# Gap filling adhesive?



## woden (21 Aug 2007)

I'm planning on knocking up a few rough wooden brackets for supporting shelves in the garage soon. Thing is I'll be sawing them by hand and as I don't want to spend much time on them the joints will most likely be a bit sloppy. So can anyone give me advice on what adhesives are good at filling gaps. I know that epoxy (with micro fibres mixed in) performs this function well but this is much too expensive to waste on a bit of rough shelving.

I was thinking of Gripfill but I just have this prejudice that the stuff - great an' all as it is - isn't a proper wood glue. It's very bulky - almost like putty it seems - and so is difficult to get into crevices and corners IMV. Plus, if you do fill a gap with it it seems to take a few days to harden. And at that, does Grip fill really harden fully like resin based adhesives? I can't get this idea out of my head that anything that comes in a cartridge is just a super duper form of silicone and will never lose its rubberiness, causing it to creep over time. I know, I know... Gripfill is a proper adhesive and not just a sealant, but still... it comes in a cartridge! :shock: 

The other concern I have is that to work properly I thought wood glue had to soak into the wood fibres of the mating surfaces in the joint. But Gripfill being a bit putty-like - or should that be more solid than liquid - just seems to sit on the surface. So, despite what it says on the packaging, how well does it really bond wood?


Furthermore, from searching the forum archives I've read that formaldehyde adhesives are also good at filling gaps. As I have a pot of Humbrol's Cascamite/Extramite/Polymite/Whatevertheyarecallingitnow-mite (urea formaldehyde I believe) this might be a better option than Gripfill. But the thing about 'mite (for want of a consistent name) that concerns me is how big a gap it can cope with before losing its strength. 'Mite is also reputed to be quite brittle so if the space is too great does this raise the possibility of the glue 'line' fracturing if knocked?

Another seeming downside of 'mite in comparison to Gripfill or Epoxy (with plenty of micro fibres) is that it's too runny to stay in large crevices. Is there anything you can mix into it (like the micro fibres you can get for epoxy) that will thicken it into more of a paste? I've been told sawdust but does this not compromise the strength of the adhesive? Could you get away with mixing the micro fibres that SP or West sell with their epoxy into 'mite as this would not only bulk the adhesive up but also strengthen it across a gap? The thinking being that micro fibres act a bit like the fibrous matting in glass-fibre? Or would something designed for epoxy be chemically incompatible with a urea formaldehyde adhesive?

Yours,
The ever bewildered woden. :?


----------



## Max Power (21 Aug 2007)

Woden,
buying a cheap new saw or better still a decent one and practicing your joints on some scrap wood would be a far better use of your time than enquiring how to make the best of a bodge up you havnt even bodged up yet. The former will learn you something of value, the latter will have gained you nothing.


----------



## AndyT (21 Aug 2007)

I've used Gripfil when I was building in some cupboards and needed to bond some straight wood to an uneven floor and wall. It worked really well, with gaps up to about 5 mm. It dried to a full strength bond, but with some elasticity - about the same as the wood itself. Ideal for rough stuff, but as you suggest, a bit too stiff to go into a wood joint. You'd find it hard to clamp hard enough to get the joint to fit.

Andy


----------



## OllyK (21 Aug 2007)

Gripfill is holding all my skirting boards on!


----------



## Keith Smith (21 Aug 2007)

What exactly are you building and what sort of joints are you planning?

The only adhesives I use to fill gaps are Gripfil Max and Sikaflex SBK, but both these remain flexible, although they stick like the proverbial.

All the other glues I've used (I'm testing 11 different ones at the moment)won't fill gaps well, mostly because they are too runny but also they are generally too brittle.

There are plenty of quick simple joints that you can make brackets from without the need to use gap filling adhesive


----------



## DomValente (21 Aug 2007)

Hi Woden.

You don't need to make joints, unless you want to practice.
Take two lengths of timber, about a foot each and two by two and cut out two triangles of ply about four inches by four inches by five. Six mil will do.

Place the two pieces at right angles to each other so that the angle makes up one side of 14" and the other of 12".
fix the triangles at the angles with about four screws to each edge then fix to the wall, I use rawlbolts and they carry hundreds of pounds in weight of timber.
Hope that makes sense, if not I can post a picture tomorrow.

