blockwork coming through the external sand and cement

tonydude

Anyone know why this occurs, my brother has built a new garage and this is starting to happen. The block work layout is coming through the sand and cement . The garage went through the usual process of plastering. Seen it in a lot of houses and it looks dog rough. Brother is fuming over it.

bbam

tonydude wrote: »

Anyone know why this occurs, my brother has built a new garage and this is starting to happen. The block work layout is coming through the sand and cement . The garage went through the usual process of plastering. Seen it in a lot of houses and it looks dog rough. Brother is fuming over it.

I've always been told this was due to NO or too thin of a scratch coat under the plaster layer... Looks sh1t

paddy147

bbam wrote: »

I've always been told this was due to NO or too thin of a scratch coat under the plaster layer... Looks sh1t

Theres a certain developer who is in deep shyte at the moment for this same reason.

A large appartment complex recently built on the northside of Dublin for affordable housing and regneration scheme of a certain area.

The slightest bit of damp in the air or a sprinkling of rain,and you can see all the blockwork behind the blue coloured plaster/finish coat.:rolleyes::rolleyes:

Dupont

its from not scudding the blocks prior to plastering another man trying to save money

martin46585

One way to stop it's from happening is to, as dupont already said is to scud the blocks first,
The reason being that the moisture is getting to the block work, and the mortar joints will absorb it more that the blocks will,
And as scudding is usually a fairly strong mix of 2/1, the moisture can not penetrate the coat of scudding,
Though sometimes in a badly vented timber frame, it can be more obvious,......

moy83

How well pointed were the blocks ? I saw this happening on a gable of a house i plastered a few years ago . It was scudded got a good scratch coat and finnish coat . The joints were very badly pointed . The joints show through if we get heavy rain . I think it soaks through the plaster after awhile , fills the joint and just takes alot longer to dry out than the rest of the gable . When i come across it now i actually take the time to repoint bad joints . Also I think too much plaz in the blocklayers mix might soak up too alot of water and hold it for longer than the plasterers mix which would show up the joints

tonydude

It was scudded but could have been better the blocks were very well finished hes a sh@t hot block layer . Water proofer was put through it as far as I know . My brother wont be paying him if it remains this way. From my experience it doesnt get better. At least I wont get the blame ( I did the roof )

Spread

Blockwork should be scudded. A few days later scratched. And after a week or so floated. Waterproofer in scratch and float coats.Total thickness 20mm+ If it's a garage and your brother did not specify a scratch coat it may be a moot point.

YouTookMyName

Wouldn't leave it a week for the 2nd coat. 2/3 days max.

tonydude

It was scudded , couple of days later scratched, then the side walls were finished off 2/3 days later, Then about a week went by when he started the gables. The weather wasnt that hot so the mix would have went off alright. The blockwork is coming through the gables a lot more than the sides.

Al Capwned

The scudding is purely to give a better bond between the scratch and the block...
Scudding will not prevent blocks showing through S&C.....

This happens for one of two reasons -

1. Scratch coat was not fully cured before finish coat was applied.
2. Plasticiser used instead of waterproofer in scratch coat!

Either way, it's dodgy plastering!

Spread

YouTookMyName wrote: »

Wouldn't leave it a week for the 2nd coat. 2/3 days max.

Any reason why?

plaster e

The Reason this happens is due to a difference in suction between the two backgrounds
that are being plastered.. Block-work / joints.. Depth of plaster will not prevent/cause
this to happen...

Cerco

plaster e wrote: »

The Reason this happens is due to a difference in suction between the two backgrounds
that are being plastered.. Block-work / joints.. Depth of plaster will not prevent/cause
this to happen...

Interesting response. So what is the solution then?

Right2Write

Paint it?

red sean

Cerco wrote: »

Interesting response. So what is the solution then?

You'll probably find it in another zombie thread!

TheLastMohican

red sean wrote: »

Cerco wrote: »

Interesting response. So what is the solution then?

You'll probably find it in another zombie thread!

Zombie or not, if the correct procedure is followed then the render should look uniform after heavy rain.
Splatter coat 2:1, scratch 3:1 with waterproofer and float out with 9:2 or 4:1 with a shot of hydraulic lime.

Bonzo Delaney

I've often heard it's because the wall's weren't wetted down enough if any before plastering was carried out
which would tie in with the suction theory

woodturner

Having talked to a plasterer about this, he said it probably only got one coat of plaster and no scratch coat. Also possibly due to no water proofer such as Cementone being added to the mix.