Mixing PVC-U PVC-C and ABS

[TerryE]

I am finalising my foul-water designs based on OSMA pipework.  OSMA use 3 different materials for their soil and waste pipe systems:

• PVC-U (Unplasticised Polyvinyl Chloride)
• PVC-C (Cholorinated Polyvinyl Chloride) which is a PVC variant with better high temperature properties
• ABS (Acrylonitrile Butadiene Styrene)

PVC-U is used for the heavy stuff such as the main 110mm pipes and fittings, and the PVC-C and ABS uses for the narrow bore wastes (50mm and bellow) as these need to be hot water tolerance.    In general ABS pipework is cheaper than the PVC-C equivalent and slightly more robust.

OSMA do a universal cleaner and a universal solvent which contain a soup of cleaners / solvents capable of cleaning both ABS and PVC.  As far as I can see you can solvent-weld within one type, and also PVC-U to PVC-C, but I can't find any manufacturers that will endorse attempting to weld ABS to PVC-U, so you have to use some form of push fit boss connector at a PVC to ABS interface.

So as far as I can see, if you want to avoid boxed-in push fit connections then you must use PVC-C waste systems.  Is this correct?

[Nickfromwales]

I've never had any issues mating either with solvent glue, and I've fitted a colossal amount of the stuff. 

Usually the 110mm pipe is branched off via a boss strap or boss socket ( stand alone fitting or incorporated on a fitting ) and then a solvent weld adaptor is used to reduced to 50mm or less. I'm not sure of the material used in those fittings tbh so I'd have to ask, but for the strap on bosses I use a cleaner, scratch the 110mm pipe with emery cloth, and then use a gap filling solvent cement, not regular solvent weld, ( the cement type usually comes in a metal toothpaste type tube ) and once set it is like any other joint, rock solid. 

I'd avoid push fit like the plague, but compression is quite reliable tbh. 

[Jeremy Harris]

I had the same question a couple of years ago, so downloaded the material safety data sheets for the ABS and PVC solvent cement.  They both seemed to use the same solvents so I concluded there was no reason for them not to work.  In practice they work fine, with some reservations. 

The FloPlast PVC solvent cement is definitely poorer on any form of solvent joint.  The pressure pipe solvent cement I got for bonding together the 16 bar PVC water pipe is far better and I ended up using that for everything.  It seems to have a gap-filling capability that the FloPlast stuff lacks and may well be similar to the stuff in the tube Nick described.  Having it in a tube would make it a LOT easier to use, mine's in a big tin like a paint tin, and I have to splash a bit of MEK in every now and again to stop it drying out.

[Nickfromwales]

This is the stuff.

[PeterW]

I've used this stuff before

http://www.ukpoolstore.co.uk/acatalog/Wet___Dry_ABS___PVC_Glue.html

It can be used for ABS to PVC but its not idea as you don't get a true welded bond. In the US you can get transition cement that allows you to connect ABS to PVC but its not easily available over here and certain states don't allow its use.

The Polypipe gap stuff is epoxy resin and a small amount of solvent - thickened epoxy would work fine although it may be a bit expensive for one joint unless you have it lying around the place.

[TerryE]

As I said there is a universal solvent for the OSMA brand that contains a mix of solvents that work liquefy both ABS and PVC, but if the resulting two plastics are immiscible then you don't really get a true weld, do you? And if there is some bonding then there's no guarantee that it will be watertight as you can easily get gaps. Send a bit risky to me.

After all, all I am talking about it when an ABS branch connects to the PVC-U stack, and this is also the weakest point for expansion cracks to form. At least a push fit spigotis designed for this scenario.

Need to think about this one.

BTW, I have 11 such 50mm and below branches connecting into my 2 stacks.

[PeterW]

Why not use 110mm ABS from the top of the rest bend as that will have a socket in it ..?

 

[TerryE]

Could do but not in OSMA. Time to discuss with Jan.

[Nickfromwales]

Are you aware of these fittings ?

The pipe terminates vertically so I'm a fan. 

[TerryE]

Yup, I fitted one in my bathroom about 28 years ago and haven't had a problem.  My issue about this form factor is that the footprint means that I would need to move the boxing-in in the bathroom out another 50-75mm to accommodate it.

