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Default mortar too weak?

I've just started to rebuild the inner leave of an external wall
(terrace house). I've decided to use engineering bricks for the first
few rows starting just below the concrete floor but above ground.

The existing bricks (located between the foundations and the newly laid
engineering bricks) are slightly damp; so, I've opted for a 5:1 mix
plus a waterproofer.
Now, 2 days after laying the first 3 rows, the mortar used for the
engineering bricks still appears to be slightly damp and rather weak.

I am thinking of restarting from scratch, and use a stronger mix (e.g.
3:1) plus a waterproofer and a plasticiser as well.

Any comment greatly appreciated,

Thanks

Alex

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Default mortar too weak?

On 9 Aug 2006 20:24:19 -0700, Weatherlawyer wrote:

wrote:

The existing bricks (located between the foundations and the newly laid
engineering bricks) are slightly damp; so, I've opted for a 5:1 mix
plus a waterproofer.
Now, 2 days after laying the first 3 rows, the mortar used for the
engineering bricks still appears to be slightly damp and rather weak.


With it being slightly damp I'd say you have to find the reason for the
damp. I would have thought the problem with the masonry was that the
mix had dried too quickly in the ho weather.

Bricks -even engineering bricks, can absorb a lot of water and in hot
weather will suck a mortar dry too quickly.

5:1 using portland cement, is a strong mix. Most use 6:1 but you can
use 8 to one. The idea is to keep the bricks apart as muchas to bind
them together.


On the topic of weak mortar mixes. I recently decided to repair
one of the walls of my standalone, block-built garage. Towards
the base of the wall, the mortar was quite robust and in good
condition. As I looked higher up the wall, I noticed that the
mortar gradually changed colour and became a lot more friable.
The mortar between the top couple of rows of block was so weak that
I could remove it by brushing it with a normal stiffness paint brush.
(I stopped before I removed too much :-)

My theory was that whoever built the garage 20+ years ago ran short of
cement and mixed each bucketful weaker and weaker as he went up the wall.

At least now the wall has an outer coating of strong mortar. I can't
say how long it will last - hopefully it won't fail before I sell
the house!

Pete

--
.................................................. .........................
.. never trust a man who, when left alone ...... Pete Lynch .
.. in a room with a tea cosy ...... Marlow, England .
.. doesn't try it on (Billy Connolly) .....................................

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Default mortar too weak?

wrote:
Weatherlawyer wrote:
wrote:

The existing bricks (located between the foundations and the newly laid
engineering bricks) are slightly damp; so, I've opted for a 5:1 mix
plus a waterproofer.
Now, 2 days after laying the first 3 rows, the mortar used for the
engineering bricks still appears to be slightly damp and rather weak.


mortar takes a month to get its full strength up. 5:1 is more than
strong enough. I take it youre using all new bricks, not salvo old
ones. If youre using old you need a different mortar altogether.


With it being slightly damp I'd say you have to find the reason for the
damp.


These are bricks located underneath the concrete slab and in direct
contact with the earth on the sides and the foundations underneath (I
can't see it, but I assume and hope there must be some kind of
foundations somewhere under those slightly damp bricks).


I certainly wouldnt assume that. A lot of 19th century houses wrere
built with sod all in the way of foundations.


The house is rather old and I would rather prefer not to go down to the
foundations to resolve the "damp problem"...and anyhow, the damp
wouldn't affect the living area as I am using 3 courses of engineering
bricks to stop any rising damp from underneath.


So is there a damp problem or not? I'm not clear. The bricks in the
soil will of course be damp, but this wont normally transfer itself to
the living area. Think more explaantion is needed.

BTW one row of engineering bricks is more usual as a dpc.


NT



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Default mortar too weak?

mortar takes a month to get its full strength up. 5:1 is more than
strong enough. I take it youre using all new bricks, not salvo old
ones. If youre using old you need a different mortar altogether.


You are right I am using new engineering bricks but planning to use
older common bricks above them...thinking of using a 6:1 mix for them.

... A lot of 19th century houses wrere
built with sod all in the way of foundations.


You mean there are no foundations?

So is there a damp problem or not? I'm not clear. The bricks in the
soil will of course be damp, but this wont normally transfer itself to
the living area. Think more explaantion is needed.


No there isn't a damp problem; I've simply assumed that laying new
bricks on top of slightly damp ones would required some waterproofer or
a new DPC. I've opted for waterproof mortar and a few rows of
engineering bricks.

Thanks for your help,

Alex

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Default mortar too weak?

... A lot of 19th century houses wrere
built with sod all in the way of foundations.


You mean there are no foundations?

Not always no.

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Default mortar too weak?

wrote:
mortar takes a month to get its full strength up. 5:1 is more than
strong enough. I take it youre using all new bricks, not salvo old
ones. If youre using old you need a different mortar altogether.


You are right I am using new engineering bricks but planning to use
older common bricks above them...thinking of using a 6:1 mix for them.


If youre using old bricks, there are several reasons not to use cement
mortar. You can of course, but lime has several advantages, especially
when used on houses with little in the way of foundations. I'd
definitely suggest using lime instead for the commons.


... A lot of 19th century houses wrere
built with sod all in the way of foundations.


You mean there are no foundations?


The only way to know is to dig down. In 1800s and earlier houses varied
greatly, some have good foundations, most have very little, some had
none at all. So who knows. 3 bricks deep is a very common Victorian era
foundation, and that may be all youve got.


So is there a damp problem or not? I'm not clear. The bricks in the
soil will of course be damp, but this wont normally transfer itself to
the living area. Think more explaantion is needed.


No there isn't a damp problem; I've simply assumed that laying new
bricks on top of slightly damp ones would required some waterproofer or
a new DPC. I've opted for waterproof mortar and a few rows of
engineering bricks.


Most 1800s houses had no dpc of any sort, and normally were fine. Damp
handling on old properties is somewhat more complex than with new
builds. There are a lot of old properties that have become damp as a
result of unsuitable maintenance, but few that are damp due to original
design.


NT

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