Designing and finishing a timber planter box

[Dengue]

I have been asked to make my niece a timber planter box, as an indoor feature and to be placed in the outdoor weather too, totally exposed to sun and rain. It will be made out of hardwood timber, 1000 x 150 x150.

Can anyone please recommend the best type of corner joints for this box, eg mitre, finger joint etc

I presume the base will be solid timber with a few drain holes, covered with a 25mm bed of pebbles to prevent the drainholes from clogging up. Is this the best type of design?

Can anyone please advise on the best finish for this box that will meet the outdoor climate and still highlight the beautiful grain when indoors?

The item will be filled with dirt and plants. Can anyone please advise the best way to seal the inside surfaces?

[Dengue]

Hi all, has anyone had any success with Jotacote 605 (the 2-part epoxy compound) on timber? Thinking of using that to line the box and make it waterproof, concerned about timber movement in rain and sun will cause it to crack and break the seal.

Also thinking Cabot's Exterior Clear might be the way to go on the outside of the box.

[Dengue]

Anyone? I priced a stainless steel inner box -$200; a 3 mm polyethylene inner box $200 too. Any suggestions please?

[Kuffy]

Sealing the inside can be done with bitumen waterproofing paint.

How to waterproof retaining walls and planter boxes: How To Guide: Crommelin

[themage21]

Hi Denque,

I'm about to give a go at using a Northane clear finish on an outdoor bench to get as many years as possible out of the natural colour of the timber. It is a 2 pack polyurethane finish that needs about 5 - 6 coats to get full UV resistance good for marine (i.e. high UV) environments.

However, one should always be aware that timber outdoors is a losing battle from the outset. In order to keep the timber's colour, I'm probably looking at having to re-coat every 3 - 4 years (light sand to clean off and then two more coats) to "update" the UV protection. I'm going to see how long I last on that regime.

If you want something fire and forget, it's best to get your head wrapped around the idea that the timber is going to be grey and get something that looks good and doesn't rot/turn to splinters once it's been out for a few years. Repeated oiling can help with the drying effects, but unless the oil has a colour in it, it won't prevent the greying of the timber.

Epoxy is pointless for outdoors unless covered by another finish, as it has next to no UV resistance at all (it's one great weakness). It can be very good as a sealer to help prevent rot, but you still need to protect the epoxy from the sun. As far as your concern with it cracking, well there's that too. There are other finishes out there that have some flex, I've forgotten all of them now that I've done my research and taken the plunge in one particular direction.

For a planter, getting a poly or expoxy finish to last any significant time is probably going to be a bit of a hassle as once the thing is full of dirt, getting it clean for the next go is going to be tough. Oils will be the way to go if you want relatively hassle free, yearly reapplication being the only real drama. I'd say that many decking oils out there would be suitable for the task. I've not got a timber deck, so I can't give you reviews on that space.

I'd have to search around to find the thread again, but a bloke on here made an exquisite timber box for the back of his ute (the great photoclysm on the forums earlier this year ate the photos unfortunately), but 6 - 12 months in the sun killed it, despite his 3 coats of this and 3 coats of that. I think a follow-up thread involved said box being converted into a base of operations by termites in his storage container and the poor thing had an ignominious end as landfill. That's the horror story, but unfortunately the reality that timber outside takes a lot of work to keep looking good.

For sealing the inside, a liner idea will work best, as the constant moisture, air and microbial activity is great for degrading timber. Using a timber that is rated highly for buried environments will help (Timber - Wood, Lumber Products & Other Building Material Information:Learn More at WoodSolutions have a pretty decent set of reference materials on them for looking up the characteristics of a particular timber), but planter soil, being generally high in oxygen and often watered to flooding is ideal for rotting timber. Treated pine will generally do ok, but not if you want to eat out of it. It normally also looks ugly as sin, even after being coloured.

The SS inner will work well depending on the grade (i.e. 304 won't necessarily last as long as 316). The polyethylene liner will probably be the better solution as it is inert organically and doesn't rely on ready access to oxygen and a particular pH/soil chemistry to prevent degradation (unlike SS). Ideally you'd have an air gap between the liner and the cladding timber, but at only 3mm thick, you may still have to support it internally. I'd have a play with it first to see how much it flexes when full of water and then take that as a guide for designing your box.

With regards to jointing, mitres will look the best, but depending on how structural they are, may need support in the form of a floating tenon sort of arrangement or dowels or such. If the outer timber is just there for looks, then a good waterproof glue would probably do. Note that water resistant will not be good enough (e.g. Titebond 3, not 2 if using PVA)

The other option is to make a steel/aluminium frame around your liner and then attach the timber to it using decking screws. That transfers the weight of soil off your timber (reducing the cross sections requires) and can also take the pressure off for absolute precision when it comes to the joints. It also allows you to leave some swelling room between the timbers so that they don't have issues down the track with movement.

[Dengue]

Thanks kindly to themage21 for taking the time and effort for a very comprehensive and entertaining post on planter box design and finishing internally and externally. It is a very valuable treatise, with lots of good information.

Currently looking at lining with a one square metre DIY fibreglass kit $65, but have never done this before. Local fibreglassers all wanted $200+

Will also be sussing out the bitumastic paint suggested by Kuffy. Looks good!

[themage21]

If you're going to fibreglass, definitely use the bitumen paint - you can get special pot sealer stuff that supposedly doesn't kill your plants with the various solvents for years afterwards.

