Warning this post is a bit long (but worth it) – if you are too busy a condenced version is available on my Sporecast blog
What does chemical DPC injection entail?
Well, it’s very simple; masonry is porous and most of it readily absorbs water. There is a tendency for any wall to ‘wick-up’ water from the ground it is built into. We’ve all seen the effects.; Rising Damp. This is what underpins my company’s existence and supports the whole damp proofing industry.
However, coat the masonry with a chemical lacking affinity to water and the attraction stops. Chemical injection DPC’s merely take this well known ‘water repellent’ effect to another level, by saturating a horizontal band of wall with water repellent, through it’s full thickness. Thus, even if a wall has it’s feet in boggy ground, damp is no longer sucked-up the capillaries (these are the pores in the bricks/stones/mortar).
Up until a few years ago (before DryZone came along), this was usually done by drilling a row of holes and injecting water repellent under pressure, to force the ‘fluid’ through the bricks and such, so that the inside walls of the pores become lined, with a layer of the water repellent molecules. No more rising damp.
Well, it is, but chemical injection DPC’s depended on some things, which can be lacking in the construction trade. How about diligence and patience? Lots of jobs demand these characteristics, but where DPC injection is concerned there’s a problem. You see, most jobs requiring these attributes are visible to clients, consumers and supervisors; any lack of diligence or a rushed job, can be seen and put right. Visible defects are only applicable to ‘half’ the work involved in installing a chemical DPC though….
Lets start with the procedure for installing a chemical DPC:
- Drill the holes for the injection.
- Inject the water repellent.
First half of the job – the holes… at the right height; under the floor timbers, above a solid floor, no nearer than 150mm to the ground. They must be the right width apart and of course in the bed-joint and drilled to the correct depth, depending on the thickness of the masonry.
These are all easy to check and woe betide any operator who gets this bit wrong.
Now then, the next half…
Saturate the pores of the masonry/bed joint at the chosen horizontal band, through its entire thickness with a water repellent. This takes time too. There are some issues in here though, which can upset the applecart:
Is the pressure setting right? Too high? too low? Are the holes in uniform material and is the wall of variable density? If so then ‘fingering’ can occur, which means that the absorption of the fluid is haphazard and gaps can be left, where water will still rise. Are there any gaps, cracks or tiny fissures along the length of the holes? The deeper the holes are, the more likely it is that these will be present. They matter because pressure injection means that the fluid will take the easiest path; most of it could simply gush through these and into the cavity or rubble, leaving the pores we were worried about untouched. It also wastes a lot of expensive water repellent.
These are things which the operator has to take into account and they dictate how long the injection will take and whether any additional injection holes will be needed (My imaginary operator is called Joe. He’s just started injecting and the drill he used to form the DPC holes is packed away in the van..)
So let’s imagine that some of these issues impacted on “Joe’s” job. It’s Friday and as he starts to use his pressure pump and 6 way injection nozzles he finds that a couple of the nozzles don’t seal correctly, because the ends are worn and the boss hasn’t enforced any maintenance since the last job, so he only has four nozzles to go at (there are spares in the van but it is Friday afternoon and why should he replace the ends when nobody else bothered)? Also, quite a few of the holes are ‘open’ which means that there is a defect in the hole and the fluid is escaping – it is not being injected into the masonry. He’s late though, so he skips to the next hole thinking, “It’s only the odd one”. However, after a bit he realises that actually, the wall is resisting the injection and the level of the fluid in the semi-opaque drum is hardly going down at all. It’s taking ages to get the fluid in and time is passing, so he reasons “The wall isn’t absorbing much DPC fluid under pressure, so it must be resistant to water anyway”.
Joe speeds up the rate of injection, sealing the injection rods in the holes, with a twist of the grips and then, after quickly switching the tap on and off, he pulls them out and moves on. After a bit he thinks “What’s the point? I may as well not bother with the tightening of the injection lance; it’s taking longer than the injection itself and that’s not working anyway. Plus, the plastic seals are getting worn; I’ve been squirted in the face twice already”.
