DIY, How To's, Outside Spaces

How To Repair A Rotten Window

Repairing Rotten Windows

As part of operation improve the kerb appeal of my home, I thought let’s strip the paint off the window sill, because that’s a good idea! Why of why did I say that?? It turns out that in places the only thing keeping my rotted windows held together is in fact the paint! Removing over 120 years of built up paint was the least of my worries. Beneath what looks like in tact paint was rot! And lots of it too. So after my initial WTF expletives of which there were many. I dug deep telling myself that this is ok. I’ve got this. And do know what? I have. I thought how hard can it be to repair a rotten window. And apart from taking time  it turns out that it’s quite simple and affordable too.


My rotten window


It doesn’t matter how old a house is for the windows to rot. That tricky thing that is water! It can make it’s way into the smallest crack in paintwork. And you’re none the wiser until you start digging. And that’s how rot starts. The timber gets wet and stays wet for a long time allowing the rot to take hold. There are also two types of rot. Wet rot and dry rot. Neither are good but if you have to have one cross your fingers that it’s wet rot. I won’t go into the differences between wet and dry rot here because a Google search will find you much better qualified blogs than this one to go into the intricacies. Needless to say though that if your windows are rotten, they need treating and some degree of remedial work.


How To Repair A Rotten Window – What You Will Need




Hot Air Gun or Paint Stripper

Paint Scraper

120 Grit Sandpaper


Wood Hardener – I use this one from Ronseal


Wood Filler – I use this one from Toupret

Filling Knife

Weatherproof Gap Sealant


Top Coat


Step By Step Guide on How To Repair A Rotten Window


How To Repair A Rotten Window


So let’s make a start shall we. First up we need to remove all the paint. You can do this either by using paint stripper which personally I feel no longer works like it used to. They seem to have removed the bit that removes the paint 🙂 Or use a hot air or heat gun. It’s quicker to use though can cause injury. Not only is it hot (er the clue is in the name) but it makes the paint very brittle so please do wear protective gloves and eye wear. Chose a starting point on your woodwork, heat using the gun and scrape away with the scraper. Some bits will come off satisfyingly easy, others not so much! Please do beware of heating up the window glass though, it will and does crack very easily. Been there! Bought the T Shirt. I always use paint stripper for that bit.



How To Repair A Rotten Window


Remove as much of the paint as is humanly possibly and then stand back to access what you have. Beware though, what lies on the surface can hide a multitude of sins underneath. If no rot if immediately apparent I use a Stanley knife to stab the wood in random places to check it. You will soon notice the difference it takes for the wood to resist the knife if you come across any rot. Any that you do find use your chisel to remove as much of it as you can. I find a hoover comes in handy to help remove the mess that you create too. Try not to panic if the hole gets larger and larger. Just look at my gaping hole 🙂 It came good in the end.



How To Repair A Rotten Window


Once all the rot is removed give the area a jolly good sand. You want the good wood to be as smooth as a babies bum. And to remove as much as possible of the old paint. Now grab your wood hardener and paintbrush and let’s make a start on fixing the rotten window. There are many wood rot repair products out there to choose from but after nursing my woodwork along for many years these are my favourites. Open the wood hardener and pour a little into the cap which is specifically for this purpose. And then using your paintbrush apply it liberally to all the rotten areas. I tend to go a little over board just to be on the safe side. I then also apply a thin layer to the good areas of wood too, just for good measure. BTW, use an old paintbrush, not your fave.


How To Repair A Rotten Window


Now go make a cuppa whilst the wood hardener dries. You deserve it. Depending on the ambient temperature and humidity it can take up to 2 hours to fully dry. Once it is give it another good sand over. Your will find that bits of rot however much you hoovered will be stuck to the wood. We’re now on the final stretch. Grab your wood filler and pour some of the powder into a throwaway tub. I keep old ice cream tubs just for this very purpose. Add water a little at a time and start mixing with your filling knife. You want a achieve a consistency of slightly over whipped cream. You know when it all of a sudden goes to thick from light and fluffy. It should be able to form stiff peaks. Now use the filling knife to press the filler into the rotten areas.


How To Repair A Rotten Window


Don’t worry if it isn’t as tidy as you would like it to look. And be aware that if the areas you are filling are very deep that you will probably need to do two applications. Apply as much filler as you can on this first attempt and leave to dry and harden. Again this is weather dependant but it should be dry within two hours or so. Once dry sand again down level with the wood. You will soon notice any missed areas. If you do have any then mix some more filler and repeat the process where needed. The filler is incredibly easy to sand. You can even use a chisel to shape it if your wood is decorative.


How To Fix A Rotted Window


To be on the extra safe side I then use a Weatherproof Gap Sealant to seal all the joins and corners of the window frame. It may be going a little overboard but it’s an extra layer of protection against the rain. It is the most disgusting thing to use too. A little like decorators caulk but much more sticky and impossible to remove from your fingers 🙂 I apply a thin bead and then with a finger that I have just dipped into soapy water I smooth it into the joins and and corners.


And there you have it. That’s the third thing on my improve the kerb appeal ticked off the list. I’ve also repointed our Victorian stone boundary wall and polished the marble steps too. Repairing a rotted window or sill may not be the most glamorous task. Nor the most fun in the world but it is very satisfying. All you need to do  is give it a couple of coats of primer/undercoat and a lick of paint. Remember too that if you are like me repairing your outside windows then use exterior paint to give it the best chance of lasting for years to come. Good luck and please do let me know if you have any questions by leaving a comment below.


Rachel's Signature


NB. I am by no means a professional carpenter but as a competent DIYer this process works for me. I’ve written How To Repair A Rotten Window as a guide to my own processes and cannot be held responsible if this does not result in the same level of repair as my windows. This post also contains affiliate links. If you decide to purchase any of the items you won’t have to pay more but I will receive a very welcome small percentage.

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