When buying some FR concrete pots, I was advised to do at least two coats. Admittedly, concrete is a bit more susceptible to staining and permeation issues than resin, but it can't hurt to whack on two coats anyway.

When designing your liner, unless you're quite confident I'd probably undersize the pot a fraction for the size of the kit. It may also pay to put an additional layer in on the corners and edges, as they'll be the most vulnerable to damage and/or degradation moving forwards. I'm not sure how thick you'd want the fibreglass to be - is that 1m2 only a single layer thick? That may be too thin unless the liner is supported structurally (i.e. it's just a waterproofing layer).

[Mobyturns]

It will be made out of hardwood timber, 1000 x 150 x150.

Is the timber sized as 1000 x 150 x150 or is that the final size of the planter?

I'm thinking its the final size, as you would need a fork lift to move a planter made from 150 x 150's .

One product I have used with success on outdoor furniture and boats is Flood's "Deks Olje #1" The Flood Company Australia » Wood Care Products » deks_olje_1 Over the years the application instructions have changed, as it used to be a thin 75/25, 50/50, 25/75 then apply 100%, but now it is keep applying until it stands on the surface. It will stand up to many years of neglect but looks brilliant if you regularly recoat with it.

[Dengue]

Thanks Mobyturns, sounds good. i particularly like it because of the oil finish. Can you get it locally?

The box will be made of 19mm thick kwila

FOOTNOTE: contacted Floodaustralia, and they advise this product is no longer manufactured

[themage21]

Is that both of the Deks Olje products or just the #1 matte finish version?

[themage21]

Sorry, just read around the internet and it looks like this is old news to boat people:

Varnol vs. Deks Olje

There seems to be some confusion as to whether "not in production" means "Australia isn't cool enough" or it's actually not made any more.

[themage21]

To continue with my mad posting, it is available. Flood were taken over and stopped local production. Deks Olje is now imported by a bloke in Queensland and is available in some chandlery stores (some even online).

The Deksolje.com.au website is pointless. Google Deks Olje Australia and you'll get some results.

[Xanthorrhoeas]

Hi Dengue,

I'm late to this thread - been busy (and not doing woodwork unfortunately). I agree with Mobyturns. I have some external Australian cedar doors that get a fair bit of sun and weather. i finished them with the Deks Olje #1 until they wouldn't take any more. Then I used a few coats of the #2. I have to recoat every two to 3 years but, seven years after installation the doors still look good. The great thing about this product is that you just clean off, give a very light sand and slop some more of the #1 on to refresh.

A word of warning though - the solvent in the #1 is pretty potent. You need good ventilation and a fan to blow the vapour away from you while you paint. There is no issue after it dries though.

David

[Dengue]

Thought it was time to publish the final outcome, after all the helpful advice I was given.

The requirements were established fairly early in the game. It was to be filled with succulents and placed on the wedding table, so it had to look swish against the four others that they were hiring. After the wedding it was to be placed out in the weather for the rest of its life. So there were quite conflicting requirements for the final finish. And it had to be mahogany coloured to match the others !

Firstly I selected kwila for the box sides, with epoxy glued mitre joints for longevity, and each joint strengthened with hidden splines. The kwila had to be prepped to wash all the tannins out of it, so selected Intergrain PowerPrep and Reviva. You can see from the photos the brown stuff just pouring out of the timber. My wife did that job while I was recovering from prostate surgery and under strict instructions to do nothing. So I took the photos

Because this box was intended to last a long time, I used a 12mm thick sheet of black polyethylene as the base, and drilled a few drainage holes. This sheet was epoxied in a groove around the bottom of the box sides.The drainage holes were extended by using small harpoon shaped offcuts from some irrigation joiners. The idea is to prevent the water seeping across the underside of the base to the box sides. A bit of overkill, but time will tell.

The internal sides were coated with Crommelins water based bitumen, designed for this purpose, and then lined with aluminium flyscreen to protect it from damage from the soil mix and pebbles, whatever.

I was asked to put some rubber feet under the box, but not so they were visible. Finally found some round heavy duty rubber feet in China, used for under loudspeakers and furniture etc. They measured 14H x 50mm diameter, and were screwed to the base corners, but not visible from the outside. The box now rests 4mm above ground level.

For the final coat, and after researching the recommendations above, I decided on 3 coats of Sikkens mahogany coloured HLSe finish. I have used this previously on our western facing front doors which cop the sun and weather here in the tropics, and it has lasted exceptionally well. The manufacturers of some of the products recommended in posts above advised they were not really suitable for my application. In some cases, the product was not made any more.

The box was rounded off with a brass plaque which was fitted into a 2mm deep recess with the aid of a template. The cutout for the template was so tight that I could not get the plaque out of the front side after a test fitting. I had installed some dental floss under it just in case, but that just broke trying to pull the plaque off the side. The plaque is still lodged in there without any glue.

The box was posted to Sydney with lots of 15mm polystyrene cut on the tablesaw surrounding it as an external skin. It arrived safely, just a week before the wedding, and was well received by my niece and her new husband.

Removing the tannin from the kwila box sides:

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Box sides assembled with hidden splines and epoxy joints:

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Irrigation line joiners used to extend the drainage holes under the base :

P1550239 (Large).jpg



Lining the interior with water based bitumen :

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The finished product, and on the wedding table :

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[Kuffy]

That does look pretty swish indeed.