pre treatment prior to tanking slurry and pre treatment of concrete floor before laying a vinyl or wood effect floor.

[Frazer G]

I have taken all the old plaster off an internal stone wall Which is now clean but uneven as the stone work is old with random sizes. I am proposing to carry out three elements of initial treatment. 

1) apply a coating of dilute PVA to "seal" the mortar (hopefully will spray it on) 

2) I will "flatten " the wall with a thin coat of 6:1:1 render (sand : cement : lime).

3) I will apply two coats (recommended) of tanking slurry

4) Apply a damp proofing membrane

 

The finish will be battens with PIR insulation between and plasterboard with a final skim of normal finishing plaster.

 

Can anyone confirm or otherwise that this is a reasonable approach to damp proofing an old stone wall? 

 

My second question is that in the same property there is a concrete floor of indeterminate age. Inspection seems to confirm that it is sound (no cracks) and visually "OK". However I am uncertain as to it's damp proofness although it seems dry. Should I apply a coating of some sort on the "better to be safe than sorry principle" and if so what coating would be recommended? I intend to lay a vinyl / wood effect floor but have not yet finalised exactly which (the boss needs to approve!).

[scottishjohn]

my advice --for what its worth 

 

don,t be stingy bugger and rake out any loose mortar  then  redner it with aproper mix 

like 3 -1 with waterproofer 

and only pva  or SBR what you are going to do that day  after severe dedusting and washing -stone is not very pourous like blocks 

yes let it just dry  but not dry for days before rendering  as it will not really bond as welland might just skin 

I have bo knoeledge of use of "tanking slurry"

 but can confirrm two coats of ehat isay is good enough to make above ground fish ponds  and in my case a firepond 

[Frazer G]

Thanks Scottishjohn, I have removed all the very loose plaster but I could actually keep raking until the house falls down. The builders of the day were apparently using quarry waste stone so the wall has every size but given the walls are about 2 ft thick they could get away with that "technique" - one occasion where quantity outweighed quality. What I need to do having removed all the surface and immediate loose mortar is stabilise what remains and fill any areas where the smaller stones have fallen out. I have read that a 6:1:1 mix is better in a stone situation as it is slightly more breathable than a full strength 3:1 mix and the lime content helps it "stick" in the cervices. While the stones are hard and distinctly non-porous the mortar is the exact opposite and the source of the damp issue hence my desire to ask for the best options.

[scottishjohn]

I maybe read it wrong 

I thought you wanted to make the wall solid and water proof 

6-1 will not make it water proof 

you either want it to stop dampness or let it breath

make your mind up 

if you do as you say you are then relying on your slurry -to be the water proof barrier  the3-1 mix with water proof addative will make your wal lstrong and water proof 

 basically same mix as you would cement rendr the outside 

 is the outside lime mortar ,if so it will let the water out that way  and not get to inside 

 

[Frazer G]

Hi Scottishjohn

 

I am guilty of not finishing the story. After the stage of applying tanking slurry i will be fitting a  mesh membrane (damp proof) which will then be plastered (not by me). My question only related to the tanking slurry part of the job. It was suggested to me that the tanking slurry would be easier to apply over a smoother surface than the random rock finish I am left with after removing all the old plaster.

[scottishjohn]

1 hour ago, Frazer G said:

Hi Scottishjohn

 

I am guilty of not finishing the story. After the stage of applying tanking slurry i will be fitting a  mesh membrane (damp proof) which will then be plastered (not by me). My question only related to the tanking slurry part of the job. It was suggested to me that the tanking slurry would be easier to apply over a smoother surface than the random rock finish I am left with after removing all the old plaster.

to use a local pgrase 

"seems along way for a short cut"

arough surface will make good bonding for the render or parge coat 

what ever you want to call it

 you did not say if outside of wall is lime mortar or cement 

[lookseehear]

Although I don't have a huge amount of practical experience, I've done a lot of research in this area because my house has similar construction for the most part. There are several schools of thought without much overlap, but in general the first question should probably be to ask why the wall is wet in the first place. Are all RWG in good working order? Is there a risk of a broken pipe somewhere nearby? You mention that it's an internal wall which would lend itself more to a problem at ground level or coming from within the wall above, rather than damp coming through the wall as you might expect if it was external. Is it on both sides of the internal wall? Is it limited to just one wall or to many walls? You mention the concrete floor appears dry. Do you have a sense of where the water table is relative to the levels of the house?

 

While tanking will stop water physically moving from in the wall to into the room, if the wall is wet it is likely to remain colder and will be more of a heat sink. If you put PIR over the top it will make the wall colder still, and any moist warm air from in the house that manages to get behind the insulation will condense on the surface inboard of the tanking slurry, and potentially lead to mould growth on the wall.

 

I'm sure tanking has a place when there are no other options, but the ideal solution would be to find a way to make the wall dry (or dryer than it is currently at least).

[Iceverge]

On 09/11/2024 at 08:45, Frazer G said:

I have taken all the old plaster off an internal stone wall Which is now clean but uneven as the stone work is old with random sizes. I am proposing to carry out three elements of initial treatment. 

1) apply a coating of dilute PVA to "seal" the mortar (hopefully will spray it on) 

2) I will "flatten " the wall with a thin coat of 6:1:1 render (sand : cement : lime).

3) I will apply two coats (recommended) of tanking slurry

4) Apply a damp proofing membrane

 

The finish will be battens with PIR insulation between and plasterboard with a final skim of normal finishing plaster.

