Help! Bondo is bubbling my painted walls

[frankiekayak]

Hello all,

So...I went the cheaper route when skinning my camper and I am paying the price. I am watching the painted wood surface deteriorate as we get hit hard with rain all day and night today. I used porch/patio paint over plywood and it's holding up nicely on all areas where the paint is directly attached to the wood. However, I made the mistake of using bondo on all of the recessed screw heads as the paint is bubbling away aggressively in just this particular day of rain.

To remedy this mistake, I am wondering if there is a special primer I can put on the bondo to repaint over if I sand off the paint on the bondo areas. Any thoughts?

One Idea I had was to sand down all of the the walls completely. Then spray paint some primer on the bondo, and paint the walls with bed liner paint this time around.

Any thoughts or recommendations? I wish I could afford aluminum sheets but it's too expensive for me (around $1K in just the sheets for a 13'x6.5' camper). PMF would have been best in hind sight but I think it's too late for that.
I was even thinking about using thin .06" 4x8 sheets of FRP from Home Depot and gluing it over the surface but I think that will break down fast by the UV rays if I've researched that properly.

I attached some photos to show the camper if it's helpful. It's still raining too hard this evening to photograph the bubbling that has occurred as of today. I'll take some shots once things clear up.

I look forward to any advice from you experienced owners.

Cheers,
Frank

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[MickinOz]

Bondo is polyester automotive body filler, isn't it? Over here we'd call it bog.
If it is, then you'd have to think an automotive grey primer in a rattle can would stick to sanded Bondo?

[Pmullen503]

If you are going to sand the paint enough to reprime the Bondo areas, you could cover with canvas.

This would be a good time to address any other areas that may cause problems in the future. Adding drains or drip edges, really inspecting doors and window mounting for leaks

Nice trailer!

[DrewsBrews]

Unfortunately Just paint or bedliner doesn't seem to be up to task of covering plywood outdoors. It doesnt seem to hold up. The surface of the plywood shrinks/splits a bit from humidity/temp changes, which splits the coating.

I see plenty of people doing it, but a year later the coating is typically already compromised. I guess it works if you are willing to repaint every year.

[swoody126]

POLYESTER is not designed/formulated to bond with wood

some get away with using the stuff butt many more don't

the solution is to eliminate it from the equation

how you achieve this is the $64,000 question

it usually involves manual labor(lots of it) to chip n scrape the stuff away

as for the plywood issue ...

that stuff is created by slicing a thin layer off the log as it spins in a huge lathe

once free of the log the thin layer is forced flat which it doesn't like and several layers are stacked n glued together to create the laminate we know as plywood

plywood and moisture are not friends

as moisture eeks it's way thru common coatings(paint n bed liner etc) the wood absorbs it and starts swelling thus breaking the fibers away from each other ... this is called CHECKING

PMF(canvas attached w/ waterPROOF glue) is one of the least expensive ways to prevent or at least reduce the occurance of these issues

if one chooses to use plywood for the exterior of his/her project the most successful way to prevent checking and bubbling is to apply a layer of glass cloth set in epoxy over the entire outside surface of the project

choices always have to be made

frankiekayak, good luck with eliminating the bondo

sw

[John61CT]

Why people use plastic and aluminum skins.

Canvas PMF used special primer discontinued now, hasn't been replaced yet.

There are crazy strong coatings used for metal dock pilings, bridges etc but cost the earth.

Want to try this out one day, polyurethane+aluminum

google Aluthane

datasheet https://www.satelliteguys.us/xen/attach ... -pdf.40647

[noseoil]

Sand it down well & use Kilz on the bad spots. Not sure, but this may be what it takes to prime those areas. I would check it first with a sample, but otherwise, it might be time to look into a better skin material (PMF or aluminum).

[saywhatthat]

the wood expanded with the Bondo did not. What grit of sand paper did you use when sanding body filler? if to fine no bite on the filler .house paint needs more bite than car paint. Because of the thickness of the material

[Squigie]

Sand it all back to bare wood and encapsulate with CPES.
It will never be stable without encapsulation.

[saltydawg]

My reply, there are many.

Bond absorbs water, and holds it, it will dry out if open to the air. You can seal it with epoxy once its cured and dry.

You need to sand the paint off the bondo, put it in a dry space for while. Even better is have a heater blowing warm air on it for 2 days after removing the paint. Then seal with epoxy, and if you want repaint or do another finish.

I like fiberglass.

[JasenC]

As has been stated bondo isn't designed for wood. My one an only filler for wood for 20 year as been Minwax high performance wood filler in the can, it's a two part filler/wood bondo.
As a residential carpenter and finish carpenter I've have used gallons of this over the years, I always have a can of it with me.

It's been harder to find around here, HD stopped carrying it and its hit or miss at Lowes. Sherwin Williams stocks it as well as Rockler woodworking if you have one in town.

[MickinOz]

If frankie used automotive filler, then he he's stuck with what he's got.
But, and I hope this is useful for others, Bondo is a brand. According to their website there are all sorts of Bondo fillers.
The automotive one is for car bodies, but they also have one specifically for wood.
We don't seem to have Bondo over here, but we do have all sorts of polyester fillers.
There is your basic auto body filler which is pretty much polyester resin thickened with chalk or something, then there are the body fillers that have fibreglass or even steel reinforcing fibres in them.

One that comes to mind is a product we have over here called Turbo Builder's Bog.
It is polyester based, like fibreglassing resins and body filler.
I've used all three products and I can attest that the Builder's Bog, marketed specifically as a wood filler, is way different to auto body filler.
If I had to to make a guess based on the texture of the uncured product, I'd say it is polyester resin made into a putty by mixing with saw dust, possibly with a healthy dose of acetone.
Old trick from back in the days when every man and his dog was extending the life of his timber boat by cladding the hull with that new-fangled fibreglass - add acetone to laminating resin to thin it and make the resin penetrate the timber. (Yes, I'm old enough to remember when glassing plywood boats was a thriving industry.)
Builder's bog is weird stuff, definitely seems able to move with the substrate. I've never had any problems with house paint letting go. And it stays stuck to the timber you put it on even if it s polyester.

[MickinOz]

Had a look at the datasheet for Minwax Wood Filler and the Wood hardener too.
The Wood Filler is around 13% styrene.
The wood hardener is 50% acetone.
I can't find out for sue, but dollars to donuts its a polyester system.