Prime before gluing exterior wood joints?

Joined
28 Jan 2011
Messages
55,902
Reaction score
4,128
Location
Buckinghamshire
Country
United Kingdom
Hi folks,

I suppose I've spent most of the last 50 years pondering this question and, in the absence of knowing a definitive answer, have undoubtedly varied my practice according to the phases of the moon, or somesuch! ....

... It's a simple question ... When gluing joints in things which will be 'exposed tio the elements', should one prime the surfaces first (after applying a preservative) or should one glue directly to bare (preserved) wood?

Intuitively, priming would seem to afford some protection should any water manage to get into the joint but, on the other hand, the glue is then being asked to stick to the primer, rather than the wood.

Kind Regards, John
 
Sponsored Links
i never like gluing anything you have to add preservative to
in my mind internal joinery or painted sealed joinery are glued
anything external with masses off expansion contraction and fluctuations in moisture levels should be designed without the need for glue
also wood glue works by soaking into the timbers so treatment may stop the glue working propperly
 
I would say its best to use a waterproof glue and fully coat both parts of the joint.

ie use PU or UF glue (polyurethane or urea formaldyhde -the latter is commonly knowm as cascamite).

External joinery is best designed to avoid trapping water -more imprtant than the glue long term

Structural green oak etc, mechanical joints are best.
 
i never like gluing anything you have to add preservative to ... in my mind internal joinery or painted sealed joinery are glued ... anything external with masses off expansion contraction and fluctuations in moisture levels should be designed without the need for glue .... also wood glue works by soaking into the timbers so treatment may stop the glue working propperly
Yes, I agree with all that. I use glue in such situations only as a second or third line of 'belts and braces' since my experience is that external joints usually eventually work loose (probably as a result of the factors you mention). In some senses, I use the glue more as a sealant' than an adhesive (indeed, I sometimes just use sealant) and I certainly do not ever 'rely on' glue outdoors.

What about internal stuff? In that situation, I would rarely, if ever, prime (i.e. I use glue on bare wood) - do I take it that you would agree with that?

Kind Regards, John
 
Sponsored Links
I think the above 2 replies may have missed out on what I think you are saying, which is a little confusing. Yes using a preservative is fine, a primer, I am assuming you mean paint based primer not so.
 
I would say its best to use a waterproof glue and fully coat both parts of the joint. ie use PU or UF glue (polyurethane or urea formaldyhde -the latter is commonly knowm as cascamite). ... External joinery is best designed to avoid trapping water -more imprtant than the glue long term ... Structural green oak etc, mechanical joints are best.
Yes, similar to what I've just written to big-all, I also agree with all that. I use PU glue outdoors (didn't know that Cascamite still existed!). I'm not talking (at least, not with current jobs) about anything structural, but the primary jointing is usually 'mechanical' and, as I've said, the glue is (at least in my mind) an attempt to delay the day when the joints start working lose. I do also do all I can to avoid any opportunity for trapped water,but water is a cunning devil, and I am rarely convinced that I haven't left some opportunities!

Talking of 'waterproof glues', I've never fully understood what 'waterproof PVA' is (there's plenty around which claims to be that) - is it reasonably water/wearther-proof?

Kind Regards, John
 
I think the above 2 replies may have missed out on what I think you are saying, which is a little confusing. Yes using a preservative is fine, a primer, I am assuming you mean paint based primer not so.
Sorry if I confused you! I certainly would always use a preservative and, yes, I was asking about also using 'paint-based primer' (what sorts of primer aren't 'paint-based', other than things like PVA and {if you're old enough!} 'size' etc.?) - but you seem to have answered that.

Kind Regards, John
 
The primer is specifically designed to counter the porosity of the wood, so I guess you can see where this is going.
 
The primer is specifically designed to counter the porosity of the wood, so I guess you can see where this is going.
Indeed - as I said at the start, one would then be expecting (relying on) the glue 'sticking to' the primer. It seems that I have an answer which, I suppose, is probably the one I was expecting.

How are things like window frames constructed (at least, 'traditionally') - would the joints not be glued?

Kind Regards, John
 
How are things like window frames constructed (at least, 'traditionally') - would the joints not be glued?

I run a joinery company and we never the joints of a casement frame. The joints have end grain sealer applied to both tenon, mortice and scribe.

The sashes are glued of course.

It is best practice to form a V where there are joints. This is because timber expands and contracts mostly tangentially. That means the bottom rail of a door will move, but the stile it is joined to, does not. Over time the movement causes the paint film to fracture and is an early point of failure. If the joint has a V -or really a small radius on both edges, the paint film will maintain its thickness around the rounded edge. We use a V joint filler as well.

External edges should have a small radius -because a paint film gets very small on a sharp edge, but is maintained around a small 3mm radius
 
I run a joinery company and we never the joints of a casement frame. The joints have end grain sealer applied to both tenon, mortice and scribe. .... It is best practice to form a V where there are joints. ... External edges should have a small radius -because a paint film gets very small on a sharp edge, but is maintained around a small 3mm radius
Many thanks for all that - very interesting anmd useful!

Kind Regards, John
 

DIYnot Local

Staff member

If you need to find a tradesperson to get your job done, please try our local search below, or if you are doing it yourself you can find suppliers local to you.

Select the supplier or trade you require, enter your location to begin your search.


Are you a trade or supplier? You can create your listing free at DIYnot Local

 
Sponsored Links
Back
Top