Screws, glue or something else?

[NittenDormer]

So, it is that time of year when a young man's thoughts turn to 'when will my garage be warm enough for wood glue to work'. So far, my baseboards (9mm ply sides) are held together via screws into blocks of softwood at all the joins. I was thinking of replacing the screws with glue, or do I need both?

 

A 600 x 1200 board is absorbing anything from 60 to 100 screws, with 9 boards to make, that is 6-700 screws, which sounds a lot? Or is this normal?

 

Would panel pins + glue be a suitable combination? Are there different sorts of wood glue? I am not sure all my edges are straight and right angled, so is there something generally recommended with a filling-the-gaps element?

[Ian Smeeton]

I used both glues and screws, however, I only put the screws on the inside of the boards I was making.

 

(Ply & Softwood sandwich, by the way).

 

I also had the advantage of doing it in August, which helped the glue go off pretty quickly.

 

A decent, level surface to work on helps, as does patience.

 

If it is still cold in the railway room, just do a bit at a time, and allow things to set.

 

Regards

 

Ian

[Nearholmer]

My favoured wood glue is Evostick Resin W Exterior, in a BLUE bottle, which is damp resistant, and, once set, ‘stronger than the wood itself’, to repeat their old slogan. Cheaper brands are available, but yer gets wot yer pays for.

 

If the joint is clamped while the glue sets, it doesn’t need any other fastening, but clamping is often difficult/impossible, so I tend to use long panel pins, but not very many, where I can’t clamp.

 

What it doesn’t do, is fill gaps, so if things are a bit gappy, you might have to use something like No More Nails, or Gorilla Glue. Again, cheaper versions available, but the same applies.

 

All of these are damp-resistant, so won’t fail if the baseboards are left in an unseated garage, but I would prime the boards all over after construction, and the best one I’ve found for that is Ronseal Flexible Primer Undercoat. I painted a big toy boat/sandpit with it, never got round to top-coating it, and it is still good after five years out in all weathers, which is quite some test.

 

You’ll enjoy this https://www.thegeekpub.com/4314/glue-vs-screws-which-one-is-stronger/

Edited February 1, 2018 by Nearholmer

[PaulRhB]

I glue all joints and use screws. The boards I've just made are 350 x 1200 and I've used 26 screws in each that's with sides and tops from ply and 1x2 blocks to strengthen the joins where the screws are.

Gluing it all is very strong and the continuous fixing helps with stiffness long term. Once it's dry I could remove the screws but I leave them in as an extra support as mine is a portable layout.

[BR60103]

I use L-girder. When I make the girder, I screw the 2 pieces together then undo them, run glue down the join, and screw them together again. When the glue is set I remove the screws. One time I neglected to and I ran a very expensive 1" bit into a screw.

For this I use yellow carpenter's glue -- not sure how it's named in Britain.

[DCB]

That sounds like a truly excessive number of screws.  What form of construction are you using?   I'm only using 24 screws in a 300 X 1200 mm board with traditional 2"X1" framing but a 3mm ply top, 12 long ones in the framing and 12 short to hold the top on.    Long experience has led me to avoid glue and pins in permanent layouts as wood has an awkward tendency to warp and it is much easier to repair if it is screwed together. Portable layouts are different as life expectancy is not as great and strength is needed so screw, glue and pin but 9mm ply sides?  Are you in the habit of standing on your baseboards?

[Jeff Smith]

I wouldn't even contemplate not using glue. The screws are necessary to clamp the joint while the glue sets then can be removed for re-use. Glue is the only way to keep the structure rigid as screws can loosen over time and, as you have discovered, you need a lot of them!

[PatB]

I did once read a fairly convincing explanation of why adding mechanical fasteners (screws etc) to a properly made glued joint actually weakens the join, although I can't now remember the means by which this occurred.

 

These days, when doing any kind of bodgery joinery, I try to design things so that the glue does all the work. Any screws or pins I might add will generally only be to apply clamping pressure or location while the glue sets. Like Nearholmer, for general work I favour a good quality PVA. Over here I'll generally buy Sika's product and steer clear of anything by Selleys (expensive but unimpressive for PVA or epoxy, although their contact adhesive seems not too bad). I do keep a big can of really cheap PVA around because I sometimes have cause to make things from papier mache and cheap PVA is great for that.

 

I do have some reservations about the really long term durability of PVA and in cases where this might matter I'll cough up for epoxy. I use this stuff because I find it to be better than the locally available Araldite (made by Selley's so it's rubbish), and I can get it for a sensible price. However I buy it for a specific purpose (gluing up large wooden blanks for lathe turning) where its performance is quite critical. It might be a bit over the top for baseboard construction . What epoxy does do, though, is fill gaps very well. It's messy to use and takes a long time to set however, as well as being rather expensive for general use..

