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Posted: Thu Jun 11, 2020 8:14 am
by caz
Hi four months ago I had block paving installed for a Patio area and at the time I noticed the sub base was laid in ballast. I queried this with the contractor and he assured me that this would be fine. As time progressed it became quite evident that rain water was pooling in one area to a depth of 7cm and a surface width of 80cm. I checked the levels and found that most of them were not correct. I decided to relay the blocks and have taken them up. I know ideally that MOT 1 should be used as a sub base but my My question is can I still use the ballast as a sub base once I have sorted out the levels?
Posted: Thu Jun 11, 2020 11:26 am
by caz
Tony additionally if you dont mind answering this further question. The blocks i have are 50mm thick and the existing ballast sub base is 80mm, the laying bed is 20mm and sprinkled with cement and it has formed a hardish crust. I have removed a section of ballast and the total height from ground level to my finish line is 150mm. If using the ballast as a sub base i take it that the 20mm laying bed will not do and i will have to dig down deeper is this correct?
Posted: Tue Jun 16, 2020 11:04 am
by Tony McC
Ballast is NOT a sub-base material. It's a rag-tag mixture of any old crap lying around on the quarry floor. It's most common use ts for making concrete, and I'm not convinced it actually suitable for that!
The particle size distribution, the nature of the rock itself, the prevalence of fine material, the lack of angularity, the fact that it's not a crished but an "as-dug" material....all render ballast as unsuitable for use as a sub-base.
Everything about this job is WRONG. Wrong sub-base material, inadequate depth of sub-base, inadequate laying course, cement added to laying course....it's all a cowboy job.
The only fix is to start again from scratch.
Posted: Tue Jun 16, 2020 6:00 pm
by caz
Hi Tony many thanks for your help, a further question if you will please. I have now laid the aggregate and compacted it down and the levels are correct. Next I am going to lay the sharp sand screed bed and want to know whether I have to compact this down first before I lay the blocks or compact after the blocks are laid. Please advise.
Posted: Tue Jun 16, 2020 10:43 pm
by Lmcd qs
caz wrote:Hi Tony many thanks for your help, a further question if you will please. I have now laid the aggregate and compacted it down and the levels are correct. Next I am going to lay the sharp sand screed bed and want to know whether I have to compact this down first before I lay the blocks or compact after the blocks are laid. Please advise.
Hi Caz,
I don’t think it is essential but it is common for builders to partially compact the sand before levelling.
You can see this done at around 5 minutes in this video https://m.youtube.com/watch?v=J__TVDrOzgo
Posted: Thu Jun 18, 2020 10:47 am
by Tony McC