I garantee this question has been asked before and I apologize for the redudancy…but you can only search through countless old posts for so long.
I’ve been undertaking some of the more extensive repairs on my PU core board using epoxy resins. I’ve cut away the glass and mixed up some resin/hardener/microballons and now find myself asking myself how much of the microbubbles should i have added. Foolishly …against my intuition I didnt do a test batch and now that is curing Im wondering if Ive added too much and if its going to turn out too soft. It seem very soft at this point…maybe a little stiffer than a memory foam matress.
Id imagine having it harden to the consistency that is as close to the density as the foam is the ideal but is this achievable with less microballoons? If so, what ratios would achieve this result given the average board foam density.
As far as I know if you have the proportions of resin to hardener correct, you mix the microballoons to desired consistency and it should get rock hard upon cure. If proportions are off, the epoxy can be rubbery after cure with or without the microballoons.
Your resin/hardener proportions should be calculated before adding microballoons.
The epoxy will exotherm hotter. Micro balloons will not thicken enough to make a good filler on repairs. You can increase the vicosity by adding foam dust, but you have to fill in layers to keep the heat down. It may look like you filled the damage, but the foam behind it may be melted. Unless the damage is very small, I never fill with an epoxy mix. I either splice in a piece of polyfoam with gorilla glue or use pour foam.
I think in general it is better to repair by replicating the original structure as much as you can, that means if a piece of foam has been damaged or removed, it should be replaced by similar material. This is usually easier than it sounds,I have found that removing the broken stuff in a way that I have straight surfaces makes the glueing in of a properly sized chunk of foam real easy. After that you shape the foam plug to match the board and glass, hotcoat etc as appropriate. For epoxy sandwich boards the same thinking just more steps as you may need to replace more than one layer of material, like a chuck of EPS core and a layer of high density foam and then glass and finish. for those layers of high density foam vacuum techniques may apply…
as for microballoons? Funny I used to luv em but… they insulate the resin causing high heat during setting, big time health hazard by inhalation, really not very useful beyond a fin install or low density blank sealing… would not use em in a ding job but that is my 2cts…
I am assuming you are using hollow glass bubbles which are sometimes called microballoons rather than the phenolic resin bubbles (Red/brown colour) which are also called microballoon. If you mix the correct proportions of resin and hardner then the epoxy will set irrespective of how much bubbles you put in. The more bubbles the easier the hardened mix will be to sand. It makes sense to me to aim for a mix that is equal in sanding ease as the surrounding area. For example if you are filling foam and have to sand the foam and filler together then aim for a mix that is as easy to sand as foam. If you are filling a hole that is surrounded by glass eg hole in glassed board then finish with mix that is quite hard like the glass. Its easier to get things smooth and flat when sanding.
It is easy to get 2 or 3 times the volume of glass bubbles to mix with resin and still have it sticky enough to adhere. Contary to PeteC you can get in enough bubbles to thicken and even to fill a hole upside down if you want to. Seems to me the more bubbles the less the exotherm. The resin is spread in a bigger volume. Depending on the quantity though you may still have to fill in layers to avoid too much heat build up. Nice thread on Surfermag JJR the surgeon is in that although using poly resin shows what is possible with repairs and use of bubbles.
It is good to have spare foam to insert bulk material into repairs as already suggested and is often faster and neater. I also often router or cut out the jagged torn edges first as it makes for a neater repair.
Looks like i have yet another repair to re-re-do lol. Thanks guys
Any suggestions for foam to use if I dont have access the extra of the appropriate stuff? I live around the great lakes so shapers and supplies are a bit of a scarcity up here.
WWmark…you were right on with the assumption as well. I used the whit micro glass bubbles and created a mix the consistency of cake icing.
Now that its all set Ive started sanding it down and found two things
1)the outer layer is quite hard. Like cured epoxy obviously.
2)in certain areas where I’ve sanded down…likely due to the crappy application of the mix …but possibly not…the result is the consistency of foam.(no…its not the foam underneath the mixture I applied…im not THAT stupid lol)
What is going on here?
Would the hard layer be water tight and allow me to surf tomorrow since I wont have time to apply the rest of the layers between now and then?
Im scared shitless of the exothermic properties now though lol. Thanks for the reminders…i had neglected them and definately applied too much at once…oops…live, learn and refix
I use Fiberglass Hawaii microballoons and Westsystems epoxy for repairing rotten wood. The more microballoons you add to the epoxy the less exotherm. I can add enough microballoons so that it just sticks together,have done up to 4 oz at a time with no exotherm. The more microballoons the slower the cure time. At first it will be rubbery and crumbley ,the inside will cure slower…I just let it sit for a few days untill it is hard all the way threw then shape with a shurform and sandpaper.
yea…turns out i AM an idiot though…i def sanded through to foam
also learned that the more microballoons added the more brittle the mixture becomes once hard. Good to know about the cure time though. The foam transplant idea def sounds the best though. Time is not something I get alot of here and waiting days for the resins to cure just isnt a good idea.
I sent the chunk of foam today via USPS. You should have it in a couple of days.
I think I would attach it with Gorilla Glue or equivalent foaming urethane substitute. Tape it in good and tight - the foaming action will fill any gaps. Sand it to size and feather the surrounding glass to allow for a flat patch.