[BWsTrains]

I did once read a fairly convincing explanation of why adding mechanical fasteners (screws etc) to a properly made glued joint actually weakens the join, although I can't now remember the means by which this occurred.

 

These days, when doing any kind of bodgery joinery, I try to design things so that the glue does all the work. Any screws or pins I might add will generally only be to apply clamping pressure or location while the glue sets. Like Nearholmer, for general work I favour a good quality PVA. Over here I'll generally buy Sika's product and steer clear of anything by Selleys (expensive but unimpressive for PVA or epoxy, although their contact adhesive seems not too bad). I do keep a big can of really cheap PVA around because I sometimes have cause to make things from papier mache and cheap PVA is great for that.

 

I do have some reservations about the really long term durability of PVA and in cases where this might matter I'll cough up for epoxy. I use this stuff because I find it to be better than the locally available Araldite (made by Selley's so it's rubbish), and I can get it for a sensible price. However I buy it for a specific purpose (gluing up large wooden blanks for lathe turning) where its performance is quite critical. It might be a bit over the top for baseboard construction . What epoxy does do, though, is fill gaps very well. It's messy to use and takes a long time to set however, as well as being rather expensive for general use..

Two issues here:

 

1) I'd be nervous of using PVA Glue alone on a big structure unless gluing identical wood types together. Wood breathes, absorbs moisture and different woods do so to different extents. Screwing provides an immovable additional bond whereas a minor movement can crack set PVA. Sometimes the PVA join is stronger than the wood it joins and it is a layer of the wood that "gives" instead. Leave screws out at your peril but you don't need many - say 3 per metre length glued. "Screw and glue" is the Mantra, data required to refute.

 

2) These days most adhesives are generic, PVA has been around at least since the 60's, remember "Unibond" in the UK, my Dad swore by it. He primed his garden shed hardboard with it and it survived a good 50 years. These days the basic ingredient is probably made in massive batches in China. Hence I'd suggest that throw away criticism for a particular brand like "it's so rubbish" are unlikely to be true since it's all much of a muchness, where's your data? Value is another issue as is shelf life.

 

To illustrate, I bought a 4L quality PVA in 1982 for a big job strengthening some cement based tile installations on my extension. I used the last of it in 2014 after careful storage below 20C. It still worked perfectly although it was a tad lumpy!

My suspicion is that the cheap PVA brands may work well at purchase but do not store well, perhaps because of inadequate stabilisation. A 4L Parfix PVA bought for the same purpose as before in 2015 is becoming very lumpy after just 2 Years.  

 

Even cyanoacrylate these days is of a pretty high standard, the raw monomer ingredient is a commodity. I buy the cheapest unless I have a specific need like gel properties. Sourced from the $2 Shop I bang them in a jar in the freezer until needed.

 

Some more specialised adhesives like contact and the related "liquid nails" cartridge glues appear to be better differentiated. I swear by "liquid nails" at home for all manner of jobs whereas cheaper brands tend to over harden on setting. Clear value add in the dearer product.

 

Edit to address "long term viability of PVA".

I've items built with PVA joinery that are 41 years old (as long as we've been here) it goes from the colds of Melbourne winters to the excesses of hot humid days inside. They've stood that test. PVA is a very fine product.

Edited February 2, 2018 by BWsTrains

[Nearholmer]

“I did once read a fairly convincing explanation of why adding mechanical fasteners (screws etc) to a properly made glued joint actually weakens the join, although I can't now remember the means by which this occurred.”

 

Probably that the penetrations and the fastenings act as local stress raisers or concentration points, whereas glue spreads load evenly over a wide area. This would certainly apply to something like fixing a skin to an aircraft frame, and if you look at the video I linked to in my earlier post, screws in timber seem to precipitate splitting. Mind you, we are talking baseboards here, not Mosquitos.

Edited February 2, 2018 by Nearholmer

[Siberian Snooper]

I use pva and a few pins, unless I can clamp the joints.

 

I built my window frames from hardwood and they are still in use 30 years later and they were glued and clamped.

[Greengiant]

I glue and screw, plus clamping while glue goes off.

Temperature is important for glue to go off, I use Titebond 3 which has a very useful self cleaning application nozel, it enables you to apply nice neat beads of glue.

Having your joints nice and flat and square helps a lot, where possible I route locating grooves which also help with self jigging.

