Parting bead groove - how thick is paint?

[mikefab]

Hi all,

I'm currently working on a replacement sliding sash window for our kitchen: it's put back the kitchen install I was planning but it makes sense to sort this first as it will be behind the new units and is in a right old state.

I'm pretty much sorted with the design, what with diagrams from the likes of Mumford Wood, Tim Nott's instructions linked from this forum, some old joinery books which I have, and of course being able to see the originals as well as the hundreds of S/S windows around Hexham.

What I can't decide is how thick the groove for the parting and staff beads should be. I assume that they should be oversize to allow for both to be painted pre installation. The parting bead I have was bought from reddiseals and is 8mm. Tim's instructions mention a 9.5 groove, but he doesn't specify the parting bead size. I suppose what this comes down to is "how thick is a coat of paint? (On 4 surfaces)". I guess it makes sense to fully paint the bead and the frame before installing the bead? They will both be painted by hand if that makes any difference.

If people would be interested I can post some photos of the window going together (not that I'm an expert, obviously!!)

Thanks,

 

[Phil Pascoe]

An idea - when I did mine, I had some nice small section hardwood to use up, but it wasn't long enough so I did the parting bead in two parts. The joint was a fraction below the the horn of the upper sash. This had an unforeseen consequence - if I had to take the top sash out, I could just remove the top bead. The bottom bead and paintwork, where it mattered, stayed intact so there was no danger of water ingress around the cill area. I also used screws and cups rather than nails, so they were easy to remove with no damage. I cannot see a downside to this.

 

[mikefab]

Hi Phil,

Thanks, that's interesting. Do the screws look OK? I suppose it's just not what we are used to seeing, that's all.

I've actually bought ready-made PB, which has a track to hold the draught seals. The supplier do 2 versions, one with track one side, that must be cut and reversed in the middle to keep the seal against the relevant sash, and a slightly more expensive one with track both sides with an overlap of about 100mm in the centre. The proposed advantage is no need for a joint in the middle, so I went for it. I suppose I could always saw it in half!!

Cheers!

 

[Phil Pascoe]

Spaced evenly, brass screws (soldiered ) and cups - 100% deliberate, looks fine.

 

[AndyT]

On all the old windows that I have worked on, the parting bead had been fixed into the groove unpainted, secured with a few small nails, and then painted with the rest of the frame.
This works, provided the bead is a snug fit in the groove, so you may need to adjust your grooves with a side rebate plane or thin down your beads to fit.
You need the bead to stay fixed in normal use but give up and come out when levered out for maintenance. The first step before removal is to run a utility knife round to cut the paint in the corner against the bead - this paint does quite a lot to hold the bead in place, but it doesn't need to go inside the grooves.

 

[mikefab]

Hi Andy,

Thanks for your reply. The difficulty with putting it in unpainted is that there will be seals set into the bead, and they slide in from the end, so have to be put in prior to installation of the bead and I fear they will be to paint around. So I was hoping to paint frame, sashes and beads prior to assembly.

 

[RobinBHM]

I think mumford and wood developed a tapered parting bead and groove due to this issue. From memory we allow at least 1mm-1.5mm for the paint (sprayed not brushed) when using reddiseals bead. However it is a problem as sometimes the bead is loose sometimes too tight and needs planing to fit. I wish there was a solution available from companies like Reddiseals or Mighton. There is an option of a plastic parting bead although I dont find it that great, it is difficult to hammer in and doesnt always sit square. I'm probably going to try Q wood parting bead next time and see if that is more consistent.

 

[deema]

Parting beads should be just a push fit, I've not seen them nailed or screwed. They were normally held in by friction / paint. They should take no load that would pull them out. I would make them so that the parting bead just slips in and out so that once painted it will be a push fit. If they come out a little sloppy, you can then brad nail if necessary

 

[Eric The Viking]

Hi Andy,

Thanks for your reply. The difficulty with putting it in unpainted is that there will be seals set into the bead, and they slide in from the end, so have to be put in prior to installation of the bead and I fear they will be to paint around. So I was hoping to paint frame, sashes and beads prior to assembly.

I don't understand the need for the strip to go on the parting bead - it's just as effective, and easier to fit, if let into the sash, and the whole will look neater and stay cleaner as it then can't be seen. Unless I'm mistaken, you'll need less of it, too.

If you really want to paint before fitting, could you put in a dummy bit of bead that you can remove before the paint hardens, to 'mask off' the slot so you only need to touch up the point where the frame and bead meet. I'd cut it to the same thickness as the groove for the bead, and give it "handles" made of woodscrews so you have something to grab and pull but painting can be easy.

I haven't done many, but I used to do parting beads in primer before fitting, then undercoat and/or gloss them once fitted. That way the awkward bit you can't easily get to (behind the horns of the top sash) has some paint protection. You have to ease the groove with sandpaper to allow for the paint,but it's a tiny amount, and snug is far better than loose, for all sorts of reasons.

