Outdoor protection

[Colarris]

I'm constructing something that will be kept outside and is put together with mainly lap joints which are screwed together. I was wondering should I varnish the wood that overlaps or can I use woodglue and would that provide enough protection against rain and the outdoor elements?

 

[marcus]

I would glue the joints with a decent gap filling exterior adhesive like cascamite. What sort of timber is it? If it is a non-durable softwood you should treat it with preservative and then paint/varnish. If a durable softwood or a durable hardwood just varnish without preservative. If a very durable timber (ie oak or iroko) then you can get away without any finish at all if it is kept clear of the ground.

 

[Colarris]

Its just old pieces of pine that I found out about, not the greatest specimems. Trouble is I have already varnished the rest of the wood, its just the lapped pieces that I was wondering about.

Many thanks for the info.

 

[marcus]

Ah, never mind, but I would definitely glue the joints....

 

[Colarris]

Actually Im sanding the varnish off as we speak.

Will the wood glue act as a form of water protection for the wood once its bonded? I'm thinking now that I WILL glue them as well and screw them together and then perhaps paint varnish into join between the two. I don't expect it to last for years and years but I hoping for at least 5 years out of it.

 

[marcus]

If you use a decent glue it will seal the wood and should help stop water ingress into the joint, which is where rot is most likely to start. And by all means give it a coat of varnish over the joints once it is together.

 

[Colarris]

Thanks Marcus.

 

[RogerS]

...... If a very durable timber (ie oak or iroko) then you can get away without any finish at all if it is kept clear of the ground.

Maybe if it is a huge timber-frame building but most definitely NOT something smaller such as, say, a cold frame. I made a couple for SWMBO...there's a WIP somewhere or other. She didn't want any finish and like a fool I listened to her. OK.....in retrospect I could have designed it a bit better (and also used proper M&T's rather than being a lazy sod ) but suffice to say all the joints have gone. The panelling is dropping out. Most of the glue lines have failed.

 

[Woodcrafts]

I would make sure that the glue used was an exterior grade, and I would treat all timber, especially the ends with a wood preservative. Use yacht varnish or similar for exterior use.

 

[nanscombe]

Over the last couple of years I've make 6 planters out of Wickes' planed timber, each of them constructed with half-lap joints.


Planter 05 (20130527_194341) by nanscombe, on Flickr

I used weatherproof Evo-stick adhesive, and pinned the joints for good measure. A couple of coats of mahogany woodstain, hazelnut for the infil panels, and finally a coat of yacht varnish over the top. For good measure a square of Duck tape on the bottom of each of the legs.

They haven't fallen apart yet ... cross fingers. :lol:

Here's an earlier one with some flower pots in it.


20120511_124324 by nanscombe, on Flickr

 

[Colarris]

Ah, that was going to be my next question...What wood glue is best? I have a pot Evo-Stik wood glue but it doesnt mention it being water proof or not.

 

[marcus]

Ideally I would suggest cascamite or extramite, or polymite, or whatever 'mite they're calling it at the moment. Or any other brand of urea formaldehyde glue. Comes as powder and you mix it with water. Though if you're only after a few years of life for the thing you could get away with a waterproof pva, though they're not as good IMO. If it is waterproof it will say on the bottle.

 

[nanscombe]

Ah, that was going to be my next question...What wood glue is best? I have a pot Evo-Stik wood glue but it doesnt mention it being water proof or not.

The weatherproof Evo-stick is in a blue bottle, and it says so on the bottle, the interior one is in a green bottle.

If it doesn't mention being weatherproof then it probably isn't.

Other adhesives may well be better but, since I don't do a lot of woodwork, that's what I tend to use because it's readily available and I probably know no better. 8)

 

[Yetty]

Epoxy.

 

[Colarris]

Thanks again, I think I will go down the 'mite route for piece of mind!

Im guessing it will bond the joints as strong as it would be using wood glue(?)

 

[nanscombe]

According to Axminster, Cascamite is good for internal and external usage and has gap filling properties.

It is supplied as a powder, which you mix with water. Tack time 1 - 2 hours and cures in 6 hrs.


I'm pretty good with my joints as I use a jig to get close and perfect them with a small router plane so I don't need to fill gaps.

I just use a weatherproof pva glue and covered the whole project with a coat of waterproof varnish as I figure the rain wil have to get through the varnish and another couple of layers of finish before it gets anywhere near the glue. :wink:

 

[Colarris]

All I could find at my local WICKS was this stuff...