Maybe I had a bad day, but a little advice please on building over DPM + DPC

[VDubDan]

I'm hoping it was just an off day, but as tomorrow is rolling round thought I'd ask! Had my blocks delivered last weekend so decided to make a start on the inner corners and basically I failed miserably.

I built it as:

Block
Mortar
DPC
Mortar
DPM
Mortar
Brick

And "ironed" the DPM and DPC down, but even so I seemed to end up with quite a thick and uneven bed.

First question, is the mortar purely there to give a flat surface? I presume the DPC/DPM will never actually bind to it?

Secondly, when I came to build up my blocks I had a hell of a time getting anything plumb and square and I'm probably going to wind up tearing the thing down. Everything just seemed really unstable.

Just after some tips, really. I might do the outer corners first instead, as I don't remember having any trouble building ontop of DPC on my bricklaying course.

 

[^woody^]

Fill any joints/frogs and then spread a very fine smear of mortar, or a thin blob every 500mm or so, and flatten the DPM to this. Then lay your bed joint and flaten it to 10mm to receive the DPC. Lay the DPC. Then you can proceed upwards with the wall.

I'm not sure how to help with the blockwork via text. You need to watch some Youtube or something. But the key is to lay an even bed, then lay the block as upright as possible and not bang it all over the place. Make sure the bottom of the block is on the line where it should be, and then put the level against it and either slowly push it plumb, or pull the top edge of the block back.
If need be, hold a piece of timber on an angle and against the level near the top and this will keep the level firm and plumb while you mess with the block.

Plumb the block it and leave it.

And make sure you have full perp joints.

You should always start with the outer leaf.

 

[VDubDan]

Fill any joints/frogs and then spread a very fine smear of mortar, or a thin blob every 500mm or so, and flatten the DPM to this. Then lay your bed joint and flaten it to 10mm to receive the DPC. Lay the DPC. Then you can proceed upwards with the wall.

I'm not sure how to help with the blockwork via text. You need to watch some Youtube or something. But the key is to lay an even bed, then lay the block as upright as possible and not bang it all over the place. Make sure the bottom of the block is on the line where it should be, and then put the level against it and either slowly push it plumb, or pull the top edge of the block back.
If need be, hold a piece of timber on an angle and against the level near the top and this will keep the level firm and plumb while you mess with the block.

Plumb the block it and leave it.

And make sure you have full perp joints.

You should always start with the outer leaf.

Cheers Woody, appreciate you taking the time to respond. Are you saying the DPC joint should be 20mm in all (plus the little bit for the DPM?)

 

[^woody^]

Yes aim for 20mm - nice if it is, but its not that critical.

If the wall up to DPC is not level, then often the wall is/can be levelled in the first course above DPC, so it could end up with a different thickness DPC joint at each end of the wall.

 

[garyo]

Are you keeping your blocks dry given all the rain we've had? Doing stuff with no suction wont help.

 

[VDubDan]

Yes aim for 20mm - nice if it is, but its not that critical.

If the wall up to DPC is not level, then often the wall is/can be levelled in the first course above DPC, so it could end up with a different thickness DPC joint at each end of the wall.

Cheers Woody, and I'll have you know my walls are level to within a couple of mm all round

Are you keeping your blocks dry given all the rain we've had? Doing stuff with no suction wont help.

Now this is a good point - no, the blocks were definitely wet when I got them and it's rained a lot since. I've just gone and covered them so hopefully they'll dry up a bit by tomorrow.

 

[23vc]

Made the mistake of doing similar the other night, with saturated bricks/site. Then it got dark and I was jointing up with one hand, iPhone torch in other hand. It was a stepped DPC which didn’t help. From what I’ve read of your job so far Dan you’re more than capable of nailing the DPC course Then forget about it and get into a flow, gets more enjoyable then

 

[VDubDan]

Made the mistake of doing similar the other night, with saturated bricks/site. Then it got dark and I was jointing up with one hand, iPhone torch in other hand. It was a stepped DPC which didn’t help. From what I’ve read of your job so far Dan you’re more than capable of nailing the DPC course Then forget about it and get into a flow, gets more enjoyable then

Thanks mate, appreciate the vote of confidence!

Got out for a few hours yesterday (Work and weather are KILLING this project, but that's life) and things went much better. Fresh day, dry blocks, maybe a stiffer mix and I had far more success. Got three corners up, and ran in the first course of two of the walls.

I am querying my decision to go for partial fill, though - that just seems like an absolute pain in the neck. Might ring round some full-fill manufacturers tomorrow and see if they're happy with it being in a rendered property.

 

[23vc]

I did full fill dritherm on mine and rendered it, and seen many others done that way too, I don’t believe there’s an inherent problem with it, I remember looking into it in detail at the time (nhbc pubs etc) and came to the conclusion it was OK, and BCO was also ok with it.

 

[VDubDan]

I did full fill dritherm on mine and rendered it, and seen many others done that way too, I don’t believe there’s an inherent problem with it, I remember looking into it in detail at the time (nhbc pubs etc) and came to the conclusion it was OK, and BCO was also ok with it.

That's reassuring - I just spoke to Knauf (Which isn't pronounced how I thought!) and they say it's fine in rendered buildings. Will check with BCO, but sounds like the way forward.