Sealing external gap around new sash windows

[Craig89]

I have just installed my new sash frames but I have some considerable gaps around the outside between the frames and the brickwork, picture below showing the worst.

My original plan, before fitting, was to caulk around and paint the caulk. But this is too much to caulk really. Im now thinking about pointing the gap. My only concern with doing this is that it wont seal the gap and seperate the wood from the potentially wet brickwork.

Now the house is cavity hard red brick construction so im using cement. The paint on the windows is waterbased so linseed based mastics are a no go.

Any help appreciated. Thanks, Craig

 

[Abi Cott]

I think burnt sand mastic is the correct material for the job.

 

[wobs]

I think burnt sand mastic is the correct material for the job.

This is what I did (used the stuff from Wickes I think), but I also packed it out with bits of slate where the gap was quite wide.

 

[Feltwell]

It's too big a gap for burnt sand mastic - that really is only meant for final sealing of adjoining materials, much as you would with a modern sealant gun & sealant. As an aside I've not had much success with burnt sand mastic, I tried and it looked great initially, but then failed after about 3 years.

Anyhow - that big gap - I'd point it up with the same mortar you've used for the brickwork, but use bits of roofing tile to help fill it. For sealing the (thoroughly dry!) mortar to the frame, I'd use a modern sealant, preferably one that is classed as overpaintable so it doesn't give you problems with future decorating.

Heresy warning - sealants are an area where I think modern materials can work best, if (and only if!) they are used sensibly.

 

[Craig89]

Burnt sand sastic is the traditional option but being oil based I could potentially have issues with decorating.

Im probably going to point it up and as Feltwell suggested seal between the mortar and frame with overpaintable caulk

 

[plasticpigeon]

I'm not certain that sash windows are ususally left like this. Mine have a scotia bead covering that gap between front lining and wall> have a look around your area for a precedent, but I doubt very much that such a gap would be filled with mortar or mastic as it is a big gap, it would be very messy to fill it and it wouldn't look great.

 

[Craig89]

That isnt a bad solution but out of 6 sash windows this is the worst gap, most are much more reasonable, its mostly down to the bricks being of varying thicknesses.

You have just reminded me that I have a picture of a neighbours original sash window and you can just see in the picture (even less so with the reduced resolution for the forum) that the gap has indeed been pointed. I will see if I can get a better picture

 

[livias]

If you go the pointing route then I would roll up a tube of stainless expanded metal lath and squash it into the hole to give the pointing something to hold onto. Wear kevlar gloves, the stuff is VERY vicious

 

[88v8]

...stainless expanded metal lath

I used that when building the verge of my garage roof and as a mortar base it works very well.

Ivor

 

[Craig89]

I have just been and inspected the neighbours window and pointing was definately the method used originally. Heres a picture

 

[CliffordPope]

Is that usual for the sash boxes to end almost flush with the side faces of the brickword, leaving a rather wide and irregular gap to fill?
Ours project about 2"out from the sides, and there is a covering board that abuts edge-on to the straight edge of brickwork forming the outer part of the slot the sash runs in. The result is a narrow and regular gap which is filled with mastic, and a pleasing outer wooden border, in our case painted black, framing the sash's white.