I am about to build an ICF house with one main floor, a walk-out basement at the front and rooms in the roof.  The site slopes, hence the walk-out basement.  All of the exterior walls will be ICF, including all the basement walls.

At the back of the walk out basement (i.e. going into the hillside) the wall above the ICF back wall (i.e. the wall on the floor above) is an internal wall.  In the UK, a lot of internal walls are built with CMU blocks rather than timber so that you get a nice solid feel and I would like to do this.

My question is whether there is any reason why I can't build a CMU blockwork wall on top of the concrete core of the ICF wall below?  Obviously it would have to be centered on the core to transmit any loads straight down.  I am ssuming that I would be using 5 inch thick blocks on top of a six inch core.

Hope this makes sense.

Andrew

edit - The material cost will be quite a lot less for a CMU wall and I am doing all the work myself so there is no labour charge.

I don't quit understand your layout, there is no structural problem with placing CMUs on the concrete of ICFs. If tensile strength or considerable compression strength is need, you can pin the CMUs to the ICF's concrete and core fill the CMUs.

Thanks for your reply, Brad.  The link below shows what I want to achieve. 

http://farm5.static.flickr.com/4071...c6db_o.jpg

Most concrete blocks in the UK are solid so it would simply be a case of building the wall up off the top of the ICF concrete core.

This internal wall could be any material that would support the roof load.  After saying that I would be more inclined to use Aerated Autoclaved Concrete (AAC) instead of solid concrete blocks to get a solid wall.  AAC weighs less and uses adhesive instead of mortar.   

How do you plan to attach the solid concrete blocks to the ICF wall?

We have glued CMUs also, it is stronger than mortar and easier for small jobs. It doesn't look as good, but if it is covered.

We have taper-topped ICFs, then you can flush the CMUs with the ICFs. I don't buy the taper topped ICFs since it is so easy to make them.

Posted By Alton on 01 May 2010 12:00 PM

How do you plan to attach the solid concrete blocks to the ICF wall?

Do I need to do anything special?  I had assumed that I could just treat the top of the ICF core as a foundation and build straight up off that.  I am not a builder so if I'm wrong then please tell me!

I understand the flexibilty that aerated blocks give but I know that quite a few builders in the UK don't like them.  In the UK we tend to apply a wet plaster finish to blockwork walls and aerated blocks have a reputation for movement and causing the plaster to crack.

Adhesive or mortar the CMUs to the ICFs.

Andrew,
I would look at Brad's ideas on gluing the CMUs in place, especially if you are doing this work yourself. Gluing and drystacking the blocks is a lot easier than using standard mortar. You may have a small problem with dimensions if your blocks are like ours here in the US, and are made with a mortar joint allowance included. However, this should not be a major issue in any case. Since you intend to plaster the walls, you might look at a product that is available here in the states called 'surface bonding cement'. It is a fiber reinforced cement product that is actually designed to structurally reinforce the blocks. It is applied in a similar manner as the plaster finish, and would offer some added strength to the wall.
Good luck.

Thanks for that Wes. I have been looking into both the dry stacking and the surface bonding cement and unfortunately neither technique seems to be either available or approved in the UK. I am sure that we will catch up one day but it hasn't happened yet!

The only "modern" masonry technique that we seem to have adopted in the UK is thin joint mortar. Are people anti-mortar because it is hard to get right or because it is weaker (is it?)? I am going to be building several internal CMU walls off the concrete slab in the walk-out basement and (perhaps naively) it doesn't scare me. There are various products available here to make sure that I get an even 10mm (4/10 inch?) mortar joint so I am reasonably confident that I can build a decent wall.

Is the glue that you talk about different to thin joint mortar? To be honest, thn joint mortar scares me more than trying to build a "traditional" wall.

Gluing is with adhesive, look for a tube adhesive for concrete. Most are stronger than mortar. If you core-fill you do not need great adhesive as it is only holding the CMUs together until you fill them with concrete. The only issue we run into is inconsistent CMU size.

Thanks Brad.