[Jeremy Harris]

11 hours ago, Nickfromwales said:

Are you aware of these fittings ?

The pipe terminates vertically so I'm a fan. 

I fitted one at the top of our soil pipe stack.  Made it very easy to run the four waste pipes from the bathrooms neatly.

[Nickfromwales]

9 hours ago, TerryE said:

Yup, I fitted one in my bathroom about 28 years ago and haven't had a problem.  My issue about this form factor is that the footprint means that I would need to move the boxing-in in the bathroom out another 50-75mm to accommodate it.

I'd be happy ( confident ) enough with these for a 'fit and forget' install, so this could go in the joist space therefore not increasing your boxing in size one jot. 

[ProDave]

12 hours ago, Nickfromwales said:

Are you aware of these fittings ?

The pipe terminates vertically so I'm a fan. 

Does anyone know one of those with 5 inlets?  Or a good suggestion of how to connect two showers, 2 basins and one bath. I don't like 2 things into one small bore pipe.

[PeterW]

Unlikely that both basins would be running at the same time, or the bath and a basin so I would combine the basins and then run all the rest in 50mm which is what Nick normally recommends IIRC

[Nickfromwales]

Use a 40mm tee to connect the two basin 32mm pipes together, and run a single 40mm back to the elephant foot. 

[ProDave]

50 minutes ago, Nickfromwales said:

Use a 40mm tee to connect the two basin 32mm pipes together, and run a single 40mm back to the elephant foot. 

But won't that requre an AAV at one or both basin's?

I might be able to route one of them along the service void and into a boss higher up the stack if so problem soled, I am just keeping my eye open for options.

[Nickfromwales]

When you upsize to 40mm at the tee, it in effect creates an air break as soon as the 40mm is running horizontal so prob no need for air admittance. When the two basins are running at max normal flow rate the water still won't fill either pipe, the 32 or the 40, so as water is going down, air travels up and over it if needed. 

The only time you'll need AAV on the basins is if there is a significant vertical drop before an air break. If your going down to floor level, then upsizing to 40, you'll have ZERO issues. It wouldn't hurt to use anti-vac basin traps, but you'll deffo not need an additional, stand alone AAV for either basins with my proposed method. If you do decide to go the longer route with the second basin, I'd still upsize to 40mm tbh as they're quite prone to gunking up over time. 

[TerryE]

Re the vertical entry gathers: agreed to all of this, but our first joist is hard against the Larson strut wall so that means that the soil pipe centre is some 95mm out from the wall. The 6.way box manifold only stands out another 2-3 cm from the pipe is you are using and remover the front bosses.  We can't drop the manifold under the floor because the gap between the two joists is too narrow.

Re using tee's connection, etc. surely a constraint here is Part H1 Table 2 and Diagram 3, plus clearing access requirements.  In our case we have a

• short stack AAV terminated in our bathroom which handles
  • 2 toilets, 2 basins, a bath and 2 showers on the 1st floor
  • 1 toilet and a basin on the ground floor
• a full stack AAV terminated in the loft which handles
  • 1 toilet, basin and shower in loft
  • 1 toilet and basin on the first floor
  • 1 utility sink on  the ground floor.

We've had to up the size of some runs to comply with table 2.

[Nickfromwales]

Most of it is common sense, but I can't actually recall anyone ever measuring them ( BCO ) 

[TerryE]

When I did price comparisons, the OSMA range seemed way over the top of some of the others, so we decided to switch to Polypipe, but when I looked around for online plumber's merchants who stock a decent subset of their PVCc there wasn't a great choice of one willing to quote decent discount prices, so configured up the entire waste and soil system and the price came out at over £1K for the two stacks, which seemed high to me.

So we then shopped around some more, and "Plumbing for less" site just so much more price competitive.  However they skip some of the less popularitems -- e.g. they don't sell the single boss adapters, but their price for a 4 boss adapter to 1×spigot adapter works out slightly less anyway.  The big prob is no Polypipe PVC-C solder fit in their range, so we decided to configure up a full 2-stack solution using their in-stock items which involve 2 core uPVC stacks with all of the 50 or less branchwork in ABS and the price came out at just over £400!!  For a 60% saving here, whilst still sticking with a reputable brand and a 5-star trust-pilot rated supplier is just too compelling.