View Full Version : How does CPES affect varnish?

04-08-2009, 07:52 PM
I have a couple of port holes that have a bit of cracking on their edges and black streaks from water intrusion radiates away from them for a distance. I was considering injecting CPES into the cracks to waterproof them and limit future damage but was wondering if that would affect the application of varnish.

Here's a pic of one.


Wooden Boat Fittings
04-09-2009, 03:37 AM
The CPES can only affect the varnish positively -- that is, it can give the varnish a better grip once you apply it. And of course the CPES will also seal the timber for you first. Whether you should try injecting it or just slathering it on with a brush is another question. (I'd settle for the second option myself.)

BUT you must make quite sure that there's no rot anywhere there before you do anything else. If there is any get rid of it all and make any necessary repairs before applying the CPES and varnish.

When you come to reinstall the scuttle make sure it's bedded properly all the way round with good bedding compound.


04-09-2009, 08:02 AM
CPES is a primer/sealer -- NOT a waterproof coating! For waterproof you need full-strength epoxy.

That said, in my limited experience it makes either a great sealer under varnish, or under epoxy with varnish over that. I'd sure use in in that location for the purposes stated...

Bob Cleek
04-09-2009, 08:34 PM
Ditto... but I'd sure try to bleach that wood with oxalic acid ("wood bleach" at the paint store) and/or sand what I could of the discoloration out of the wood. (The wood is likely perfectly sound and just waterstained, not rotten.) Whatever discoloration is there, when it's soaked with CPES, will pretty much be forever. Might as well get it looking like new before you put the finish coats on it.

Definitely, use CPES as a SEALER beneath varnish. Just apply it with a brush. (Natural bristle only... I use chip brushes and crimp the ferrules so bristles don't fall out. The solvents are liable to eat up a plastic bristle brush... and a foam brush will dissolve for sure!)

04-10-2009, 11:44 AM
Yeah I was figuring to use Oxalic on all of the wood once it's stripped bare. some of it is pretty gray....

Jay Greer
04-10-2009, 11:57 AM
Sorry guys. I never have used CPES as a sealer and never will. I can see no justifiable reason to use it under a clear finish. The only thing it will accomplish is to make the wood impossible to bleach should a stain develope under the sealed surface.

The time proven method of dealing with small checks in varnished wood is to strip, bleach, rinse well and then apply one thin coat of varnish that has been cut with turpentine followed by one full strength coat. Once the surface is dry, Dofinite Bedding Compound should be used as a filler for the cracks on light colored wood such as teak. Mahogony colored oil based seam compound can be used on Honduras colored woods. I find that an artist's pallet knife is a good tool to use for this. Excess compound can be wiped off with a bit of thinner on a rag. Once the compound has skinned over the varnish job can proceed as normal.
You might check to see if the port hole spigots are too tight a fit. This can cause cracking of the wood as the sides of the deck house expand and contract with changes in heat and humidity. In the case of dead lights the same is true if the glass is a tight fit.

04-10-2009, 12:42 PM
Maybe try working the surface down to bright wood, and see what it looks like? The picture appears to be showing us a some sun-bleached wood, some water stained wood, and it looks like some mottling of remaining varnish. You're going to have to go down through the sun-bleached stuff, and take off all the old varnish if the idea is to refinish.
I'd also get the varnish off the end-grain of the portlight cut-out, and inspect the end grain in way of those black-stained cracks. It may become apparent that the cracks are fairly deep, in which case you might want to put in a graving piece, or fill with goo, or something.

Jay Greer
04-10-2009, 06:21 PM
Often working the surface down to non sun bleached wood will take off too much material. This can often be found on boats that have not had fittings such as window frames removed during the process. Sometimes it can be seen that an alarming amount of wood has been removed. Some boats even end up with the shafts of drift bolts showing through their cabin sides. For this reason and in order to not allow UV to bleach the wood, I use filler stain on woods other than teak prior to applying varnish. Filler stains will not sun bleach as they are made of natural earth pigments and will retain their color indefinatly. Here, it is advisable to apply one coat of clear acrylic lacquer over the wood first in order to prevent the stain from soaking in too much and "muddying" the grain. Now no longer available at marine hardware stores; clear acrylic was once sold by Z-spar but, it is nothing more than clear automotive lacquer that has been cut with lacquer thinner in order to be nearly water like in consistancy. Unlike penetrating epoxy, the acrylic sealer can be disolved by paint remover should the wood need stripping in the future. One thin coat is all that is needed prior to applying stain.