2 weeks ago I scratch coated a brick boundary wall, 2 x 5 mtr, 1 to 4
mix (50 year old render fell off) no problems with it apart from an
aching back.
Today got on with the final coat, 1 to 5 mix, applied around 6 m2 and
went in to get a drink, came outside again and saw that about 3/4 had
fallen of the wall so went back in for a stronger drink to ponder the
situation.
Any ideas? I scratched the first coat so did not use PVA and hosed down
the wall, I am wondering if I counted the wrong mix of cement as I was
distracted at the time (no not with a busty girl walking by but the
swmbo, mind you she is not short in that department but that is sadly a
distant memory)

--
Corporal Jones
"Don't panic don't panic"
Life will go on albeit somewhat reduced

On Jun 7, 3:44*pm, Corporal Jones
wrote:
2 weeks ago I scratch coated a brick boundary wall, 2 x 5 mtr, 1 to 4
mix (50 year old render fell off) no problems with it apart from an
aching back.
Today got on with the final coat, 1 to 5 mix, applied around 6 m2 and
went in to get a drink, came outside again and saw that about 3/4 had
fallen of the wall so went back in for a stronger drink to ponder the
situation.
Any ideas? I scratched the first coat so did not use PVA and hosed down
the wall, I am wondering if I counted the wrong mix of cement as I was
distracted at the time (no not with a busty girl walking by but the
swmbo, mind you she is not short in that department but that is sadly a
distant memory)

--
Corporal Jones
"Don't panic don't panic"
Life will go on albeit somewhat reduced

Possibly too hot a day, direct bright (hot) sun etc

Assume yr using opc/sand not lime/sand

"Corporal Jones" wrote in message
...
2 weeks ago I scratch coated a brick boundary wall, 2 x 5 mtr, 1 to 4 mix
(50 year old render fell off) no problems with it apart from an aching
back.
Today got on with the final coat, 1 to 5 mix, applied around 6 m2 and went
in to get a drink, came outside again and saw that about 3/4 had fallen of
the wall so went back in for a stronger drink to ponder the situation.
Any ideas? I scratched the first coat so did not use PVA and hosed down
the wall, I am wondering if I counted the wrong mix of cement as I was
distracted at the time (no not with a busty girl walking by but the swmbo,
mind you she is not short in that department but that is sadly a distant
memory)

--
Corporal Jones
"Don't panic don't panic"
Life will go on albeit somewhat reduced


What I do is get a bucket of water and a large paint brush and flick water
on to the area to be rendered. This stops the wall being thirsty and sucking
the moisture out of the new render.

mark

In article ,
Corporal Jones writes:
2 weeks ago I scratch coated a brick boundary wall, 2 x 5 mtr, 1 to 4
mix (50 year old render fell off) no problems with it apart from an
aching back.
Today got on with the final coat, 1 to 5 mix, applied around 6 m2 and
went in to get a drink, came outside again and saw that about 3/4 had
fallen of the wall so went back in for a stronger drink to ponder the
situation.
Any ideas? I scratched the first coat so did not use PVA and hosed down
the wall, I am wondering if I counted the wrong mix of cement as I was
distracted at the time (no not with a busty girl walking by but the
swmbo, mind you she is not short in that department but that is sadly a
distant memory)

That problem is existing render too dry, and has sucked too much
water out of the finish coat. A second problem (which you didn't
get as far as hitting) is that the finish coat probably won't
bond very well to the scratch coat.

For sand and cement, finish coat should be done 24-48 hours after
scratch coat. This is for two reasons - the scratch coat moisture
level will be about right for the finish coat to stick, and the
scratch coat is still setting and will cross-bond with the finish
coat.

At this point, I suspect you'll need to do it as for a reskim.
That means water to kill the suction in the scratch coat, probably
mixed with a bonding agent to help the finish coat stick to the
scratch coat. I'm not sure what bonding agent to suggest.
PVA is water soluable so might not last for too long outside.
EVA (Exterior PVA) is more water resistant, but only in a cement
matrix (not as a bare glue), so it might work. SBR is probably
too waterproof and might lock moisture in the wall.
A cement slurry is sometimes used as a bonding agent.
Maybe someone else can suggest the right bonding agent?

--
Andrew Gabriel
[email address is not usable -- followup in the newsgroup]

On 07/06/2011 18:09, Andrew Gabriel wrote:
In ,
Corporal writes:
2 weeks ago I scratch coated a brick boundary wall, 2 x 5 mtr, 1 to 4
mix (50 year old render fell off) no problems with it apart from an
aching back.
Today got on with the final coat, 1 to 5 mix, applied around 6 m2 and
went in to get a drink, came outside again and saw that about 3/4 had
fallen of the wall so went back in for a stronger drink to ponder the
situation.
Any ideas? I scratched the first coat so did not use PVA and hosed down
the wall, I am wondering if I counted the wrong mix of cement as I was
distracted at the time (no not with a busty girl walking by but the
swmbo, mind you she is not short in that department but that is sadly a
distant memory)

That problem is existing render too dry, and has sucked too much
water out of the finish coat. A second problem (which you didn't
get as far as hitting) is that the finish coat probably won't
bond very well to the scratch coat.

For sand and cement, finish coat should be done 24-48 hours after
scratch coat. This is for two reasons - the scratch coat moisture
level will be about right for the finish coat to stick, and the
scratch coat is still setting and will cross-bond with the finish
coat.

