Browse Forums Landscape & Garden Design 1 Nov 25, 2008 11:20 am Hi all,
I need to install retaining wall along the boundary with my neighbor. It will only be up to 450mm high. My side is the higher side. And I will be paving along my side and up to the retaining wall. Most landscapers advise to use treated timber sleepers as this is the most cost effective. However, one advised to use masonary because timber sleepers will not last and will cause problems with the paving in a few years time. This guy also advised to put concrete under the paving as well. This will guarantee that pavers will not be moved out of place. Paving on road base will still move over time. My paving area is just backyard area and the side of property, not driveway nor any heavy traffic area. Is this guy's advice valid? Any advice is much appreciated. Re: Paving and Retaining wall - Is treated pine reliable? 2Nov 25, 2008 11:30 am We pave onto yellow sand in WA and it is never a problem. Just lay mortar around the sides once you are done and sweep fine sand into the cracks and all good. Re: Paving and Retaining wall - Is treated pine reliable? 3Nov 25, 2008 12:57 pm Hi is going way overboard with his advice and he will make your rather simple cost effective job into a more difficult expensive job. As fu manchu said a compacted sand base is a good option. As for the treated pine just seal any cut ends of the timber and it will be fine. Re: Paving and Retaining wall - Is treated pine reliable? 4Nov 25, 2008 6:58 pm I would avoid treated pine in case you or your neighbour ever intend to grow any fruit or veg in the area. The arsenic from the treated pine can seep into the the soil and contaminate it.
Timber sleepers will also shrink and expand with the weather, which will cause the sand behind them to shift as well. This can cause problems for your paving. I would advise that you use a limestone or masonry retaining wall, but you probably don't need concrete for the pavers unless they're very thin. Re: Paving and Retaining wall - Is treated pine reliable? 5Nov 25, 2008 9:01 pm Sounds like compacted road base should be fine. There is still a mix opinion on treated pine. I think I will ask my landscaper for a quote on masonary to see the price difference before I decide.
Anyone else got treated pine wall? and what do you think? Re: Paving and Retaining wall - Is treated pine reliable? 6Nov 25, 2008 9:26 pm Fu Manchu We pave onto yellow sand in WA and it is never a problem. Just lay mortar around the sides once you are done and sweep fine sand into the cracks and all good. Mortar on the side is very good and reliable, make sure it's dry before you use it. Re: Paving and Retaining wall - Is treated pine reliable? 7Nov 29, 2008 12:29 pm There is a term for that (like capping or footing?) when you cement at the edge of the paving to make sure they stay in place, but certainly never heard of cementing under the whole lot. Re: Paving and Retaining wall - Is treated pine reliable? 8Nov 29, 2008 3:44 pm I always just referred to it as "mudding up the sides" Re: Paving and Retaining wall - Is treated pine reliable? 9Nov 29, 2008 8:29 pm its called haunching
http://www.abc.net.au/gardening/stories/s1113260.htm rigid paving or paving on concrete with wet bond application is the only method that meets the Australian design standard for construction and tollerance, and when constructed correctly the life expectancy is 10 fold versus flexable (sand) paving Da Vinci Outdoor Living Architectural landscaping http://www.davincioutdoor.com Re: Paving and Retaining wall - Is treated pine reliable? 11Dec 30, 2008 8:37 pm amilelka I would avoid treated pine in case you or your neighbour ever intend to grow any fruit or veg in the area. The arsenic from the treated pine can seep into the the soil and contaminate it. Timber sleepers will also shrink and expand with the weather, which will cause the sand behind them to shift as well. That is an absolute load of bollocks. It has been proven in many countries both governmental and privately that CCA treated pine does NOT leach arsenic into soil. CCA has been in use since 1931 - nearly every grape plantation in the world has CCA poles supporting them - has anyone ever died from arsenic poisoning from drinking wine?? If CCA leached into soils and posed a threat to people, do you not think they would ban the stuff? The best practice for retaining walls is to line the inside with black builders plastic, this can stop any sand/soil escaping and also prolongs the life of the timber by keeping constant damp moisture off it. Re: Paving and Retaining wall - Is treated pine reliable? 13Feb 12, 2009 10:32 am Dukekamaya The best practice for retaining walls is to line the inside with black builders plastic, this can stop any sand/soil escaping and also prolongs the life of the timber by keeping constant damp moisture off it. I am just re-visiting this thread. I spoke to a landscape about lining plastic before the timber, but he doesn't seem to think this is necessary. He was suggesting to put geotec fabric (not exactly sure what this is, is this some kind of filtering fabric??), and that will block the soil escaping. Is lining plastic common practice? Will it also block drainage or force all the water going to one side of the wall and cause flooding?? Building Clarendon Brighton - Done and moved in Sept 2009 Re: Paving and Retaining wall - Is treated pine reliable? 14Feb 13, 2009 8:19 am Hi eho,
