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Moisture Content Weather Red Cedar slats

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Hi all,

Haven't used WRC before, loads of other timber, not this. I know it's very durable, good against moisture and outdoor environment. However, just wanted to know the ideal mositure content for cedar slats.

45mmx18mm and they're light as a feather, but the mositure content reader says they're between 22% and 29% moisture. I know kiln dried is usually anywhere up to 12% and anything 17% or over is not great.

However, I need to treat with osmo, so does it need to be much drier before I treat?

Thanks all.

Best, James
 

bjm

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For application of any finish they would need to be dry to about 12-15% to allow the fiish to adhere (check with the manufacturer though.

As for service moisture content, that will vary across the season. If they are above 25%, and I wouldn't rely to much on an moisture meter, they will naturally dry down to around 18% (around winter) and will dry further around summer. It is normal to see a cycling in moisture content as wood reacts to humidity levels and adjusts to reach what is called 'equilibrium' at a a certain level of temperature/humidity. In the UK, wood outdoors (but rain protected and not in ground contact) will normally vary between ~9-18% mc. Rain only raises this for short periods and it will naturally revert. Just make sure there is no ground contact as this is a different scenario.
 
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For application of any finish they would need to be dry to about 12-15% to allow the fiish to adhere (check with the manufacturer though.

As for service moisture content, that will vary across the season. If they are above 25%, and I wouldn't rely to much on an moisture meter, they will naturally dry down to around 18% (around winter) and will dry further around summer. It is normal to see a cycling in moisture content as wood reacts to humidity levels and adjusts to reach what is called 'equilibrium' at a a certain level of temperature/humidity. In the UK, wood outdoors (but rain protected and not in ground contact) will normally vary between ~9-18% mc. Rain only raises this for short periods and it will naturally revert. Just make sure there is no ground contact as this is a different scenario.
Amazing, very helpful. I've cut all I need, so will keep the heated workshop to help dry out until staining on the weekend. Don't want to subject it to too much heat in case it splits. I was just going to apply two coats of osmo and then assemble the labels. Only half of one panel night get some rain impact, the rest just UV. The majority is under a porch, just a fascia. So not fussed about rain damage. Will just be subject to humidity. It was pretty cheap tbh, but otherwise straight and seemingly dry. Cheers. James
 

bjm

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Don't try and force it to dry or you can build up stresses in the wood. You're better off letting it dry naturally. The rain won't damage it but the UV will degrade the surface over time (regardless of what the product marketing says!). Just make sure you key it first.
 

Chrispy

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This might be a compleat load of tosh but I think Western red Cedar is exported green , basically it dries so easily and without alot of shrinkage that it's not worth seasoning in the conventional sense let alone kiln drying.
 

bjm

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It's used a lot for shingles so there is no need to season it for that but I would expect it to be dry for other purposes.
 

yetloh

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I'm sure it is shipped green.

I have recenrly been making soem greenhouse frames with it and, as bought it was very wet. For external use I see no point in trying to dry it; it will soon find it's own level. It is also in my opinion pointless to treat it with Osmo ( or anything else) It has a very open texture and no finish is likely to last long. Much better to allow it to weather to its natural silver grey colour and save yourself endless maintenance.

Jim
 

Keith 66

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It is good to remember that it is classed as one of the most toxic woods, Dust from it causes asthma & other nasty conditions, i had a bad reaction to it about ten years ago & cant go near the stuff now without a full powered respirator.
 

Steve_Scott

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As others have said, WRC is often supplied green and I’ve worked, or rather gave up working, with some that was saturated like a sponge!

Regarding the choice to treat with Osmo... it’s personal preference but I like to retain the colour rather than let it grey out (albeit Osmo doesn’t retain the true colour). I believe Osmo recommend letting cedar weather for a while before treating it... food for thought.
 
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Thanks all, much appreciated. Another question, is it advisable to use stainless screws or stainless pins/nails? I have tons of pins for the dewalt gun, but apparently it's best to use screws due to splitting?

Thanks
 

yetloh

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Thanks all, much appreciated. Another question, is it advisable to use stainless screws or stainless pins/nails? I have tons of pins for the dewalt gun, but apparently it's best to use screws due to splitting?

Thanks
splitting csn be a problem but, in my experience , only in very narrow sections. My 25 year old greenhouse made by a then top bespoke maker has wedged mortice and tenons which are also nailed with black non-rusting oval nails throughout. These or stainless versions would be good as plain steel will stain. Haven't used a gun but WRC is so soft that you may need to be careful they don't go too deep. Hope this helps.

As regards finish, long term tests by a user on this forum (can't remember who) showed pretty conclusively that Sikkens Cetol is by far the most durable for exposed external use. It's expensive but worth the money.

Jim
 

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