Tanking a basement

[HawkEye]

Hi chaps,

I'm looking at taking on a big job over the coming weeks - DIY tanking to my cellar/basement area.

Now, I've had a survey so far and the guy seemed very knowledgeable. The house is very old with no DPM or DPC.

Unacceptable moisture readings are through the floors and large sections of wall throughout the cellar.

I'm waiting for the cost in the quotation and expecting it to be in the thousands. The guy suggested a membrane or sheeting system over a cementitious system, as a small gulley or channel will be fitted to drain the water away. He said with the cementitious system, the pressure of the water or hydrostatic pressure, can build with nowhere for the water to go, so it finds its way out elsewhere. Which research suggests to be true.

Now my question is, do I go with his advice and fit my own membrane system (I need to find some good systems if anybody can recommend them??) or use the cementitious system?

Also, as I'm going to construct new partitions on this level, so if I'm applying some sort of substrate to the floor, how do I fix studwork??? Will this bridge the substrate I have applied and leave passage open to moisture rising?? Help appreciated

 

[the_g_ster]

How big is the area that you are looking to do?

The best way is to have the gap, so nothing can bridge it. It is a very specialised thing to do, as it relies on 100% accuracy, if you mess one joint up then of course it means you still have a damp smelling room.

I would first err on the side of getting it done by a pro, and maybe seeing if you can assist to bring the labour cost down.

If you want to do it yourself, you have to think how long you will be in the house for. The preference would be something like this, as the drain system will be easier to fit, and doesn't rely in your ability to render 100% perfect.

http://www.safeguardeurope.com/applicat ... oofing.php

Or, if you are only in the house for a few years, you could try a bodge of some DPM battened and sealed with silicon to the walls, then a self contained bit of studwork in front of that, so as to not go through the DPM. Then board over. It would be cheap, and last a few years.

Though I would err on getting it done properly if you are going to use it for putting tools in, or if only a few cases of wine and beer, just leave it.

 

[Jacob]

I dried out the earth sub floor in a basement here (half underground), and cured dry rot in the process, by fitting periscope vents i.e. 4" drain pipe from below the timber floor taken up high to a vent on the outside. Might help your cellar problem. It can take a long time for wet masonry to dry so you'd have to wait some time to see an effect, maybe a year.
NB you can get flat section pipe and conceal it if you take it up the inside of the building. Ideally all the way up to the ridge (see "Passivent") but however high you took it would have some benefit.

A large component of damp in cellars can be condensation onto cold walls and ventilation cures this at least.

PS if condensation was part of the problem you could expect to notice it at the moment with warm humid air about, and expect it to be drier in winter. But there are lots of variables.

 

[No skills]

If you went with the membrane system - do you have a gravity drain away for the water build up or would you need a pump/sump setup? possibly an extra cost to factor in.

Just a thought.

 

[HawkEye]

Thanks chaps.

Truth is I don't know what to do. Floor area must be about 8 x 12m off the top of my head. Still not had a quote back from the damp surveyor and I don't want to shell out thousands as this will be a rental property. I want to have a go at the DIY but because I don't have confidence in what I'm doing because I don't know if its the right thing, it makes me not want to do it

How much will a pump set me back and the running costs?? What if the tenants pineapple something up downstairs, I'd be worrying about it non stop...

 

[HawkEye]

G_ster, I was planning on making 2 bedrooms and a bathroom in the cellar !!!

 

[RogerS]

What happens when the pump fails?

How are you going to get all that s**t out of the basement. Saniflo?

Habitable space...aren't there rules about ventilation? Light? Would you want to live in a lightless hole in the ground?

This looks useful http://www.homebuilding.co.uk/advice/ex ... ment/guide

and here http://www.basements.org.uk/

 

[John51]

Would a 2 part epoxy paint work? As in isolate the space from the damp.

 

[HawkEye]

Right,

Well I've made some progress with this, somewhat.

Both surveyors I had told me that a membrane system was the one to use. Both quoted over £5000.

Now I'm thinking why do I need to pay that when there are DIY products on the market such as SIKA.

So I'm in the process of contacting SIKA, to get an approved SIKA installer to come and do a free survey... only problem is they will ALSO be pushing their system in me...

