less likely to damage the paving with the water jet and / or acid.
- If you haven’t used Acid Wash before, lay 2 or 3m2at 25mm thick on some polythene next to the job you are doing. You can test the acid washing off on this, prior to washing the main job.
If in any doubt at all, call the PICS Technical Department.
Red Shute Hill Industrial Estate