Our technical team frequently get reports of customers looking to remove a whitish residue from substrates such as brickwork, concrete or floor tiles. If you have noticed construction looking like the below pictures, you may have come across laitance or efflorescence.
We would like to explain the differences between the substances to help our customers understand how to prevent or remove the issue quickly and easily.
Laitance vs Efflorescence
Laitance and efflorescence look quite similar are actually really two completely different things. Both are white, powdery residues, which can be confusing to contractors when identifying solutions when they occur.
In short terms, laitance forms when there’s too much water in a concrete mix. Soluble salts in the bricks or the mortar causes efflorescence.
Both laitance and efflorescence can present both cosmetic and structural problems.
How To Prevent Laitance
In general, the word laitance is used to identify a thin, flaky layer of hardened but weak hydrated cement and fine sand which began life as a milky scum on the top surface of concrete.
Laitance can be avoided by controlling the amount of water in the concrete mix during construction. If too much water is introduced into the concrete various other issues can occur such as greater shrinkage with the possibility for more cracks and reduced compressive strength overall.
As you increase the amount of water in a mix, you also increase the porosity of the hardened concrete. Many more canals are formed as water migrates to the top of a slab. Increased porosity also results in more efflorescence, causing the colour of the surface to be whitish.
How To Remove Laitance
Thankfully, laitance is relatively easy to remove. Promain provide a range of acid etching solutions suitable for the removal of surface salting:
Some etching products require dilution – check data sheets prior to application.
It is important to keep the concrete wet while your acid etch works. While the product is working, you will find that the acid fizzes as it fights the salts. Due to the nature of acid etching, it is important to work in a well ventilated area and to wear appropriate protective clothing. Once the acid etch has worked, wash the concrete thoroughly with copious amounts of clean water. If the work will be done inside, you should allow for drainage. It is best for you to check data sheets, but usually the solution mixed with the water can go down standard drains.
For areas larger than 100m2, we recommend the use of a mechanical device such as a diamond grinder. This is the preferred preparation prior to application of an epoxy floor paint.
How To Prevent Efflorescence
As efflorescence is a natural occurrence, it is difficult to prevent it completely from happening.
However, during construction of brickwork you can prevent efflorescence or at least minimize it. This can be done by selecting materials free of harmful salts and by preventing water from penetrating the masonry. This may be accomplished by the use of good solid, tight mortar joints, capped walls and effective flashing.
You can also prevent it by the use of adequate weather protection of the masonry, such as an appropriate paint or sealer.
To find out which paints and sealers would be suitable to prevent efflorescence on brickwork, it is best to contact our technical team to discuss your individual requirements.
How To Remove Efflorescence
Thankfully, efflorescence is also easy to remove. Promain provide a range of phosphoric acid solutions suitable for the neutralisation of salt:
You should protect all items you do not require to treat carefully. Using a low pressure sprayer, spray the surface with the acid etch as per the manufacturer’s instructions. Depending on the intensity of the efflorescence, you may require a repeat of the treatment. As with laitance, rinse off the solution thoroughly with copious amounts of water.
Do you require further information in regards laitance or efflorescence and its effects? Please contact our technical team via the contact page, or call us on 01462 421333.