 

Can anyone confirm or otherwise that this is a reasonable approach to damp proofing an old stone wall? 

 

My second question is that in the same property there is a concrete floor of indeterminate age. Inspection seems to confirm that it is sound (no cracks) and visually "OK". However I am uncertain as to it's damp proofness although it seems dry. Should I apply a coating of some sort on the "better to be safe than sorry principle" and if so what coating would be recommended? I intend to lay a vinyl / wood effect floor but have not yet finalised exactly which (the boss needs to approve!).

 

 

Ok.

 

 You really need to think about removing the conditions which moisture accumulates and promoting it's dispersion. Sealing anything is risky, espically when you do it at both sides of an old wall so in principle would avoid this 

 

Here is where I would start. 

 

1. Bulk water. 

 

This means french drains to lower water tables. Functioning guttering, appropriate pointing externally. Silicone brick creams. Eliminate leaking pipes etc. 

 

2. Ventilation.

 

Mechanical ventilation internally. A couple of dDCV fans as a minimum. These are cheap ~£70 and swap straight out for a bathroom fan. These will pull damp air out of your house and allow the structure to dry to the inside. Additionally you'll get fresher air inside. Other methods of ventilation like heat driven stack effect and manual opening of windows are typically very expensive or just don't get done. 

 

3. Airtighess. 

 

Believe it or not almost all the moisture problems that originate in a building are from the inside out. Vapour from breathing, showering, cooking etc. When you have cracks in your structure. Gaps and cracks around fixings, joists, windows, outlets all allow this to get "blown" into the wall where it risks condensing and causing issues like structural decay and mould.

 

4. Insulation. 

 

In your case internal insulation which is a double edged sword. On the one hand it'll keep the internal temperature higher promoting drying towards the inside but on the other hand it'll make the actual structure colder promoting condensation on the stone wall. If you avoid rigid boards of very low permeability like PIR and make an excellent job of the airtighess you'll mitigate most of these issues. 

 

Ok my suggestions. 

 

1. Deal with Bulk water as above.

2. Buy some greenwood cv2GIP dDCV fans.

3. Use a parge coat of sand NHL cement 3:2:1  to form an airtight layer on the stone. It can be trowelled or brushed on. Tape all windows to the parge coat with appropriate tapes. Similarly joist ends, pipe and wire penetrations. And seal to the floor and ceilings too. This is critically important to any internal insulation job. 

4. Install some 63mm stud walls internally to the stone walls with 70mm insulation in between the studs. (You can vary depth depending on your circumstances. 

5. Plasterboard and skim. 

 

 

 

 

 

 

 

 

[Iceverge]

On 09/11/2024 at 08:45, Frazer G said:

second question is that in the same property there is a concrete floor of indeterminate age. Inspection seems to confirm that it is sound (no cracks) and visually "OK". However I am uncertain as to it's damp proofness although it seems dry. Should I apply a coating of some sort on the "better to be safe than sorry principle" and if so what coating would be recommended? I intend to lay a vinyl / wood effect floor but have not yet finalised exactly which (the boss needs to approve!).

 

Again I think your thinking about this in the incorrect way. 

 

Rather than "sealing" it you should think about how you allow it to "dry"

 

Ensure the water table around the house is low by digging a french drain. 

 

If it is damp it will dry out assuming the conditions in the house are appropriate (warm/ventilated). 

 

Then you can lay your floor. Ideally something that isn't too vapour impermeable itself like cork or carpet.

 

 

[Frazer G]

Thanks for all the input. I am familiar with French drains as I did one for my daughter in Cardiff where the water was running down hill and meeting her property wall. It is a very successful method where the site allows it but in my current case the house is on a hill with the water running away so we are talking about residual ground moisture  not a water table as such.  I have chatted to my local building control team about this as contrary to many views in my experience if approached they are a mine of information based on local knowledge. They have suggested "off the record" that in the area of town all the houses circa 1890 were rough stone quarry waste and a type of coarse lime mortar and as such I and my children's children are unlikely to see it dry! A solution which they would approve but which does not need a formal application due to the size of the project would be to seal the existing wall with PVA if the surface is dusty / loose and then build an insulated stud wall with a gap between new and old to maintain air circulation.

 

Strangely having previously costed the tanking etc I have found that the new option is actually cheaper although cost was not a factor as I want it right not cheap! 

 

Regarding the concrete floor they were less convincing so I will probably follow Iceverge suggestion and use a decent quality carpet instead of the wood intended

 

 

 

[scottishjohn]

9 hours ago, Frazer G said:

build an insulated stud wall with a gap between new and old to maintain air circulation.

would always be my first suggestion  to isolate the problem to start with 

 

 remember for the air to gap work best it needs to be a clear gap vented to the eves  or cold roof space

I would still seriously consider a parge coat with water proof addative on the  internal stone work  and make moisture go  back out through your stone work and not in

 If you are wnaitng to keep the stone look outside 

 

 to fit stick down LVT the moisture level in the concrete floor needs to be less than 3.75%

 maybe be worth buying a suitable humidity meter to check the walls and floor now

 took 2 weeks of my UFH on  at 20c the dry out the concrete sub base and screed + self lveling coat  on top of the UFH and the sub base had been laid for nearly a year 

 so that sounds like a non starter

 

can you suffer loosing some head room  and fit a dpc across the concrete then a thin screed?

 or at least a liquid tanking coat going up the walls  about a metre ?

 rising damp does not go any higher than that  I am told