by kfpsoton »
Thu May 30, 2019 4:28 pm
Your problem is that when the slab was a conservatory it was protected from the rain. Once it is a patio it will get wet. This gives you two problems; the first depends on where the concrete surface is in relation to the damp proof course in the house wall. The usual recommendation is that the patio surface should be three brick courses below the DPC. If it is not then one solution would be to create a french drain. This means cutting a channel about 100mm wide along the edge of the slab next to the house so that water on the patio does not come into contact with the house wall. At least one end of the channel need to drain free and it can be filled with pea gravel if you wish.
The second problem is that the conservatory floor was probably laid level but a patio need to be on a slight slope or fall so that rain falling on the patio drains away from the house. You might be able to accommodate this by having a thicker bedding close to the house that at the far side, away from the house. The usual fall is 1:50. You might find that fall allowance plus minimum bedding thickness (25mm?) plus slab thickness means that the surface next to the house ends up higher than internal floor level!
