Why does concrete need to be acid washed?
The acid washing of concrete is a requirement after the concrete has cured sufficiently, in order to remove surface efflorescence and to open the pores before sealing. This will help the sealer to penetrate and result in a superior bond between the sealer and the surface. Floors that are acid washed before sealing will have greater colour enhancement and will appear darker than floors that have not been acid washed.
Acid washing is a critical process and should be approached with care and carried out in a controlled way. The correct protective clothing and safety gear should be worn whilst acid washing.
HOW TO ACID WASH
See below Acid to Water mixing ratios. Acid should never be applied without being diluted with water first.
All concrete to be acid washed must be free of any previous sealer or paint treatments, oil, grass, overhanging plants, leaves, soil etc.
Prior to acid washing, the concrete should be thoroughly saturated using a hose or watering can. Ensure that the acid solution is poured on wet surfaces only. If the concrete dries during the acid washing process, it should be wet again before applying acid to the surface.
The acid washing process is better managed with the Involvement of two people. Whilst one person pours the acid solution out of the watering can, the second person brooms the surface in a circular motion to spread the acid whilst it is reacting with the surface. A bubbling/foaming reaction is evidence of the reaction between the acid and the concrete surface and no
areas should be missed, ensuring that the reaction is visible over the entire surface. Avoid walking on areas that have been worked already. The acid stops reacting with the concrete after approximately 30 seconds so there is no need to scrub the surfaces for too long.
On completion of the acid washing and before the reacted acid is allowed to dry, the area should be flushed well with water, ensuring that all the neutralised acid is removed from the surface.
CONCRETE SHOULD BE 100% DRY BEFORE SEALING
| Type of Concrete | Acid to water ratio | Coverage per 1ltr Acid |
| Exposed Plain Concrete | 1 part Acid to 6 parts Water | 10m2 |
| Exposed Coloured Concrete | 1 part Acid to 14 parts Water | 20m2 |
| Broom or Textured Coloured Concrete | 1 part Acid to 12 parts Water | 30m2 |
| Hard Trowelled Coloured Concrete | 1 part Acid to 10 parts Water | 15m2 |
| Concrete Floors after 3 month | 1 part Acid to 12 parts Water | 30m2 |
Hi, what sort of acid does this guide apply for?
Thanks
Hi Jon,
Thanks for your comment. This guide is for 33% Hydrochloric Acid, we have this available for purchase if you require.
Thanks, the team at Permacolour.
Should I apply a second coat of sealer?
Hi Brent,
We generally recommend 2 coats of sealer are applied when you are initially sealing with the first coat thinned down, however if you are resealing only 1 coat un-thinned is required. Please call us if you have any further questions 0508 444 555.
Thanks, the team at Permacolour.