Mating surfaces for solvent weld

[MJNewton]

For our new kitchen I need to tap into an internal soil stack in an adjacent to provide drainage to the sink and dishwasher. With it being an existing soils stack (therefore being unable to add a proper branch) I am going for a solvent weld strap boss. I am all too conscious of the fact that I've got one shot at this; and just to make life a bit more difficult access is quite difficult. Oh, and it's my first ever solvent weld.

 

 I opted to go for a quality make (Osma), that also matched the make of the existing pipe, and was a little surprised when I picked it up this morning to find that the mating surfaces weren't perfectly smooth. In particular there are mould lines that you can hopefully make out at the 3 and 9 o'clock positions in the second picture below:

 

 

 

My understanding was that solvent weld isn't an adhesive but rather loosens the polymer chains of the mating surfaces which, when reformed, bind them together as one. Would non-perfectly-smooth surfaces inhibit this, or is the welding action quite significant in terms of how deep this loosening goes? Perhaps there are gap-filling properties also, or would that bring it back into being an adhesive?

 

I did ask the guy on the plumbing counter if it was definitely okay but I could tell halfway through my question that he either didn't have a clue or couldn't care less either way (perhaps both!).

 

I did wonder if I should smooth it out when a stanley blade, but didn't want to potentially cause a problem when one might not already exist!

 

Any comments?

Edited November 1, 2019 by MJNewton

[Carrerahill]

The solvent is just that, solvent, it chemically reacts with the PVC so having it smooth or rough is not really going to make much of a difference, it will "melt" the plastic. In none of the guides or technical documentation does it ever say to roughen anything. I would suggest not doing, it just takes a a deep groove that may not fill with solvent and end up leaking (why you shouldn't clean up copper pipe for solder too roughly).

 

If you look at and smell the solvent weld it is just a sort of thickened solvent - so the filling properties are from the gooey plastic squishing up and sealing it. There has never been any adhesive or real substance to this stuff in any of the brands I have used. First ever time I was sceptical because the fittings (both same brand) had quite a loose fit. But right enough slap on the old pipe melter and it formed a sort of solvent plastic soup which just filled everything up. I have since used bottles and bottles of it.

 

If you paste some onto a piece of wood it will just flash off and you are left with a very slight residue. 

 

A tip I would say if you have never used it is work fairly quickly (but don't rush like first timers do). Get all your pieces setup and cleaned and dry. Undo the lid, paste up liberally both sides of the mating surfaces, line up the pieces then push together and give a little wiggle twist to mix up the melted plastic then hold it and keep it firm. On a boss like this I would hold it for about a minute or support. Different on pipe sections where you can make joints up and lay them down to set.

 

I did have 1 union earlier this year where I stuffed the pipe into it, held it for a bit and didn't pay attention and it snuck out about 4-5mm - it did end up leaking but it was my fault for thinking it would stay put (it was a long piece into a Tee so the pipe wanted to drop) - to be fair it was a final piece and I was concentrating on the other end.

 

 

 

Edited November 1, 2019 by Carrerahill

[bassanclan]

You should be roughening the surfaces to be solvent welded before applying the solvent weld 

[ProDave]

And just to add, solvent weld cement comes out of the tin (with it's built in applicator in the lid) quite thick.  You paste it onto both halves and there is no doubt the two will weld together.

 

Once you have mated the 2 parts, do up the clamp quickly then leave it alone. You don't want it to be moving as it sets, which takes a few minutes.

[Carrerahill]

8 minutes ago, bassanclan said:

You should be roughening the surfaces to be solvent welded before applying the solvent weld 

No, you do NOT need to do this. 

Edited November 1, 2019 by Carrerahill

[Temp]

If the mould lines are very big I'd scrape them off but I've never bothered to roughen up the surfaces.

 

Adhesive on both surfaces as ProDave said. 

 

Solvent welding isn't quite as bad as using contact adhesive. If you use enough adhesive there is time to twist a joint to get elbows to line up in the right plane.

