glazing silicone and making good windows

[Fred]

Hi,

When we moved, the surveyors report said the windows had not been finished properly. It seems that the glazing company screwed the frames into holes in the wall and left it at that. There is no sealant along the sides.

From what I gather, the windows were fitted circa 1981 by a company now out of business, so I can't get them to finish the job!

OTOH nothing terrible seems to have happened in the thirty years they have been "unfinished" but I was thinking about running some sealant down the sides to keep rain out. I am very confused by all the different tubes available. I have found tubes labeled "high modulus silicone suitable for brickwork and upvc" and tubes labeled "low modulus silicone suitable for brickwork and upvc" as well as special glazing silicone labeled "suitable for brickwork and upvc". What are a high and low modulus and what are they good/bad for?

Since all these tubes say they can be used on brick and upvc, does this mean any would be suitable, or is one better than the others? Should I use the specific glazing one?

If you have seen my recent thread about insulating a room, I knocked off the old plaster in one room and there is a gap around the window where I can see all the way outside! So I am thinking of using foam to fill this space.

That will be easy in the room where I have demolished the wall but I don't want to have to demolish the walls in the other rooms. What is the best way to fill around the frames in the other rooms, without disturbing the inside? I was thinking of using foam from outside but taking care not to have it overflow onto the brickwork. What's the best way to do this? Inject foam every foot or so?

TIA

[Tim Watts]

Fred wibbled on Wednesday 21 April 2010 09:21

Hi fred,

When I installed my new windows, I only had a 1/4" gap to inject from the outside. It is possible to get foam in there without too much ado.

Masking tape on the frames right up to the edge if you don't want to deal with cleaning any mishaps off. Masking tape on the bricks if possible. I couldn't - had rustic (herringbone deep surface pattern) LBCs.

Try to move the gun nozzle along at such a speed, with slow injection of foam so that the immediate expansion of the foam lies 1/4" or so below the surface of the frame. Foam is less sticky in the secondary expansion phase so although parts may extrude out, leave them until dry. They mostly come clean off.

After a day or two, use a razor sharp blade to trim any extrusion off and finish with frame sealant over the top.

If any does get onto the bricks, leave until dry and use a bronze wire brush, fine wire, to brush it off.

Injecting from outside is sufficient to seal against any draughts or water ingress.

However, if the frames are securely screwed into the wall and the gap is small, just use frame sealant. It is after all what the did in the old days before foam.

Cheers

Tim

[Steve Walker]

For our purposes, modulus = stretchiness. So high modulus for sealing gaps which flex and move (bathtubs, light door-frames), low modulus for more stable gaps. For keeping rain out of the gaps above, it really doesn't matter - any decent brand of silicone sealant will do it well enough.

[fred]

Think you have that the wrong way up, high mod is stiffer than low mod, counter intuitive but true nonetheless.

As I think Tim has said, foaming the gap will give a good robust and mostly airtight base and surface sealing with an _acrylic_ frame sealant will give the o/p the option of painting over later. For the o/p, acrylic sealants hide under many descriptions but anything that is specified as paintable will be acrylic or a modified (paintable) silicone and will be suitable.

[Fred]

Thanks, the stiffness definition makes sense, so you choose the sealant's modulus depending on the amount of movement in the joint.

I vaguely remember Young's modulus in physics, is that all part of the same thing?

I am sealing around a upvc window, so there shouldn't be any movement unless the frame expands and contracts in the sun/shade. I will be sealing the gap between brick and upvc so I don't think that "over-paintability" is something that is necessary for me.

Thanks again.

PS I'm not a fan of DOGS either; what's the real reason for them: to prevent you recording their programmes?

[Fred]

I have a similarly patterned brick, so it's important to keep anything out of the grooves. I shall try the masking tape, if it will hold.

I have put foam around the window I have access to from inside and it didn't expand explosively, so I must be getting used to applying gentle pressure to the trigger at last ;) I even had to put a second layer in.

When was foam invented? I thought I had lazy installers at first but perhaps it wasn't used in the early 1980s?

Thanks again.

[fred]

In article , Fred

Pass, I looked it up at one time to work out why it appeared to be the wrong way up and forgot the reason but remembered the practical part.

I agree that you have what should be a low movement situation so high modulus should do fine. It has the added benefit of being more robust too, increased flexibility has its disadvantages. The acrylic frame sealants are more robust still but are perhaps less flexible.

In response to your question about the before foam days, I think things were made to closer tolerances and sticky mastic was used in place of silicone. Going back further, my C1900 sash windows in sandstone openings were bedded in a plaster like facing of about 20mm deep to make up the irregular gap between window and stone (a bit like foam today) which was weathered with mastic mortar. Nowadays, when these need repaired the average tradesman packs the gap with highly moisture resistant newspaper, spreads on mastic mortar and scarpers.

I think content protection is the real reason although many falsehoods are spread to justify their presence. The brand identity one I think is the least convincing, I chose channels by content and don't have any problem identifying which channel I am viewing. The info button is always there for the hard of thinking or remembering. If they absolutely must have them then C4, E4 et al seem to have a more acceptable delivery with translucent logos that sit in the corner of the widescreen picture rather than floating at what would be the corner of a cropped 4:3 frame. For me the ultimate insult (in this context) is a solid white logo on dark or night-time scenes such as with Five or Five USA, with wildly contracting logo colours such as those on BBC3 and ITV2,3,4 coming a close second.

Anyway, a positive outcome of my distaste for intrusive logos is that I am watching less television and getting more done elsewhere.

Good luck with the windows.