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Damp Proofing

Do you need to remove plaster in order to put in a injected damp proof course? alternatively is installing solid wall insulation at the same time a good idea?

We've been advised to reinstate injected damp proofing a 1920's semi. Previously undertaken about 30 years ago. We understand we need to remove the plaster to a meter up to guarantee the work. Is there anyway to avoid this?

Alternatively, we are considering taking it all off and fitting internal (solid wall) insulation. We are only really considering this for a staircase wall - how long would a job like this take and what kind of prices might we be looking at? Any advise would be welcome.

Finally, I have come across injection damp proofing that goes into mortar rather than a course of bricks, any experience, knowledge or advise on this would appreciated?

Many thanks in advance

6 Answers from MyBuilder Damp Proofing Specialists

Best Answer

Great question, I can understand your confusion.

Ok, firstly. The plaster will need removing to erradicate any trapped moister within the substrate. The plaster requires hacking off to a height of 1.5 meters because water can rise to 1.2 meters, at 900mm gravity tends to stop the rise, however the plaster being porus can "wick" the moister to around 1.2 meters high, so remove it to 1.5 meters to be sure.

A chemical DPC is injected from outside. It's aim is to be sucked into the brickwork to form an integral layer to which water cannot penetrate. Just like the normal black plastic put into a course of brick. However this is rarely suitable for anything other than a home that is fairly new, I digress.

The walls will fill naturally with debris from the cavity, this can fill up past the dpc level and form a direct passage for moisture and in most cases wet rot etc. If you inject the walls on top of this, it would ammount to trying to stop the titanic sinking using an egg won't work. Unfortunitly most people these days advise a hack off, injection and re plaster.....this in turn will fail within 3 to 4 years, but they have been paid and you are left in the same situation.

The solution would be to chemically inject the walls with a rated (not a certain e bay bought fluid!) injection fluid. Then the internal side of the wall can be tanked, it works like a swimming pool effect, holding any and all water out of the internal finish of plaster. The walls can then be further treated in a certain way to a finish for decoration.

This way, if properly installed by someone who knows what they are doing will be able to then give you and insurance backed 30 years plus guarantee and it will be the end of your issues. I have purposefully left out little details of the exact way to install as this can be read by anyone, and it cost us quite a lot to become a registered approved installer so we have to be careful ha ha.

Anyway, hope this helps, good luck, and try not to let it get you down.


Answered 12th May 2011

If you dont have the confidence to do it, I would suggest get a damp proof company out to survey, price and carry out the work, this way you should have the job done properly and a new gaurantee issued.
If you want to save money, do the hacking of etc, preparing everything ready for them.


Answered 12th May 2011

Holcombe Building has given good key points and very agreable with most of the advise.
But as for the plastering yes it is the key element and without this the Damp Proof course is a waste of time.If you left contaminated plaster with salts visible or not to the naked eye it will still have issues.
As for hacking off first find how far the moisture has travelled up the wall by getting in a CSRT (Certified Surveyor in Remedial Treatments) they will probe the wall in a upward fashion and may find 1 metre is a adequate level to remove plaster or it may be higher in some areas and not uniform in its pattern.
New Plaster is a must with a new Damp Course and you will be at ease in the knowledge you will have a Guarantee aswell.

Good luck and heres hoping for a safe and damp free home.

Scott Cannon.
Cannon Preservation.


Answered 15th May 2011

So what you are saying really is that the property has had injection damp proofing 30 years ago and is now starting to fail so reinstatement is required. So the easiest way is to redo the damp proofing using BS standard cream/injection damp proofing. This work could be done on a diy basis but you will need to follow instruction to the manufacture requirements which if you pay the right money for a good kit will also have Hygrometer.
The plaster needs to be removed normally to 1.2 meters and would require spacial treatment before replastering.
Call some local contractors for free quotes and obtain at least three seperate quotes along with references


Answered 11th May 2011

For rising Damp you might need to remove the old plaster but it depends what the old plaster is like it may dry out on it own but with out looking at the job you just cant tell. Jim Beveridge.


Answered 11th May 2011

just to add to the above, the cream injection system only works if the wall is damp/wet as this interacts with the cream to form the barier,regards Terry.


Answered 12th May 2011

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