Thread: Drilled clean through garage floor slab - am I in trouble?

That is not going to cause you any grief , 90mm for the slab is fine.

Originally Posted by Beardy

That is not going to cause you any grief , 90mm for the slab is fine.

Phew! Thanks

For the floor to have cracked, there has to have been movement at some stage, as I doubt that the floor has cracked in multiple places due to shrinkage alone. If the concrete continues to move, I suspect that it will try and pull the flat 75x35 with it, so in time you newly laid floor will develop waves as well. The fastenings should seal holes that they are in reasonably, but I would be sealing any other holes to minimise moisture entry.

Originally Posted by malb

For the floor to have cracked, there has to have been movement at some stage, as I doubt that the floor has cracked in multiple places due to shrinkage alone. If the concrete continues to move, I suspect that it will try and pull the flat 75x35 with it, so in time you newly laid floor will develop waves as well. The fastenings should seal holes that they are in reasonably, but I would be sealing any other holes to minimise moisture entry.

I would say so. Not sure if it is still moving. I filled a part of the big crack about 6 months ago with some mortar crack repair. I wanted to see if that repair also cracked over time. But it hasn’t so it has either stopped moving or is moving very slowly? I don’t know anything about slabs so no idea really.

Hopefully it doesn’t move too much over time.

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Originally Posted by malb

For the floor to have cracked, there has to have been movement at some stage, as I doubt that the floor has cracked in multiple places due to shrinkage alone. If the concrete continues to move, I suspect that it will try and pull the flat 75x35 with it, so in time you newly laid floor will develop waves as well. The fastenings should seal holes that they are in reasonably, but I would be sealing any other holes to minimise moisture entry.

I would say so. Not sure if it is still moving. I filled a part of the big crack about 6 months ago with some mortar crack repair. I wanted to see if that repair also cracked over time. But it hasn’t so it has either stopped moving or is moving very slowly? I don’t know anything about slabs so no idea really.

Hopefully it doesn’t move too much over time.

Cracking in concrete slabs can be due to a number of issues, some construction related, soil movement, and some from use i.e. loading etc.

Cracking caused by soil movement is seasonal and highly dependent upon the soil type the slab is on, the foundation preparation, slab design, slab reinforcement and the placement and finishing of the concrete.

With most of Oz having been through a very significant drought and now facing record rains and associated flooding, soils will have transitioned from one extreme to the other with maximum soil movement.

Perhaps the best advice is to place a moisture membrane between the slab and the pine joists, seal as many as the cracks as is practical and have termite protection treatment done before laying the flooring. Termites love damp pine!!!!!

Originally Posted by Mobyturns

Cracking in concrete slabs can be due to a number of issues, some construction related, soil movement, and some from use i.e. loading etc.

Cracking caused by soil movement is seasonal and highly dependent upon the soil type the slab is on, the foundation preparation, slab design, slab reinforcement and the placement and finishing of the concrete.

With most of Oz having been through a very significant drought and now facing record rains and associated flooding, soils will have transitioned from one extreme to the other with maximum soil movement.

Perhaps the best advice is to place a moisture membrane between the slab and the pine joists, seal as many as the cracks as is practical and have termite protection treatment done before laying the flooring. Termites love damp pine!!!!!

yep will just have to wait and see how it goes with movement.

I’ve laid down a thick plastic sheet and used H3 pine. So hopefully all good on the moisture and termite front!

i don’t think drilling 100mm holes through the slab is correct. You’re only trying to hold down 35mm of pine.

Originally Posted by springwater

i don’t think drilling 100mm holes through the slab is correct. You’re only trying to hold down 35mm of pine.

Yeah I think I over did it on that front. I got 100mm anchors as some of floor was 40mm lower. So I figured that would work out to only 25mm of anchor in the ground (100-40-35). But then it meant for the areas that were level or near level already, I had to go deeper. And I left some space at the bottom of the hole in case of any dust/debris I couldn’t get out. But went a bit too deep. If I did it again I would maybe try for a consistent, shallower depth hole and use different length anchors to fit based on how far out of level the floor was. Hindsight is 20/20 I guess…

I'd just shoot em down with a Ramset gun. A squirt of builders adhesive under the batten at each nail point and go to rat with the ramset. All done in an hour. Simples.