- Thread starter Demelza
- Start date
Gervase
Member
- Messages
- 1,500
- Location
- North London
Short answer - because it doesn't work.
Longer answer - because chemical creams and potions will always follow the line of least resistance. In a traditional brick wall with lime mortar bonding, that line is likely to be the mortar course.
In a rubble stone wall, with irregular bonds and an indeterminate core, full of a mix of impermeable stone and voids, there's no way of telling which way the gel/cream/liquid will go. It's a safe bet, however, that it will follow any existing void before it seeps into mortar or any less permeable material.
Thus, from experience, I've seen expensive silicone material pumped into a wall only to gush out of some loose pointing 10 inches away, and failing completely to pervade the mortar.
Needless to say, the chemicals can't soak into impervious stone, so they're best when used in mortar courses. The trouble is, maybe 80 per cent of firms who offer such treatment drill holes in the stone rather than the mortar (because it's easier, looks neater and is more likely to impress the customer). As a result the treatment is completely wasted.
There are some companies who will offer a limited guarantee on chemical DPCs in stone. Such guarantees will insist that a full cementitious plastering technique is also used, and it is that rather than the DPC which keeps the damp at bay (temporarily).
Believe me, chemical DPCs in stone don't work.
Longer answer - because chemical creams and potions will always follow the line of least resistance. In a traditional brick wall with lime mortar bonding, that line is likely to be the mortar course.
In a rubble stone wall, with irregular bonds and an indeterminate core, full of a mix of impermeable stone and voids, there's no way of telling which way the gel/cream/liquid will go. It's a safe bet, however, that it will follow any existing void before it seeps into mortar or any less permeable material.
Thus, from experience, I've seen expensive silicone material pumped into a wall only to gush out of some loose pointing 10 inches away, and failing completely to pervade the mortar.
Needless to say, the chemicals can't soak into impervious stone, so they're best when used in mortar courses. The trouble is, maybe 80 per cent of firms who offer such treatment drill holes in the stone rather than the mortar (because it's easier, looks neater and is more likely to impress the customer). As a result the treatment is completely wasted.
There are some companies who will offer a limited guarantee on chemical DPCs in stone. Such guarantees will insist that a full cementitious plastering technique is also used, and it is that rather than the DPC which keeps the damp at bay (temporarily).
Believe me, chemical DPCs in stone don't work.
Lime
Member
- Messages
- 2,749
- Location
- East of England
I agree with Gervase.
If mould is appearing it means the wall surface is damp but that can be caused by either condensation, damp in the wall or both.
My immediate "cure" would be to increase the ventilation to the mouldy area to reduce the damp.
Then I would ensure that the soil outside is well below the interior floor level and that all water pipes, guttering and drains are not leaking into the property.
however, once mould is present it is quite difficult to prevent it's recurrence because the mould spores lie dormant until damp again and then burst into life.
If mould is appearing it means the wall surface is damp but that can be caused by either condensation, damp in the wall or both.
My immediate "cure" would be to increase the ventilation to the mouldy area to reduce the damp.
Then I would ensure that the soil outside is well below the interior floor level and that all water pipes, guttering and drains are not leaking into the property.
however, once mould is present it is quite difficult to prevent it's recurrence because the mould spores lie dormant until damp again and then burst into life.
Gervase
Member
- Messages
- 1,500
- Location
- North London
Ordinary household bleach is quite good at killing mould spores, but even better is a dairy disinfectant like Deosan or a similar hypochlorate-based compound. Some farm shops won't sell it to 'civilians' but you could always try buttering up your local dairy farmer!
Nemesis
Member
- Messages
- 9,402
- Location
- Planet Earth
Buttering up the local dairy farmer?
Worthy of Penners that one!
Worthy of Penners that one!
The effectiveness of chemical DPC's depends wholly on the property's structure. As Gervase has said, silicone and the like follows a path of least resistance and, as stonework is irregular, it's nigh on impossible to create an effective barrier.
Incidentally, while DPC's of this type in stone are a "waste of time", in any cob structure they can be catastrophically damaging. Don't do it under any circumstances.
Incidentally, while DPC's of this type in stone are a "waste of time", in any cob structure they can be catastrophically damaging. Don't do it under any circumstances.
Matt Green
Member
- Messages
- 675
Lime said:
Mould indicates a fresh water source, the salts disolved in ground water and deposited near the wall surface impede its growth.
Likely to be condensation, especially if the surface is impermiable.
Matt Green