From what I have read about building retaining walls the purpose of putting drainage aggregate behind the wall is to prevent the build up of water behind the wall thus placing excessive strain or pressure on the wall. The aggregate provides a free draining path for water to flow, usually there is a pipe at the bottom (agi pipe) to collect this water and efficiently channel it away from the wall. The geotech cloth serves two functions 1. It prevents dirt fines getting into the drainage aggregate which would reduce ability to channel water down to the agi pipe efficiently and 2. It prevents dirt coming from behind the wall through any small gaps there may be in the wall. The geotech fabric is so finely woven that it allows water to pass through it but not fine dirt. In torential rain there may be excessive amounts of water build up that the aggregate and agi pipe can't cope with, if this is the case the water must get away and in a timber wall there is plenty of gaps that will serve this purpose however if you have placed black plastic behind the wall you have in effect created a perfect dam. Now not only does the wall have to cope with the dirt but it has to cope with the weight of water as well.....it may start to fail in these conditions. I don't think flooding is really the worry here, if there is that much rain the ground will saturate and the water will start to flow over the top of the wall, in short if there is that much rain you are going to get a flood regardless of black plastic or not. The concern is creating a dam and placing substancial additional pressure on the wall that can be easily avoided by using a material that will allow water to pass. If you want to appreciate this drainage idea more get three buckets fill one with aggregate, one with dirt and one with a mix of aggregate and dirt. Get a single smaller bucket of water and pour it into each bucket one at a time and observe how fast the water flows through the material. The clean straight aggregate will win every time. The aim is not have water build up behind the wall, water it the biggest killer of retaining walls. Re: Paving and Retaining wall - Is treated pine reliable? 15Feb 13, 2009 12:00 pm GottaMow, your explanation is great. Now I think about it, if the plastic is only lined vertically between the timber and the soil, it will prevent constant moisture on the timber. Aggregate will drain excess water to prevent water build up and create a dam situation. Is that right? Building Clarendon Brighton - Done and moved in Sept 2009 Re: Paving and Retaining wall - Is treated pine reliable? 16Feb 13, 2009 3:36 pm Close but not quite.
In theory there should be no soil up against the timber only the aggregate. Soil will hold water therefore making the timber damp and promote rot conversly the aggregate drains water away and the timber can dry out easily. This is not the main reason for using aggregate but it is a plus stopping water build up is the number one priority. I go back to the statement I made in the previous post.....if there is sufficient rain to overload the drainage capacity of the aggregate plus agi pipe then you still need to get this water away some how rather than contain it with black plastic. Timber walls will have gaps in them it is unavoidable due to timber shrinkage etc so there is a final line of defence so to speak that water can get away between these gaps. H4 Treated pine is guarenteed for 40 years under extreme wetting which is pretty good so constant moisture is not the end of the world but keeping your timber dry has to better than allowing it to stay damp. Some small walls (200mm to 400mm high) I have seen don't seem to have geotech, aggregate or even agi pipe for that matter and they seem to last for ages. My next door neighbour has a 1200mm high wall (treated pine) with 150mm x 75mm posts put in vertically to a depth of 600mm in sloppy, muddy ground and in 10 years they are only leaning out about 15mm at most at the top. Behind the wall he has black plastic then rocks then dirt....no filter fabric so go figure. I have trolled the net for info on walls and the resounding answer to the black plastic conundrum is "don't use it at all" in my humble opinion if one of the key success factors for a retaining wall is draining water away from the back then you sure as hell don't put black plastic behind it.....if you where building a swimming pool or a dam you would go to town wacking black plastic left right and centre but you are not. Maybe you are putting to much emphasis on the timber getting wet??? Treated pine is pretty resilient stuff as far as getting wet is concerned and if you use the aggregate then after rain the water is going to dry out in rocks pretty damn quick......try growing a plant in rocks they will be screaming out for water pretty quickly cos rocks just don't hold water. Davinci recommended scoria (I had never heard of it) for the drainage behind the wall as it is free draining and light. I used recycled concrete cos it was cheap (like me!) but I do like the sound of the scoria. Re: Paving and Retaining wall - Is treated pine reliable? 17Feb 13, 2009 8:53 pm Once again, thanks for your in-depth answer!
