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What filler for epoxy/glass?

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Cuban806/10/2015 14:25:52
2772 forum posts
13 photos

Will be trying my hand at an epoxy/glass cloth covering job in the near future and I'm wondering what will be the best filler to use to fix the inevitable imperfections prior to priming and paint. I suppose polyester fillers are out because of their incompatibility with epoxy, so what will be an easy to apply material that will rub down easily and form fillets etc? A lot of American tutorials on YouTube use Bondo Cellulose stopper, but that product appears to be unavailable in the UK.

A friend at my club said he uses lightweight polyfiller but I'm not sure about how well that will take to the epoxy surface. Having seen the superb finish on his models it clearly works for him, but any/all advice gratefully received.

Edited By Cuban8 on 06/10/2015 14:27:40

olav sivertsen 106/10/2015 14:46:43
3 forum posts

Hi.I always mix micro balloons with the epoxy resin.Mix enough to make a thick paste and apply.Sands very well and is also lightweight.I find a very fine grade wet and dry abrasive paper gives the best results.

Martyn K06/10/2015 14:49:00
4986 forum posts
3624 photos

I have used Halfords Cellulose knifing putty and also Isopon P38. I prefer the latter, the putty takes ages to harden


Don Fry06/10/2015 14:55:29
4063 forum posts
47 photos

For bits of dinks and dents and minor surface imperfections, i.e. the majority, ordinary lightweight balsa filler does the job.

Ernie06/10/2015 15:03:55
2513 forum posts
20 photos

Hi C8,, I have recently used lightweight filler from the local DIY shop. I was directed on this very forum to pick up all the filler tubs, and take the one that was empty. I mix it with a water based resin......It's very good


Andy Meade06/10/2015 15:58:44
2655 forum posts
679 photos

Isopon P38, 3M red stopper / glazing putty, and lightweight homebase filler too. All bond fine to epoxy & glass finishes in my experience yes

Chris Barlow06/10/2015 17:03:03
1836 forum posts
1240 photos

I use either...

Micro balloons with epoxy,

Fine surface filler/cellulose knifing putty, and...

polyfiller/balsa lite filler.

When prepping an epoxy glassed surfaces for painting I always finish with filler primer (or high build primer) & sand nearly all of it away just leaving any hollows and scratches painted. Seems like a waste but I hate seeing dimples and scratches in the finished paintwork.

Cuban806/10/2015 19:13:20
2772 forum posts
13 photos

OK chaps, many thanks for the suggestions. yes

Engine Doctor27/10/2015 09:13:53
2317 forum posts
28 photos

Hi have look at or try Ronseal Woodfill . Its a polyester type filler that sets very quickly .It sands easily at a similar rate to balsa when fully cured , much easier than P38 and far lighter. It adheres well to most surfaces that are not too flexible . Ive used it on epoxy with no problems of it lifting. Knifing putty is OK for tiny blemishes but as said takes for ever to harden and can then sink needing another application.

Levanter27/10/2015 09:41:12
881 forum posts
436 photos

Polyester materials over epoxy generally works fine. It is the other way around that is a problem unless the polyester is very well cured indeed.

Only snag could be a "bloom" on the epoxy that should be removed with a slightly damp cloth or sponge (not solvents) This should be done before sanding the surface to provide a mechanical key.

P38 or equivalent for me every time as it sticks, can be easily carved when green and is a pleasure to sand. If I was able to get Ronseal Woodfill in Spain I would definitely try it.

Martin McIntosh29/10/2015 21:53:49
2956 forum posts
1086 photos

The best way by far is to use fairing compound from Bucks Composites preferably mixed with the same resin as used for skinning but you will have to wait 24 hrs. with this. The thicker it is, the easier to sand. Other than over epoxy it can be used with David`s Fastglass but you will need to be quick and only mix small quantities at a time although the compound and polyester resin can be pre mixed, only adding a minute amount of hardener as required. Carve/sand when nearly set: later on it will be like concrete.

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