Dom


----------



## Max Power (21 Aug 2007)

Dom ,correct me if I'm wrong ,but surely the structure your recommending involves a BUTT JOINT. Wouldn't it would be advantageous to encourage members to develop their skills and make square cuts rather than looking for the easy way out


----------



## Max Power (21 Aug 2007)

In the same manner as I am attempting to improve my typing skills. :?


----------



## paulm (21 Aug 2007)

As others have suggested, the key to the shelf supports is making them mechanically strong, either through bracing with ply triangles, or by letting the ends of the triangular supporting batten into the vertical and horizontal battens so that added weight just locks them tighter.

If I could use sketchup I could probably explain a lot better than in words  !!!

Glue of any type has little role to play in this kind of situation, focus on getting the mechanical, designed in strength which doesn't require super accurate joint cutting just basic reasonable joinery skills which can be done with a pencil, handsaw and chisel in suprisingly little time, especially if you batch some of the components and do a few at a time.

Sure someone will be able to explain better than me after a glass or two of vino ( it's been a hard day)!!! :shock: 

Cheers, Paul.


----------



## JFC (21 Aug 2007)

I think Dom is trying to help the OP make some down and dirty brackets that are strong rather than telling him how to make sloppy joints that wont be strong. The OP didn't ask how to make a perfect joint , if he did i'm sure Dom would have told him how to do it properly. In fact i hear Dom is a master at sloppy joints but he keeps his secrets close to him :lol:


----------



## Max Power (21 Aug 2007)

JFC,
Dom does indeed give out some excellent advice ,as do many others on the forum but wouldnt you agree that simple projects like this are an excellent opportunity for the less experienced members to extend their skill level .


----------



## JFC (21 Aug 2007)

Not when they don't want to no .


----------



## DomValente (21 Aug 2007)

Agreed Alan it would be an excellent opportunity to practise joint making even mitred tenons.
But as JFC said and OP asked


> I'm planning on knocking up a few rough wooden brackets for supporting shelves in the garage soon. Thing is I'll be sawing them by hand and as I don't want to spend much time on them the joints will most likely be a bit sloppy.



I think that if OP is intending to make say twenty brackets he may well give up woodworking forever

Dom


----------



## Scrit (21 Aug 2007)

DomValente":3tae8oha said:


> I think that if OP is intending to make say twenty brackets he may well give up woodworking forever


Unless he discovers the joy of dovetailed nailing! :lol:


----------



## Max Power (22 Aug 2007)

Point taken Dom,
although I still feel it would be an invaluable lesson to learn to cut timber square as it makes everything else so much easier


----------



## woden (22 Aug 2007)

Thanks for the responses, guys.

I understand where you're coming from, Alan, regarding an opportunity to practice, but in this instance I just want to knock up some rough brackets as quickly as possible. I was going to go for something more complicated than Dom's 'down and dirty' :lol: solution - making a right-angled triangular bracket out of three lengths of timber and lap joints - but now I'll go for the quicker plywood/timber option.

As to why I'm looking for a gap filling adhesive, it's not because I want to bypass good joinery work - I'd love my joints to one day be as tight fitting as some of the examples on this forum. I just want a good failsafe that I can fall back on when doing a bit of rough carpentry that needs to be done in a hurry or when, heaven forbid, I mess up and cut a lose joint when doing 'proper' woodwork. Also I'm still doing the bulk of things by hand and precision seems to take much longer to master when following this path.

On the point about using Gripfill, I've gathered the impression from experience that it's an adhesive that doesn't like too much clamping. Seems to need a gap or lose joint - after all it was designed with this in mind. Am I on the money here or conversely can you clamp it as much as white or yellow glue?

As for formaldehyde glues, just how much of a gap can they bridge before they loose strength. While it might fill a little I imagine the likes of Extramite hasn't got anywhere near the same gap filling properties as Gripfill. And what about the micro fibres/filler that comes with either West or SP systems epoxy - would this stuff be compatible with urea formaldehyde? Has anyone ever tried this? :?


----------



## DomValente (22 Aug 2007)

As promised Woden.
I actually made these with one long length and three short, make sure you leave enough room at the corners for stacking.