[Carrerahill]

5 minutes ago, ProDave said:

You don't want it to be moving as it sets, which takes a few minutes.

Key thing - it's like very slow solder joints going off! Move it and you run the risk - like I said I did with one of my connections earlier this year. 

[Jeremy Harris]

All I've ever done is give the mating surfaces a wipe over with a cloth damped with a bit of acetone, which both cleans the surfaces and also slightly softens them, making for a better solvent bond.  The nuisance is that UK solvent weld adhesive isn't like the US stuff, so it's not that easy to see that you have a good, even coating, so a bit more care is needed to ensure that both surfaces are coated.

[Carrerahill]

Another thing, use fresh solvent and don't be tempted to use stuff that is old - every time you open it the solvent flashes off some more. 

[Carrerahill]

1 minute ago, JSHarris said:

All I've ever done is give the mating surfaces a wipe over with a cloth damped with a bit of acetone, which both cleans the surfaces and also slightly softens them, making for a better solvent bond.  The nuisance is that UK solvent weld adhesive isn't like the US stuff, so it's not that easy to see that you have a good, even coating, so a bit more care is needed to ensure that both surfaces are coated.

Yeah, the North American stuff is usually blue or purple isn't it? I also note they almost always use a proper product to clean and prime the pipes - looks like it may just be a solvent or indeed acetone. 

[Jeremy Harris]

2 minutes ago, Carrerahill said:

Yeah, the North American stuff is usually blue or purple isn't it? I also note they almost always use a proper product to clean and prime the pipes - looks like it may just be a solvent or indeed acetone. 

 

 

Yes, with a primer more often than not.  I managed to buy some of the stuff when I was jointing 25mm PVC pressure pipe, but it's not readily available here, which is a pity.

[PeterW]

4 minutes ago, Carrerahill said:

Yeah, the North American stuff is usually blue or purple isn't it? I also note they almost always use a proper product to clean and prime the pipes - looks like it may just be a solvent or indeed acetone. 

The US pressure stuff is different - it’s ABS Schedule pressure pipe and needs a slightly different adhesive and the use of MEK as cleaning solvent is not unusual. 

[Jeremy Harris]

2 minutes ago, PeterW said:

The US pressure stuff is different - it’s ABS Schedule pressure pipe and needs a slightly different adhesive and the use of MEK as cleaning solvent is not unusual. 

 

The pressure pipe I used was this 16 bar PVC stuff :https://www.pipestock.com/pvc/pvc-pipe-metric/pvc-pipe-16-bar

 

Looks and feels much like the US stuff, but PVC rather than ABS.

 

The solvent weld stuff is much the same for both PVC and ABS usually.  The solvent is usually a mix of either tetrahydrofuran or cyclohexanone and MEK.  It used to have acetone in, but I think the switch to MEK may have been because it's slightly safer.  Not much to choose between MEK and acetone in terms of the way they react with PVC or ABS.  If thinking of thinning out some solvent weld that's dried out a bit, it's always the tetrahydrofuran/cyclohexanone that evaporates first, so adding MEK makes the stuff weaker.  MEK will soften PVC/ABS but won't dissolve it fully, the tetrahydrofuran/cyclohexanone is there to do that.

[MJNewton]

Thanks everyone; it doesn't sound like my concerns are really concerns afterall. I suppose given that the surface of the soil pipe will be softened then even if the mould lines were going to present a ridge they would just 'bite' into the pipe anyway.

 

I note that whilst the boss adapter (Osma 2S399) will be solvent welded into the strap boss it just has a push-fit connection seal for the incoming 40mm pipe. I was expecting this to be solvent welded also, and perhaps would've preferred this given the joint will eventually be inaccessible. Shouldn't be a problem if properly inserted and supported I suppose.

 

 

(Good to see it has mould lines too!)

Edited November 1, 2019 by MJNewton

[SteamyTea]

When I used to make spa baths, I had two fitters.

