Fairing question using a notched trowel?

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piperdown
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Fairing question using a notched trowel?

Post by piperdown » Mon Oct 01, 2018 8:08 pm

Have read a few posts about using a notched trowel to put on fairing compound. Sand the highs down smooth and the low spots will still have a bit of a "V" left, so you know they are low spots. So some parts should be smooth and others (the lows) will have the grooves left.

A couple questions came to mind.

Which coat? First, second, third? I guess I was thinking a very thin first coat, just to fill the weave. Then use a notched trowel on the second coat, sand, then hit the low spots on their own for the 3rd? (Or 4th, 5th, 6th, 7th and 8th, knowing my skills 8O )

If you're using epoxy fairing compound isn't the sanding needed for the next layer mechanical bond? What I'm getting at is if you have low spots do you leave the grooves in the low spot and just cover that with the next layer? Are the grooves rough enough for the next mechanical bond? Or do you mark that area (pencil), sand into the low spots to knock those grooves down, then just hit those areas with more compound? :help:

Lastly, if I'm using the marinepoxy from BBC for the first couple of coats do I need to have it fully cured for 7 days to then switch to Quikfair? Thought I saw something about when switching brands to let it cure fully before using another brand.


Eric (aka, piperdown)

"Give an Irishman lager for a month and he's a dead man. An Irishman's stomach is lined with copper, and the beer corrodes it. But whiskey polishes the copper and is the saving of him." --> Mark Twain

fallguy1000
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Re: Fairing question using a notched trowel?

Post by fallguy1000 » Mon Oct 01, 2018 9:46 pm

piperdown wrote:
Mon Oct 01, 2018 8:08 pm
Have read a few posts about using a notched trowel to put on fairing compound. Sand the highs down smooth and the low spots will still have a bit of a "V" left, so you know they are low spots. So some parts should be smooth and others (the lows) will have the grooves left.

A couple questions came to mind.

Which coat? First, second, third? I guess I was thinking a very thin first coat, just to fill the weave. Then use a notched trowel on the second coat, sand, then hit the low spots on their own for the 3rd? (Or 4th, 5th, 6th, 7th and 8th, knowing my skills 8O )

If you're using epoxy fairing compound isn't the sanding needed for the next layer mechanical bond? What I'm getting at is if you have low spots do you leave the grooves in the low spot and just cover that with the next layer? Are the grooves rough enough for the next mechanical bond? Or do you mark that area (pencil), sand into the low spots to knock those grooves down, then just hit those areas with more compound? :help:

Lastly, if I'm using the marinepoxy from BBC for the first couple of coats do I need to have it fully cured for 7 days to then switch to Quikfair? Thought I saw something about when switching brands to let it cure fully before using another brand.
First, the notched trowel method is not always best. The best place to use it is where you know you have varied fill heights and you can easily determine the high areas after notched fills.

So, it is early coats.

But, if you are fair enough to weave fill; then the notched trowel is misplaced.

Look ahead at the job. If you have large areas with uneven fill heights; you use the notched trowel and sand with battens, but only those areas where things are bad.

You'll get the hang of it in a hurry.

No need to wait if it is epoxy. The faster you can sand without corns (uncured epoxy), the faster you can sand and reapply and even get some primary bonding.

Quikfair is really fast if you can keep ambient temps above 75F. Great product.
My boat build is here -------->

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TomW1
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Re: Fairing question using a notched trowel?

Post by TomW1 » Tue Oct 02, 2018 1:35 am

Eric no need for a toothed trowel on your little GF16. I like using a drywall hod with a 10" spreader. You will build up coats as you go filling in low spots and going over high spots. Put on two layers like this sanding between layer one and two lightly. You should be able to see or feel the low spots for the second layer. After the second layer do a sanding and a third layer and get it as smooth as you can. Now before you sand do a scratch coat of paint, graphite or the special coating they sell for this purpose. It will give you a dotted surface. Once it dries in 15-20 minutes sand again and you will have only a few spots left to fill in.

Tom
Restored Mirror Dinghy, Bought OD18 built by CL, Westlawn School of Yacht Design courses. LT US Navy 1970-1978

piperdown
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Re: Fairing question using a notched trowel?

Post by piperdown » Tue Oct 02, 2018 7:30 am

Thanks FG and Tom, that makes sense.
I'll be getting the runners and splash rail on within the next week so fill coat and fairing are not that far off.
Making a long board too, probably a couple of sizes since they're cheap and easy to build.
Eric (aka, piperdown)

"Give an Irishman lager for a month and he's a dead man. An Irishman's stomach is lined with copper, and the beer corrodes it. But whiskey polishes the copper and is the saving of him." --> Mark Twain

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