Upon closer inspection the type 1 sub base – referred normally as MOT1 (crushed stone), appeared to be correctly laid and compacted, the area had been levelled of but the rain water just wasn’t soaking down to the soil.
The only solution was unfortunately to remove all of the artificial lawn and sub base and perform more detailed investigation.The artificial lawn couldn’t be saved, with the best will in the world you wouldn’t been able to remove the odour and it was in fact badly cut into position and the joins were also questionable. I did suggest to the lady to contract her gardener to get his views on the problem but unfortunately he has moved back to Poland.Yes a reinstatement of a real natural lawn would have been wonderful but this didn’t meet the requirements due to the small size, large dogs and the area is well known for heavy moss infestation .I submitted a detail quotation for the complete removal and reinstallation on the assumption that they wasn’t any major unforeseen issues, (we knew that a collapsed drain couldn’t be an option as upon checking with the council all the drains have been laid to the front gardens).The quote was duly accepted and work commenced on Good Friday to remove the existing artificial lawn and sub base so that we could see if there were any underlining issues.Access to the rear garden was very limited and unfortunately the materials had to be dug out by hand and barrowed out to a skip. We took five hours to remove 30 m2 area with depths ranging from 7mm to 20mm. During most of this time the rain was consistent with the occasional heavy downpour and true to form the minute we had finished the rain stopped and the sun came out!We believe that we have found the problem, when the garden was originally landscaped the builders laid what appears to be a double layer of damp proof membrane on the soil which went under the central pond feature and then laid various depths of shingle. The gardener simply laid a mot1 sub base directly on the shingles and once compacted a geotextile weed membrane was laid followed by the artificial lawn.The soil under the membrane was very dry and as soon as this was removed, the rain water quickly soaked into the soil and naturally drained away.The damp proof membrane certainly done its job! It stopped water from escaping and just caused the rain water to be soaked up by the mot1 sub base with limited run off to the borders.We are back on site tomorrow to check that the area removed hasn’t become a swimming pool and if we are happy that the root cause has been correctly identified we will commence a proper install.Day Two.We encountered fairly heavy rain Friday evening and into Saturday. The drive to the clients caused me some concern as there was a lot of surface rain water and I wasn’t too sure what we would find!On arrival we found that the area had drained off nicely with only a few small puddles. The soil was firm under foot and most importantly you could smell fresh air!
One or two areas were clearly wetter than the rest, nothing major and we dug a couple of inspection pits but didn’t find anything to cause any concerns. However the side path clearly has some issues with surface rain water. I have a bad feeling about this area but unfortunately the clients are out all day and felt it prudent not to dig their path up or remove their raised borders without first seeking their permission.In one area which was the driest we encountered a concrete slab. Upon removal we found a brick built drain housing, all we could gather that this was possibly from the guttering down pipe. There was only 1 or 2 cm’s of clean water at the bottom of the pit and no visible way of the water escaping! This area was flagged and will need to discuss the possible implications with the clients.
A more pressing concern was the skip still being on site and awaiting to be collected and until it has been removed our supplies couldn’t be delivered! This now required the materials having to be carted over in the vans and with limited opening times over the Bank holiday we would be struggling to get everything on site.However as all other areas appeared to be fine, it was decided that we would commence the sub base installation and monitor how well the area drains off as we have plenty of rain over the next few days. And in good old Easter holiday tradition it started to rain!!To the areas were there is no firm edge, we installed a tanilised timber edgingLaid a geotextile weed membrane (this will prevent the sub base sinking in to the mud).Filled the area with mot1 which was evenly spread with a rake.
The mot1 was then compacted with a wacker plate
Finally a thin layer of sharp sand was laid and again compacted with the wacker plate.
Normally at this point a second layer of geotextile weed membrane would be laid to prevent any weed growth before finally laying the new artificial lawn. However we felt it prudent to delay this for a day or two to see how the sub base performs and besides there were still small areas that required a little more sand to be applied as we couldn’t get all the materials over in the limited time available.The plan is to return tomorrow to discuss the concerns with the client and see how well the sub base has faired. If everything appears to be okay the binding off with the sand will be completed and the second layer of geotextile weed membrane laid. We will leave the actual installation of the artificial lawn for a few days longer and hopefully when the rain has stopped and the sun is shining. I just hope that the client doesn’t let her four dogs loose in the rear garden for a few days!!SundayQuick visit to the client to discuss our findings and agree on some minor remedial action. The sub base was very dry which was reassuring considering the volume of rain we encountered yesterday afternoon and overnight.Job scheduled to be completed on Tuesday as we require the skip to be collected or would have problems getting the new lawn past it and also nice to have a day or two rest!Tuesday 6th AprilEarly start to pick up the new lawn, due to the Bank holiday it was hit and miss as to what actual day we would get the lawn delivered so opted to drive down to pick it up.We completed the remedial work and blinded off the area with sand and then laid the second layer of geotextile weed membrane.The artificial lawn was unrolled and left to settle for a couple of hours in the sun. This helps makes the lawn more workable and allows any creases to be smoothed out.
The lawn is then cut it to shape using a sharp Stanley knife.Joins were then glued and once set, finall trimming of the edges were undertaken using a sharp Stanley knife. The blades must be replaced every 2 to 3 meters - it is amazing how quickly they go blunt.Finally, using 6 inch galvanized nails, the turf was pinned every 6 – 12 inches around the edge.
For this particular project we suggested installing NAMGRASS Green Meadow which is ultra soft and ultra realistic, with its long multi tone green fibres and low down dense thatch effect. The cost per per square metre is currently only £19.95 Inclusive of VAT and represents great value for money and suitable for a wide range of uses.