Lime mortar or not? Will cement render be ok?

[peaps2]

"We know that efflorescence is a fine, white, powdery deposit of water-soluble salts left on the surface of masonry as the water evaporates. These efflorescent salt deposits tend to appear at the worst times, usually about a month after the building is constructed, and sometimes as long as a year after completion."

http://www.masonryinstitute.org/pdf/612.pdf

 

[tim00]

peaps,

And? How will the insulation be blocked? Why would DPC "cover the cavity"? If it did it would be bridging the cavity.

CWI certainly does cause many problems, but we are not even certain that the walls in question are cavity walls. Neither had the OP mentioned CWI prior to you.

The black effects may indeed be mortar ash, but it may also be something else, and the OP is on site to eye-ball and ID it.

Regarding the salts, are you insisting that salts only appear after drying out?
Perhaps you are confusing this issue with efflorescence?

 

[tim00]

peaps,

I've just posted in response to your 2.51 post and see that you have another 2.59 post.

Yes, there are efflorescent crystals on the exterior brickwork, but that is irrelevant to this remedial situation. Here, we are discussing hygroscopic chlorides and nitrates at lower levels and penetrating damp at higher levels of the walls.

 

[peaps2]

peaps,

And? How will the insulation be blocked? Why would DPC "cover the cavity"? If it did it would be bridging the cavity.

CWI certainly does cause many problems, but we are not even certain that the walls in question are cavity walls. Neither had the OP mentioned CWI prior to you.

The black effects may indeed be mortar ash, but it may also be something else, and the OP is on site to eye-ball and ID it.

Regarding the salts, are you insisting that salts only appear after drying out?
Perhaps you are confusing this issue with efflorescence?

He PMed me and yes it is a cavity and insulation was done before they purchased the house.

If the render from the floor was soaking water up the wall you would expect the soft mortar to be below the dpc also.... This is one of the reasons I suspected the insulation. We have no idea how the dpc was installed or if it bridged the cavity, fact is that it's done regular. Debris is also a problem at the dpc level as the house is built up mortar etc fall into the cavity.

No confusion about salts, here.

http://en.wikipedia.org/wiki/Efflorescence

Efflorescence is salt.

Yes it may be black ash mortar of damp stain or... I would advise that he knocks off the internal render also. Redo inner and outer walls.

 

[peaps2]

peaps,

I've just posted in response to your 2.51 post and see that you have another 2.59 post.

Yes, there are efflorescent crystals on the exterior brickwork, but that is irrelevant to this remedial situation. Here, we are discussing hygroscopic chlorides and nitrates at lower levels and penetrating damp at higher levels of the walls.

Not irrelevant since it's an indication the wall is drying and it would be a good idea to neutralise the problem before the render goes on....


Bell cast bead is the way to go though.

 

[peaps2]

peaps,

I've just posted in response to your 2.51 post and see that you have another 2.59 post.

Yes, there are efflorescent crystals on the exterior brickwork, but that is irrelevant to this remedial situation. Here, we are discussing hygroscopic chlorides and nitrates at lower levels and penetrating damp at higher levels of the walls.

salts appear at all levels, above and below the dpc from the pictures.

 

[StephenRJames]

Thanks for all the help your giving, i understand the bell cast bead and was going to put it in the the re-render project, Tim00 you said put it just above the upper dpc, but what do i do with the exposed bricks under that? just render and leave space before bell i guess, and is it ok to take the lower section to the ground level or better of leaving a gap to path?
The dark bits on the back wall are what seems to be a very hard cement render with a light very thin skim of grey plaster/something, this thin coat is whats blown and the hard cement render seems to be solid all over but does seem to change colour if its rained for a couple of days.
I should of said i had a survey done about 8 weeks ago because of some render cracks which he said were just that and nothing to worry about, he couldn't even find out if i had cavity walls or solid and just went on what i said.

 

[peaps2]

Thanks for all the help your giving, i understand the bell cast bead and was going to put it in the the re-render project, Tim00 you said put it just above the upper dpc, but what do i do with the exposed bricks under that? just render and leave space before bell i guess, and is it ok to take the lower section to the ground level or better of leaving a gap to path?
The dark bits on the back wall are what seems to be a very hard cement render with a light very thin skim of grey plaster/something, this thin coat is whats blown and the hard cement render seems to be solid all over but does seem to change colour if its rained for a couple of days.
I should of said i had a survey done about 8 weeks ago because of some render cracks which he said were just that and nothing to worry about, he couldn't even find out if i had cavity walls or solid and just went on what i said.

