Seal hull with epoxy before fiberglass?

shawnwaite · Post by **shawnwaite** » Mon Aug 23, 2004 10:27 am

I searched and didn't come up with much.. I'm sure its been covered several times in here.. so if maybe someone could send me to a link?

Should I seal the ext hull with epoxy before I lay my 'glass down?? I've read somewhere that the cedar may "gas" and leave bubbles if it's not done? Is that a start temp -> end temp thing?

And is it thinned any..?? I have concerns on weight.. so...

Thanks....

Sorry for redundant questions.

S.

Glen Smith · Post by **Glen Smith** » Mon Aug 23, 2004 1:08 pm

Some builders don't use a precoat and some do. I didn't precoat the four first boats I built and the hulls look a bit blotchy in some places. That is probably epoxy starved cloth! The last three boats were precoated and there is no blotchiness at all. I don't feel I added any extra weight because the wood will absorb a certain amount of epoxy whether the epoxy is applied to glass cloth or bare wood. It is, however, an extra step and means taking a bit more time to build the boat.

WarpedBoard · Post by **WarpedBoard** » Mon Aug 23, 2004 5:11 pm

The previous reply is correct. Especially in softer woods like the cedar, you will find that one thin coat of epoxy will give you the best overall final finish. That cedar will definitely starve the glass in areas where the epoxy is not applied as thickly and you won't discover this until it's too late. Better to do that pre-coat one day and follow with glassing the next. These 2 steps can be done as close as 8 hours apart (right conditions) allowing for a late afternoon application followed by glassing the next morning. Variables can change this some, but you will be happy with the ultimate results.

Steve Lansdowne · Post by **Steve Lansdowne** » Mon Aug 23, 2004 8:13 pm

I used Raka 5 oz. cloth which had some difficulty wetting out, and that fact, coupled with the fact that I did not precoat and used a Raka clear epoxy which set up relatively quickly given the temperature, gave a less than stellar finish. It works, but up close you can see various small spots where the cloth did not saturate. While Ted feels you don't need to pre-coat, that is with the West System products he uses. I think it is safer to precoat, as the total amount of epoxy you'll use shouldn't be much more than if you con't precoat, it is just that there is one more step involved. In the long run, you may be glad you did precoat.

John Michne · Post by **John Michne** » Tue Aug 24, 2004 5:10 am

Hi Shawn -

I found precoating to be a waste of time and epoxy, with nothing significant to be gained. For a discussion on fiberglassing in general and precoating in particular, see the article on my web site, http://www.michneboat.com/Fiberglassing%20-%20101.htm.

John

shawnwaite · Post by **shawnwaite** » Tue Aug 24, 2004 11:00 am

Thanks again everyone!

Most appreciated... that was a long read John ... but educational I must say. I can't get help until FRI for the wet out so I have time to do a pre-coat if I decide.. but I'm leaning towards not. (Let's hope your right)

BTW, I am using West System 105/207.

S.

KenC · Post by **KenC** » Sun Aug 29, 2004 1:46 pm

Don't assume that a seal-coat will prevent offgassing during glass application. It ain't necessarily so.

If you do choose to do a seal coat, and you are working in uncontrolled temperatures (ie. an unheated garage), you should still wait until late afternoon or evening, when temperatures are dropping, to wet out your glass.

I glassed the next morning after sealing the prior evening, and ended up with a few small bubbles under the glass -- presumably due to offgassing.