block mortar mix for internal single skin 7.3n celcon blocks

[LSB]

A mortar question for you guys. I am laying Celcon 7.3n blocks using a mortar mix of 5 to 1 (measured out by eye on the shovel) with blue circle cement and building sand from Travis Perkin and an additive to help the mix. The problem that I am getting is after a week or so the strength of the joint is surprisingly weak with little effort or pressure required to break the block off usually with a neat break with the mortar “delaminating” from the adjacent block or concrete foundation. Where am I going wrong ? What do I need to do to get a stronger bond.

 

We had concrete floors poured on Friday and there pump pipe knocked down 4 blocks as they went from area to area.

 

The wall has gaps for doorways so is only 4 blocks, is it just that this is too few blocks for a very heavy pipe.

Obviously, as it's built up it will be supported by lintels above the door ways.

 

The blocks were laid weeks ago, prior to us preparing the floor ready for pouring.

 

 

[Nickfromwales]

5/1/1 sand cement lime. You adding lime or not? 
 

Also if the blocks are dry and dusty they should be getting a quick dunk in a barrel of water before laying.

 

@nod?

[Russell griffiths]

Wrong blocks, you will not get a good bond onto celcon, you need to use a weak mix as the blocks are so weak the mortar ends up stronger than the blocks. 
a free standing wall will not have a lot of strength until the wall plate is on and it’s loaded with a roof structure. 

[nod]

Most of the new house builders are moving away from the lightweight blocks and back to solid concrete blocks 

Theres no strength till there is weight on and prone to blowing over 

Another  issue is they get knocked about by the fall protection when the joiners are putting the chambers in 

Brickies having to rebuild the internal walls on most properties 

 

Your dilemma is Do you risk strengthening the mortar and risk cracking the blocks 

 

If you add a waterproofer to your mix It will at least hold it back and give it time to grab 

 

Also measure your mixes in buckets Your probably a bit weaker than 5-1

Edited Sunday at 10:53 by nod

[LSB]

5 hours ago, Nickfromwales said:

5/1/1 sand cement lime. You adding lime or not? 
 

Also if the blocks are dry and dusty they should be getting a quick dunk in a barrel of water before laying.

 

@nod?

no lime added 😞

 

[LSB]

4 hours ago, nod said:

Most of the new house builders are moving away from the lightweight blocks and back to solid concrete blocks 

Theres no strength till there is weight on and prone to blowing over 

Another  issue is they get knocked about by the fall protection when the joiners are putting the chambers in 

Brickies having to rebuild the internal walls on most properties 

 

Your dilemma is Do you risk strengthening the mortar and risk cracking the blocks 

 

If you add a waterproofer to your mix It will at least hold it back and give it time to grab 

 

Also measure your mixes in buckets Your probably a bit weaker than 5-1

self build by hubby, he decided on these because they are only 9k whereas the solid ones are 18k and when he started he found them too much.

He's stronger now after all the work so changing will be feasible.

 

[JohnMo]

7 hours ago, LSB said:

Celcon

 

If you wet the blocks before cementing, they will stick together way better. The blocks suck all the water out of the cement and you are left with nothing to cure. Hence it being very weak bond.

[nod]

42 minutes ago, LSB said:

self build by hubby, he decided on these because they are only 9k whereas the solid ones are 18k and when he started he found them too much.

He's stronger now after all the work so changing will be feasible.

 

???

[Russell griffiths]

In this weather you can happily stand and soak the blocks with a hose pipe before laying, just soak the stacks of blocks while the mixer is getting loaded up.