At this point, I suspect you'll need to do it as for a reskim.
That means water to kill the suction in the scratch coat, probably
mixed with a bonding agent to help the finish coat stick to the
scratch coat. I'm not sure what bonding agent to suggest.
PVA is water soluable so might not last for too long outside.
EVA (Exterior PVA) is more water resistant, but only in a cement
matrix (not as a bare glue), so it might work. SBR is probably
too waterproof and might lock moisture in the wall.
A cement slurry is sometimes used as a bonding agent.
Maybe someone else can suggest the right bonding agent?


IME pva is fine. It doesn't need to be waterproof as its only purpose is
to partially seal the scratch coat long enough for the final coat to
set. If you overseal, the next coat tends to slide initially but, once
suction takes over, it hangs on ok

On 07/06/2011 18:42, stuart noble wrote:
On 07/06/2011 18:09, Andrew Gabriel wrote:
In ,
Corporal writes:
2 weeks ago I scratch coated a brick boundary wall, 2 x 5 mtr, 1 to 4
mix (50 year old render fell off) no problems with it apart from an
aching back.
Today got on with the final coat, 1 to 5 mix, applied around 6 m2 and
went in to get a drink, came outside again and saw that about 3/4 had
fallen of the wall so went back in for a stronger drink to ponder the
situation.
Any ideas? I scratched the first coat so did not use PVA and hosed down
the wall, I am wondering if I counted the wrong mix of cement as I was
distracted at the time (no not with a busty girl walking by but the
swmbo, mind you she is not short in that department but that is sadly a
distant memory)

That problem is existing render too dry, and has sucked too much
water out of the finish coat. A second problem (which you didn't
get as far as hitting) is that the finish coat probably won't
bond very well to the scratch coat.

For sand and cement, finish coat should be done 24-48 hours after
scratch coat. This is for two reasons - the scratch coat moisture
level will be about right for the finish coat to stick, and the
scratch coat is still setting and will cross-bond with the finish
coat.

At this point, I suspect you'll need to do it as for a reskim.
That means water to kill the suction in the scratch coat, probably
mixed with a bonding agent to help the finish coat stick to the
scratch coat. I'm not sure what bonding agent to suggest.
PVA is water soluable so might not last for too long outside.
EVA (Exterior PVA) is more water resistant, but only in a cement
matrix (not as a bare glue), so it might work. SBR is probably
too waterproof and might lock moisture in the wall.
A cement slurry is sometimes used as a bonding agent.
Maybe someone else can suggest the right bonding agent?


IME pva is fine. It doesn't need to be waterproof as its only purpose
is to partially seal the scratch coat long enough for the final coat
to set. If you overseal, the next coat tends to slide initially but,
once suction takes over, it hangs on ok
OK will cover with PVA tomorrow & have another go!

--
Corporal Jones
"Don't panic don't panic"
Life will go on albeit somewhat reduced

On Jun 7, 7:25*pm, Corporal Jones
wrote:
On 07/06/2011 18:42, stuart noble wrote:



On 07/06/2011 18:09, Andrew Gabriel wrote:
In ,
* * Corporal *writes:
2 weeks ago I scratch coated a brick boundary wall, 2 x 5 mtr, 1 to 4
mix (50 year old render fell off) no problems with it apart from an
aching back.
Today got on with the final coat, 1 to 5 mix, applied around 6 m2 and
went in to get a drink, came outside again and saw that about 3/4 had
fallen of the wall so went back in for a stronger drink to ponder the
situation.
Any ideas? I scratched the first coat so did not use PVA and hosed down
the wall, I am wondering if I counted the wrong mix of cement as I was
distracted at the time (no not with a busty girl walking by but the
swmbo, mind you she is not short in that department but that is sadly a
distant memory)

That problem is existing render too dry, and has sucked too much
water out of the finish coat. A second problem (which you didn't
get as far as hitting) is that the finish coat probably won't
bond very well to the scratch coat.

For sand and cement, finish coat should be done 24-48 hours after
scratch coat. This is for two reasons - the scratch coat moisture
level will be about right for the finish coat to stick, and the
scratch coat is still setting and will cross-bond with the finish
coat.

At this point, I suspect you'll need to do it as for a reskim.
That means water to kill the suction in the scratch coat, probably
mixed with a bonding agent to help the finish coat stick to the
scratch coat. I'm not sure what bonding agent to suggest.
PVA is water soluable so might not last for too long outside.
EVA (Exterior PVA) is more water resistant, but only in a cement
matrix (not as a bare glue), so it might work. SBR is probably
too waterproof and might lock moisture in the wall.
A cement slurry is sometimes used as a bonding agent.
Maybe someone else can suggest the right bonding agent?

IME pva is fine. It doesn't need to be waterproof as its only purpose
is to partially seal the scratch coat long enough for the final coat
to set. If you overseal, the next coat tends to slide initially but,
once suction takes over, it hangs on ok

OK will cover with PVA tomorrow & have another go!

--
Corporal Jones
"Don't panic don't panic"
Life will go on albeit somewhat reduced- Hide quoted text -

- Show quoted text -

Mix a little sand, cement, water and PVA in a bucket and brush this on
after the PVA coat on the wall.
Put your next coat on while this is still wet.
This helps a lot,
Be sure to "nip" the mix as you apply when you come to the end of a
stroke.