I suggest you get an independent survey to pinpoint the problem before undertaking any remedial works.
Damp proof concrete garage floor.
Damp affecting concrete floors.
Fully isolate the dampness in the floor using a surface damp proof membrane dpm damp proofing concrete floors above ground damp proofing for extensions.
I believe a damp proof sheet was used under the concrete floor as indicated by the telltale black sheeting used before the concrete floor was poured.
It could also be bridging by the internal plaster or a failure of the wall floor joint.
Concrete s porous nature means that water from under your home can seep up through your concrete floor making it damp.
After the construction was finished i painted the concrete floor in the new extension.
Either a damp proof coating can be applied to the surface of the concrete or a damp proof membrane can be laid on top of the concrete.
All seemed good and it dried well.
Damp rising through concrete floor slabs is fairly common causing damp issues on carpets and floor coverings warping wooden floors and increasing the likelihood of low level mould growth.
Damp in concrete floors are much more difficult to treat than having damp walls.
Sometimes the issue can be bridging of the damp proof course by the concrete floor assuming is was timber prior as this often occurs.
When damp proofing a concrete garage floor a plastic dimpled membrane is required if the floor is going to be boarded either with chipboard plywood or similar or if a concrete screed is going to be laid.
The damp proof membranes used during construction of concrete floors are often thin and can easily become torn before they are laid rendering them.
Floor membrane from property repair systems roll out and lay on either chipboard plywood mdf or screed.
However typically these are often fairly thin and are sometimes damaged even before they are laid.
But if these methods are non existent or if they have failed in some way here are some ideas to resolve and reseal your damp garage floor.
I m guessing that this sheeting is the vapour barrier you talk about.
Damp proof membranes for concrete.
How to damp proof concrete floors.
This can cause issues with mold and mildew especially if you have carpet or.
Most damp proof floor coatings are applied directly to the concrete floor.
Floors can easily suffer from moisture ingress otherwise known as penetrating damp.
This is because damp rising up through concrete floors is a pretty common issue.
A damp proofing concrete floor solution is particularly important.
When faced with damp in concrete floors there are two options available.
The reason for this is that concrete is a very porous material meaning that water can rise through capillaries and therefore lead the property to suffer from having damp floors.
Dig up the old concrete floor install a new damp proof membrane and lap up edges before replacing the concrete slab.
