Crack Repair in Concrete Roof




About: Professional problem solver, Technology geek. Electronic Engineer. Mexican. Clean energy promoter.

Hi, thanks for reading this Instructable.

This time, i'll describe how to find, seal and repair a crack on a concrete roof.

I needed:

-Electric extension


-Full Body harness

-Eye protection

-Good Rope


-Round wire brush (for the drill).

-Paint Brush

-Polyurethane sealant

-Silicone gun

This is where i live (left); it's a house that used to have a waterproof asphalt coating. It kept the water away, but absorbed a lot of heat (really), and that's a problem living in a tropical weather in the Mexican Coast.

The difference of temperature between the first and the second floor was so remarcable, that you could feel the termal shock just a half way on the stairs. The main room felt like the inside of an oven; the bed was hot, and you couldn't rest before 10 p.m., or at least 40 minutes of air conditioner. This of course had an effect on the electricity bill.

So i decided to remove it, and use a waterproofing with thermal insulation. Worked fine, the heat reduced a lot, just like it did my bill, but the roof had a surprise for me.

Step 1: Reveal the Problem.

The fun in this problem was this.

On heavy rain there was no problem, but with a light drizzle, i had a constant drip and couldn't find the source.

After a while, i came with the idea of using a red flannel, and it worked like magic. The shape of the drip was revealed and i had a clear view of what to look for on the roof.

When rain stoped, i searched for a diagonal crack, and it was very easy to find once i had a clear shape in mind.

I used a gray spray paint (it was the only in my house, the color is unrelevant) to mark the working site.

WARNING: Make sure to NOT let spray paint it on direct sunlight, especially if you live in a hot weather zone.

Step 2: Preparation.

The crack was located on a tilted roof, a complicated position that require special security measures. So i tried to work the safest posible.

I bought a full body harness and a life line (not seen in picture).

I tied myself to the base of a water tank (where i live have very poor water pressure, so we need to lift it and use gravity). It was the strongest fixed point available.

I got a truck rope (Home Depot); i considered it enough because on an incident, i wouldn't be hanging my full weight on the rope, just in case of a slip, i would need the rope to endure to not roll over to the edge.

Also, i left very little rope, so i was far away to the edge.

Step 3: Work Itself.

Once located the crack, and safety measures taken, i got to work.

I foolish man, tried to use a hand wire brush, on noon, on a tropical weather, over a roof with no shadow.

The heat beated me. I had to stop and rethink my strategy.

I came back with a power tool, and a pair of round wire brush. I advanced more in 5 minutes than in the previous half hour.

So, i found many layers of coating.

The first was white, the waterproofing with thermal insulation.

Then i found the remainings of the asphalt coating.

For some reason, after removing the asphalt and after a while of brushing, it turned a SILVER color.

After that, i had to move around the wire brush to remove the remainings from the inside of the crack.

Finally, the raw concrete has to be in a dark gray color, and clean view of the crack.

Step 4: Sealing Crack.

After a while, i had the entire crack clean, and used a Polyurethane sealant.

I aplied it in the secuence of the image, to make sure water not have a chance to leak.

In the step 3 of the secuence, i used a spatula to flat the product.

And that's it.

I forgot to repaint with a coat of waterproofing with thermal insulation, and even so, there hasn't been another leak.

Hope you can find this method usefull.




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    3 Discussions


    Tip 6 weeks ago

    How do roof crack slow rain linkage in water


    1 year ago

    One way I suppose .They make cement based fillers that expand on curing they are used to seal leaking concrete water tanks . Lamposil is one . Some PVA glue down the crack first would help. This sealant you have chosen will expand and contract at a different rate to the concrete so it is doomed to fail fairly quickly

    1 reply

    Reply 1 year ago

    Thanks for the feedback. I have to seal another crack on a roof top on my father´s house, and i'll try to find the product you mentioned.