How can I seal the concrete lip in this building's rooftop?

This lip is about 5" wide, and I need to seal it. At the same time, it needs to be even with the rest (ie.it needs to look "square" ).

What materials and tools do I need for this job?

I don't have much experience with concrete, so I prefer not having to mix with water.

This is more or less what was suggested: enter image description here

enter image description here


That’s called a “parapet” and I can see why it needs to be repaired.

You’ll need “form boards” installed along the inside and outside, plus you’ll need to install a strip of foam to seal the board to the wall, so nothing runs down the wall. Set the form boards level with the top of the existing wall to give you that “square and matching” look you want. Use “form ties” to hold the outside form tight to the inside form.

I don’t see any rebar sticking out of the existing concrete wall so you’ll need to install 2 - 1/4” anchor bolts about 24” apart plus’s 1 - 1/4” anchor bolt in each end of the broken out portion. Then, fasten a 1/4” rebar to each anchor bolt with wire.

Now, you can buy “pre-mixed” concrete. It needs water for the cement to “react” and for it to flow around the rebar. Let it set for 3 days before you remove the forms. (I’d use form release agent, but it’s not necessary, if you remove the forms at day 3.)

I’d use a bonding agent to make sure the new concrete seals to the old too.

  • Thanks for the reply. I created a drawing that I added to the initial question. I assume that the "form ties" will hold the left and right foam boards up against the wall. If that part is correct, then I'm on the right track. – rbhat Nov 22 '17 at 14:28
  • What I don't understand is what the rebar's for. Also, how do I level the top part? Do I use another form board that I lay horizontally between the two vertical foam boards? – rbhat Nov 22 '17 at 14:30
  • The form boards are even at the good areas on both sides. You fill the form with concrete and a trowel or even a board could be used on the top to finish it. When I want a nice finish on the side I will put plastic sheeting on the form boards and tap with a hammer after filling this moves the air bubbles and makes a very smothe face. I would also drill a bunch of holes just big enough for a 16 penny nail to sit in at least 1" deep these will keep the repaired section in place. – Ed Beal Nov 22 '17 at 18:34

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.