What is lime bloom and how can you get rid of it?

Lime bloom on brickwork

When refurbishing the façade of a residential, commercial or industrial building, or applying render onto a new build project, obtaining the perfect finish will not only satisfy your customers but will also fill you with a sense of pride. In some cases, lime bloom may stop your render from looking as sleek as you had hoped, but worry not – there are a number of solutions for this issue.

In this blog, we discuss the effects of lime bloom and how to get rid of it.

What is lime bloom?

You may be wondering what lime bloom actually is, luckily, we have all of the answers. Lime bloom — also known as efflorescence — is a natural phenomenon, and while it’s unsightly, it’s usually nothing to be concerned about and doesn't have a detrimental impact on the render itself.

Although it's reassuring to know lime bloom may not damage your work, in many cases it will affect the appearance of a building which is why efflorescence is a problem.

What does lime bloom look like?

Lime bloom appears as a general lightening or discolouration on coloured cement-based products that are otherwise sound and fully cured. It doesn’t result from a fault with the product, but rather from the intolerance of cement to certain conditions during its early stage of hydration. It can occur when rendered elevations are subjected to damp conditions and/or low temperatures during early curing, saturated backgrounds, or excessive moisture in the atmosphere (such as rainfall during or soon after application).

Whilst the resulting thin film of lime doesn't affect the integrity of the render, it can be unsightly. With this in mind, you may want to know how to remove efflorescence. 

How to detect lime bloom

If you are at all unsure of whether or not the substance that you are dealing with is lime bloom, there are ways of checking so that you can be certain. A simple way to determine whether or not lime bloom is the culprit is to dampen the surface with water. If it disappears and the colour of the render unifies to what it should be, and reappears patchy when dry, it is more than likely lime bloom. From this, you can tackle the subject of how to remove efflorescence and help clear up the problem in an attempt to get the building back to looking as good as new.

How to remove efflorescence with a mild hydrochloric acid cleaner

Providing the building is exposed to the elements, lime bloom will weather away naturally by itself over time, however, the owner of the building may not be so patient. You can speed up the process by washing the affected area with a mild hydrochloric acid cleaner.

We suggest that you use a product with a strength of between 16% and 20%. You may need to apply more than one application in some extreme cases of lime bloom increasing the strength of the acid mixture slightly, however, you should limit the applications to 2-3 maximum as to not have an effect on the surface of the render.

Please note: Before applying to a large area, the wash should be patch tested on an inconspicuous spot to make sure it’s suitable. Start with a dilution of 1-part clean water to 1-part hydrochloric solution and increase the strength if needed depending on the severity of the lime bloom.  It is also important to note that the surrounding areas should be protected before applying this solution as it can be corrosive to a range of metals including aluminium, chrome, copper, stainless steel and galvanised enamel. It may also mark materials such as paint, leather and laminates.

Step-by-step guide

Dampen down or soak the area to be treated with clean water to avoid the acid cleaner being drawn into the surface of the render.

Use a non-wire brush to apply the cleaner over the whole of the affected area. If you’re working with a vertical surface, work from the bottom up.

Allow the cleaner to work for 10 minutes.

Thoroughly rinse off with water, using a jet washer on the fan setting, at a strength of no higher than 60 bar, working from the top down.

In a few cases, after an acid wash the render still remains stained from weather damage. Providing the integrity of the render has not been affected, then decoration with a product such as webersil P silicone paint can be considered as a way of unifying the colour again.

Stay safe

When using acid-based cleaners, it’s important to follow the health and safety advice provided by the manufacturer.

At Weber, we care, and we’ll be more than happy to advise you on how best to deal with lime bloom. Please feel free to get in touch with us:

We’re available Monday to Friday, 8:00am until 5pm.

Click Compare to help you choose the right product for your project, if you need further assistance please email technical@netweber.co.uk