How do I identify external render as lime or cement render?

[dubbs]

Hi guys, first post to the forum.... I've been lurking for a while!

I've got an Edwardian house with a damp problem along one or two walls. The damp seems to be penetrating damp coming in from an external wall that had an incorrectly built french drain where the concrete was touching the wall rather than the french drain going down to earth. I've corrected this and need to dig a little further but also have a problem with render that has been put in from soil level up to about 1-2 feet above the driveway.

I believe the render that has been put in is cement render and during the course of time this has now got some hairline cracking which is trapping water and causing the penetrating damp.

It's my intention to remove all of the cement render and to replace with a lime render to the same height - I believe this to be a better solution to allow the wall to breathe properly and correct the problem. I'm not sure as to whether a hydrating or non-hydrating lime render would be best but this will also coincide with me adding some additional vent bricks.

Can you please advise as to whether this is correct, other things I should think of and how I can identify the render I have to know whether it is already a lime render or not? I'm wondering as maybe it was a cmement render with lime added... I doubt it but would be silly to take it all off only to replace like with like.

Thanks in advance for any assistance.

 

[tim00]

From what you say, it's difficult to visualise conditions as they are - can you post a diagram?
Until you have eliminated all likely possibilities hold fire on knocking-off render.
Lime render will have a grainier texture than cement render, and crumble more easier.But you would need to compare with cement render - for what it's worth if you are going to remove all the render.
Research posts on this subject to help you in eliminating possibilities and finding remedies.
Lime render typically, has a 1L:1C:4S mix.

 

[dubbs]

Hi Tim00 - yep, can see why it might be difficult to visualise sorry!!

I've taken extensive photos and put explanations next to them in my album...


View media item 41499 View media item 41500 View media item 41501 View media item 41502 View media item 41503 View media item 41504 View media item 41505 View media item 41506 View media item 41507 View media item 41508
I hope these help show the issue, I have put captions next to them all so that should explain.

Thanks!

 

[tim00]

Thanks for the pics,but a diagram is still needed to locate the pics in context with the house plan and the interior damp walls.Pics of elevations to eaves line would help.

1. your path/ground levels seem too high in places, esp. where a vent is almost covered.Have you investigated your sub-area and joist tails? Please show in-situ vent positions if you post a diagram.
2. green staining is typically from splashing often from broken gutters, or RWP's, or cills throwing water off.
3. the render is essentially a cement mix with chippings, and perhaps a smaller run of lime render. Be aware that plinth renders such as yours are a wicked idea and are actually pulling up moisture from the ground.
4.the hard pointing has merely been smeared on - 20mm depth of soft pointing is required.
5. if you intend to crack-out all the rendering, perhaps it will come away and leave a clean, if perished, brick face. Hence, replacing selected damaged bricks, and properly repointing the rest, might be the way forward.
6. is the french drain business working, and why only a partial installation?

 

[dubbs]

So... not a great diagram but to put pics in perspective here's a plan view of the house... colour key as follows:

orange: block driveway, shared across my and neighbour's properties
brown: earth
green: rear garden
yellow: concrete
blue: french drain
red areas damp are showing internally, at skirting level and up the wall no more than 1m

View media item 41512

 

[dubbs]

Questions answered where I can:

1. your path/ground levels seem too high in places, esp. where a vent is almost covered.Have you investigated your sub-area and joist tails?
Please show in-situ vent positions if you post a diagram.

I am adding some vents as I've seen same problem as you - this was also agreed by damp "specialists" I asked to come in who simply wanted to put impermeable render 1m up the wall then use chemical damp course to treat "rising damp". I'm adding an additional 9x6 vent at the front and another at the rear. Currently none at the side where the french drain is located so I am considering if I need a couple of 9x3 vents at either end.

I've only been able to look at one joist tail so far and it looked ok - I need to, and will be, checking others.


3. the render is essentially a cement mix with chippings, and perhaps a smaller run of lime render. Be aware that plinth renders such as yours are a wicked idea and are actually pulling up moisture from the ground.