You aren’t an idiot… Ding repairs can be a real pain especially when you’re having issues with the resin. The foam splice should be a better filler than straight epoxy/microballoons for that size hole.
I’ve been wondering how I was going to get the seams level…does that require careful sanding until you can start to see the fibres coming through? and then overlap this area with the new cloth as well?
If you’re ever back in the area we’ll have to settle with a few beers and maybe some ripples on the great lakes lol…
I have repair spots that look blended when wet but when sandied or are dry there is a distinctive outline…they havent been polished or anything yet (not that I know how…I keep hearing clear coat…ie spray can clear coat…but no thanks). Would polishing mask these lines?
Is this possibly the result of using epoxy on a polyester board? I’m not saying that this is what has happened but because no one has been able to definitively say weather the board is epox. or poly. it has been a guessing game. It’s a global industries 7s and their website is useless for specifics such as building materials. The little sun cure ive used for polyester blended perfectly and easilly but at the time I blamed the difference of results on using thhe epoxy in temps that were always too cold while the suncure was practically fool proof.
Hi - Yes ‘cut back’ or scuff maybe 20mm - 30mm on the undamaged area. You want a slightly sunken border around the damage so the new glass patch overlaps and can be sanded flush without leaving a raised overlap. Sanding to the bare glass would be about right. I usually mask off outside the repair zone and feather the repair down to the tape. That leaves the original undamaged area clean.
Is there a reason you are using Epoxy to repair a board glassed with Polyester resin? I think you are making it harder for yourself by doing this. Its useful for some repairs but its much easier to use the same materials the board is made from. If you can see the edge of the repair hotcoat when dry then its likely you havent sanded the repair down to meet the old surface enough. No need to go hiding this with polish or rattle cans etc just do the job right. Did you check out that link I posted? It gives so much good advice and quality photos too. Main think I learned about ding repair is its all in the preparation. The further past your ding you prep, glass and hotcoat the easier it is to blend in. Seems quite drastic to sand a couple of inches past a repair but much easier to make a good repair this way.
In order of occurance, lack of information (from the resin supplier. They literally told me they didnt have any poly. resins. Now they say they do. I havent confirmed yet if they’re clear resins…but I’ll soon find out), and curently lack of cash has led to using the epoxy. Im actually holding off on any further repairs until I can get poly. resins based on my experiences with the poly. uv sun cure res.
Clearly I HADNT checked out that site eh. lol…thanks for pointing it out again WW. Good to read.
Im baffled that the site has stated cubisol(probably spelled incorrectly here) and microballons are the same though. Cubisol is a clear drying thickening agent and microballoons are white drying glass bubbles(the latter of which i now know for a fact after having worked with them), which also thicken the mix HOWEVER dont have the same antisag properties as cubisol. At least this is what prior research has revealed. Something isnt adding up there for me.
Yes its a mystery to me too why people who are obviously good at the job say Cabosil when they mean Qcell or microballoons or glass bubbles etc. At first I put it down to different names for things in the US as opposed to UK but its really just lack of clarity. There is a thread somewhere going into this but got this from boatbuilding site:-
Qcell, Microballoons, glass bubbles are fillers that are hollow spheres
which makes them good for sanding and absorbing water therefore not a
great choice under waterline. Polyester resins do not have the water
resistant properties to seal and protect these from water intrusion.
Epoxy is a much better choice. Cab-o-sil and Aerosil are fumed silica
and create dense hard (hard to sand) puttys but are much more water
resistant. Any polyester work below the waterline should be sealed with
epoxy or gelcoat especially if it is structural.
Let's start with what is perhaps the least understood of the three chemicals,
cabosil. Cabosil is silicon dioxide, or fumed
silica. It is a very fine white powder, very light in weight. The function of
cabosil is to act as a "thixotropic agent." This 50¢
word means?essentially?"thickening agent," but thickening of a very particular
chemical sort. After all, adding mill fiber,
Q-cell or pea gravel to your resin will also thicken it, but not
thixotropically!
Think of a thixotropic agent as a bunch of chemical S-hooks. When introduced to
certain liquids (like vinyl ester resin) in
proper proportions, it "hooks" onto the molecules of the liquid and holds them
together. When agitated (stirred), the
thixotropic hooks let go and the gelled mixture liquefies until the agitation
stops, at which time it gels again.
and polyester has poor water resistance properties?!
both things that ive never heard before. …now im debating…if im just going to have to cover any poly work up with an epoxy what’s the point of bothering with the poly res in the first place…that waves i ride rarely get that big anyways and not likely to cause damage.
Is a gelcoat/gloss coat the poly res with the wax additive?
Boatpeople recommend only epoxy with glass bubbles for below the waterline. In board repair we are using the bubbles and resin mix as a foam substitute. As long as its as good as the foam in strenth/water adsorbsion the use is fine. When I use Epoxy and glass bubbles for large hole filling ( Foam if v. large) I vary the ratio depending how hard / light I want it. I. Sometimes add Cabosil also to change this. If its a poly board I sand then glass over in poly as normal. If an epoxy board I glass in epoxy.
