Help me understand the correct procedure for Alexseal

[Commander-147]

I have never worked with fiberglass before I started restoring my commander. So I am having to learn as I go. I have gotten pretty good at using Epoxy for the structural work that needs doing. But now I'm thinking ahead to what I will need to do in the finishing stages.

First the hull needs a significant amount of fairing. Is epoxy with microballons the best fairing compound for that job? After I finish the recore on the deck I will need to fair that out also. I have the same question as the one just asked for the hull surface in regards to the best fairing compound.

I have spent time reading what is available on the Alexseal website. Please tell me if my understanding is correct or flawed.

First after the fairing is complete I should use the Super build 302 primer. Allow that to dry completely and block sand everything.
Next I should use the finish primer 442 and allow that to dry until it gets to the recoat window (12 to 24 hrs) and then follow with 3 coats of 501 topcoat.

[Tim]

I use shop-made epoxy/microballoons/cabosil mix for most of the fairing. Microballoons will leave pinholes when sanded, so once you have all the fairing and filling complete, to prepare for primer you should apply a fine fairing compound as needed (such as the excellent one manufactured by Alexseal), which will fill these pinholes nicely. Do your best at this stage, but there's another opportunity to improve the final surface following high-build.

You'll likely find additional pinholes revealed by the high-build primer--even when you think you got them all--so between high-build and finish primers use more of the fine filler to take care of these. Consider the high-build as part of your surfacing system, rather than a primer, because it's really a sprayable surfacer, not a primer.

You can use the Alexseal filler for more of the fairing, if you prefer, but it's substantially more expensive than the typical microballoon/epoxy mix. I only use the Alexseal for final surfacing.

I always sand the 442 finish primer before applying topcoat. Spraying this primer leaves a very flat, smooth surface, but it's smoother after sanding.

[Commander-147]

Thanks Tim that helps a lot. I appreciate your response.

If I may ask one more question, what kind of ratio do you use for the microballons to cabsil for the fairing compound?

[Tim]

Ratio of microballons to cabosil is 27.3 : 6.42

Just kidding. I have no idea; it's completely by eye and feel. Some cabosil is required to make a microballoons mixture properly thixotropic, however.

[Commander-147]

Well that gave me a chuckle.

Wish I had you calculated eye and feel.... guess that will come with time and screwups.

So as a starting point I'm guessing 3 or 4 parts of microballons to 1 part of cabosil would be a good place to start. I'll just have to make my mistakes so I can learn.

Thanks again Tim

[Hirilondë]

So as a starting point I'm guessing 3 or 4 parts of microballons to 1 part of cabosil would be a good place to start. I'll just have to make my mistakes so I can learn.

Parts by volume? Or parts by weight? :)

That is probably a good place to start. No mixture in this range will ruin your boat. If the final result cures harder than you would like start cutting down on the cabosil.

[Commander-147]

Thanks Dave

You mean you can't read my mind about what kind of parts I'm talking about???????

In my mind I was visualizing parts by volume. It's the way I tend to do my measuring.

I appreciate your input.

[Tim]

...that will come with time...

Yes.

The idea is that in a fairing mix, the cabosil is just to bring the material to its final desired consistency. Microballoons alone will not ever thicken a mix properly, but once you've mixed in what you think is the right amount, adding a small amount of cabosil will finish it off and make the mix as thick as you want it.

4:1 or so is reasonable, if you must put numbers on it, but don't be a slave to any sort of set ratio when mixing fillers. It takes what it takes. But the cabosil is not a large part of a fairing compound mix--just a small, critical one.

[Commander-147]

Thanks again Tim

With the guidlines you and Dave have offered I'm sure I will figure it out after mixing using and sanding a few batches. I really appreciate the responses.

[Chris Campbell]

If only I had read this post before mixing my first batch of fairing compound. I used only micro-balloons, no cabosil, and had it drip off of the rounded cabin top in small rivers. I can clean it up, but it would have been nice to not need to!

I'll know better next time...

Thanks!