Dom


----------



## beech1948 (22 Aug 2007)

Woden,
I made mine very similar to Dom's...just batten and ply triangles. Works well and currently holds 58 planks typically 8ft long and 2 inches thick.
Main diference to Dom's was that I used two M8 bolts instead of screws to fix to the uprights. It all works very well and has lasted without problem for 6 years.

regards
alan


----------



## woden (23 Aug 2007)

Thanks for the pics, Dom. I'm amazed that such small and thin plywood triangles can hold all that. I'd thought I was going to loose a lot of space beneath the shelf by putting on a huge triangle that would nearly extend to the end of the horizontal timber batten. But then I'd only thought of using one plywood triangle as opposed to two.

I was going to use rawlbolts for this job as well but what type have you used. Most of the ones I've encountered have either the threaded bar type end with a lose nut or the sort of engineering bolt end. But yours seem to have a round screwhead like end. Are they pulled tight with one of those star/torx bits?

Which type would you suggest is best for this sort of job?



On the subject of a gap gilling adhesive I did a test with some Extramite and micro fibres. I mixed up two small portions of the adhesive and then stirred micro fibres into one sample until it became a thick paste. Then I glued two pieces of softwood to some ply - one with the plain adhesive and no gap and the other with the micro fibres and a gap that I filled up. Both pieces had the same surface area and a screw was used in each to place some pressure on the joint as instructed by the info. on the Extramite tub.

I'll see which breaks apart the first later today. Does anyone know how long Extramite needs to cure fully? Says six hours on the tub but is that just for an initial bond?

Having said all this I think I'll have to do the test again as I mixed in too many micro fibres turning the test sample into something resembling cream potatoes. Also I hadn't quite enough adhesive mixed to fully fill the gap in the second joint so it probably won't be a fair comparison. :roll:


----------



## DomValente (23 Aug 2007)

Actually Woden those are not Rawlbolts they are Rawl rawplug hammer in fixings the type you see with the grey rawlplug attached to the screw.
I use rawbolts on the metal bracket type.
Those in the picture are 6 inch screws.
The brackets are at about 2 foot intervals,
Dom


----------



## woden (25 Aug 2007)

Strangely, the tighter bond in my very unscientific test broke much more easily than the one involving a gap bridged by Extramite mixed with micro fibres. Probably not very reliable though - especially as the Extramite may have been past its shelf life - but I was surprised nonetheless.

One disadvantage of Extramite used over a gap is that anything more than a thin layer takes much longer to cure. It'll still be rubbery for a day or two. This compares with a fillet of epoxy where the stuff seems to harden as quickly as a thin layer in a tight joint. The other thing about Extramite is that it shrinks as it goes off (because of the water evaporating?) whereas two part glues like Epoxy don't. Means that if you have the glue line nice and flush with the surface there'll be a little hollow there the next day when using powdered urea formaldehyde.

But maybe the shrinkage has benefits too - would it pull the mating surfaces closer together to create a stronger bond?

I spoke to the technical chap at Polyvine - the company that's taken over Humbrol/Humbrol's wood glue operation - and he thought that the idea of mixing an inert filler like micro fibres into what's now Polymite was an interesting one. He said it had never been tested at their end but might be worth doing. One tip he did give me for using powdered urea formaldehyde was to use water that had been kept cool in the fridge when mixing. This replicates a cold day and gives you a much longer open time. Apparently the open time with Polymite can vary from as much as 1 1/2 hrs to only 30 mins depending on the temperature.

Another thing he mentioned is that urea formaldehydes hover just at the bottom of the b4 category in the standards for how waterproof an adhesive is. This means that while joints using UF can take a soaking they shouldn't be continually submerged in water or the resin will eventually break down. Boat builders take note - alright for dinghy construction but not the stuff to use when gluing up your rudder for that year long Mediterranean cruise in the newly built 50ft wooden yacht. :shock:


----------



## Losos (25 Aug 2007)

DomValente":2hqkudqa said:


> As promised Woden.
> I actually made these with one long length and three short, make sure you leave enough room at the corners for stacking.
> 
> Dom



Thanks for posting those pics Dom - As it happens I've got to put up some shelving in several rooms in our cellar and *they could be just the thing.*

I'm still likely to need some gap filling adhesive, *not* for the woodwork but to fix the verticals to the walls 'cos I'll be drilling into big stone blocks about 2 foot square which are almost like rock and I can't get in very far :x Sadly I have not yet got an SDS drill


----------



## David C (25 Aug 2007)

West Epoxy or similar, mixed with colloidal silica.

If sufficiently stiff, this will stick to the ceiling and fill gaps very well indeed, endgrain included.

Not really a bodge at all.

David C


----------

