Tanking general questions

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cowen70

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This is something I haven't even remotely approached in training yet but I am having to do it.

When you tank a wall do you use a cementone cement slurry and paint it on the walls and then use something like Limelite Renovating Cement based plaster or do you just use a cementone cement render on the wall and skim over the top?
 
@Arti is the man to ask he knows his stuff regard damp/tanking etc :RpS_thumbup:
 
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cowen70 said:
This is something I haven't even remotely approached in training yet but I am having to do it.

When you tank a wall do you use a cementone cement slurry and paint it on the walls and then use something like Limelite Renovating Cement based plaster or do you just use a cementone cement render on the wall and skim over the top?
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MAny many ways to tank,one way is to scud ie sbr brushed on cement paste, or a splatter scud coat, scratch coat on top the next day,2.5 sand to one cement with waterproofer following the guidelines for whichever one you use, don't use anything that plastisizes ,you can scoop the render onto the floor in a rounded fashion.second coat 3.5 to one,bang it on, rule it as flat as possible, when it pulls in,give it a splatter coat without waterproofer, nex day bang on floating coat 4/1 sand to cement with water proofer, rule flat,float it in.keep dampened for seven days without getting electrocuted. Remember each coat must over lap each other ,(no joins) I would only use limelight a week later if it ended straightening.if you are skimming over it, do a grit coat on top firstly
 
It all depends on the form of water pressure you are trying to stop ,from a 12inch high ground level ,to a basement
 
as mentoned, a few ways to do it..................my 1st question is why does it need tanking ?
 
Just got a PM from CT Plastering considering having him around to do it, have to talk with the family first.

It needs tanking because there was a big problem with some jokers who installed guttering and left water pooling at the foundations and running down the wall. Had to replace pointing, fix guttering and to be on the safe side put in a chem DC (dryzone). But the walls will be soaking yet and well before I knew better plastered and all the salts and moisture just came right through!
 
cowen70 said:
Just got a PM from CT Plastering considering having him around to do it, have to talk with the family first.

It needs tanking because there was a big problem with some jokers who installed guttering and left water pooling at the foundations and running down the wall. Had to replace pointing, fix guttering and to be on the safe side put in a chem DC (dryzone). But the walls will be soaking yet and well before I knew better plastered and all the salts and moisture just came right through!
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How long ago has the gutters etc been fixed................sounds like it been penetrating damp. the walls might just need time to dry out. Got any pics??
 
Arti said:
How long ago has the gutters etc been fixed................sounds like it been penetrating damp. the walls might just need time to dry out. Got any pics??
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I'll take some tomorrow, in each case it was directly around the base of the guttering downpipe where the pointing was mush. In the room I've already inexpertly tanked (looks like I did it right if roughly based of a message I've received) the damp only appeared around the gutter. In the room I am doing now it is on both sides which.

Tonight I was thinking and reading a bit and also didn't think to check if the two walls in the front and the back yard wall are creating a bridge to allow damp in.
 
we used Newton Membranes on a converted stone steading with a soaking solid wall which is now bone dry to this day. The source of water we guessed at but was never identified. For that reason we wouldn't put our name to it & used a damp proofing co for guarantee as t is a commercial project. Very little hassle
 
johniosaif said:
MAny many ways to tank,one way is to scud ie sbr brushed on cement paste, or a splatter scud coat, scratch coat on top the next day,2.5 sand to one cement with waterproofer following the guidelines for whichever one you use, don't use anything that plastisizes ,you can scoop the render onto the floor in a rounded fashion.second coat 3.5 to one,bang it on, rule it as flat as possible, when it pulls in,give it a splatter coat without waterproofer, nex day bang on floating coat 4/1 sand to cement with water proofer, rule flat,float it in.keep dampened for seven days without getting electrocuted. Remember each coat must over lap each other ,(no joins) I would only use limelight a week later if it ended straightening.if you are skimming over it, do a grit coat on top firstly
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Can I ask why you don't let each coat dry john? Surely with damp issues it's best left to dry before next coat.
Isn't this what you say about externals?
 
bobby said:
Can I ask why you don't let each coat dry john? Surely with damp issues it's best left to dry before next coat.
Isn't this what you say about externals?
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Tanking due to the strength of each mix and following sika guidelines, its scud first day with 1/1 sand cement,sika remaining constant at 10/1 water to sika 1. Second coat 2.5 directly on top, third coat is a splatter coat for key that evening, float coat next day at 3.5 to one,
 
bobby said:
So your saying as the mix is stronger it dry's 3/4 days quicker?
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To be honest, we always worked to sika guidelines on this,
the idea was also to keep it dampened to stop it drying possibly a waste of time considering its waterproofed,but there is the fact that its on top of soaking walls..
 
