The Brew Cabin

Hi Tony,

I've just brought a 8.5' x 10.5' aluminuim green powder coated greenhouse made by Robinsons. Although it can be placed directly onto my grass lawn I thought it would be better to put bolt it on to a concrete plinth. What size do you think the plinth should be and what mix of concrete/sand/gravel should I use?

I would also like a mowing edge around the greenhouse. Once again what do you think would look best. I don't want it more than 12" wide.

In terms of the inside of the greenhouse what kind of a finish do you think would look nice? I'm not keen on plain grey slabs. I want something that is traditional and will look good against the dark green finish of the greenhouse. The greenhouse should last more than 30 years so all materials will ideally need to last as long.

I have a Travis Perkins near me so if you recommend anything they stock I will be able to view it quite easily.

Thanks very much for your help.

Max.

Hi again Max,

good to see you back in the Brew Cabin, and what a good choiuce of Greenhouse - I wish I had the room for something a bit bigger than my little ally 6x8, as it's bursting at the seams, thanks to my love affair with fuchsias!

For the base, you coulkd either go for a solid slab that is roughly 300mm larger than the GH, giving 150mm of 'spread' on each edge, or you could go for the 'strip footing', which is a concrete-filled trench. The latter gives you direct access to the soil, but many modern gardeners, myself included, like to have a solid concrete floor and then rely on gro-bags or pots etc, rather than the underlying soil.

The concrete should be at least a C20 equivalent, as described on the Concretes page, and you can knock this up yourself, or buy-in as Ready Mix. Whether you go for the 'raft' or the strip footing, the concrete only needs to be 100mm thick, as it's not taking any vehicles.

For the Mowing strip, I quite like using the larger tumbled pavers, such as Tegula/Drivesett by Marshalls, Woburn from Charcon, or Alpha from Brett. The Tegula/Drivesett are 240x160x50/60 and, laid 240 wide, they make a great mowing strip, and look quite naturalistic in the garden. They cost around 18 quid per square metre, which, when laid as a single course, 240mm wide, works aout at around 4.50 per linear metre.

Inside the GH, I like to use plain concrete flags. They're not 'on show' as it were, so anything will do, from reclaimed 2x2s scrounged from a local driveway redo, or even the budget stuff from the DIY sheds.

In my GH, I have a solid concrete floor (a raft), on which is built a low wall, just 4 courses high (300mm) topped with a wooden batten and the GH itself is fastened to that. This arrangement gives me extra height in the GH. The central path is made from 600x600x40mm Marshalls Heritage riven flags, laid on a cement-bound bed, so that they are, roughly, 100mm higher than the concrete floor.

Your first decision, though, is whether to go for a raft or a strip footing. You decide and I'll do the calculations for you. :)

Hi Tony - Hope your visit to the hospital went well.

Thanks very much for your comprehensive reply. I'm in that difficult position in that I've had to spend a lot of money on the greenhouse but don't know if I can justify spending a load more getting it up (so to speak).

I had a look in a few gardening books and I have to admit that my favourite was the use of a small basketweave path around the edge of the greenhouse and also as a central path in the greenhouse. Either side of this in the greenhouse I would have gravel on top of a weed suppressent membrane. I'm not sure what type of blocks would look best against a green coloured greenhouse with lawn around it.

I was thinking about using a concrete plinth/strip footing to put the greenhouse on. Do I need to put in a sub-base for either the greenhouse or any of the paving I lay? Also is there any similar need for a sub-base below the gravel. I will have a look at my Marshalls catelogue tonight to see the pavers you have mentioned. They certainly sound nice.

Thanks very much for your help.

Max.

The hozzy want me back for some further sugary later in the year, but, if it cures the angina, it'll do for me! :)

If you fancy a basketweave path, go for it. The narrowest feasible basketweave would be 400mm wide, assuming you use 200x100mm block pavers, which is fine for a mowing strip, but I'd definitely go for 600mm wide down the middle of the GH itself. 400mm is awkward for standing on - you can't escape the feeling that you're about to 'fall off' at any moment.

Just about any blocks would go with a Green GH, but, inb garden settings, I prefer the more natural colours. In the Marshalls range, the Burnt Ochre (a multi-brown) is, to my eyes, more garden-friendly than a multi-red brindle or a loud yellow (buff). Have a look at the Burnt Ochres (Brown Multis) on the Portfolio page - that's a job we did some years ago in Rochdale.

For the paths you're proposing, I wouldn't bother with a traditional construction - I'd bed everything on 75-100mm of lean-mix concrete, say a 8:1 mix (C7.5 equivalent). Even with a 600mm wid epath, by the time you bedded the outside edges on concrete to hold everything in place, there's only a 400mm gap left to fill, which is hardly worth the effort of placing sub-base and then a sand bedding layer.

I'll post a drawing to this thread later. :)

For the strip footing: dig a trench roughly 100-150mm deep and 300-450mm wide, and fill it with C20 equivalent concrete. Tamp to level, and it will be ideal for carrying your GH - I'll add a drawing of that, too, but only after I've watched Countdown and had me tea! :)

Thanks in advance for your help. I was going to put a 1 metre path in the greenhouse for the reasons you mentioned and use lengths of timber to stop the edges wandering.

Would I not get away with a mowing edge around the greenhouse with a width the same length as a paver(200mm)?

If you go for a basketweave path laid on a sand/cement bed (C7.5 concrete equivalent), that will preclude the need for any timber edges - you can use the bedding to haunch the edges, as shown in the drawing.



Going back to the mowing strip, 200mm means you can't do a proper basketweave, but you can do a sort of half-basketweave, I s'pose....