So now Joe ‘s method evolves and he’s using one injection lance only, giving each hole in turn a quick squirt of fluid to fill the hole, wash the dust away and leave a trail of fluid down the wall, where he’s been. He’s satisfied now because the job is speeded up and he’s convinced himself, that all is well.
This is a nightmare scenario for the consumer and the company paying Joe. The botched job remains undetected and a guarantee is issued. Years later the wall is damp and a complaint is made. Expensive and disruptive remedial work is needed and the contractor (if he is still around) has to pay. Joe is long gone (he didn’t like the boss and the pay was rubbish) and often so is the contractor. Unless he was a member of the PCA and issued genuine Guarantee Protection Insurance, the client is left with the expense and the pain of the disruption.
Worse still (for the industry as a whole), the client, his surveyor, his architect, his engineer and his neighbour is left with the impression that Chemical injection Damp courses don’t work. Thanks Joe!
Let’s not be too hard on Joe though. He was never well paid, supervised or competantly trained. He didn’t have much self regard, because his boss didn’t seem that interested in what he did and only ever asked him one question; “Is the job finished Joe”?
So how can a change of method from, injecting DPC fluid under pressure, to caulking a thixotropic cream into the same holes, make such a difference?
Now Joe’s DPC’s injections work – how come?
Joe is using DryZone cream now – which his boss insists on. Remember that the drilling can be checked so must be done correctly. With Dryzone cream, Joe is matching the fast pace he set when ‘splashing’ DPC fluid into unsealed holes and the result is an effective DPC! His new boss is pleased.
He uses one nozzle and fills the hole with the cream. It takes seconds per hole and then is greedily absorbed into the wall over the coming hours, whilst Joe is in the pub watching Leeds United. He couldn’t make the job quicker if he squirted the cream down the drain, which is not something he would do anyway; bear in mind that he only started skimping the chemical pressure injection, because it was a flawed and monotonous job, which he became convinced was not needed anyway.
So, for reliable chemical DPC installation always specify DryZone cream. It improves the chance of the chemical DPC working by 50%.
There are other chemical DPC creams too and I have nothing against them. However, moving from the operator, who has been virtually removed from half the job, I now need to know that the product is fulfilling its part. DryZone is the most widely tested cream around and has a very high siloxane content. Many creams have virtually no testing and have a much lower active ingredient. Great for them, cheaper by miles. The thing is, these creams claim to do the same as DryZone with less testing and less product; it doesn’t add up for me. If I was developing a product on the basis of less active content I’d want more testing – not less. I’m no chemist though, so I remain to be convinced.
Is a switch to DryZone really enough to get a 50% improvement in quality? Almost I’d say, but Joe and others like him will always be the single most important part of the quality and service equation. Remember that Joe is just a regular guy; his character is not that much different these days and he likes a pint and his football too.
For maximum quality and service improvements add these….
Joe’s at another firm now, he’s an NVQ level 2 trained “Damp proofing and timber treatment technician”. He has his PPE on and sees more of his new boss. Joe’s advice and opinions on his day to day tasks are sought and apparently valued. His boss asks him “How did it go this week Joe”? and “What have you done to go the extra mile for our customers this week” and better still “Is there anything I can do to make your job better”?
His new employers are PCA members and he’s attended and passed the PCA technicians exam. The company are Investors In People accredited- he’s now very proud of his work and holds his head high.
Not many firms will go as far as this, but just a switch to Dryzone is a start and demonstrates initial commitment.
Would I use chemical injection under pressure to install a DPC? Yes, provided it was properly supervised. However, that would take BT Preservation much longer than DPC injection using DryZone cream, so it would be more expensive for the client and more troublesome in operation, so I don’t.
oh – here’s a video about DryZone cream: