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Uneven surfaces

Discussion in 'Kit Cars' started by cheekymonkey, Jan 22, 2016.

  1. cheekymonkey

    cheekymonkey New Member

    Having ground out a load of filler on the rear wing of the lotus I'm restoring there has previously been a pretty shoddy repair which is really, really uneven & jsut made good with filler.... i'd like to repair properly using GRP so how do i best go about levelling the surface (we're talking 10-15mm tollerances across a 2ft sq area) so that when i put layers of mat on top my finish surface is the shape i want for the wing?

    i wondered about simply mixing up some resin & chop mat & cabo sil to make my own 'filler' and shaping that & laying onto that while still wet?

    Any advice appreciated... i'm jsut trying to avoid having any filler where i dont need it!
    Last edited: Jan 25, 2016
  2. Martin @ EC Tech

    Martin @ EC Tech Tech Staff Member

    HI , by any chance could you send pics of the effected area so I can get a better understanding of what you have to work with? if you have any problems uploading to the forum please send to sales@ecfibreglasssupplies.co.uk
    Kind rgds Martin
  3. cheekymonkey

    cheekymonkey New Member

  4. Martin @ EC Tech

    Martin @ EC Tech Tech Staff Member

    That's quite job you've got on your hands there, usually filling with easy sand would be the easiest option, however we do have a filler with exceptional strength http://www.ecfibreglasssupplies.co.uk/p-2930-autofill-k-tech-filler-reinforced-with-kevlar.aspx
    this contains Kevlar strands too. you could try formulating your own filler using gelcoat, glass bubbles and fibres, however we do not have a recommended formula to make up a sandable strong filler, this would take some time experimenting with different mixes. The K-tech auto fill is already formulated and made for such an application.
    If you have any really deep areas we have our own brand of fibreglass filler to help build up to a level to be skimmed with the K-tech. I hope this helps. regards Martin
  5. cheekymonkey

    cheekymonkey New Member

    thanks Martin that's helpful.
  6. cheekymonkey

    cheekymonkey New Member

    Hi Martin - have been experimenting & think I may go down the glass bubbles route for my application as i want to keep weight down, there's a fair amount of similar work to do on the front end of the car to reshape it too. (see here https://drive.google.com/file/d/1t2s1_F1FdWW9-DOG7ArSaMCRHYkwB5U5IQ/view?usp=sharing)

    two questions before I order some...

    1. Is there any rule to roughly work out how much i need? i.e. how far will 5l (400g) go
    2. Is it best to fill, shape & sand then apply a layer of mat over the entire area once I have the desired shape to provide best strength?

    Thanks again for your help
  7. Martin @ EC Tech

    Martin @ EC Tech Tech Staff Member

    Glass Bubbles are primarily used to reduce weight in resin when filling a cavity. It is used in some auto fillers but with other ingredients too, that composition unfortunately, I have no knowledge off.

    If you were to use glass bubbles to make a fairing compound it is going to take some playing around with and a lot of glass bubbles , maybe start with 2 parts glass bubbles to 1 part resin (by volume) then add more until you have a thick peanut butter consistency. Or instead of resin use gelcoat which already has some body to it. There is no basic formula that I know of to create a body filler compound or fairing compound from glass bubbles. To be honest I would say an already made auto filler would be easier as it will most likely have a better tried and tested formula than just glass bubbles and resin and would save you time too.

    The more you add glass bubbles to resin, the weaker the mixture becomes due to the tiny bubbles in the mixture (imagine an aero) . however the more you add , the easier it becomes to sand. so its kind of a catch 22 situation between strength versus easy sanding. higher performance auto fillers such as the K-tech have kevlar fibres to add lost strength back to the mix.

    Applying matt will cause more low points due to its rough texture. A lot of fiberglass car restorers use surface tissue, If applied neatly with no overlaps , usually a couple of coats of resin afterward flattened back between layers will smooth it off. kind regards Martin
  8. cheekymonkey

    cheekymonkey New Member

    Hi Martin, thanks again for input. Didn't really explain my side fully - what I've been doing so far is grinding out damage, layering up mat then finishing with tissue, rubbing back & getting near perfect finish with zero filler, tiny amounts will be required prior to paint I'm sure.

    My fear on just a filler product for the car and finishing there is that there is no overidding strength holding everything together, not from a structural point of view so much, but more to stop cracks etc appearing around the areas of previous damage through movement/vibration etc later, so for example my thought on the nose of the car where it has been poorly repaired is grind it all back to remove anything loose or any filer, fill with something that can be shaped (either filler as you have suggested or a bubbles/resin mix fairing compound, getting everything back to the right shape (there's a lot of curves) then literally wrapping the nose again in mat (i bought a twill from you) and then finishing with tissue over.

    Going back over what you've suggested do you think the filler as a one stop shop product will be suitable & not have any future issues? Will I need ot put anything on top or literally fill, sand, job done.?
    thank you again
  9. Martin @ EC Tech

    Martin @ EC Tech Tech Staff Member

    If you can get the twill cloth applied neatly without any overlaps or creases, you can fair off with just a resin to fill the low points, similar method for surfboard repair. This will give you more strength to the surface. Any areas where you think may flex or cause problems will be best beefed up at the back with more matting and resin to re-enforce. a real belt and braces approach would be epoxy based coating and fairing compounds but this could be expensive compared to polyester an you would have to ensure the paint supplier has a suitable epoxy primer.

    Unfortunately I have no hands on experience in a auto refinishing or fibreglass car restoration to advise on a method that definitely wont present problems with surface cracks in the future , it may be best to seek advise also from someone in this industry that may be able to give some other tips. Kind rgds Martin
  10. John Dickens

    John Dickens New Member Staff Member

    If that was my car I would go the whole hog and make a proper GRP repair part panel.

    I would use a cheap filler to smooth and shape the area then take a partial mould from the repaired area.

    I would use the mould to produce a part panel then cut out the whole of the damaged area and glass in the new repair panel.
  11. cheekymonkey

    cheekymonkey New Member

    Hi John,

    You can buy a new section moulded to wherever you want, but at a huge cost compared to materials to repair. (and my time which is free) It's been strengthened inside & is rock solid the exterior will be purely cosmetic to avoid using filler again & to regain the shape to mound the flush bumperettes on the front. I've got some bubbles and will give that a go. I spoke with a local ish firm who have worked on these cars (and fitted my new subframe) & they suggested bubbles, shape & glass over the top once the right shape found. Body filler is crap & will crack in time & GRP fillers would be excessively heavy. I'll let you know how i get on

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