odd one but I want to attach a sheet of HPDE plastic to a piece of plywood . screwing could be an option but the plastic is only 3mm thick and would need the screws to be countersunk .

Horizontal use , not sticking it to a wall or anything .

Ta!

How large are the things you’re sticking together?

On a larger scale contact adhesive and a youtube tutorial about applying laminate to wood. On a smaller scale ‘jelly tape’ aka ‘VHB’ Tape (very high bond).

Thanks , 2000mm by 1000mm sheet of HDPE to same size piece of plywood .

Sounds like a contact adhesive job then. Look at a few how-to vids. Trick is to have a bunch of spacers to keep the two surfaces apart when you position them. People suggest dowels but they cost a fair bit. So find any cheap thin sticks. The last time I did it I used the cheap plastic channel used to protect cables in plasterwork.

The two glued surfaces will stick to each other but won’t stick to something without glue on – so glue them both up then put a layer of sticks across the plywood – lay the plastic on top and position – then pull out the middle sticks so that the plastic sags onto the ply and bonds then just keep pulling sticks out to the ends.

Ah, so that’s what the guys were doing when I saw them fitting the new office kitchen.

Ah, so that’s what the guys were doing when I saw them fitting the new office kitchen.

No – they were playing kerplunk. 🙂

Great tips about the technique thanks, any particular contact adhesive I should look out for?

Disappointed. Expected to see ‘sniffing’ on clicking the thread. 😀

any particular contact adhesive I should look out for?

You can get it as paint / roll on adhesive or in spray cans. The liquid stuff I’ve found quite challenging to use – can go quite stringy and lumpy as you’re applying it and I’ve found branded stuff (evostick etc) thicker and harder to use and spread well. This is with the caveat that I’m usually working in quite cold conditions but I find it a bit of a battle to spread the thicker gooey stuff out before it dries – but cheap own-brand stuff from screwfix seemed to be thinner to spread better.

Cans of spray contact adhesive work well though – you get a thinner application and maybe less out and out strength but much quicker, easier neater results. I think with the spray stuff I’ve only used Screwfix / B&Q ‘no-nonsense’ own brand. Cheap you can afford to buy a bit more than you’ll need and not worry about running out mid-glue. (they’ll refund any unopened cans).

Its a shame you weren’t doing this yesterday on Halloween as cans or spray adhesive are how movie cobwebs are made!

Nothing will glue HDPE. Its part of the reason for its existence. Totally non-stick. If there is no load on it you might just get enough tack to stop it moving but it won’t be held well and wont resist much force.

Roughening the glued side of the HDPE would give the glue more to stick to.

If you need more adhesion and if it doesn’t matter that he plastic is mated absolutely flat to the ply then ‘Toffee Tape’ sticks to frikkin anything – its similar to the gummy snot that freebies are stuck to the front of magazines with. I buy it online from a film props company called “The Source” in Manchester – who, if you’re lucky, also throw a packet of biscuits in the box before they post it!

Even stickier still is ‘Butyl Strip’ which you can get in rolls on ebay

But in both cases they have a thickness so will hold your plastic a couple of mm proud of the plywood.

How about a combination of countersunk screws and glue? Had planned to rough up the glue side of the hdpe

Glue the whole then screw the edges to prevent them lifting if caught / bumped. Or if the plastic is smaller than the ply support hold the edges down with a metal trim – like carpet edging.

I always just use screws or bolts. The glue won’t add much. What are you actually trying to do?

Building a snowboard box rail.

They use thick hdpe due to the need for the boxes to last a number of seasons and God knows how many impacts, which is not the case for us. Thick hdpe costs a lot however!

No way glue will do much there. The different thermal expansion rates of the two materials plus all the impacts will dislodge it easily. Maybe you can get hold of some reject or slightly used thicker HDPE. Or just screw your 3mm down. Can’t see a few countersunk screws stopping it working. Just need to be careful of exposing the screw heads as it gets used and worn

Ta much appreciated

can screw up from the reverse side into the HDPE?

If not think about using set screws through to the other side – if the heads get damaged you can take the nut off and push the bolt out using th threaded end. Washers will also spread the load on the mounting boards out more – wood screws might pull out?

3mm doesn’t give as lot of depth to countersink and anything you have sticking up is going to ruin a board I suppose. So a lot rides on how carefully / accurately you can countersink as if you go too deep the screws will just pop through. (you’ve just reminded me that I’ve lost my festool countersink bit and I’m furious with myself)

Careful choice of screws will help – the smaller the diameter the shallower the head will be – but smaller screws with fine threads can pull out easily. Although they cost a bit more ‘Screwtite’ screws from tool station have a thread that bites well in smaller sizes.

If its for your own use and you can afford a bit of trail and error I think it would be worth trying the Butyl strip first. Its perpetually sticky rather than a glue that sets and it stays soft so it can cope with any movementment between the plastic and plywood and its waterproof – its principle use is for making waterproof seals. Give the plywood plenty of paint (both sides) to seal it as the butyl will stick better to a slick/sealed surface than an absorbent one. If it proves not to work to well you can them augment that with screws but I suspect you’d be happier if there was not scratch metal i there.

Hdpe melts?

Leave an overhang heat it and form it round the plywood box.

Screw the sides into the box.

Hdpe melts?

Leave an overhang heat it and form it round the plywood box.

In my experience its got a bit of a memory – when you heat it up it tends to try and spring back to the shape it was extruded from – so it shrinks and thickens.

Cancel that then 🙂

How about using countersunk nylon screw and nut ?

@mikey.b cheers for the suggestion is there an advantage? Softer I guess if they are not flush and stick out a little ?