Building Cob on concrete??!!!

Hi there,

We are building a cob playhouse for a local charity. Originally the plan was to build it on the grass next to a lovely walk way. However things changed when a cob expert told me it is best to build cob at least 5m from a tree to avoid the building cracking in a few years. So the only place left to build (as there are allotment holders on the site, a playground, wood turning and cattle!) is on a concreted over site which is not currently in use. The location itself is better than the original and will look great but I am concerned about building on concrete.

We were thinking we could:

1. build a plinth wall directly onto the concrete and continue with the rest as planned.

or

2. Possibly use the earthy ship tyres as a plinth to raise the cob? I've seen a picture of this done on a playhouse before.

Can someone please advise me as we would like to get this on the go asap!

Thanks so much.

Hello Lynda, welcome to Permies!

Both sound plausible...Can you provide photos of the site and the concrete slab?

Regards,

j

Hi j,

Thank you, I have to admit I've learned much from the permies forum over the years and this is my first posting!

The site was previously used for compost (many years ago) and then was given a concrete base (so we've been told by the bosses there) and then filled with sand to support potted saplings; this has since become overgrown. So unfortunately the only photos I can post will be of a very overgrown site! Although I'm in work now but will post them later

We will be clearing the site and assessing the concrete for thickness on Saturday so we'll know more then really. It's the rising damp I'm concerned about, this is our first cob structure on our own and we'd like to be able to add it to our portfolio.... hence we don't want it falling apart with damp in 4/5 years!

Sorry I haven't much more to tell you at the minute!

Hi Lynda,

I just noted you are in the U.K....from when I read your use of the term "rising damp." I always get a big laugh out of my U.K. friends and there conversation about RD. I write on several blogs, and forums, some of which is on historical restoration and the "out of control" rising damp industry in the U.K.. I have many colleagues and friends there "battling" this issue and the RD industry with all there "gimmicks" and "unnecessary products." Don't misunderstand me, I understand the concepts behind "cohesive diffusion" in masonry matrix of all types, yet rising damp as it is typically described there in the U.K. is more fallacy and hype than actual affect of the interstitial wall matrix.

When you get the site all clean up, then post a few shots here and I will give them a gander. I would also love to know where your project is, as I have a number of "Cobb Contacts," in the U.K.. I look forward to your success in the project,

Cheers,

j