So an impermeable concrete render is sucking up moisture from the ground? I can understand how as it fail the cracking will allow water in to the brickwork but how would it be drawing moisture up from the ground? As the bricks are permeable I expect they also do this up to the point of the damp course? In which case I'd need to ensure the bottom of the french drain is 150-200mm lower than the damp course to ensure it isn't bridging across to the brickwork above the damp course?

If the concrete render is drawing water up as well then I'd need to remove all of that as well - all houses in our road have render of some sort at ground level up and it appears to be part of the original design so not sure complete removal without replacement would be a wise option, especially in the french drain.


4.the hard pointing has merely been smeared on - 20mm depth of soft pointing is required.

The pointing of the brickwork? Yes I'd noticed it has been repointed at some point, no point in trying to remove it now but as/when it fails I'll have it replaced with lime mortar

5. if you intend to crack-out all the rendering, perhaps it will come away and leave a clean, if perished, brick face. Hence, replacing selected damaged bricks, and properly repointing the rest, might be the way forward.

As the render seems to be part of the original design of the house I'm unsure as to whether this is best course of action... I'm tihnking that it would have been lime render before so if this has been "rejuvenated" and raised with concrete then that would cause the problem.... that's my thinking anyway - all viewpoints and advice kindly considered!

6. is the french drain business working, and why only a partial installation?

No idea and no idea! Originally it had concrete from the base of the driveway connecting the render to the driveway so it had definitely not been done properly. I've chipped out the concrete and then dug down to earth along the full length of the drain... I now need to go a bit deeper to get 150-200mm below the damp course line... as the "alleyway" between the two houses is quite sheltered I'm hoping that this will be enough to sort the problem out (with any required render remediation) otherwise I'm guessing I'll need to dig the drain to slope out then install a pipe or similar to go to a soakaway...
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[tim00]

3. Capillary action between the plinth render and the brickwork will pull moisture up and into the wall - note all modern external renders have a bell cast at the base and stop short of ground contact. All internal plasters stop short of solid floors.

Your paths and hard standing were installed too high; there would have been no need for french drains or plinths if the surface level had been kept 150mm below the DPC. Your original DPC was probably bitumen.

Leave the french drain alone, or dig it out deeper and fill to below vent or DPC level with chippings. No "slope" or "soakaway" needed.

You mention "a wise option" - it's failed, you either live with it or do something about it. The crazed cracks in the plinth, and the pulling away from the wall, indicate a hard polished surface crazed by freezing, water ingress and differential movement with the brick background.

I think you should have a week-end of researching previous posts on this and allied subjects and perhaps discuss with old established neighbours what if anything they have done.

 

[dubbs]

Interesting... thanks for the info as it confirms my thoughts on the subject.

I believe the "wise option" of a lime render at low level was the original design and may have been apurely decorative one. This probably worked fine originally and then as that has worn or broken over the last 100 years it has at some pooint been re-rednered with concrete which is what we are seeing now. As that does extend down to DPC level then the moisture level you're talking about play - would that make sense to you?

Drive - yep shame but was definitely installed to high.. still without 1000's spent on rectification I need to try and see if I cam put in enough protection to make the problem go away.

DPC is slate and is quite a way down in to the french drain you saw. I'm wondering if an option would be to remove the render as you say but then, and after allowing sufficient time to let the bricks dry out apply a bitumen pain to the bricks that are in the french drain but aboce DPC to protect them against water ingress either from the drain or possibly from splash back?

I'm doing lots more research and will have a good look on here for further info... cheers!

 

[tim00]

I wont go on , but "the problem" wont "go away", it's built-in since 1. the DPC was rendered and bridged, and 2. the paths were raised.
Perhaps your best bet is, on your affected interior wall(s), to hack off from a level line 300mm above any signs of damp, and render with 1L:1C:4S ( or 2L no cement ) and skim with board finish.
Dont apply any kind of waterproofing or "bitumen paint", it will only cause further difficulties.