So at the moment finding it very difficult to get the right information

 

[HawkEye]

What happens when the pump fails?

How are you going to get all that s**t out of the basement. Saniflo?

Habitable space...aren't there rules about ventilation? Light? Would you want to live in a lightless hole in the ground?

This looks useful http://www.homebuilding.co.uk/advice/ex ... ment/guide

and here http://www.basements.org.uk/

It's already a habitable space, but in answer to your other questions, asking me what I don't know the answer to is not going to help me mate

 

[RogerS]

What happens when the pump fails?

How are you going to get all that s**t out of the basement. Saniflo?

Habitable space...aren't there rules about ventilation? Light? Would you want to live in a lightless hole in the ground?

This looks useful http://www.homebuilding.co.uk/advice/ex ... ment/guide

and here http://www.basements.org.uk/

It's already a habitable space, but in answer to your other questions, asking me what I don't know the answer to is not going to help me mate

Well, the questions were somewhat rhetorical but were intentioned to give you food for thought. Shouldn't have bothered, clearly.

 

[twothumbs]

Take look at (1) Visqueen Self Adhesive Damp Proof Membrane, and others which I cannot remember at the moment...I will remember at 3.00 in the morning. Self sticking with primer paint and an easy DIY material. Pop into a trade builders merchants to see them in the roll. There are other issues of water pressure and insulation so cost the visqueen and see what it works out at. Visqueen web site worth a look at, and they may be good and give you some assistance on technical matters. Any material needs to be protected from physical damage. Best wishes.

 

[billybuntus]

Just before you commit yourself.

What are you intending to utilise the space for? Our cellar (badly tanked with cement render) was hopeless when we moved in.

It has a huge CFM fan pulling air through it direct to the outside. This was the first problem. It moved air at such a rate to change the air temp depending on what the temp outside was = condensation with the fan off I saw 65% RH and 85%+ with it on.

I simply fitted a small dehumidifier with an external drain off. Then fitted a condensate pump with automatically removes the water from the dehumidifier and pumps it up and out into the ground floor drain.

It took around 2 months to even out and not I have it set at 55% RH which is great for storing wine\beer\tools etc etc

You could easily work down there if you so choose.

 

[StevieB]

Oldroyd do membranes that are available to the home user and have a range of options.

I looked into this some 5 years ago when doing my cellar. In the end it was dry enough that I simply put in stud walls with CLS, kingspan and OSB, then plasterboard and a skim over the top of that. Stayed dry and sound ever since.

A word of warning - if you are calling the cellar 'tanked' then it need guarantees if when you want to sell the house you want to call it a habitable room. If you do not have guarantees (ie you did it yourself) estate agents will ONLY call it a cellar room, not anything else (bedroom, hobby room etc). Doesn't matter how dry or sound it is - tanking is the only recognised way of making the room habitable. There are, as you have discovered, multiple ways of doing this (waterproof plaster, synthaproof, membrane etc) but it will not count as 'tanked' if you do it yourself for house selling purposes - this can really affect the value when selling, as I found when putting my house on the market by all 3 agents who valued it.

Steve

 

[Eric The Viking]

Starting from first principles, what does the house look like? By that, I mean, is it on a slope, at the top/bottom of a hill, and how does the basement relate to the ground surrounding, and where do the drains run, etc. What type of soil and geology is it in (I'd guess London clay if it's in the basin)? What's the ceiling height in the basement, how far down are the actual footings, and when it was built what were the rooms intended to be used for (you can guess this usually)?

How old is the property, and has a previous owner had a go at this problem in the past? If so, what did they do, as far as you can tell?

This information is important for two reasons: sorting out where the dampness is coming from and what options you have to deal with it. It's not like fixing a failing DPC in a no-basement property, but it's hard to suggest an approach unless you give us the basics.

Any basement room without air changes will smell musty. Because it's cooler in the summer than the rest of the property, moist air falls into it and the moisture condenses out on the cooler surfaces. Result = damp. If it's worse than that, if you've got obvious damp between flags on the floor, for example, you need to take a view as to how it's getting there. Hydrostatic pressure only occurs because the water table is higher surrounding the basement floor. Knowing why this is (location, position of water courses, natural land drainage, etc.) determines what you can or should do.

Pictures would also probably help a bit (inside and out).

E.