Membranes are for joiners, to do the job right you need to stop the moisture coming in not re-route it into a sump pump.

What they don't tell you is that a moisture laden environment is ideal conditions for dry rot, I have looked at a dry rot job with that stuff on the wall and it was rather impressive how it fed of the moisture behind the membrane and munched its way through joists and studwork lol.

That stuff is for green roofs not basements, do the job properly with a proper tanking system like heydi k11 or vandex.

Last time I looked down the local swimming baths they didn't have that lining the pool lol.
 
Why tank it when you can let the wall dry down? Tanking the wall will hold the damp in the wall and push the damp to other walls and increase the moisture content in the bearing end timbers that will cause decay, if the client wants a dry finish ASAP use a ventilated membrane with a thermal plasterboard.
 
Haha ok an even cheaper solution is to buy some breathable roofing membrane and counter batten it to the wall.

To do it properly, you have to do it the hard way.

The moisture will always be there, masking it with expensive visqueen is not going to cure it, don't tell me the "Rep" told you it would work :RpS_thumbup:

If the "Rep" told you to put your hand in the fire would you ?

I have first hand knowledge of these magic plastic sedum roof rolls, and one of the failed jobs floods on a regular basis as the area is prone to flooding from tidal ground water.

He was quoted £35k to have the job done to the correct spec, instead he paid £15k and it still floods, I am sure the "rep" did well on the commission on that job :RpS_thumbsup:

I am old school mate and not one of my jobs has flooded you, bone dry and well ventilated, part of the design has to have ventilation check your building regs.
 
Against my better judgement I've done the tanking myself. I've taken some images as well.

Now ever mindful of forum members time, considering some of my work is getting shown I've prepared some colourful phrases to describe it to save you the effort:

Flat as the welsh countryside
Waves like the Pacific
Curves like Pamela Anderson
About as straight as you are!

Take your pick :RpS_blushing:

So this is what I've done and hopefully I've sorted it and spotted all points that could have been causing a problem.



Front of house:​

Tanking general questions

First thing I did was to repoint everywhere in those red lines, around the window. Above and below the lintel, along where the CDC was put in.

Tanking general questions

These are the damp locations on the interior walls

Tanking general questions

This guttering was put in and was emptying into an old cast iron downpipe that ended a single foot from the wall. It was also really over run with plants and had a lot of rubbish piled around the wall. It was here that the mortar was just mush in the walls particularly around the base of the guttering which made me wonder if water was pooling or splashing back on the walls due to the incomplete nature of the guttering job. So I cleared it out, had a hell of time finding the same size guttering so I've just done something for quickness and ease to get the water away from the foundations.

But after researching damp extensively I found something I hadn't considered. Bridge points for damp to enter a building. So I was hoping one of you (Oli? CT?) could look at this terribly built wall and see if that might be part of the problem.

Tanking general questions

Inside this is what I've done. Two good coats of the mixture recommended by CTPlastering. My second attempt (as flat as Welsh Countryside) was at least better than my first. Just wondering how thick you all would have done it? Can also see where the dry bricks have pulled the moisture out, but the damp corner remains very dark.


Back of house:​

So here we had guttering that had been emptying into an underground pipe that feeds into the main drain (I checked it definitely does) but my Grandad in his infinite obstreperous old git wisdom had filled with expanding foam and had the guttering just emptying onto the ground below where I've attached the bucket pipe.

The concrete underneath had a small void that I filled. The walls were covered in a extremely thick gloss paint. My pointing is bloody tidier than that ordinarily but I could barely see where the bricks were to use the grinder or bolster. Obviously I'm aware I should have sanded them all down, but I don't have that equipment. The entire back has been done. I feel fairly certain given that the mortar was gone right around where the water was gushing out that this was the problem.

That brick wall adjoining on the back yard is a disgrace, but the mortar next to it is showing no signs of water damage.

Oh and there was not an airbrick so I put one in.

Tanking general questions

Hope I can get some input from you fellas :) I should not have done that tanking myself, maybe in a years time after the course is done but I'm a little happy with myself and if I have properly sorted the problems out I'll be even happier again.
 
Skimmy1 said:
Why tank it when you can let the wall dry down? Tanking the wall will hold the damp in the wall and push the damp to other walls and increase the moisture content in the bearing end timbers that will cause decay, if the client wants a dry finish ASAP use a ventilated membrane with a thermal plasterboard.
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Well I've been learning a lot about this and would like to think I've got a basic good grasp of physics in general and I'd disagree from my laymans point of view.

