Vertical DPC

[Wangerman]

Hello all

will installing a vertical DPC stuck below and above the existing DPC and the trench backfilled with shingle help stop rising damp. I am having a DPC injected but want belt and braces ?

Reason for this is Patio has breached damp course about 4" higher and new house is very wet on the ground floor

 

[^woody^]

Rising damp travels vertically, and so a vertical DPC is not going to be much use

 

[Wangerman]

Rising damp travels vertically, and so a vertical DPC is not going to be much use

Thanks

Although will it hurt cutting back the patio and doing the shingle trench ?

I already have the DPC and 20mm stone now

 

[^woody^]

The shingle trench is only going to be effective/necessary if you have surface water running back towards the wall or lots of water dripping off the roof or face of the wall - and even so it will need to be as deep as the foundations and include a perforated drain to move the ground water away from the building.

A shingle trench at the same level of the patio will still cause splashback up the wall, and so your new DPC still needs to be 150 above ground/patio level.

 

[Wangerman]

The shingle trench is only going to be effective/necessary if you have surface water running back towards the wall or lots of water dripping off the roof or face of the wall - and even so it will need to be as deep as the foundations and include a perforated drain to move the ground water away from the building.

A shingle trench at the same level of the patio will still cause splashback up the wall, and so your new DPC still needs to be 150 above ground/patio level.

Cheers for the info

I guess I will do it anyway as I have the gear now but do it as you say and hope the injected DPC works

 

[^woody^]

Ideally, the problem should have been diagnosed and the appropriate remedy used

If the damp problem is just due to a breach of the DPC with some minor splashing, and you can't just cut the patio back, then injection should work.

If the moisture is entering the wall under relatively high pressure, and is constant, then it may overcome the resistance of the injection - it depends on what chemical system is used

Presumably you have a solid wall which is allowing moisture across to the internal room? If so, be aware that the higher ground level against the wall creates a cold thermal bridge which can cause a band of condensation (and mould) along the bottom of the wall. This is another reason for cutting the patio back

 

[Wangerman]

Ideally, the problem should have been diagnosed and the appropriate remedy used

If the damp problem is just due to a breach of the DPC with some minor splashing, and you can't just cut the patio back, then injection should work.

If the moisture is entering the wall under relatively high pressure, and is constant, then it may overcome the resistance of the injection - it depends on what chemical system is used

Presumably you have a solid wall which is allowing moisture across to the internal room? If so, be aware that the higher ground level against the wall creates a cold thermal bridge which can cause a band of condensation (and mould) along the bottom of the wall. This is another reason for cutting the patio back

Wall is cavity 4" brick them gap then 2" block company came round and injected internal wall with creamy wax stuff hacked off plaster then made good patio is tight to wall and I cannot see the dpc an old builder mate of mine said it wouldn't hurt to try and he has used this method before

Is it normal to only inject internally ?


You are a star thank you for your help

 

[^woody^]

If this is a cavity wall, then there must be a load of mortar/brick in the cavity which is allowing moisture to cross from the external to the internal

Injecting a blocked cavity wall does not always work as the stuff in the cavity either does not receive adequate chemical, or large voids render it ineffective. Also, it is hard to determine the extent of the blockage, and so how does the company know how much to inject. Often they just guess and hope

Also the thermal bridge potential remains, and this can cause dampness just as bad as before the injection

Injection is really for moisture coming up, and if you already have an effective DPC on the internal wall, then potentially this is the wrong solution for moisture coming across the wall. In these situations, you could get water coming down the external wall (or in the cavity) and then moving across to the internal leaf above the injected area - or just sit on the top of the debris in the cavity.

The point is that this has potentially been mis-diagnosed and an injection may not be the best solution. It may work, it may work for a while until moisture moves up and over the level of injection, or it may not work.

The best remedy for dampness bridging a blocked cavity is to clean it out.

 

[Wangerman]

If this is a cavity wall, then there must be a load of mortar/brick in the cavity which is allowing moisture to cross from the external to the internal

Injecting a blocked cavity wall does not always work as the stuff in the cavity either does not receive adequate chemical, or large voids render it ineffective. Also, it is hard to determine the extent of the blockage, and so how does the company know how much to inject. Often they just guess and hope

Also the thermal bridge potential remains, and this can cause dampness just as bad as before the injection

Injection is really for moisture coming up, and if you already have an effective DPC on the internal wall, then potentially this is the wrong solution for moisture coming across the wall. In these situations, you could get water coming down the external wall (or in the cavity) and then moving across to the internal leaf above the injected area - or just sit on the top of the debris in the cavity.

The point is that this has potentially been mis-diagnosed and an injection may not be the best solution. It may work, it may work for a while until moisture moves up and over the level of injection, or it may not work.

The best remedy for dampness bridging a blocked cavity is to clean it out.

finished the Vertical DPC now. Found a buried drain under all of the sand and have cleared that out and overlaid with the shingle. Found the existing concrete path below the patio which sloped towards the drain so hopefully all of the water will drain through the shingle and fall into the now exposed drain. The new dpc is now well above the level of the existing patio.

The walls are not cavity after all but are up to about 3 feet then they become 9" solid which I thought a bit strange but hey I am only a sparks so what do I know

Thanks again for all of your help