 

Martin

Edited February 4, 2018 by Greengiant

[PaulRhB]

screws in timber seem to precipitate splitting. Mind you, we are talking baseboards here, not Mosquitos.

They do if you don't use pilot holes near ends or in the end grain.

The screw acts as a localised clamp where most of us don't have a pile of big sash clamps or that we like to make odd shaped boards. Ideally you want to drill a hole so only the thread is biting into the wood and countersink it too.

One of the advantages of the hex shaft holders for a drill is you can swap quickly between drill, countersink and screwdriver if you only have one drill.

This little corner filler would split if you didn't drill and countersink. It's not structural, it just to guide a 3mm strip of edging, and once the glue dries it will be nice and solid.

Note the two screws that need more countersinking but I'll do that when it's dry as I did it from the other side and didn't drill it deep enough

Edited February 2, 2018 by PaulRhB

[Nearholmer]

Paul

 

It’s worth watching the video. Very interesting.

 

The screws were put into good pilot holes, but they still seem to have acted as the initiating point for spilts along the grain.

 

That was under extreme load though; a deliberate test to failure. I’m not suggesting that properly piloted screws will split wood in ordinary conditions.

 

Kevin

[PaulRhB]

Yes it still compromises the wood but you can minimise the effect by not forcing a 2-3mm shaft in between the grain

As you said above they aren't critical or subject to fatigue anywhere near a Mossie's body is subject to

Edited February 2, 2018 by PaulRhB

[Jeff Smith]

Years ago I worked with an engineer who worked on Mosquitoes just after the war. He remembered installing equipment inside the moulded ply wood fuselage. In order to attach it brass internally threaded ferrules had to be araldited into half-depth blind holes.....

[NittenDormer]

Ok, it sounds like I will need to buy more screws then (I was hoping to reuse them elsewhere once replaced by glue). I may try and find a compromise, where the 'important' joints are glued AND screwed, and the non-important ones are glued and pinned. Or something.

 

For those of you with concerns about the volume of screws and over-engineering of my baseboards, here is one (of 9 needed in total).

 

 

It is 4 feet x 2.5 feet (1200mm  x 750mm). It has 3 x 1200mm uprights, and 5 x 750mm (approx. 1 foot spacing).

Each join has 2 x 44x18 timber blocks (1 at top, the other at bottom).

Each block has 2 screws (1 connecting it to the 1200mm piece, the other to the 750mm piece).

That is 10 blocks along the front, and 10 more along the back = 20 blocks, 40 screws.

When I get round to doing the same for the 1200mm centre piece, that will be another 10 blocks and 20 screws.

When I get round to attaching the track beds, that will be, erm [pauses to use fingers] 20 screws for the each level (2 screws holding a softwood support to the baseboard, 2 more to hold the trackbed to the support x 5).

And there we have it, 100 screws.

 

(Also, I tried a 6mm ply 'sandwich' approach, but the ply felt too flimsy, like I could squeeze the 2 layers together and break them between the softwood blocks.)

[Nearholmer]

Phew!

 

If that is all 9mm ply, it is going to be one super-strong construction, if glued, and one heavy old beast.

 

I recommend at least four Rolls Royce Merlins to get you layout airborne.

 

It looks precisely cut, so you ought to be able to get good glued joints.

[LBRJ]

For general purpose sticking bits of wood together I use Gorilla Glue quite often, or whatever tube and gun type stuff I have to hand (often Evo Stik's Sticks like Sh*t cos its fun to buy ) . Normal PVA works pretty good though.

I dont use any screws for plywood baseboards, just bang in a few panel pins to hold it all in place while the glue goes off; oh and a few clamps certainly helps the job along.

 

600-700 screws does seem massively excessive, the sort of quantity used building a deck in the garden!

[NittenDormer]

Phew!

If that is all 9mm ply, it is going to be one super-strong construction, if glued, and one heavy old beast.

I recommend at least four Rolls Royce Merlins to get you layout airborne.

It looks precisely cut, so you ought to be able to get good glued joints.

Thanks for the complement, photoshot does wonders! If only it was precisely cut, although I am getting better with practice.

 

Maybe I should set up a thread on 'how many screws have you used?'

 

I can't be the only one going through this sort of volume.

[Nearholmer]

You seem to be screwfix’s best mate, so far.

[polybear]

When it comes to baseboards I'd suggest over-engineering is far better than under-engineering, which is sure to bring a whole load of pain later on.....