 

[Phil Pascoe]

All the beads I've come across have been nailed and more often than not the nails have rusted, hence when the bead is removed it's removed in half a dozen pieces.

 

[deema]

Hi Phil,

It's probably a regional thing, nailed screwed or loose.

 

[mikefab]

Thanks for all the replies!

I'm going to take the same route as RobinBHM and allow 1.5mm clearance and paint the bead and frame before installation.

Why seals on the parting bead? Well, that is what all the commercial manufacturers seem to do, I suppose there must be a reason! I also have some things called flexislides from reddiseals which are set into the side of the sashes. They mainly stop it rattling and make it slide nicely, but also do a bit of sealing too.

This window is going to be the prototype in some ways - there are another 14 waiting to be done but they are going to be a slow burn project!

 

[RobinBHM]

Seals are required both on the parting bead, staff bead, possibly outer casing as well as edges of sash. The sash edges could be weatherpile or flexislide. Bottom of lower sash needs a bubble seal, aquamac 21 or similar. Also a seal is required for the meeting stiles.

Seals are needed on face and edges to prevent paint to paint rubbing as well as draught sealing.

I would recommend buying the sash fasteners before making in case you find there is not enough space.

Dont forget the meeting stile of the top sash has no profile mould - or you wont have anywhere for the fastener.

Also allow enough tolerance - the seals need quite a bit, Id allow about 7mm overall on the width.

Meeeting rail is not in the middle -the height of the glass line is generally the same, but the bottom rail of lower sash is deeper.

 

[Benchwayze]

Always nailed them dry-fitted myself. I found it easier to use a push-pin too. If I removed a sash for fixing weights, etc., I generally renewed the beads as a matter of course. They usually got dameged on removal, but it also depended on what the tenant was happiest with.

 

[mikefab]

Robin, thanks for the useful tips. Particularly about not profiling the top sash meeting rail - I had to read that twice then the penny dropped!

I have already got various seals following phone advice from reddiseals. Sofseal bubble seal for the beads, and sofseal P for the top/bottom of the sashes, inside of the outside casing and the meeting rails (which will have a strip planted on to overlap its opposite number and hide the seal).

The bubble seal wouldn't have worked easily for the outside case as it has to be slid into a track and therefore couldn't be installed or replaced post-assembly while the sofseal P is just pushed into a groove (as is aquamac 21 I see) so this will be easier for that location.

In terms of gaps I am going for the middle of the specifications ie sofseal bubble says seals a gap of 1.5-2.5mm so I am allowing 2mm per seal. The sofseal P spec is 2-5mm gap so I am allowing 3mm per seal. I was going to recesss the flexislides into 2mm grooves in the sash stiles then allow a 2.5 mm clearance per side.

Does that all sound sensible?

Thanks

 

[AndyT]

Just to answer the question of why the seal is in the bead... Having it that way round makes it easier to overhaul a window. You just take it apart and put it back with new beads.

If you wanted the brush seal to be on the sash, you would need to have a router and use it round each sash. You would be cutting through the existing paint when you made the grooves, so ideally you would be painting as well. It would be a longer, more fiddly job.

 

[Jacob]

Parting bead should be an easy push fit before painting. No nails or screws required they just make them harder to remove later.
Seals aren't necessary in a properly made trad sash - they are very draught proof if everything fits properly. Seals become a problem over the years especially with paint. You definitely should not have them at the meeting rails and the bottom rail as this is the route for condensation to escape.
Glass size - all panes should be exactly the same size

 

[Phil Pascoe]

Glass size - all panes should be exactly the same size

Why?

 

[Jacob]

Glass size - all panes should be exactly the same size

Why?

It makes them look right.
That's how they were always done (except for the obviously varying sizes , margin glazing bars etc where they are supposed to be different).
Even if the sashes are different e.g top with 3 panes, bottom with 6, they are made with the same size pane. But it's a bit of a teaser when you are drawing up the rod!

 

[Eric The Viking]

Sorry Andy, have to disagree about the brush strips.

You have an awkward groove to cut in the parting bead, both sides and one that goes half way along, with an overlap in the middle, on an already thin piece of stock (5/16", IIRC), unless you want the brush strip to show. And if you don't go the whole length (so the strip shows), the window will rattle ferociously once open because it'll then be loose fitting. And the PB is far more likely to get destroyed if you ever need to remove it, because it's even more fragile, it's much harder to paint because you have to watch overpainting, and so on.

So yes, on the sash you have to rout a groove in the stile, but you have to do that anyway on the top of the top rail, but I'd far rather do that than do a tricky bit of surgery on the parting bead make it weak, and have the stuff show.

I haven't done any for a while as we're uPVC casements here (mainly). I love the look of sashes, but I really don't miss the maintenance of them.

And round 'ere it will pick up diesel smuts and become filthy, and be a nuisance to clean.