Dear Tony,

I've had a chance to go down to my local TP and look at the blocks/setts. I've also got the Marshalls 2003 catalogue. I've narrowed my selection for the basket weave mowing strip and greenhouse path to the following:

Chapelgate brick pavers in Red Multi (page 53 in the catalogue);
Old Mill Brick in Sunset (page 100/101).

I would like to point between the pavers so that I get that "olde cottage look" to the finish. However, I noticed that the cataloue says the Old Mill Bricks are "...primarily intended as a walling material. When used as a decorative paving feature, it must be noted that the surface will abrade under foot traffic". Do you think this will affect me to any great extent since only the path in the greenhouse will be affected by foot traffic and even this will be limited to the spring/summer months. Also what do they actually mean by "abrade"? If you really think neither of these is a good choice please do let me know.

You mentioned earlier in this posting that I should bed the greenhouse path in a 8:1 (8 parts sand:1 part cement) lean mix concrete. Does this also apply to the mowing strip? Also what mix should I use for the pointing between the bricks/pavers? I would also like to include lime in the pointing mix if you think this will make the finish look nicer and be easier to maintain long term. If so what should the mix be?

I've also decided to go for the strip footing but without any walls. The greenhouse frame will be bolted to the footing. I've got someone coming round on Saturday morning to go through exactly what I want so that he can give me a price. I'll let you know the outcome.

Thanks for your help as always.

Max.

Hi Max,

well, I think you can get better value brick pavers than the Old Mill facing bricks, and the catalogue is right about them 'abrading' (wearing away) under regular traffic, but, for what you're planning, I think you'd be OK, as it'll only be you doing a bit of pottering, won't it?

Have you been quoted a price on these items yet?

You can use the 8:1 bedding for the path and the mowing strip, and then use a 3 or 4 to 1 mix of building sand with cement for the pointing.

Take photos during the works - it's always good to look back on just how much of a change is made by putting down a bit of paving and a mowing strip. :)

Thanks Tony. Price from TP is about £450 for bricks (inc vat) and £366 (inc vat) for the pavers. This is for about 9 sq. metres and includes 1 metre "wastage".

You're right my wife and I will only be pottering about in the greenhouse. I've got a fairly heavy duty mower to go over the mowing strip.

This is going to be one expensive greenhouse when it's finished. I'll get some pics. on a digital camera and send them to you.

Dear Tony,

I went to see the Old Mill bricks in real life and didn't think much of them. I have now decided to go for the Marchalls Chapelgate clay pavers instead. The builder came round on Saturday to discuss the base and he said the best solution was to put down strip footings and then lay up to 2 courses of bricks to make the base level with the surrounding ground. He will also put down a 400mm mowing strip and 800mm path in the greenhouse. Either side of the path he will lay down a membrane and put 10mm gravel. I have 3 questions for you:

1. Since some of the brick course might be below ground level will he need to use engineering bricks? I have asked him to use reclaimed bricks but I'm not sure if it is possible to get reclaimed engineering bricks.

2. Is it ok to lay the clay pavers on a weak mix? Or do they have to be laid on sand?

3. When it comes to using building materials such as sand and cement does it matter if they are branded products from companies such as Blue Circle or are the "own brand" items from Wickes/B&Q just as good?

Thanks for you help again.

PS. The 2 quotes I've had so far are £980 and £3000. The second company has done a lot of other building work for me to a very high standard and think it will take about 6 days. I've not used the cheaper one but they were recommended by the place where I brought the greenhouse from and they say it will take 2 days.

Thanks as always for your advice.

Engineering quality bricks are the best choice for brickwork in contact with the ground, but you can probably buy new engineering brick for less than you'd pay for reclaimed. If the brickwork is not going to be seen, you could use concrete commons or trenchblocks to keep down the cost.

Seeing as your path is quite narrow, I'd suggest laying all the pavers on a lean mix concrete as shown in the sketch I posted earlier in this thread. Lay the pavers onto the lean mix, tap down to level using a clonker (a small rubber hammer) and then just brush in jointing sand. No need to use a plate compactor, as that would only scatter the pavers.

There's no real quality difference in using B&Q branded sand and cement, or sand and cement from a BM, as sand is sand is sand, and cement has to comply with BS12 to be sold as cement. For the type of work you're undertaking, the B&Q stuff will be fine.

Finally, 3 grand and 6 days seems a little bit OTT to me. The quote at just under a grand sounds far more realistic.

Thanks for the advice. The bricks will be partially in contact with the ground because they are being used on a slope to create a level base for the greenhouse to rest on.

Anyway I'm going to give the go-ahead to the cheaper guy to do the work.

OK - let us know how it goes.

Hi Tony,

The base was completed last week. It looks good although a couple of blocks were cut to size at the front of the greenhouse when they could have been done at the rear where they would have been less visible. Anyway once I get some pots on top they will hopefully be hidden anyway.

The blocks were laid on a wet mix as you suggested. However, there is a gap between the blocks which has not been filled. Can you please tell me whether dry kiln sand should be used or something else?

The greenhouse goes up on the 26th. I have got a couple of pics for you and will send them when the greenhouse is up.

By the way what started as a straight forward project went over-budget because the contractor had miscalculated the slope. He said that I need a 6 course retaining wall for the block paving as the slope was too steep. I agreed to it reluctantly since I just wanted to get the job done. Otherwise I would have had to get more quotes which I am sure would have not been less than even the revised price.

Just in time for the main growing season, Max! Let's hope the summer is as glorious as is today - if it stays like this until November, I'll be a very happy Tony! :)

Use kiln-dried sand for the jointing - it'll be fine in a greenhouse. Looking forward to seeing the pictures - looking out of my window, I can see that the door to my GH is still shut, and my beloved fuchsias will be sweating in this heat, so I will now slope off and have an hour in the sun with them, and make sure the ventilation is right. :)