Timber choice for greenhouse and sheds

[TFWS]

hi

i've been around lots of timber over the years doing diy and now i am starting out on my own but i am still confused about timber choices for garden projects.

i am constructing a timber greenhouse now and i've gone for treated timber which has the rounded corners and green tinge to it. the timber hasn't got a particularly natural finished but it will be painted eventually and the rounded corners challenge accuracy.

now, when you buy a B&Q shed for example the timber often looks like prepared planned finish but stained being brown on golden in colour so what's going on? can anyone "shed" some light on things?

i suppose what i am asking is, if you a constructing something in timber for outside and the timber is on show and exposed like a greenhouse or shed what would you use?

 

[gog64]

I think the brown stain on sheds is just a bit of preservative slapped on. You are normally instructed to properly paint it straight away if you want it to last any time.

When I've made tables for outdoors, I've just used planed timber (of whatever type the project called for) and then carefully finished it with exterior grade paint or timber treatment according to the manufacturers spec. I happened to see a large table I built a few years ago at the weekend and it was still perfect, all mortice & tenon joints still in perfect nick, all of the legs (laminated in this case as it was a really chunky table) still perfect, despite being out 24/7 on a patio. It would have been nice if the blighters had given it a coat of something every year though, it was looking a bit weathered!

 

[Blackswanwood]

There was a post a few days ago where someone was repairing some decking (I cannot find it) which quoted BS8417 .. I think you are looking for Grade 3 for sheds:

BS8417PreservationofWoodCodeofPractice.pdf

Hope this helps!

 

[Cabinetman]

Very tongue in cheek, for a Green house it should be Green wood

 

[TheTiddles]

You can get sheds in dip treated and pressure treated. Dip is just that, the treatment is on the surface and you need to protect it repeatedly or it’s toast. Pressure treated the treatment goes into the wood more (ideally totally) and you don’t have to keep repeating it, but as it ages it does kinda help prolong its life.

For a greenhouse I’d be looking at a timber that doesn’t need regular painting as that’ll get un-fun very quickly. So cedar, larch and Accoya are often used.

Treated CLS is never going to be nice wood for building nice things, it’s for frames etc it’s often fast grown and soft.

 

[thetyreman]

canadian western red cedar is what I'd use, it isn't cheap though! but definitely durable.

 

[TFWS]

thanks everyone

@TheTiddles are we saying that "dipped" could be some sort of cheap planed prepared software?

 

[johnnyb]

yes I was confused about my decking repairs. the majority I'd had sawn and treated especially. one joist was from b and q. that one joist had almost totally rotted. the others were perfect.
a wendy house was brought from a well known shed supplier. few years down the line its just disintegrated. the floor has holes everything's loose. whereas as she'd we brought in the late seventies is still fine and has been moved several times. structural strength has a part to play as well as preservative.

 

[MikeJhn]

Use a micro pores's exterior stain, don't paint it will crack and let water in with the sunshine that obviously a Greenhouse will be in all the time.

 

[TheTiddles]

thanks everyone

@TheTiddles are we saying that "dipped" could be some sort of cheap planed prepared software?

Yep. I know a guy who works at a joinery shop making gates etc... 3 of them make several hundred gates a week and dip them on site

 

[Billy_wizz]

Dip treatments are mostly little more than colour these days

 

[mikej460]

I suspect the timber you have used is KD (Kiln Dried) pressure treated. As a greenhouse if left unpainted it will last 5 years or so as long as rain doesn't get into joints or allowed to pool. If you paint it with Garden Shades this will extend the life considerably and more so if you repaint every few years. I speak from experience here and am just about to build a new greenhouse from the same timber.

 

[Awac]

I have praised this stuff before, it works, and it is so cheap, not often that happens! Apply once, that's it.

UK Agent.
https://www.harrodhorticultural.com...html?Aff=GPL&gclid=CLfQg7qNi9ICFYoaGwodWlkLzg
Manufacturer (more info and pictures).
https://ecowoodtreatment.com/

 

[MARK.B.]

A little tip if you go to a timber yard and buy treated timber and select from the pack , don't be tempted to pull off the top couple of layers to get " the good stuff underneath " the timbers on the outside of the packs tend to absorb more of the treatment and those towards the middle less and also those from the middle can contain a fair bit more moisture as it takes a long while to dry out inside . If you do pick your own timber do yourself a favour and restack what you don't want , trust me when i say ,you will get more help from the yard staff next time you visit ,leaving a mess on the deck will have you're name on the naughty list and it is suprising how quickly all the staff become to busy to help

 

[TFWS]

@Awac what sort of projects are you using this eco product on? the blurb suggests to be applied on previously untreated timber and cannot be over-painted for example

 

[TFWS]

so i've persevered with building this greenhouse/potting shed from the kiln dried pressure treated timber on the basis that it will be painted over and i must admit even with my limited experience the timber is rough, bowed, knotted and you name it....

i have done areas of cladding in redwood timber shiplap so what should i use as preservative on this before painting?

 

[johnnyb]

screwfix do a water based preserver about £22 for 5 l. I spray it on twice with dry time. then it needs sealing otherwise it leaches out. making then spraying creates a barrier. whereas using pressure treated allows weak endgrain( unless well treated) coating wood has been the same process for years(until teknos et al) make..preserve...prime....undercoat...gloss.

 

[robgul]

I'm just completing a garden project - horizontal cladding on battens on a blockwork wall - using Thermowood ("baked softwood") that's about 25% of the price for Western Red Cedar and, they say, will outlast the cedar even with no finish. Have to say it's easy to work with and looks good - at the moment it's almost cedar coloured but will fade to a silver/grey which is what we want. Fixed with Spax stainless screws - by gum they're expensive!
We're also getting a traditional greenhouse that's also made from Thermowood.

 

[Awac]

@Awac what sort of projects are you using this eco product on? the blurb suggests to be applied on previously untreated timber and cannot be over-painted for example

I would expect clean untreated timber is always the best, but in a mad artistic moment I handmade a window frame for my wife's workshop and carved it. I thought then some linseed oil which I had (spoon carving y'know...lol) would maybe give it an interesting look ( yeah, yeah)....jeez the sun in France laughed at me and started drying out the frame, so that's when I found this stuff, applied it over the top of previously oiled frame and it has worked well. As long as it can get to the timber it will work. Under £20 for a gallon. Worth a try, not much to lose eh? Have applied it on top of pressure treated wood, no problems, looks great in my mind.

Oh, and it's the green alternative, which I will always use if possible.

 

[TFWS]

@Awac thanks for that. useful to know. i assume we're looking at it as a treatment as you describe and a final finish ie. the blurb suggests it cannot be painted or stained over?