west system filler problems

Discussion in 'Boatbuilding' started by rogerball0, Dec 4, 2012.

  1. rogerball0
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    rogerball0 Junior Member

    Hi there

    I'm currently restoring a 40 yr old westerly , amongst other jobs are giving it a coat of paint so during the summer i dug out all the star cracks and crazes in the gel as part of the prep.

    I did all this during the summer and wet sanded everything to 400grit , i used both west systems 404 and 407 filler for the job, now the problem i have is after running my hands over the hull yesterday every ding and scratch i filled is now protruding quite noticably (not smooth).

    Its winter here in the uk so damp and cold, the boat is in a ventilated shed.

    Would anyone have any ideas?

    much thanx in advance

    roger ball

  2. TeddyDiver
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    TeddyDiver Gollywobbler

    Print trough.. after curing and then sanding helps..
  3. PAR
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    PAR Yacht Designer/Builder

    400 grit is awfully fine for sufficient "tooth" on the substrate. In other words, not much to grip (too smooth). Smoothing is part of the finishing process, which takes place after the fairing process, which takes place after filing operations.
  4. rwatson
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    rwatson Senior Member

    I am not sure what Teddys cryptic comments mean, he may be able to expand on it a bit more.

    My thoughts are that you may have to make sure that the epoxy has cured at temps of over 20d C for 24 hours before you start sanding to a fair hull. Epoxy cures slowly, and often not totally until higher temps have been encountered, and then expands.
  5. rogerball0
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    rogerball0 Junior Member

    Cheers for the quick replies, I initially filled the hull blemishes summer 2011 on a blazing hot day, I then fine filled and rubbed back flush with 400 w&d in preparation for primer. One thing I didn't mention is that all the dings and bits of damage on the deck are still nice and smooth, I was told by a grp repairer to do the same repairs but with polyester and glass bubbles as the hull is poly but that to me seems counter intuitive. Also the laminate schedule of my hull is a little strange as the lay up appears to be almost entirely gel coat although having shown pictures of it to surveyors I'm told it was common practice to pigment lay up resin so don't know if that has some bearing on the quality of the bond between the two different resins. I'll post some pictures tomorrow of what I mean.

    Cheers roger
  6. DCockey
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    DCockey Senior Member

    What resin and hardner did you use with the fillers?
  7. PAR
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    PAR Yacht Designer/Builder

    Roger, you have to knock it down again, basically re-fair the area. Yeah, it sucks, but not that uncommon. I'm sure the goo has had sufficient time and temperature to cure, but it may have been not quite ready, the first time around. Pull out the board of pain (long board) and knock it fair again. If using a high build primer, don't polish it up with 400 grit, 220 is more than enough to be filled by a good quality primer and offers a bit of tooth, for the primer to cling too. When ready for finish coats, again 280 is easily filled by top coats, assuming sufficient film thickness. I rarely go over 220 grit and have little difficulty getting primer or top coats to fill the scratches in.

    Your GRP buddy is correct, the hull could have been repaired with polyester, though this isn't as easy, nor as durable as epoxy, for the novice laminator.
  8. rogerball0
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    rogerball0 Junior Member

    Cheers Par and once again thanks for your time on this, i think i'll grind them all out as you said then use the transom as a test piece, i'm going to do a couple of scratches with poly and bubbles and a couple with 404 and 407 and see what happens.

    Its strange as i thought repairing a polyester hull with epoxy would be bulletproof but this has proved otherwise.

    Heres some pics to explain:


  9. PAR
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    PAR Yacht Designer/Builder

    West 404 is quite hard and not the best choice as a fairing compound. West 407 is phenol balloons (also a small amount of wood flour and silica) and very easy to sand, making a good choice for a fairing compound. 404 would would only be used if you needed a structural mixture.

    Epoxy is generally bullet proof, though application is everything, which also includes the other resins as well. I'm not sure what caused your fairing compounds to stand proud, but 99% of the time it's surface prep or techniques, not the actual products.
  10. mastcolin
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    mastcolin Senior Member

    I have seen problems with filling old (and new) polyester boats with fillers also.

    But then you can get problems also filling old epoxy filled hulls(eg steel and aluminium hulls) with new filler.

    It is often to do with the differences in the hardness and flex of the fillers being different from the original substrate, be that filler or polyester. Dark colours show this problem more. presumably due to the greater heat they absorb. The continual expansion and shrinking can often then show up the repair.

    The cure for you?

    1) 400 grit is too fine. The filler would be harder than the polyester. You never sanded it perfectly fair in the 1st place i imagine. You will sand the gel more than the filler. (the gelcoat is easier to sand than the epoxy)
    2) make sure you use some sort of hard block that is larger than the filler patch so you cut across the filler patch following original hull form.
    3) Did you prime the filler patches and hull before painting? The primer will help prevent this shrinking/expanding effect. Bare in mind that the filler should be cured to reasonable degree before sanding and overcoating to prevent any subsequent shrinkage/movement.
    4) small dings are probably better filled with a polyester filler. These seem to move more in agreement with the original gel...but also no guarantee.

    Sand the patches as suggested with rougher paper(it doesn't have to be done wet...in fact dry is probabbly better. Machine sand the area with something finer to remove the blacksand scratchmarks and repaint. Cross fingers.:( It may keep showing through. The more guaranteed cure of applying 150micron of highbuild primer over the whole surface isn't probably what you want to do.
  11. Milehog
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    Milehog Clever Quip

    A cabinet scraper is invaluable when leveling and smoothing epoxy.
  12. PAR
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    PAR Yacht Designer/Builder

    Scraping is the "experienced" method, if your elbows are like mine anyway. A trick I often employ, especially on small areas like this, is to use a Mylar sheet over the wet epoxy, I lightly roll it into the goo with a roller. Not trying to mash it flat so much, as make the surface reasonably fair and smooth, plus prevent O2 from getting at the unreacted surface amines, which will prevent blush. If the area is "developed" you can nearly fully fair with the Mylar sheet, making finish work quite minimal. This is also a trick I use on flat or developed brightly finished parts, to produce a mirror like surface with little effort.
  13. michael pierzga
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    michael pierzga Senior Member

    In future avoid mixing your own fairing compounds and use pre mix. fewer surprises.
  14. tunnels

    tunnels Previous Member

    for fine sanding you have to use a hard block and sand lightly , i use a carpenters pencil and lightly pencil mark the whole area in 360 angles then lightly sand with a hard block and use 320 wet and dry sand paper first off. if you are filling epoxy the use epoxy fillers . if you filling gel coat then use gel coat to fill with . when you change fillers to something other then the same then you have a conflict of differant materials , differant hardness and one will always sand easyer than the other !the paper will simply ride over the top of the harder and so sand the softer more than the hard :p:D

  15. gonzo
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    gonzo Senior Member

    If all you did was sand gelcoat cracks with 400 grit, the cracks are still there. You bridged the edges of the crack with epoxy, but they will show up again. The proper repair is to sand the gelcoat off and then re-coat.
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