Can you use expanding foam instead of Mortar ???

[Pieinthesky]

We are having an extension built and are a bit worried that some of the work is sub-standard.

The latest thing is how they have installed the stone sills under the windows.

They set the stones on pieces of plaster board - (to get the correct gap I presume) and installed the windows. They have now filled around the stones with expanding foam - it looks like they have removed the plaster. I would have thought that these stones would be built into the wall with mortar - as they are on the main house.

Pic below shows one of the windows, the stone is completely surrounded by foam, no mortar whatsoever - though I suspect they will point over the foam at some point. I can push a metal rod right through. All the stones are done in this way.

Before I get the builder wound up by questioning him again, is this an acceptable way of doing this?

All advice much appreciated.

Thankyou

Mike

 

[Swwils]

Also if this is a typically cavity wall the window is likely in completely the wrong place in the reveal.

 

[Pieinthesky]

Thankyou Swwils

I assume by the smilie that it is not right?

By the wrong place in the reveal I presume you mean front to back in the hole (Sorry I don't know the correct terminology). If so, they have copied how it is in the main house - and the whole estate - so I assume they have done that correctly. The plastic sill sticking out over the stone sill is a bit odd.

 

[Swwils]

Do your internal finishes attach to the outer brickwork or sil?

 

[Pieinthesky]

It is a normal cavity wall (350mm I believe)

They have plastered up to the windows so I am not sure what is underneath, they had fitted plastic panels over the cavity before fitting plaster board and skimming.

There are no internal window sills fitted yet so I can safely say that nothing is attached to the stone sill - I don't think even the windows are touching.

If you can explain why you are asking I will go and have a look.

Thanks

Mike

 

[Swwils]

The outer brick work is say 100mm deep, the window frame often 70mm deep. If the window is installed flush with the outside brickwork then this leaves 30mm of brick inside of the window frame.

If your internal plasterboard is attached to this; guess what happens when that brickwork at -3C meets your inside temp?

 

[Pieinthesky]

OK

So it is OK for the plasterboard to touch the window and the plastic cavity cover but not the bricks - I will go and have a look.

 

[Pieinthesky]

Looks like they got that correct at least The inside face of the window frame is inside the bricks and I don't think the internal finishes touch the bricks or the sill - just the cover and the window frame.

On one of the windows there is still plasterboard underneath the sill block at each end - I cannot see on all of them - will that swell when it gets wet?

Do the sills need re-doing? It seems like they do to me but I would appreciate a clear yes or no from someone who knows their stuff.

I have to have this out with the builder in the morning and need to have my facts correct.

Thanks

Mike

 

[Swwils]

Post pictures

 

[Pieinthesky]

First pic is a view into the corner of the window from the inside. You can see the sill (which is flush with the inside of the bricks) the window and the plasterboard butting up to the window.

This is a different window, taken from down in the cavity looking up. Hope this helps.

 

[Swwils]

Can you see a cavity tray? It should be ruining from under the stooled cill up to the inner blockwork around the level of the window frame. Or be a preformed object. If you've pushed a rod through under the cill deep enough you may have punctured it.

Basically the ideal with a stooled cill is to avoid stress, and to accommodate movement; this is why they *generally* have loose DPC as slip planes and sometimes even bed joint reinforcement underneath them. You'd bed just the stool ends and leave a free area under the cill. You generally do not mortar above the cavity tray between stooled ends. At the end of the job you use a compressible backing rod rather than foam, but you see expanding foam used alot (most foams can over time can lose elastic properties).

From your pictures it does look like the stooled ends are mortared, you can see the colour difference to the foam; so your primary worry is solved; but the other details with DPC, tray, weeps are not easily visible in your pictures.

When did the window sizing survey happen?

 

[Pieinthesky]

If a cavity tray is a piece of damp proof membrane sloping down towards the outer wall then there is nothing there. They did do this in all the openings but it is much lower down and now hidden under the insulation. There is nothing I could possibly puncture anywhere near the sill.

I assume you mean something like below. This is how you say it should be done - everything else I can find online just shows them laid like bricks.

I don't think there is any mortar anywhere, the stooled ends are supported by plasterboard packing, plastic packing or foam.

I don't know anything about a window sizing survey - the builder must have arranged it.

Thanks

Mike

 

[Swwils]

Oh so the only thing under the stooled ends is plasterboard and not mortar?

 

[Pieinthesky]

No mortar anywhere, no damp proof membrane - just foam and plasterboard - not sure if they all have the plasterboard but they probably do.

Too late to add them I would guess?

There are bricks held in by just foam too - see first photo

 

[^woody^]

Whilst it looks OK, and may well be OK once pointed up, it is certainly novel and non standard, but I'd not go as far as to say it's a bodge.

I suspect the installers were not skilled in brick laying, and have avoided smudging mortar all over the bricks - which is a good thing.

If the pointing was at least 25mm deep on each side of the wall, not a token gesture, then I'd be inclined to leave it. The alternative to remove it and have it redone with mortar may make it a right mess but not any better.

You don't need a DPC under the cill, just vertical on the back when the cavity is closed.