Damp problem... DIY chemical damp-proof kit?

[Mike D]

I've cured most of the rising+penetrating damp in my 100-yr old house house by raking out the cavities to below DPC-level wherever there was a problem. The original slate DPC seems to be in good condition.

However, in one place, there is a 2-ft wide pier which was possibly added after the original build. It was built into the cavity. (It is

9" thick, and stands proud of the inside face of the inner sking by 2" and proud of the inside face of the inner skin by the width of the cavity, i.e., it actually fills the cavity. It supports an RSJ which runs accross the room at that point, supporting a first floor outer cavity wall. The ground floor was extended forwards at some stage. Hence the addition of the pier and the RSJ.

The pier has had a damp problem all the time I've owned the place, and the damness can be felt up to a higher point than the other places that had dampness.

How can I cure the damp in the pier? Chemical injection? The outside of the house has been painted with Dulux Weathershield for the past 15 years, so I guess it cannot be the penetrating damp. I suspect that the DPC was omitted from the pier, or they filled the cavity with brick and mortar at the point where the pier was built and neglected to add DPC to bridge the filled cavity.

If chemical injection might be the answer, can anyone advise where I can obtain a DIY-er's kit - (preferably from a well-known DIY chain) ?

I could just paint the wall with damp-seal, but I would like it to pass a surveyor's dampness inspection when I come to sell the place shortly.

Thank you,

Mike D

[DIY]

You can hire damp proof injection equipment and buy the fluid from most tool hire firms and from some builders merchants such as Jewsons. I haven't seen this stuff in Been & Queued or Homebase.

[Chris George]

Dear Mike Firstly lets identify and separate penetrating damp from rising damp. The former is most unlikely to be the cause of your problem unless the pointing is bad, the brick porous and you live in a part of the country that has horizontal driving rain commonly. The cure is NOT an external paint of whatever sort as sooner or later that will micro crack and let in water but not let it out! so if there is penetrating damp due use the cavity not a paint! Rising damp is due to hygrosopic (yes that is spelt correctly) salts absorbing water from the atmosphere. It is caused by decades of migration and evaporation of salt solutions from the ground in the MORTAR of the wall to the surface plaster where water only evaporates off leaving salts behind. Clorides and nitrattes etc. The cure is two fold.

1) stop the salt solution rising 2) if NECESSARY hack off the contaminated plaster (which cannot be cured) and replaster in a cementation - non gypsum plaster A word of warning you need to inject not the bricks but the mortar layer with a continuous layer of hydrophobic material to make the mortar water resistant I have used in my house DryZone from Safeguard Chemicals. It workeed. It only requires a bit of commonsense to follow the instructions and a dirty great big applicator gun with lance on the end. You could rig up your own system with aluminium or steel tube and a LARGE mastic gun. Test the plaster as follows with a damp meter (hire or borrow) every few cycles of humidity high and low and see if it alters the readings. Test the pattern of existing readings - If there is a "high tide" mark somewhere 300 to 1000 above the ground with lower readings above and below - that is probably rising damp! If you replaster use a 3:1 render with Sika No 1 water proofer and you wont go far wrong In fact you could do that without the dpc and probably get away with it but not recommended. Good luck Chris

[Roger]

The message from Chris George contains these words:

Not in my dictionary.

OTOH hygroscopic is.

[Mike D]

Chris, Thanks for your input. All of what you said concurs with my own understanding of the issue. The house was built with lime mortar, so that prabably helped. Yes, the damp meter shows a higher reading near ground level and in most places the walls are much drier above 1 mtr above floor level. I agree that your remedy is the thorough approach, but hacking the plaster off the walls and replastering is, of course, extremely disruptive and messy, to say the least. And the plaster that has been used is not easy to remove.

Cheers,

Mike

[Mike D]

OK - thanks..

Mike

[meow2222]

wrong diagnosis, wrong treatment. Ask the experts

[Chris George]

Mea culpa - missing "C" not to be confused with hydro....

[Chris George]

IF and only if it is certain that the wall has hygroscopic salts in it (and you can verify that by testing or as described earlier) then you have no choice but to replaster or live with the damp. The objection to re-plastering is often based on the fact that most commercial companies, quite wrongly, recommend it - regardless of whether or not it is necessary - to protect themselves. By all means try to keep it if it is borderline - you may get away with it if the prospective purchaser's surveyor comes after a dry period. Chris

[Mike D]

That's helpful - thanks again...

Mike D

[Mike D]

[Maris]

The only problem with this method is that the fluid will just shoot away into an abyss if there are any irregularities in the old mortar (and there usually are), which I discoverd to my cost (and DPC fluid isn't cheap). If I need to repeat the treatment (and the indications are that I will) I will use those wax stick things that slowly melt and permeate the bricks/mortar course much more effectively.

I wouldn't recommend using render - you could end up with condensation problems instead. In my previous house I used Limelite Renovating plaster, which worked a treat. I don't think they make it any more but I think there are equivalents. I am busy tearing off the render off my damp party wal and it is not going back on. The previous owners had made doubly sure that the damp would remain in the wall by using vinyl paint on top of the render!

Maris

[Chris George]

DryZone operates on precisely the same principle! It is a gel-like cream which disperses slowly over the next few days. It does not operate like a fluid but clearly to be injected has fluid (albiet very sluggish) properties. Its spread far exceed frozen sticks - (if that is what you are referring to by "wax" sticks. If it is indeed wax the melting point is such that at NRT it wont melt so I assume you are referring to AQUEOUS sticks with "wax-like" ingredients. If I am wrong, I would be interested in the trade name.

Condensation occurs due to the dew point having been reached and I have never found in the last 30 years of specifying both an example where the difference in U value between Limelite Reovating (a vermiculite-containg sand cement render) and a cement render has tipped the balance to condensation forming. Limelite Renovating is a great product (be careful not to be confused with other manufacturers "renovating" plasters based on gypsum!)but there are plenty of occasions where it is not suitable and this is one. It has practically no capacity to prevent salt migration to the surface and efflorescene is common. Its adhesion is questionable where you have variable absorbent substrates - just try tapping it after and you will find more "hollow" sounds than with render. Where there is limited risk of salt contamination and no lateral penetration - go for it if you can find it but don't fear appropriately specifed sand cement render. If you really want a good product where limelite would be OK why not be a purist and put on an original lime render using a lime putty (NOT bagged lime!) but that is quite another post into which I have not intention of further travel!

In my previous house I used Limelite Renovating

[Maris]

We are probably talking about the same thing. I couldn't remember what the contents of the sticks was but sticks they were.

Condensation does not depend so much on the U value of the construction as on the conductivity of the surface. i.e certain surfaces (e. granite, metals) will always feel cold to the touch (and therefore likely to induce condensation) whilst others such as timber will feel warm. The U value does, of course, play its part. Limelite renovating plaster was developed for damp situations (something also referred to in a forum about Limelite that I just viewed) whilst standard Limelite backing plaster was for non-damp locations. I will concede that it is sometimes a bit prone to losing its adhesion. My main reason for using it (and Limelite backing) was it insulation properties. Carlite has similar properties, of course, but is as hygroscopic as they come.

Maris