PDA

View Full Version : crracking varnish on Lyman deck seams



stephen page
10-29-2016, 04:24 PM
I have a 25' Lyman, which has quarter sawn 1/2" mahogany planking laid over the original deck. The seams between the planks ( 6 - 9" wide) , have been routed out with a quarter inch bit, and filled with 1/4" foam backer bead overlain by 1/4" of white 5200. The decks were then stripped and coated with 8 coats of epifanes. Over the course of 4 years or so, the varnish has cracked along most of the seams and/or lifted adjacent to them. It appears that the inevitable expansion of the wood in summer sun has caused the coating failures. Moreover, the varnish seems to adhere more strongly to the 5200 than to the wood. Any suggestions ?

Jay Greer
10-29-2016, 04:29 PM
Don"t varnish the seams.
Jay

Bob Cleek
10-29-2016, 05:11 PM
Jay's right. Don't varnish the seams. Any varnish will crack if given half the chance. What you've got there is a varnished "rubber band" and when it moves, the varnish cracks. Bright finished "decks" on power boats (not to be confused by decks which are regularly walked on, and which should never be varnished for safety reasons) are usually stopped with white putty that dries relatively hard, along the lines of glazier's putty. (Traditionally, white lead paste thickened with whiting.) The 5200 was a poor choice for the reason you've encountered, but good luck ever trying to get it out short of ripping up the deck. (A very sharp knife used to cut it from the sides of the seam might allow pulling it out if the foam beneath it lets go easily, but figure that for a fairly tedious job.) You'll have to sand down to the point where the varnish isn't on the 5200 anymore, mask the 5200, and then varnish. (That's going to be tedious, too, but "you gotta' dance with the girl your brung" now. Expect your varnish to start to lift fairly quickly along the edges. Keeping a good eye on it and refinishing ASAP when anything starts letting go will prolong the life of the brightwork. Trust that many in here feel your pain.

carioca1232001
10-29-2016, 06:50 PM
I have a 25' Lyman, which has quarter sawn 1/2" mahogany planking laid over the original deck. The seams between the planks ( 6 - 9" wide) , have been routed out with a quarter inch bit, and filled with 1/4" foam backer bead overlain by 1/4" of white 5200.

Did you consider filling the 1/4" seam that you routed out with a epoxi-sealed white wood, like maple or some such,+ Sikaflex instead of the 1/4" foam backer bead ?

I recall a time that Sika actually marketed a non-stick, thin plastic-film for laying at the bottom of seams, over which one could overlay with whatever....... sealed wood + Sikaflex, or just the latter sealant/adhesive.

A more favourable outcome could have ensued with the 1/4 " seam taken up with a sealed wood strip - whatever colour - matching mahogany´s swelling carachteristics ?

This is something for our WBF experts to comment on.



The decks were then stripped and coated with 8 coats of epifanes. Over the course of 4 years or so, the varnish has cracked along most of the seams and/or lifted adjacent to them. It appears that the inevitable expansion of the wood in summer sun has caused the coating failures. Moreover, the varnish seems to adhere more strongly to the 5200 than to the wood. Any suggestions ?

It may come across that I am more interested in this subject than most forumites, but I must admit that I have a vested interest, as my bow deck has been stricken for the second time with a similar malady, compounded with leaks into the bow cabin.

I will not bore you with endless details....but a wood carpenter of old at my Yacht Club commented a couple of weeks ago:

'The fasteners holding down your 10 cm wide, 17 mm thick mahogany planks over the bow arches / frames, are grossly inadequate....just take note of the play as I walk over this deck, and I weigh no more than 65 kilos....we should take the lot out and refasten with nş 8 screws, some 1 " or 1 1/4 " long....'

We accomplished the refastening last week, to include bunging over with some 250 mahogany wooden-plugs.....it feels as firm as a rock, although 3 to 4 slots of around 1.5 mm width and 75 cm length, where the planks curve over to the bow´s dictates as one approcahes the covering boards (side-decks) ......seem to have withstood our refastening efforts

The latter we hope to get rid off by infusing said slots with thin epoxy, tainted with mahogany stain + etc. etc...

pcford
10-30-2016, 04:20 PM
I have a 25' Lyman, which has quarter sawn 1/2" mahogany planking laid over the original deck. The seams between the planks ( 6 - 9" wide) , have been routed out with a quarter inch bit, and filled with 1/4" foam backer bead overlain by 1/4" of white 5200. The decks were then stripped and coated with 8 coats of epifanes. Over the course of 4 years or so, the varnish has cracked along most of the seams and/or lifted adjacent to them. It appears that the inevitable expansion of the wood in summer sun has caused the coating failures. Moreover, the varnish seems to adhere more strongly to the 5200 than to the wood. Any suggestions ?

I really cannot understand this original post and since the original poster did not favor us with an image, we will have to proceed with what he has written here. He writes he has "quarter sawn 1/2" mahogany planking laid over the original deck. The seams between the planks ( 6 - 9" wide) , have been routed out with a quarter inch bit..." Deck planks 6 to 9 inches wide are going to work too much. The seams will open and close.
This is the way decks are done on speedboats...and a 25ft. Lyman is closer to a speedboat than what other writers here have prescribed. The deck planks are roughly 6" wide and 3/8" thick. The planks are divided into three by running a saw kerf down the plank at 1/3 and 2/3rds of width. Thus, every third seam is a true seam; the other two are fake. After several coats of varnish have been applied, the seam compound is inserted. The fake seams use glaziers's putty with a tablespoon of varnish added to a quart. The true seams are caulked with Sika 292. (or that is what I used...there may be another product these days.) 5200 is not elastic enough for this use. I would guess that the 5200 made a horrible mess as well. After the seams are caulked, the next step is to varnish the whole deck. After you are satisfied with the way the varnish looks, then you paint the seams white with an artist's brush. So, the seams are varnished and then painted.

The requirements for a speedboat deck are quite different than the normal boat: THEY ARE NOT MEANT FOR STROLLING ABOUT! Walking on them will possibly crack them. I hope this is useful.

Finally, David G referred to Dannenberg's runabout restoration book and his advocacy of 5200 between layers of bottom planking. I prefer traditional bottoms...it is not at all uncommon to see a 60 year old Chris with the original bottom. Thus, most owners will not outlive a new traditional bottom. Dannenberg's book is in general fine and "5200 bottoms" are a respected way of doing bottoms. I just don't care for goo bottoms.