You tank the inner wall you don't trap moisture you stop it spreading internally but it doesn't stop it drying out in the cavity or moving elsewhere, the other side of the bricks are not tanked after all and the mortar which seems to carry it likewise. It would only be trapped if you tanked the cavity and the exterior wall as well. Having adequate ventilation and air movement around the walls and through the bricks will stop moisture just hanging around but dry it out - IF - if you have sorted out what was causing the moisture to be there in the first place. In my case I feel sure it was a clutter/gutter/bridge issue.

Does any of that make sense?
 
Sorry I didn't know it was a cavity wall! There is no reason to tank a cavity wall still though, penetration from a gutter leak wouldn't normally come through to the internal skin. If it was the first thing is good diagnosis. If you are not a specialist in damp diagnosis it is best to leave it to somebody that is as you could be liable for any loss especially if you are carrying out unnecessary works that may not fix the defect or cause other defects.
Thermal imaging paints the best picture on this type of defect, but if this isn't possible it would be best to remove a brick or use an endoscope and check for internal snots of mortar bridging the cavity or wall tie or even wet insulation. Tanking will push damp around the walls, it's vapour permeable but not much, all built in bearing end timbers are at risk of decay. In the first instance of any leak or penetration rapid drying of the structure is recommended before any remedial work is carried out. Read Bre on walls drying down and this will explain on drying times.
Hope this helps
 
Sorry it is not a flaming cavity!

I've done this for two aged grandparents and I've almost entirely rebuilt there groundfloor rotted through with woodworm (all floors, and joists) and this has led to various other jobs getting done and we've blown the last money we have available to spend for them on the property so we'll have to see what happens.

I'll just have to hope that is enough and if its not we'll sort it out...er morbidly after certain things happen (Both 88,89 and ill with cancer) and we'll be tearing the place apart anyway and hopefully I'll be more experienced then. Come at a bad time as my savings are at their lowest especially due to retraining and the folks well they've paid what has been spent so far.
 
Normal tanking 5 coat system.

3/1 sand cement render non scracthed coat up to 12mm thick containing an integral water proofing agent such as render guard or sika1

then whilst its all still green apply by brush or trowel two coats of tanking slurry ( tt55-vandex or nvirol) up to a total thickness of 3mm)
then top coat it with a 3/1 sand cement mix allow to set then skim it the next day.

don't let the first coat go of or the tanking set as you wont get it to stick ...

This is a basement spec , you can add sbr to the first mix if you fill the need and don't over trowel the skim as you will close up the pores stopping the wall from breathing.

only use bagged plastering sand as its been washed so most of the muck and salt has been washed out of it, ideally use a grade m sand such as Leyton buzzard.
 
I just looked at your pics, the ground level is high and a bridging plinth with sub floor ventilation 1ft up the wall.....no wonder it was damp, looks like its pointed with s&c would be a better job if it was lime! The chances of that wall drying down will take a long time, it will also be cold in the winter and most of the bottom half will be below dew point and cause a condensation problem.
@dampworks....skim the next day. don't thinks so, the plaster will pop. How you could scratch, 2 coats of tanking, top a basement in day is beyond me!
Anybody that tanks a basement deserves to be in court, 220mm of hydrostatic pressure will put a 100mm floor into flotation and the walls will go into bending. Can you tank a basement BS 8102:2009? If you read the standard it will tell you about design philosophy and the risks especially with defects. You a brave man lol
The reason most people get away with cementitious tanking in a basement is because it never floods its mainly just damp.....get some water around and its ******, and so are the built in timbers.
 
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What's you answer then skimmy ? hack the walls of and have dehumidifiers running 24/7 ? or would you use the sedum roofing plastic to channel away the moisture ?
 
Skimmy1 said:
I just looked at your pics, the ground level is high and a bridging plinth with sub floor ventilation 1ft up the wall.....no wonder it was damp, looks like its pointed with s&c would be a better job if it was lime! The chances of that wall drying down will take a long time, it will also be cold in the winter and most of the bottom half will be below dew point and cause a condensation problem.
@dampworks....skim the next day. don't thinks so, the plaster will pop. How you could scratch, 2 coats of tanking, top a basement in day is beyond me!
Anybody that tanks a basement deserves to be in court, 220mm of hydrostatic pressure will put a 100mm floor into flotation and the walls will go into bending. Can you tank a basement BS 8102:2009? If you read the standard it will tell you about design philosophy and the risks especially with defects. You a brave man lol
The reason most people get away with cementitious tanking in a basement is because it never floods its mainly just damp.....get some water around and its ******, and so are the built in timbers.
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Any suggestions on how to improve the situation? I'm not going to lie I'm not 100% I understood your post, my fault not yours.
 
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