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Exterior woodwork - specifically sill help!

Morning all…

I have returned to an 18th century cottage to “freshen up” some woodwork.

I was last here about five years ago when I carried out some pretty extensive decoration after years of neglect.

Five years on, most of the redecorated window frames are still in pretty good condition but nearly every sill and lower beading has failed :frowning:

This despite days and days of extensive rubbing down severely weathered oak sills and taking the time to apply full coats of primer/undercoat & SuperOpaque top coat.

I am assuming that I have missed something at the prep stage with the oak sills…

In particular where I have two-packed sections on the sills, these have all delaminated :frowning:

On weathered oak, would a shellac primer (BIN) achieve a better result that the Dulux Weathershield primer ? When I raised the issue with Dulux technical they said don’t use dark colours on sun facing elevations… Not quite the advice I was anticipating !!

Any suggestions welcome !

As a follow up, my customer has been on the internet and is asking if I am going to:

  1. after wiping with meths, give it two coats of aluminium primer then undercoat/top coat with Dulux Weathershield ?

  2. just use Weathershield. Primer/undercoat/topcoat


To further complicate, there re some areas of open grain. Normally I would put wood hardener on, two pack and proceed normally but I’m doubting myself now and wonder if I should be using the hardener at all and wondering if the two pack filler should go over the Ali primer not underneath it…

Lots of stripping/rubbing down to do whilst pondering… At least it’s not raining !!!

… And typically since investing in my shiny nee Mirka Deros system, I’ve been outside for two weeks and haven’t had the opportunity to play with it properly :frowning:

Struggling to add images will add to a new post,check above.

The sill is the part off the window worst affected by the whether elements,for primer,you,could use zinsser cover stain,is the wood solid?

Hi Guys,

Despite some great efforts, there are a few classic mistakes I can see as to why your systems are failing, which is mainly in the prep!

1). DONT use polyester fillers (2pk) fillers externally, they will IMO fail!

Why? Despite manufacturers claims of “For Interior or Exterior use” a polyester 2pk filler will basically act like a sponge over time, absorbing moisture and eventually causing the paint system to fail.

As with Darlic’s repair, I can see what your trying to achieve but in all honesty, that repair, depite your great effort will most likely fail by this time next year, if not sooner. You basically have 3 different substrates all attached to each other, the hard wood (original sill) will expand and contract naturally at a different rate to your softwood (repair), this will over a short period of time cause a hairline crack that will intern allow the ingress of moisture. The 2pk polyester will not expand and contract but take on moisture. If your going to do ‘splice in’ repairs such as this, use like for like substrates. Better still, I would have removed that sill completely and put in new or use the repair-care system.

Similar thing has happened with Markyb, the black sills that have failed most will most likley be on the south facing elevation, where it gets the most sun. Dark colours (Black especially) absorb the heat and will cause the wood to move at a much greater rate than the 2pk polyester. Moisture is then allowed to ingress under the paint layers, causing de-lamination.

BIN is only recommended for spot priming externally as it becomes to brittle due to its shellac base. Coverstain could be an option or aluminum wood primer.

Markyb, get that 5" disc on your new Deros and get blasting those sills down with some 80g abranet.

Please guys no more 2pk on exteriors

Good luck and press on!

What filler would be recommended for exteriors?

For skimming over your open grain, you need a spachtel type filler such as gras a lacquer: This would make for a much better repair than the 2pk. If your splicing timbers in use the repair-care system. Their 1 hour resin can also be used for fine surface repair (stopping). The problem with 2pk polyesters is they wont naturally move with your timber and that’s where the problems start.
You could try this: but again you need that elasticity in a filler for the movement. This is probably one of the better ones but keep away from car body fillers for exterior work

100% agree - for exteriors - Repair Care is the system to go with whether repairing small areas of rot/damage or using with timber fill or for Planned Preventative Maintenance such as construction joints at end of cills and front doors.

Its no slump properties make it superb for damage to mouldings too as it sculpts and shapes easily. The adhesive bonding is solid and not achieved by 2 pk. The flex properties are superb in heavy front doors which contract and expand in our variable climate

But its not a DIY pick-it-up from the shelf and start using it product - the day course is essential to get the most from it as a product and a business opportunity.