The Damp Buster is reader supported. When you buy after clicking a link on our site, we may earn an affiliate commission.
Does chemical damp proofing work? In this article we will discuss whether a chemical DPC is a good solution and when you shold use it.
Damp proof courses are an important feature in properties. They create a waterproof barrier just above the outside ground level of a property.
The goal of your damp proof course (or DPC) is to stop moisture from rising from the ground and into your property. It is usually placed at around 150mm above outside ground level. This is commonly in the mortar joint above the second course of bricks.
Having a DPC placed in new properties, was first made mandatory in the 1870’s in London. Following this it became a regulation for all new build properties in the UK.
The most common materials used in the late 1800’s and early 1900’s, were less porous building materials such as slate.
Following this, other materials were used such as bitumen. In more recent years new build properties are installed with a plastic DPC. This is usually made of a material such as low-density polyethylene
The most recent type of damp proof course to come on the market is a chemical DPC.
This is not used during the construction phase. Instead, it is a convenient way of replacing or repairing an old damp proof course.
If you are replacing or adding a new damp proof course, then chemical damp proofing can be a good option. It is much easier to install. Especially compared with the alternative of replacing the original DPC.
This is because chemical DPC’s are injected into the mortar, via drilled holes. Replacing the original is a much more complex job, which involves structural work to the property.
But does chemical damp proofing work?
Chemical damp proofing can be extremely effective when installed correctly. The DPC is injected into the mortar bed, at intervals of 100-150mm. This is usually a silicone based formula, which fills the pours in the mortar to create a completely waterproof barrier.
Once the injection has completely gone off, it should provide an effective damp proof course for at least 20 years.
Most companies that install chemical DPC’s will even offer a guarantee of 20 years. This is because they are confident the DPC will not fail before the guarantee period ends.
The same is true for most DIY damp proof injection kits. These are kits that can be bought online and at most good builder’s merchants.
In recent years, the quality of these kits has really improved. So, this is a viable option if you are reasonably competent at DIY.
When should you use a chemical DPC?
A chemical DPC is often installed, following the discovery of rising damp in a property. This could be the result of a failed damp proof course. Or in some cases, where the property was build pre-1870’s, a DPC may not already exist.
Rising damp will be visible near ground level. This is usually seen above skirting boards, up to around 1.2m. At this point gravity usually stops the damp from rising any higher.
It will often look like tide marks and there may be a white residue left on the internal walls of your property. These white marks are a sign of hygroscopic salts, that have been drawn from the ground and brickwork.
If you are seeing these types of damp symptoms, there is a reasonable chance you are having an issue with rising damp. However, it is important to point out that rising damp is one of the most mis diagnosed forms of damp.
You should always rule out other potential causes before you assume it is rising damp.
Most common mis-diagnosis
The most common mis-diagnosis would be for penetrating damp and possibly a form of cavity bridging.
To rule out penetrating damp, you will need to carry out an inspection. The goal of this is to try and identify any possible causes for the damp you are seeing internally.
Firstly, you should examine the outside wall adjacent to the damp inside. Here you need to look for any obvious damage or defects.
Defects could include damage, or wear and tear to bricks and the mortar (pointing). It could also be damage to any existing render, which has been applied to the outside of the property.
You should also look around and above the area. There is a chance that water is entering via a defect elsewhere, then moving down the internal cavity wall. This could then be bridging across and into the property where the damp is present.
If you manage to rule out any external issues, then there is a good chance that your DPC has failed and it needs replacing.
What if you are not sure?
If you are not 100% sure, it might be a good idea to have a professional damp proofing expert look at the issue. Because you have already identified the problem, this will not require a full damp survey.
You can usually have a damp expert come out for a free inspection, or a small call out charge.
If you do decide to go down this route, we highly recommend using a comparison site to find the best damp proofing company locally. One of the best online comparison websites is Bark.
Bark will put you in touch with up to 5 local damp companies. Plus, they will all have profiles on the comparison site, which makes it easy to find the best professional. You can see all their qualifications and reviews via their online profile. So, you know you are hiring a trusted professional.
The vast majority will come and assess your job for free, so if you are in any doubt it is worth having an expert check.
Will chemical damp proofing work for penetrating damp?
If you have found external defects and have ruled out rising damp, you will still need to repair the problem, to stop penetrating damp.
So, does chemical damp proofing work for penetrating damp? The simple answer to this is no, it will not stop penetrating damp.
Firstly, it is likely penetrating damp is above the DPC.
Secondly, even if it were below the DPC, there would still need to be an issue with the DPC for the damp to rise. If this were the case, you would still need to replace your damp proof course, as well as repair the external defect.
Basically, a chemical DPC is designed for a very specific damp problem (rising damp). If rising damp is not the issue, then you will need another solution to solve your damp issue.
You can learn more about penetrating damp and potential solutions by clicking here.
Chemical DPC – DIY vs professional
Does chemical damp proofing work best when done by a professional? or is DIY the best option?
The truth is both can work very well. The process just involves drilling holes and injecting the chemical cream. Most good DIY kits come with step by step instructions, so it is relatively straight forward.
If you are a keen DIY’er, you can read more about our favourite DIY chemical DPC kits by clicking here.
If you are less confident doing the job yourself. Or if you don’t have the tools required, such as a good drill, you may want to hire a professional.
Again, for this we would recommend getting quotes from multiple local companies.
It might even be worth getting the quotes and comparing the price of doing the job DIY.
You may find that the overall cost is similar. In this case, you might be better off hiring the professional to do the work for you.
The other advantage with hiring a professional, is they will usually guarantee the work. This could be for up to 20 years. So, if you have any issue, they will need to come out and fix it. This is a luxury you won’t get going down the DIY route.
Basically, the DIY or professional route are both viable options. Your choice will depend on your situation and your level of DIY confidence.
There is no right or wrong answer here. Just be aware that you will have better guarantees with a professional. Plus, they have experience in doing this type of job correctly.
To conclude, chemical damp proofing can work very well when it is used for the right job.
It is a good alternative to replacing a standard DPC. Due to the ease of application it tends to be cheaper, easier and causes much less disruption compared with the alternative.
Whether you do the work yourself, or hire a professional, a chemical DPC should provide good protection against rising damp for many years.