One, Cornish as it happens, was always in a hurry, generally an angry man. He very really used cleaner in the pipes.

The other fellow, the one that did not look like a pirate, was meticulously neat, spent what seemed like forever cleaning things up.

He never, as far as I remember, had a leak.

He also finished jobs quicker.

Odd that, wish my current boss could see that a bit of organisation and calmness saves time.

[Temp]

Just wanted to add that not all pipe can be solvent welded. For example pipe designed for push fittings often can't be solvent welded (and frequently it's a slightly different diameter despite being nominally the same). Test the solvent on the existing pipe as you might need a strap on boss instead.

Edited November 1, 2019 by Temp

[MJNewton]

Would that concern apply to soil pipe? 

[Temp]

I think all/most 110mm pipe can be solvent welded but Google says shouldn't use solvent welds below ground.

 

 

 

[Onoff]

11 hours ago, MJNewton said:

Would that concern apply to soil pipe? 

 

I did make the unfortunate mistake of using a length of brown underground soil pipe where I should have used black / grey solvent weld. It's still pvc but feels more "rubbery" and less "brittle". I was also mating it to a different make of fitting. To boot it was female uphill, male downhill. The joint to me felt a bit loose. I cleaned the surfaces, roughed them up and used pvc gap filling cement that seemed to take. A smear of CT1 for good measure. 

 

 

[MJNewton]

This pipe is white and so I was making the assumption it was an 'above ground' pipe and thus likely to accept solvent weld. Given what Temp had said though I was still a bit worried, particularly as I could see on another soil pipe in the house it went into a pushfit socket where it entered the floor. However, poking around at the top end of this other soil pipe I could see there was a barcode stuck to the top which I could just about retrieve and it said 'Osma 110mm Solvent Weld Single Socket' so I can breathe a sigh of relief! 

[Jeremy Harris]

TBH, the underground stuff seems to solvent weld as well as the above ground stuff in practice.  The only reason you're not allowed to solvent weld underground joints is to do with cracking, as underground pipe joints are designed to be able to tolerate a small amount of movement and stay sealed, just to allow for things like clay heave, roots pushing them, etc.

 

One slight issue with solvent welding underground pipe may be that some of it seems to have a core that's a slightly different formulation, it has a orange/brown outer and inner skin over a white core.  Not sure quite why some of it's made like this, or whether it has any effect on a solvent welded joint made to the stuff if used above ground, but it might possibly.

[SiBee]

Just to add from when I was an apprentice installing a massive cooling system using large pvc stuff. We had a site visit from a rep for the manufacturer to show us good installation practice. Key the mating surface and then clean using the solvent cleaner. Assemble joint quickly and then leave to cure/set. The only leaks we ever had came from joints that someone forgot to glue and just assembled dry?

 

I recently helped our friends young lad fit his bathroom and he is a freshly trained plumber. He just cut pipes, applied the cement and assembled the joints. Said he was shown this way, never had leaks and they don’t have time to faff about on jobs.

[MJNewton]

I'm still a bit nervous about this job, mainly due to the limited access to the soil pipe and consequences if I don't get the weld good. I stumbled across the McAlpine mechanical stap boss which seems to get good reviews on the Screwfix site, several of which note a preference over the solvent weld variety. Has anyone used one? I am warming to it given I think it'll be a bit more forgiving than the 'one chance, dont mess it up' solvent weld strap boss option...

 

(For those not familiar with it, this photo is of it with the winged installation tool present which is removed after fitting)

 

I figured I could also add a ring of silicone on that mating face for added reassurance over just the expanding doughnut.

[PeterW]

Weld will be fine - the trick is to drill the hole slightly over the size of the lugs and a quick smear of glue on the pipe with a reasonable amount on the fitting. 
 

I use a clamp to hold the ends of the band together for 20 mins before putting the nut and bolt in - leave for an hour or two before you fit the pipes.