Black ash render sets hard.

 

[tim00]

FWIW:I should like this to be this will be my last post on the subject, however, if i can help you a little further Stephen i will:

1. If you are privy to further information perhaps it would be generous and helpful to share it. No mind readers on here.

2. Efflorescence in this kind of remedial situation is quite irrelevant - you are chasing a red herring.
Do you believe that all the money, materials and craft that goes into a "damp" situation is to chase out any efflorescence?
Precisely, how will efflorescence affect the application of a tight scratch coat to the extn walls? How will it affect the rendering of the internal walls? I'm asking you for precise details, please.

3. How in the name of God, can the wall be drying-out given the OP's original complaint, and everything that we can see, tells us that the wall is anything but drying out? Have you read a book on this subject and post without prior experience?

4. Why do you refer to the ground level as "the floor"? Now you seem to be suggesting that rendering below the path is of little significance?

5. The brick course below the lower DPC can be seen to be clearly soaked, even with the bad pic.

 

[StephenRJames]

i take it black ash render is bad? will be if i got it suppose. Does it need removing internally or ok if water problem solved?

 

[tim00]

Stephen,

1. Leave the brickwork below the DPC's exposed - do not render over it - period. The lower course of bricks can be cleaned off, replace perished bricks and repoint.

2. the path is lower than the bottom DPC so leave well alone after doing the above.

3. Hire a small breaker chisel to remove stubborn backing.

4. ref the "surveyor" - you typically determine the wall thickness with a simple measurement - anyone with experience can eye-ball it.

 

[tim00]

Stephen,

Black ash whatever is not bad, but if you are going to render up to the 1m line then knock off all below it to the bare brick.

 

[tim00]

peaps,

"We have no idea how the dpc was installed or if it bridged the cavity"
What nonsense is this? Then why mention it so positively and use a meaningless pic to back up your fantasy.
I have never encountered a DPC that spannned two skins and a cavity, esp. a bitumen ( which we have in-situ ) DPC.

"fact is that it's done regular" I dont know what you are talking about.

" no confusion about salts, here" First, i've never heard anyone in the building trades refer to efflorescence as "salts", second it seems to be one of the few things that you are not confused about.

 

[peaps2]

2. Efflorescence in this kind of remedial situation is quite irrelevant - you are chasing a red herring.
Do you believe that all the money, materials and craft that goes into a "damp" situation is to chase out any efflorescence?
Precisely, how will efflorescence affect the application of a tight scratch coat to the extn walls? How will it affect the rendering of the internal walls? I'm asking you for precise details, please.

http://www.buildingconservation.com/articles/salts/salts.htm

It may be secondary that would cause the brick to decay, why cover up what can be quickly neutralise while you have no render on it?

3. How in the name of God, can the wall be drying-out given the OP's original complaint, and everything that we can see, tells us that the wall is anything but drying out? Have you read a book on this subject and post without prior experience?

It may be that when it rains it's at it's wettest and a period of dry will cause salts to appear, Salt appear through evaporation of water so yes it has to be wet at some point.

4. Why do you refer to the ground level as "the floor"? Now you seem to be suggesting that rendering below the path is of little significance?

No I did make a point that the bell cast bead was the way to go.....

5. The brick course below the lower DPC can be seen to be clearly soaked, even with the bad pic.

Could be run off from the path? Fact remains the softest area is above the dpc the bottom doesn't seem to be affected, this suggests the problem may be above the dpc.

This house was built in the 1930s when they had just started building cavity brick walls. Common problem with 1930 builds is they have had damp problems due to dpc bridging.... It might have been because brick layers were used to solid wall construction where bridging was not an issue.

 

[peaps2]

peaps,

"We have no idea how the dpc was installed or if it bridged the cavity"
What nonsense is this? Then why mention it so positively and use a meaningless pic to back up your fantasy.
I have never encountered a DPC that spannned two skins and a cavity, esp. a bitumen ( which we have in-situ ) DPC.

1930 builds had a problem with bridging, it was common. The pic illustrates a modern wall that the dpc has bridged.

"fact is that it's done regular" I dont know what you are talking about.

Need to get out more then.

" no confusion about salts, here" First, i've never heard anyone in the building trades refer to efflorescence as "salts", second it seems to be one of the few things that you are not confused about.

http://www.buildingconservation.com/articles/salts/salts.htm

The opposite is the case with me, it's salt. Above link must indicate they are not in the trade since they don't use the word efflorescence instead they use the word salt....

Hope I've answered your questions.