Porous Concrete Issues .... Advice Needed.

Discussion in 'Landscaping and Outdoors' started by OSBAli, Jan 23, 2018.

  1. OSBAli

    OSBAli New Member

    Hi Peoples. Its been a while. Was hoping to get some help. I am nearing the end of a personal job to build an gym/pergola/man cave/glorified shed. 6x3 structure, consisting of 3M 100mmx100mm posts that sit in metal shoes, that sitting in a concrete foundation. Im not a tradesmen so just learnt as i went along really, so i know things havent been done as they "should" be.

    The issue I have is, we laid concrete over an existing flower bed, and didnt really go that deep. was about an inch or 2 of concrete - and now it does look like I have some water ingress seeping through in parts. Assuming where water is collecting, or could be coming from undeneath. Area where we live also has a high water table. Not really feasible at all to lay more foundation and dig as the structure is complete now.

    I need to lay down gym mats on the floor, so this was a worry. My plan was one of the 3 below to alleviate the issue:
    1. to put down some leftover roofing felt down, then some polythene sheets, followed by a some cheaper rubber mats, and my final more expensive mats on top. IT just worried me it didnt really resolve the issue, and months, years down the line would i find a bigger problem underneath at some point.
    2. Timber frame to create an air gap between concrete base and mats which are laid on top. More cost, which i am loathed to do or can afford.
    3. Ontop of the current concrete base put some sort of levelling compound, which i am hoping you can get with some waterproof properties? Purely a guess and not sure if this is possible.

    Appreciate you dont have the full history, but given the scenario above would be keen to hear your thoughts?
  2. KIAB

    KIAB Super Member

    No dpm to stop moisture raising, concrete rather thin, can't see it lasting, should be 100mm minimum, with a subase.

    Leveling compound is a total waste of money, no good for this job.

    You could lay a epoxy liquid membrane,two coats might be enough, then lay a supended timber floor.
  3. Was there any hardcore etc under the concrete?

    If not, then it is going to fail, just a matter of when.

    Expensive lesson maybe, but it might even be better to stop now and reassess totally. If that base isn't strong enough anything else you do will be wasted money and effort.

  4. KIAB

    KIAB Super Member

    It's is better to rip the lot up & start again, but I don't think OP wants to go down this route.

    Laying a suspended floor on concrete might work for a while, but eventually concrete will crack & break up, so making any liquid dpm totally useless.
    Last edited: Jan 24, 2018

  5. 2 inches of concrete on a flower bed, with nothing else under it. Throwing good money and effort at it in my opinion if not correcting the main problem.

    For a man shed/cave/gym ?
    KIAB likes this.
  6. OSBAli, if that concrete floor were strong enough, then there are things you can do to make it water-tight, probably the best being a cement tanking slurry.

    However, if your concrete floor is really only a couple of inches thick max and then not even on a compacted hardcore sub, it's gonna crack and crumble. And the tanking slurry will have no effect; just like the cove who built it, you'll have a bleedin' geezer.
  7. teabreak

    teabreak Screwfix Select

    I guess I can only add to the doom and gloom above, but one bodge that might sort of work is to combine your ideas lay a dpm or overlapping roofing felt then lay a suspended timber floor on sturdy battens over the dpm. I might be too springy for gym use though.
    Otherwise dpm/felt with paving slabs on dabs of cement to spread the load. Both will reduce head room.
    All bodges though, the real answer is to start again:(
  8. Dr Bodgit

    Dr Bodgit Super Member

    If you don't want to reduce headroom, then you could lay a suspended timber floor on padstones/paving slabs, which are resting on solid (at least 4" concrete) foundations. But that means digging up your existing floor and more time and expense. I can't see a cheap and easy solution to this I'm afraid.
  9. I have just re read the 1st post.

    The issue I have is, we laid concrete over an existing flower bed, and didnt really go that deep. was about an inch or 2 of concrete.

    Probably not even 2 inches of concrete?

    Seriously, jump on it, it will crack. Don't waste more money.

    From Dr Bodgit.... I can't see a cheap and easy solution to this I'm afraid.
  10. Dr Bodgit

    Dr Bodgit Super Member

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