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Damp can cause a variety of problems in your home. Most will be cosmetic issues, but when left long enough more serious issues can occur.
For most people who have a damp problem in their home, it will usually affect their internal decorations. This will include things like:
- Peeling wallpaper
- Flaking and bubbling paint
- Damage to internal woodwork, such as skirting and architraves
- Mould growth
- And damage to internal plaster work.
When your home is suffering with penetrating or rising damp, the water travels through the masonry to enter your property. The first material it will meet is your internal plaster.
When damp seeps through your plaster it can cause it to deteriorate over time. This can cause the plaster to blow, crack and crumble. The main reason for plaster blowing, is that it has lost adhesion to the surface it was applied to.
How the surface can affect plaster blowing
When plaster is applied, it uses suction to stick to the wall or ceiling as it dries. This relies on the pours in the surface. Obviously, some surfaces offer more suction than others.
High suction surfaces
High suction surfaces are great for plastering, as the wall provides a great deal of suction to hold the plaster on the wall. However, they can still result in plaster blowing because of damp. There are also other reasons your plaster could blow on very porous surfaces.
If you are plastering onto a high suction surface, this can sometimes cause problems. The main reason for this, is this type of surface can pull moisture from the plaster too quickly. This means, as it dries, it doesn’t get a good grip on the wall, which can cause the plaster to blow.
In the case of a high suction surface, the solution is to dampen the wall before plastering. This will prevent the moisture being sucked from the plaster.
Because the surface is high suction, this will provide an extremely strong finished plaster. One of the only things that can cause problems after this point, is damp penetrating from outside.
Due to the wall already being very porous, if there are defects allowing water in, this can result in damp plaster. At this point, it is possible the plaster could lose adhesion and come away from the wall.
Older properties tend to use more porous materials. The houses themselves were designed to be breathable. If this is the case, you could consider using a lime plaster, to allow the walls to breathe. This could prevent your plaster blowing.
However, if the damp is serious, it can still cause the lime plaster to deteriorate over time. Eventually, this will lead to the lime plaster blowing and coming away from the wall.
Also, the application of lime plaster is a specialist job, and you will need to find someone qualified to carry out the work.
Low suction surfaces
A low suction surface can also be affected by damp. But the walls are less porous and penetrating damp is usually less of an issue. However, it is still a possibility.
If there is a defect outside allowing a lot of water in, it is possible that damp will still get through.
In theory, due to less suction with smaller, and fewer pores, this could result in more pressure applied on the back of the finished plaster.
Also, because the wall is lower suction, the plaster may not have adhered as well.
Combine these two factors and this could cause the plaster to blow.
However, the main reason for plaster blowing on low suction surfaces, is poor adhesion. This is almost always a result of bad preparation.
If the wall is not prepared prior to plastering, then the plaster will not grip the surface and will easily blow and fall away.
To avoid this, you need to make sure the plaster can get a good key (grip) to the wall. To do this you will need to make sure the surface is completely clean and clear of any dust and debris.
Next you will need to apply a bonding agent to help the plaster adhere to the surface. Common options are PVA, SBR, or for extremely low suction and smooth surfaces, something like blue grit can be used.
What if damp is the cause of your plaster blowing?
If you have identified damp as the main cause of your plaster blowing, then there are steps you can take to resolve the issue.
Firstly, you should locate and repair the damp problem. Don’t even consider re-plastering until this problem is completely solved.
You may even need to wait longer, to allow the wall to properly dry before new plaster is applied.
Once you are confident that there is no risk of this damp problem resurfacing, you will need to remove the affected plaster. This could involve removing a small, isolated area of plaster, or in some cases it may all need to come off.
For isolated patches, remove all plaster until you reach a point where there is solid adhesion to the wall. Once this has been done, you can patch the area, and in many less serious cases this will be sufficient.
However, you should also check for other areas that might have blown. Simply tap on the wall, if there are areas that sound hollow, this is a clear indication of blown plaster. The amount you remove will depend on the scale of the issue.
If there are multiple areas that seem to be blown, you may be better removing it all and fully re-plastering.
Also, areas that are damp but not blown should also be removed. These damp areas are likely to have taken on hygroscopic salts. These salts are extremely absorbent and can draw moisture. This can also lead to future damp problems.
If rising damp was the issue, it is best practice to remove all plaster on affected walls up to 1.2m. This is the approximate level that damp can rise to. It is usually recommended that you re-plaster up to this point.
When you do re-plaster, you can use a specialist damp proofing product, such as Dryzone damp proofing plaster.
You can read more about this product by clicking here and read what past customers say about it.
There is also the option to fix a damp proof membrane to this area of the wall. Finally, if you prefer, you could even apply batons and then board and skim.
If you are in this situation, it is likely that you will be using a damp proofing company to repair your damp issue. If this is the case, they will often carry out this internal work for you.
Need help solving your damp problem?
If you do have blown plaster due to a damp problem, it may be a good idea to have a damp proofing expert look at the job.
Most companies will come out for a free inspection and will help you identify the issue.
Following this, you can get quotes and decide if you want a professional to do the work, or if you go down the DIY route.
The main advantages of hiring a professional are:
- A pro will have years of experience identifying the exact cause of damp.
- They will probably do a better job fixing the issue.
- And they usually offer some form of guarantee, should the problem resurface.
Professionals are also quite easy to find online via comparison websites. These sites allow past customers to rate and review damp companies, so you know who you are hiring (avoid any cowboys).
It’s also usually much cheaper hiring this way. Companies are competing for the job, so quotes tend to be extremely competitive. We have seen discounts of more than 50%.
Damp is one of several causes for blown plaster. The most common cause for this problem, is poor preparation on behalf of the trades person (the plasterer).
However, a damp problem can damage even the best plastering job.
When you do find damaged plaster due to damp, the most important thing, is that repairing the damp problem is your priority.
It doesn’t matter how good the plastering is, if the damp remains your plaster is likely to become damaged again.