My retaining wall is not very high, up to 500mm. Because I will have paving above the wall, I don't want the wall to start leaning in a few years time and I need to redo the paving. I want to make sure I won't regret in a few years time by going timber and saving $$$ now and not build a masonry wall. With masonry wall, with footing and blocks, it costs heaps more $$. Your explanation ease my concern a bit. I will just need to make sure there are good amount of drainage aggregate behind the timber and it should be good. Building Clarendon Brighton - Done and moved in Sept 2009 Re: Paving and Retaining wall - Is treated pine reliable? 18Feb 15, 2009 2:34 pm Hi Eho,
I feel your pain, the juggling act between cost and longevity in the retaining wall game is brutal and I have spent many a sleepless night pondering the same things as you. I can give you an update on drainage. I put my western boundary wall up just before christmas (and I have extensive additional walls to go elsewhere on my block) and this weekend it is experiencing the most severe rain so far....it is bucketing down out there. I just wandered down the back then with umbrella in hand to inspect the agi pipe outlet at the base of the wall and much to my surprise water is absolutely pouring out of it...waaaaaaaaaaaay more than I expected. It is a 65mm agi and I reckon I am getting about 1 litre every 3 to 4 seconds I am soooooooooo glad I put the extra effort into ensuring a good drainage path to prevent build up. After witnessing and fully appreciating the amount of water that is getting processed through this wall system I reckon it is crazy to build walls without giving serious consideration to drainage, even low walls and eho once again, in my humble opinion, forget the black plastic using it is just asking for grief. Other things that came to mind when I was thinking about your predicament is the orientation of your posts (this is only if you are using rectangular sleepers instead of round posts). In my opinion putting posts in with the long face of the post parallel to the wailings is wrong. The longest face at right angles to the wall is the most structurely sound. Try getting an everyday plastic ruler, now hold it at one end so it is straight up and down infront of you and you are looking at the thin edge. Now grab the top with the other hand and bend the ruler from left to right....it will bend easily now try pulling the ruler towards you whilst resisting with the hand at the bottom...the ruler will be very strong in this direction. The same concept applies to the posts. In my searches around the neighbourhood for examples of walls I saw so many with the posts orientated with the long face parallel with the wailings and they are all leaning out. Also I intend to paint the treated pine, the manufacturer recommends this to increase the longevity of the timber and stop it drying out and cracking. When you think about it, it makes sense we paint our timber houses to make them last why not paint timber retaining walls...they are subject to the same destructive UV as the house is. Also I think it looks better as the treated pine turns a bit ugly after a while. In my opinion if you build a structurely sound 500mm wall with decent posts spaced at 900mm or 1200mm with good drainage and compact the dirt behind the wall as you back fill then you shoud have a good base for paving that will last you for a long time with probably only minor movement that will cause no great long term problem. If you dodge it up with undersized posts that are not far enough in the ground and spaced too far apart and ignore the drainage then you are most certainly looking at trouble down the track. This approach I believe would be the major failure that you are worried about with your wall. Finally at the end of the day money (as always) will drive you decision, basically if you cannot afford the cost of a masonary wall then you are only left with timber and there ****** the compromise....build it well lay your pavers and live with it. If you go in to this project with a view that yes! there will be some minor movement in a well constructed wall over the years and the gaps in your pavers may open a smiggen and when they do I will just bung in a bit more sand and cement and no one except me will any the wiser then you can be happy and sleep easy at night. Re: Paving and Retaining wall - Is treated pine reliable? 19Feb 15, 2009 9:18 pm GottaMow, thanks much for you advice! I feel I am now much equipped when talking to my landscaper now.
I think I will also get a quote for a masonry wall, instead of just being told they are much more expensive! At least I will be able to compare properly. In regards to the posts, it is important to have the posts outside the wall? It seems more structurally stronger to be outside. But it is more ecstatically nicer if they are hidden insider the wall. Building Clarendon Brighton - Done and moved in Sept 2009 Thank you again Simeon.. I will call my certifier for that. Have a good day 4 5852 DIY, Home Maintenance & Repair Are you going to have the frame exposed or are you cladding it with something. Usually if you are making an exposed frame you would use solid legs around 100x100 or… 3 6672 Iām just in the process of replacing 2 stud walls that have been severely damaged by termites and am planning to use h2 blue pine. I just wanted to if anyone can advise… 0 52913 |