Rebating a wood casement for a Slimlite DG unit

[RichD1]

About to make some replacement casements for my bay window.

Working out the sections including the rebates, I was wondering why the putty or beading is always fitted on the outside of the casement.

Is there any problems with having the retaining beading on the inside? The front of the casement can be machined with a chamfer to resemble the putty and allow water shedding.

Richard

 

[Richard1970]

I would put the glazing beads on the inside being a joiner and glazier it's a pain replacing glass and double glazed units on a ladder

 

[Notch7]

Outside.

you will find it impossible to glaze internally and be 100% certain that you have made a waterproof seal.

slimlite units arent fitted like conventional double glazed units which are fitted with a drained and vented system.
slimlite units are fully encapsulated and the perimeter seal on a slimlite is smaller than usual which compromises the mastic used to seal unit.

when doing the face putty, the unit should be bedded on silicone, then the small gap filled and a small bead on the outside. When dry the puttying should be done with a special mastic putty like dry seal MP.

if it isnt done right the double glazed unit will break down -possibly within months

 

[RichD1]

Not sure why fitting it the other way round risks water ingress.

I was thinking to bed the unit in silicone and wiping it level with the rebate top on the outside and then when cured applying the wedge of MP on the top to produce the traditional putty line. Surely this wouldn’t be more or less prone to failure compared to external putting.

 

[Richard1970]

Double glazed units should not be siliconed in as wood moves with the weather you should use butyll putty also silicone breaks down the units if you ask your glazing manafacture

 

[RichD1]

I was thinking of using butyl putty but read somewhere that it was not preferred as it remained soft and easily removed security wise. Also many of the double glazing companies I’ve looked at on the Web state silicone.

Would you still use MP dry seal on the top of the butyl?

Richard

 

[RichD1]

Just found the Hodgsons website which makes interesting reading regarding the various bedding, sealant and hybrid putty products. They also mention internal and external beading and products for slimline DG units.

Think I’m going to pursue my thoughts of internal beading.

Richard