[PatB]

Two issues here:

 

1) I'd be nervous of using PVA Glue alone on a big structure unless gluing identical wood types together. Wood breathes, absorbs moisture and different woods do so to different extents. Screwing provides an immovable additional bond whereas a minor movement can crack set PVA. Sometimes the PVA join is stronger than the wood it joins and it is a layer of the wood that "gives" instead. Leave screws out at your peril but you don't need many - say 3 per metre length glued. "Screw and glue" is the Mantra, data required to refute.

 

I'm something of a student of wooden aircraft construction. I can't think of any design I've seen which uses mechanical fasteners to reinforce glued joints except, possibly, in areas where there's something else going on at the joint (attachmennt of metal fittings etc.). There are construction methods which use small nails to hold gussets in place but this is purely to apply clamping pressure. No, aircraft aren't held together with PVA, but they are held together with epoxies, resorcinols and/or urea-formaldehydes, any of which are quite capable of pulling away the surface layer of timber or plywood. Indeed, to be permissible for aircraft use, they must do so under test. As a result, I'm not too worried about this particular failure mode. PVA itself failing can happen, but I like to use nice big gluing areas where possible (something else I've picked up from the aircraft world) which helps.

 

2) These days most adhesives are generic, PVA has been around at least since the 60's, remember "Unibond" in the UK, my Dad swore by it. He primed his garden shed hardboard with it and it survived a good 50 years. These days the basic ingredient is probably made in massive batches in China. Hence I'd suggest that throw away criticism for a particular brand like "it's so rubbish" are unlikely to be true since it's all much of a muchness, where's your data? Value is another issue as is shelf life.

 

No formal data, but extensive private and professional use of a variety of adhesives over 40 years or so. Nothing I have bought bearing the Selleys brand name, since I arrived here 22 years ago, has performed to my expectations, apart from their contact adhesives, which I've found to be sort of OK. Their Araldite, in particular, has been very disappointing, being consistently soft and weak. I haven't had the same problems with other brands used identically. I've also found their PVA to fail at an early age, which is a bit rich considering what it costs. Again, other brands haven't exhibited the same problems. So yes, I've established to my own satisfaction, that there are differences between brands.

 

To illustrate, I bought a 4L quality PVA in 1982 for a big job strengthening some cement based tile installations on my extension. I used the last of it in 2014 after careful storage below 20C. It still worked perfectly although it was a tad lumpy!

My suspicion is that the cheap PVA brands may work well at purchase but do not store well, perhaps because of inadequate stabilisation. A 4L Parfix PVA bought for the same purpose as before in 2015 is becoming very lumpy after just 2 Years.  

 

Possibly true. However, as I live in WA's inland climate without the benefit of aircon, I have to rely on the inherent stability of products in storage and assume that Bunnings (or whoever, has also stored them unrefrigerated before I bought them. Keeping anything in the workshop below 20 degC for more than 6 months of the year is an impossible dream.

 

Even cyanoacrylate these days is of a pretty high standard, the raw monomer ingredient is a commodity. I buy the cheapest unless I have a specific need like gel properties. Sourced from the $2 Shop I bang them in a jar in the freezer until needed.

 

Some more specialised adhesives like contact and the related "liquid nails" cartridge glues appear to be better differentiated. I swear by "liquid nails" at home for all manner of jobs whereas cheaper brands tend to over harden on setting. Clear value add in the dearer product.

 

Edit to address "long term viability of PVA".

I've items built with PVA joinery that are 41 years old (as long as we've been here) it goes from the colds of Melbourne winters to the excesses of hot humid days inside. They've stood that test. PVA is a very fine product.

[Siberian Snooper]

I would use full depth 18mm x 18mm fillets the full depth of the joint, glued and clamped to the cross piece and when dry glue and clamp the longitudinals. It will be strong enough to withstand most handling. Our club had 4 boards 6ft x 2ft 6ins built with 9mm ends and the rest of 4mm thick ply with diagonals glued from the outer corners to the centre spine at the first cross pieces and in 18 years none of it moved a mm. This included a two year spell in a steel storage container, which was outdoors. One man could pick a board up and move it.

[NittenDormer]

I would use full depth 18mm x 18mm fillets the full depth of the joint, glued and clamped to the cross piece and when dry glue and clamp the longitudinals. It will be strong enough to withstand most handling. Our club had 4 boards 6ft x 2ft 6ins built with 9mm ends and the rest of 4mm thick ply with diagonals glued from the outer corners to the centre spine at the first cross pieces and in 18 years none of it moved a mm. This included a two year spell in a steel storage container, which was outdoors. One man could pick a board up and move it.

Thanks, is that glue alone, or screws as well?