Double or Triple Thickness Render on Breeze Block Wall

[Cej238]

We are having a rear extension built to our 1930s semi-detached house. Differences in wall construction and boundary lines mean than the new wall doesn't align exactly with the existing dining room wall. There is a pillar supporting a RSJ between the two lengths of wall and the new wall one side of the pillar is about 5cm further into the room.

We want to fit a kitchen along this wall and want it to look flush. We can work around the pillar, but the kitchen units are more troublesome. The units have a 46mm service cavity, so even removing this completely (which we wouldn't really want to do) won't quite make up the difference.

The obvious thing would seem to be to make the old wall 2-3cm thicker. That would mean the walls are only 2cm difference and we can even that out by trimming our cabinets.

What is the best way to do this?

Is there a limit to how thick render can/should be? If it is normal for ~10mm first coat, then ~15mm second coat, can we just add a couple of extra coats? Any downside to doing this?

We want solid walls (and they will have a lot of weight hanging off them with the kitchen units), so have been shying away from dot and dab, which I suppose might be the obvious choice. Should we reconsider this?

Any other options to bring the existing house wall out 2-3cm?

Thanks!

 

[Alastairreid]

Yes you can build it out in layers of 10mm with bonding plaster no probs.
Just keep this in mind when you are fixing the units get plugs long enough to fix to the brick.

 

[Cej238]

Thanks. Do you agree that building it up in a couple of extra layers is the best thing to do? Are there any alternatives that are better / cheaper? Our builder will be doing it, and if he thinks extra plaster is a big faff and would rather board it etc, keen to know what the pros and cons of approaches are.

Thank you!

 

[Alastairreid]

dot and dab much quicker, probably your builders preference.

possibly even bring it out with a couple of coats of render.

 

[Cej238]

I've just been out measuring the difference in wall thickness. If we assume 25mm render on top of the new block wall, we would need 80mm render to bring out the original brick wall to the same level. As an amateur, that feels like a lot...

With that level of depth required, does dot and dab start to become more advantageous? Any downsides when hanging a bunch of kitchen cabinets? Am I right to think that with the correct fixings, dot and dab is OK in that situation?

The wall wasn't specified as aligned either side of the pillar in our plans/contract, so significant extra labour to even it out we'll get charged for. And since we've basically run out of budget we want to minimize that. Sounds like dot and dab will be the way forward?

Picture attached.

Thanks!

 

[Alastairreid]

80mm is a bit much.
The wall could be strapped, plywood then p/b to give you a good hanging surface for your units.

 

[Cej238]

Thanks. Just been googling plywood strapped walls. Seeing a variety of construction methods. What would be the best way to do it given we are working walls which are currently brick with render? I imagine we'll have to strip all the render off anyway as it is old and we are also removing a chimney breast from that wall.

I saw this image (attached). Is that the sort of thing we are talking about? 2x4 timber, screwed to walls? Does it matter if the longer lengths run horizontally or vertically?

Many thanks for your help.

 

[Alastairreid]

A 50mm stud hard against the wall with 12mm osb, 12.5mm pb would leave you a 6mm skim finish.

No need to remove any existing render.