Ronseal 2-part high performance wood filler only lasted one month

14 Sep 2021
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United Kingdom
A month ago, my door and window frames needed repainting. Three parts of the frames had started to rot (2 bad-ish, 1 not so bad spot). In these places, I dug out the rot and some surrounding wood, used a lot of Ronseal wet rot wood hardener, gave it ages to dry, gave it a rub down with a metal scourer (the box said to use a wire brush but I didn't have one - this is the only instruction I think I didn't follow; I had been following the instructions on the packs and on Ronseal's website very carefully), used the 2 part wood filler and, again, gave it ages to dry. In the morning it seemed absolutely solid. I then sanded all the door and window frames with 60 then 120 grit, and painted with Ronseal 10 year exterior wood paint. It all looked very good for the next week or so that I inspected it.

One month later, I have noticed that in all three places the filler appears to be pulling away from the frames. On one window sill, it seems to be pulling the wood up with it - making a really long crack. I would like to get it sorted before the winter, but I don't know what to do - I used expensive stuff that I thought was the gold standard for this kind of repair but, as it failed in all 3 places I used it, it doesn't feel wise to do the same again (with a wire brush this time!) The paint is all fine in the places I didn't use any filler, so it's something to do with the hardener or filler. When I pull off the cracked parts it's a thick layer of filler (all of the filler comes off) plus a bit of wood.

I am out of ideas, and would really appreciate some help. I have no idea why this might've happened. Can anybody help? Thanks



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No help but I did the same recently on a my porch door and have experienced the same. It's blown in a few places.
Used the same ronseal products as well.
This was after heavy rain so assumed its just the wood swelling.
A bit gutted
No help but I did the same recently on a my porch door and have experienced the same. It's blown in a few places.
Used the same ronseal products as well.
This was after heavy rain so assumed its just the wood swelling.
A bit gutted
Alright well hopefully we're not just idiots who missed something obvious :LOL:
I did read on this forum that repairing rotten wood like this makes you very, very good at repairing rotten wood like this. Cos' you have to keep coming back and repairing it...
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Really? That's not what the Ronseal product description would have you believe!
This wood filler will crack where it joins with the old wood sooner or later.

This wood filler will also crack if you fill near to where there is a natural join in the wood such as near a window sill mitre.

If there is a natural movement in the wood, expect some cracking, particularly on larger areas.

Sometimes you can fill the crack, and it doesn't seem to come back.

Decorators caulk is useful on a persistent crack.

If you are filling very large areas, shoving a few screws (with them sticking out) in the remaining wood can help, as it gives the filler something to cling to.
Ideally, you would have used epoxy resin fillers. They are two pack products but much more expensive that the polyester resin filler that you used.

Unfortunately you often need to buy the special (proprietary) skeleton guns to go with the double barrel tubes. I am only aware of one that can be used with a standard gun.

It is however the most expensive per quantity.

Epoxy resins will flex, your two part filler will not. The products however are so expensive that they are normally used to splice in new timber or alone for minor holes.

The cheaper of the ranges is Timbabuild. The gun alone is up to £30 and the tubes are about £30. You have to be religious about mixing them. If you don't mix them properly they will not cure. As a rough guess they take 4 times longer to mix than the filler you used.

The above firm also, makes a two part wood hardener. You have to use a throw away brush though, you will need to bin it after about an hour (on a hot day). Personally, I don't have much confidence in one part wood hardeners. Frankly one should remove as much soft timer as possible.

Epoxy resins are not magical though. You still need to prep the area and paint them with the correct products.
you should be replacing rotten timber with fresh timber and filler only for small gaps
you also need a clear groove under the front edge to shed the water
I have used Ronseal 2 part wood filler and found this happening with window ledges and soffit wood where hot sunshine or heat from inside the house has caused expansion and contraction. With the soffits I first pulled out a strip of caulk which I now think I should have left as it was probably used for having the right properties.

The worst case was a low wooden ledge at the foot of a very heavy wall-sized sliding door onto the patio. Nothing I tried would stop the cracking and then I realised that it was the vibration of the sliding door causing it to crack and separate between the wood and the metal.

I thoroughly cleaned out the crack between the wood and the metal and sanded the rest of the wood of the ledge. I then used the 10 year wood paint on all wood surfaces allowed it to dry thoroughly and filled the whole crack with brown silicone using the scraper to get it flush with the surface of the wood.

The silicone is almost the same colour as the painted wood and shows no signs of cracking or deteriorating after a year. Of course you cannot paint the silicone but it all looks fine and I expect it to last decades without deterioration despite the vibration and sun exposure.
If you used MS polymers, eg CT1, you could have painted over them - most need sealing with a waterbased paint first. They are almost as flexible as silicone.

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