DIY Builds
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Can you put gravel straight onto concrete?

Yes, you can. Nidagravel gravel grids are the ideal way to stabilise gravel that is to be laid directly over concrete, tarmac and block paved driveways. In fact, a gravel grid is the only way you can install gravel successfully over a solid slab.

nidagraveluk.co.uk - Gravel Stabilisation Grid FAQ's
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When installing any of our gravel stabilisation grids for paths and driveways, it is not uncommon to find manhole covers of varying shapes and sizes located where you are installing your gravel grids. One of the most common places to find a manhole cover on your property is on the driveway as drains often exit a property down the driveway where they join up to the main sewerage system. Depending on the age of the property the design and construction of the manhole or inspection chamber will vary along with the size, shape, and type of manhole cover that sits on top. The only way to find out what type of manhole you have is to lift the lid and take a look. Older properties may have a brick-built manhole and a cast iron manhole frame and cover sitting on top. Modern and newly build properties will usually have a plastic circular inspection chamber with a base unit at the bottom and a number of riser sections fitted on top which lead up to the finished ground level and the inspection or manhole cover. Manholes can vary in depth from 400mm to 1m deep or more. Once you have identified the type of manhole you have you can decide how you want to deal with the manhole cover. We will cover the steps required to adjust your manhole cover in the sections below.

Changing Levels - New gravel driveway

You may be changing the levels slightly when installing a new gravel driveway or refurbishing an existing driveway, which means you may have to adjust the height of your manhole chamber before you can change the manhole cover. This might sound like a daunting task, but it is in fact not that difficult to do and a competent DIYer should be able to complete this.

Changing Levels - Refurbishing a concrete or tarmac driveway

Where customers are refurbishing their existing concrete or tarmac driveway with Nidagravel grids to create a gravel driveway surface then manhole covers are usually raised slightly so that they finish flush with the Nidagravel surface that sits on top of the concrete or tarmac. Nidagravel grids are the only way to effectively stabilise gravel on a concrete or tarmac surface. The thickness of our gravel retention system when installed varies slightly depending on the grid used, but manholes are usually raised by 50 to 70mm or in accordance with new site levels where adjustments have been made.

Choosing and changing your manhole cover

Manhole covers come in various shapes, sizes, and colours as we have mentioned before, which means there are plenty of options available when it comes to changing your manhole cover. It is important to remember that a manhole cover is there to allow you to inspect your drains and to allow access for drainage rods that are used to unblock a drain, so the frame and cover need to be installed properly and allow access. When it comes to choosing your manhole cover your first decision to make is - do you want to see a manhole cover or would you prefer to make it blend in with the driveway surface. If you are happy to see the manhole cover, then if your existing manhole cover is in good condition - simply re-use it. It's the quickest and simplest option and you know it will fit onto your chamber. If your manhole cover is old or damaged, you can replace it like for like. If you are doing this you should measure the frame and cover or better still take them will you to your local builder's merchants and find a suitable replacement. You may have a circular, square, or rectangular cover in place. Older properties will probably have a brick-built inspection chamber and the underground pipework is probably salt-glazed pipework, rather than plastic pipework which is used today. Original manhole covers are often made of cast iron and are pretty heavy. You can still purchase cast iron manhole frames and covers today, so there is no problem replacing an old damaged one. Replacing a manhole cover and adjusting the height of the inspection chamber does not interfere with your drains, it is usually a small adjustment to suit the new finished surface level. To reduce the height of a brick-built manhole, you simply need to remove the cover and knock off the frame with a lump hammer and chisel. Then you can knock off one, two, or three courses of bricks to take you down to the required level, taking into account the thickness of your new manhole cover. It is a good idea to put a plastic sheet or similar inside the chamber while removing bricks so that any debris is caught and can be removed (obviously, remove this when you are finished, do not leave it in the drain). You do not want half a brick falling into your drain as it will cause a blockage. It's also a good idea to request that no-one uses and flushes the loo whilst you are working on the manhole chamber or you might get a nasty fright! Once you have reduced your brickwork, simply mortar the new frame and tray into position at the correct level. Point everything up neatly inside and out and you're done.

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If the manhole cover is too low. Then it is simply a case of adding extra layers of brickwork to bring the chamber up to the required level and fitting the new manhole frame and cover. Again take precautions to prevent debris from falling into the drains. Modern inspection chambers are often made of plastic. Usually, there is a base section, where the pipe entries are, and then a number of connecting risers that are added on top of the base and lead up to the finished height with a frame and cover on top. The principle of reducing the chamber is the same as a brick chamber, but instead of knocking off courses of brickwork, you will cut down the plastic riser with a saw. The simplest way to do this is 'in situ'. So if you need to reduce the height of the chamber by 150mm, for example, you can dig out around the manhole riser giving yourself approx 30cm clearance all around and to a depth of about 200mm. This will give you access to saw the riser down whilst keeping it in position. There are often lines in the plastic that you can follow to ensure you make a level cut. You may find the manhole has not actually been set level or the riser section has moved a bit over time. When making your cut, you can factor this in and make a correction so that top of the riser becomes level. Then you can simply backfill, compact, and mortar your new frame and tray into position. This technique will work well for medium to deep chambers. If you are working with a particularly shallow chamber then you may have to take a slightly different approach to achieve the same result. To increase the height of the chamber, you will need to buy a new riser of the correct diameter that will fit onto the risers below. The risers are normally sold in standard heights. So, you may still need to cut the new riser down a bit to finish at the required height when fitted. To fit the new riser, again it is best to dig out around the top of the chamber a bit and clean off the top of the riser you are adding to. Make sure there is no grit or mud left on the rim, so that you get a nice snug fit when you put the new riser on top. Again backfill and compact as required and mortar the new frame and tray into position.

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nidagraveluk.co.uk - Gravel Stabilisation Grid FAQ's
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