Polyester Resin over plywood on deck extension

For you guys who have done deck extensions and coated them using poly resin instead of epoxy resin. Did you do anything special to prep the plywood (rough it up, wet with acetone, etc). I did a little experiment before coating my actual deck extension and had poor results. I am using pre sanded cabinet grade(only because it was on sale for $27 a sheet) 3/4" plywood. My test resulted in an easy delamination of the cured resin from the plywood test peice.

I suspect four possible causes. One the temps were pretty low ~55 degrees, two I did not rough up the plywood first (it is not as smooth as a baby's butt but it is pretty smooth) three I believe the resin needs to be thinned with acetone to get better wood penatration and four maybe I should have given a longer cure before I tried to delaminate it from the plywood. I gave it a good 3-4 hours and it seamed to be pretty well cured. BTW for this test I first applied a wetting layer of poly resin, then let it get pretty tacky before adding a layer of 1.5oz CSM and wetting that out very well, then let if cure for 3-4 hours.

Unfortunately it was pretty easy to pull apart.... uisng a putty knife I could remove pretty good size chunks of glass.


Modified by rwainwright at 10:06 AM 1/31/2012

Ideally air temps should be around 65 - 75 for laminating resins to fully cure, the closer to 70 the better.

Rough up the wood, not only does it give the resin something more ot bite , it will also remove any contaminants that may be on the wood from the mill, shipping, etc.

The first few coats of resin should be thinned with acetone about 15 % to let it absorb better into the wood pores.
Make sure you are using laminating resin and not finishing resin

Thanks Basscat, but just for peace of mind, I think I may go with epoxy resin.

My original thought was "its just deck extension" so I wanted to see how the 3M Poly resin from Lowes would work, but I dont want to have rebuilt it in a couple of years, so I think I will go ahead and order the epoxy resin from uscomposites.

The challenge I have now is temprature.... I am working in a small un-insulated shop so I cannot fit the entire boat in to shut the doors so it will be a challenge to maintain temps above 70. Daytime is ok but at nights it will get well below 45-50 degrees. I was thinking of ordering the fast-cure 4:1 Epoxy. Any advice on that?

Polyester resin done right will last a long time.

Epoxy is a little better, but also more $$$$. Epoxy resin is more gluelike that polyester.
The 3:1 epoxy should work in temps down to the mid 50's, the 4:1 down to the mid 40's.

The epoxy will be thicker at these temps and take longer to absorb into the mat. It also has to be measured a lot more accurate than the polyester resin when mixing.

Assuming it will be covered with carpet to protect the resin as the resin itself has no UV protection and if not covered will degrade from the sun in a few years.

Dang man, now you have me re-thinkng going with poly resin. It "is" just a casting deck extension on a trailered boat and it will be covered with carpet. So I may go the poly resin route to keep cost down. You think one layer of 1.5oz CSM on the top surface is enough.....its 3/4 plywood.

1 layer should be fine, 2 layers will be about 1/10" thick glass.

if you go with poly resin order 435 from uscomposites.com the stuff that lowes sells sucks

Thanks for the advise sandbarDan but If I were going to go to the trouble and expense of ordering anything from uscomposites and paying shipping costs then I would have used epoxy all along...............the whole reason for using poly to start with is becasue I can buy it locally

I built a deck extension for my '95 PII a couple of years ago. I used the poly from Lowes and it worked fine. I completely coated my plywood with resin and let it cure for 24hrs, then put a layer of cloth/resin on both sides and let that cure 24hrs before gluing on the carpet. It has held up fine so far.
http://www.bbcboards.net/zerothread?id=372891

The 3M from lowes is ok. Its just naturally thick and I think I know what happened is that your wet down with that resin was too thick and just sat there, didnt soak into the wood. Maybe try thinning it out a bit. Also, you may have gotten a bad gallon in that the shelf life of poly is supposed to be not that long.

rocketsauce I think you are dead on about it being too think to saok into the wood. because after some advice from BASSCAT7 I thinned another batch with Acetone (and really roughed up the surfurce of the plywood)and did another test and it does not delaminate like the first test