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I am trying to do a structural repair to a brick wall that has some large gaps - 1-3" between some of the bricks due to some foundation movement over the last 300 years. The gaps are essentially vertical cracks where the mortar has broken loose and the bricks are separating. I know that any foundation movement will cause more cracks but I want to at least stabilize the cracks so that the wall does not collapse. I am thinking that a mixture of something like sand or pea gravel and a strong adhesive will provide the support I need. I have tried Gorilla glue in matrix material but the foaming and expansion just doesn't work well. I think a tube adhesive with a high tensile strength will work, I just have little experience with the new ones out there.

Any ideas or suggestions are appreciated. I always do a "proof of concept" before going full scale so I can try several ideas.

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Three inch gaps seem quite large - even for a 300 year old wall.

You just need to use a good mortar mix (sand and cement) on the narrower gaps.

Clean out all the old, lose material first to make sure that you get good adhesion and then push the mortar right into the gaps as far as it will go. Work on a small area (1 m2) at a time.

Adding pea gravel to give the mix more "body" might work on the wider ones.

However, I'd get a professional to have a look at the wall first to make sure you're not going to have to redo this work in a couple of years time. If the foundations have gone it might need something more substantial work doing.

Is the wall part of a house or just a garden wall? If it's the latter then dismantling and rebuilding might be the best long term option.

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The house is on the National Register so any repairs have to be done carefully and not visible as "non-period" type repairs are forbidden. The brick walls are the outside walls of the house ruins that burned in 1922. It is just 4 walls with window and door openings. The walls are moving outward and the cracks are the result of that. We want to make a structural repair to the cracks to give us time to get "real" approved repairs done. So we want a joint that will adhere - I know about cleaning - and is as strong as the brick. Not easy but we have to try. – user1798 Feb 20 '11 at 15:20
@Daryl - you do need to be very careful with the repairs and a rebuild would probably be out of the question too, unless done through the proper channels. – ChrisF Feb 20 '11 at 19:21
That I know but if we do nothing, it is going to fall this year for sure. We know we are skating on thin ice but we have to do something. I just want some ideas on a matrix of maybe sand and adhesive that will bond with the brick and be as strong as brick. We think this will give us time to get things figured out because once it falls, it's over. – user1798 Feb 21 '11 at 1:30

I don't think you can 'repair' the cracks. You'd have to repair the wall or foundation.

Please be aware that bricks don't 'stick' to the substrate as with a glue or bonding agent. A mechanical agent, like a brick tie, is used to keep bricks 'stuck' to a wall. The main force keeping bricks in place is gravity, and if you've got other forces working against it (like wind or soil load), you need mechanical help.

If you want to fill a large crack you may want to start with a backer rod or material of some sort. Very often products made to fill cracks are designed to work wide but not necessarily deep.

Backer rod is a dense foam product that simply occupies space so that your filler material doesn't have to.

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