Dovetail joint on Concrete Block


Old 02-24-08, 11:50 AM
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Smile Dovetail joint on Concrete Block

I have a horizontal crack on my concrete block at the joint (where the 2 blocks meet). Everyone agrees I need to do a dovetail joint and then put in vinyl or hydraulic cement. I have read numerous posts in this forum on dovetail joints, but none clearly explain how a dovetail joint is done. If I chip out the crack, my understanding is the inside of the crack (where the end of my chisel would be) should have a vertical height greater than the opening of the crack. How can I do this without making the crack on the surface of the block the same size.

Also, when people say "wider", does this mean vertical or horizontal length. Lastly, what is an "undercut". I was hoping to find a video or picture, but all the pictures show a side view rather than an actual picture showing the face of the block.

Note I also own a grinder.

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Old 02-24-08, 12:58 PM
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Dovetail joint on Concrete Block

The intent is to create a joint that will prevent the hydraulic cement plug from being moved by high pressure or wall movement. Ideally, a dovetail does this on paper or if you are a carpenter building furniture.

In reality, if you can clean it out well with a relatively square profile, this would be adequate since the rough surface will increase the holding power. The cement expands as it cured, increasing the bond.

Make sure the joint is clean and wash out any dust. The joint may be slightly moist. Force the hydraulic cement mixture into the joint. Do not mix it too far in advance since it can set relativelt quickly.

Hydraulic cement is not like portland cement.

It has a long history of being used to plug leakage on many commercial and civil projects (dams, etc.). It will do nothing to improve the present strength of your wall, but it will prevent leakage.

Old 02-24-08, 09:19 PM
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dick's right,,,

but since you have a grinder ( 4" ? ), here's what we did often,,, cut 2x w/1/4" tuckpoint blade,,, 1st time w/blade approx 15 degrees down then 15 degrees up,,, try to make the 2nd cut in the same slot as the 1st - VOILA ! ! ! DOVETAIL ! ! !

' wider ' means towards the outside ( dirt ) of the wall,,, & i stay at motel 6's :-)

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