how is building attached to footing

Submitted by Pilgrim (not verified) on Mon, 20/09/2010 - 11:24

Can you please answer these questions that were given to me for this build:

These are Questions given to me by the people coming to pour the footing and foundation and i thought they are good questions to post here for others. Can you please give me the answer to these questions so that I might explain to them. Thanks

Question: " OK so what keeps moisture from getting between the plaster and the blocks? It just seems if nothing is done it will be a natural place for moisture to fill and then it will get worse - just my guess."

My Explanation: the plastic sheeting, if we were to use that as the anticapillary, there is a layer of cement on the footing, then plastic and then another layer of cement and then the blocks.

Question/remark "So here again the walls do not bond to the footings - they have a slippery surface between. I am sure they feel fine but time I GUARANTEE will allow the building to shift and forget moving as a unit in an earthquake",

"This I realize just understand the footings are to support weight and provide stability if the building is on the footings but not bonded walls can and will move and cracks will form - this is why relief lines and cuts are made in most cases of masonry and the manual shows this for windows - an obvious source of strain."

Can you please address how exactly this all work as far as the building be bonded to the footing?

Submitted by Geoffrey (not verified) on Tue, 21/09/2010 - 00:30


There are 2 things that are important:
1. - An anti-capillary layer that will keep the walls from sucking up water from the ground. There are many ways to do an anti-capillary layer; mortaring plastic film, applying bitumen, adding a waterproof additive to the cement mortar. I think that it is a worthwhile investment of time to make yourself some simple demonstrations/tests of the ones you're interested in using (click here for an example). It only takes a short time to begin to see what works and what doesn't. You could even test a stone foundation. I think that is what they used in the California missions.

There is some concern about the bonding between the anticapillary layer and the blocks. The adhesion between plastic and cement can be increased by roughening the plastic as one roughens a rubber inner tube before applying a patch.

2. - Firmly attaching the wall to a heavy foundation so that the building will stay put during vertical and horizontal accelerations in an earthquake. A good example can be found on (pdf)page 30 of Build Change's Manual's chapter on Connections. It shows steel rebar anchored in the foundation and cast into a tie beam.