Testing foundations with a hammer

[vincentianpinner]

Hello, I remember reading on here a quick way of testing foundations is hitting it with a hammer. I'm talking about doing it yourself not using specific equipment or companies. We're hoping that would be good enough as the foundations aren't very old and are deep and wide enough for modern buildings regs.
Obviously I'd have liked to hit it hard with any type of hammer and not left any sign of damage. Unfortunately a claw hammer does leave at least a mark and a bit chips away. Admittedly the concrete isn't particularly smooth and flat which might not help but is what I've described so far a sign that turning a one storey into a two storey is unlikely. Thanks.

 

[noseall]

Hello, I remember reading on here a quick way of testing foundations is hitting it with a hammer. I'm talking about doing it yourself not using specific equipment or companies. We're hoping that would be good enough as the foundations aren't very old and are deep and wide enough for modern buildings regs.
Obviously I'd have liked to hit it hard with any type of hammer and not left any sign of damage. Unfortunately a claw hammer does leave at least a mark and a bit chips away. Admittedly the concrete isn't particularly smooth and flat which might not help but is what I've described so far a sign that turning a one storey into a two storey is unlikely. Thanks.

I have never had a BCO or a Structural Engineer, base their suitability of existing foundations on a hammer strike, no.

Gound conditions, concrete depth and thickness are what is important. You'll need to get the shovel out.

 

[stevie888]

There is in fact a technique for testing foundations with a hammer, but it relates to cast in situ piles and it's a rather speciial hammer.

Depth is the only issue that really matters with conventional strip footings: they need to be deep enough to be on stable soil accounting for trees and soil type. If the one storey extension went though BC then they should have info on record, if not you may have to dig a trial hole to confirm

We don't particularly design strips until we get to 4 stories high

So long as the concrete is basically stronger than the soil you're fine.

 

[noseall]

If the one storey extension went though BC then they should have info on record, if not you may have to dig a trial hole to confirm

They will want to visually confirm.

We built an extension (all inspected and signed off) and 14 years later we added another storey to it. I explained that i had put the original foundations in and that they were pretty hefty. They still wanted to come out and check once they were exposed.

Where we actually dug along side the existing concrete, happened to be where I'd dug out extra deep to allow for a 'sump' so that we could pump the rainwater out (clay ground). The concrete was about 800mm thick and 1.2m deep.