How to prep cured epoxy for next layer?

I know this is a question that I should know the answer to, but I just want to make sure considering the price of my WEST System epoxy. I am currently replacing my transom from the inside of the boat. I have added a layer of 1708 to the inside of the outer skin. My WEST System book says that the amine blush can be removed with soap and water. Other posts say to use acetone. I understand that the glass needs to be sanded to get a "tooth" for the epoxy to key into. The 1708 is a pretty heavy weave, and I obviously can't sand all of the low spots in the weave? What do I need to do? My next step is to install the first piece of 3/4" marine ply using thickened epoxy to glue it to the transom. I want to ensure a good bond

Thanks
Dan

 

Yes! Clean off the amine with a stiff plastic brush and and water. Personally, I don't use soap, just to avoid any contamination. Then pick up with a wet vac or rags.

With the heavy mat you can use a new SS wire brush and then clean it with MEK afterwards. If you're in a confined space use a reperator or HEAVY ventalation for the MEK use. The problem with acetone is it dries too fast.

The next layer of epoxy will bond just fine. If you have a lot of voids you might want to consider a filler to make a paste rather then just a thick liquid that may only contact the high spots.

enjoy..................................._/)

 

Will the bond be strong by simply cleaning with water and MEK, or do I still have to use the SS wire brush to abrade the surface? Thanks for the info.

 

I was also wondering how fair the surface of the 1708 needs to be before installing the first layer of ply?

 

I would definitely scratch the surface very good with the wire brush. I've seen epoxy lose its bond when applied to a smooth surface- a little too much strain or shear and the whole thing pops loose.

I just finished reinforcing my transom - I put six layers of 3/8 marine ply with a layer of 1.5 oz mat between. I used regular epoxy (can't remember what they call it, just the regular thin stuff for layups) but rolled it on plenty thick. I have a curved transom (radius = 24') that I had to put screws about every 6" to suck it down tight to the layer beneath.

 

Also, you want to coat the plywood first with some resin so that it soaks it up and doesn't create a dry spot which won't bond.

 

Yeah! Still use the wire brush, a big one, not the tooth brush size. After wire brushing, then use the MEK to clean off the gray dust. The wires will get down into the lower areas and create a texture for bonding.

If you use a filler to make a paste, that will fill the voids in the 1708 and do a 100% bond to the ply. Kind of like laying tile on a floor.

As for the ply if you give it a thinned out coat of epoxy first it soaks right into the wood and it will tear it apart before it ever comes loose.

To thin epoxy, use about 5-10% MEK so it's more like water then surup. Not too thin though, it needs to leave a little bit of a finish on the ply. Once it's cured sand it with 80 grit to break the sheen and the little wood neddles.

Your two surfaces will never come apart after that......................_/)

 

Hey Dan,

Follow west system's advice on removing the amine blush. Before you install your first piece of core material you should put a layer 11/2 oz of chopped strand mat between the 1708 and the core material. This will ensure a good bond between the core and the 1708 and also level thing out a bit. You can put the layer of mat on, wait until it is not to tacky and then install your core member with a resin thickened with milled fibers and cabosil to the consitency of vaseline. If you have transom clamps this can all be done at once, if you don't the other method will work fine and you will not have to clean any amine blush and you will have a chemical bond. I know west is a good product but I use a non blushing type epoxy like Mas epoxy.If you are going to install another layer of 1708 on this core piece after it is installed you should again put a layer of mat between them. I personally feel that you could laminate both pieces of core material on a table with 11/2oz mat between them and then installed the whole 1 1/2 thick transom piece in one shot. A transom gains its strength from the outer and innner skin thickness sort of like an I beam. If your outer and inner skins are both around 5/16-3/8thick you should be fine. Good luck Dan.

 

Dan,
You should prime your ply with unthickened resin too.

 

I appreciate all of the replies. I am now feeling pretty confident with the process

Dan