Small caravan box by Tom

[dales133]

Looking good Tom.
Good idea with the Teflon too

[ipy]

Do you know such product as a lasure? It is something like a varnish but as far as I can understand it is better as it protects wood from water and allows it to breathe and seems to be more durable than varnish. Producer claims it gives full protection up to 8 years.

I bought lasure and plan to cover my caravan box with it. But on Polish caravan forum people say it won`t be a good solution as plywood will absorb water and increase its volume even though covered with lasure. Also they say lasure will break on large pieces of plywood and fall off. Instead, they suggest me to laminate the whole thing, which seems to require a lot of work, time and skills I do not have.

What is your opinion about lasure?

[Sheddie]

Hi Tom, as I said on my previous post you need something that will be absorbed well into the ply with a good build up to seal the ply and keep the water out. I see that they recommend at least 3 coats, you would also want to do a regular re-coat as needed to maintain the surface. The other option would be paint, or paint and canvas as a lot of people are using on this site, again getting good saturation into the ply. My preferred method would be fibreglass cloth and epoxy resin as we used on our ply boat about 30 years ago.

[ipy]

What if I apply 3 coats of lasure and then cover the whole thing with a paint? Would I need to repaint it every year?

Can I use fibreglass cloth with paint after I applied lasure?

[Sheddie]

If you want to fibreglass it you need to use an epoxy resin to saturate the cloth directly on to the ply. Basically you lay the cloth over the ply and apply the resin with a brush or roller to soak through the cloth and in to the ply. Use a fairly light weight fibreglass cloth. The finer you go the less work to prepare before painting (also requires less resin). After it has set you can then sand it and paint or varnish over that.
This would give you the best life expectancy (I would probably recommend using paint). You wouldn't do this over lasure or paint.
If you use the lasure direct on to the ply, you could paint over it, but you would need to check with your paint supplier what paint is compatible and depending what you use you could get a good life span out of it. Or other wise exchange the lasure for a good primer/undercoat followed with top coat.
The canvas and paint method, could be ok, but you would need to here from some of the others on site for application methods.

[dales133]

I'd go paint and canvas if I was you.
I have read somewhere recently people using polyurethane and fiberglass cloth with good results to cut costs but you might as well just use bedsheets and paint if your going to use that.
I think the product you've got is similar to the bondall product I've sealed all my frames with. If it is its designed to be top coated with something if exposed to the elements.

[Sheddie]

Hi Tom, I definitely wouldn't recommend using polyurethane with fibreglass cloth. You need to use fiberglass cloth with an epoxy resin or polyester resin (two pack) this will give you the most durable robust finish and a better material for finishing to a smooth finish. It is the same product that gets used for boat building. As I said before I built my boat 30 years ago, ply construction fibre glassed over that, then painted with reaction lacquer. Paint has not been done since then. You may spend a bit more now, but it will save you big bucks in the long run.

[ipy]

I returned lasure to the shop and visited another shop with laminates. The crew recommended me using epoxy resin as well as a fibreglass cloth. But, they only have a heavy (thick) cloth (300 grams per a square metre).

Can I use only one layer of a fibreglass cloth, supposing it is strong?

Should I laminate the whole thing or just a roof and front and rear walls? Side walls are still covered with paint (which is very difficult to remove) and looks like nothing bad happened to it during the rain a week ago. What do you think?

Today I installed the last part of the roof. Filled all gaps- tomorrow, after it is sanded I will apply filler last time.

I also built a lower part of the capsule. Used an OSB framed with impregnated wood from my first version. Only sides are new, made from a plywood.

[Sheddie]

One layer is the way to do it, over the top, front and back. It will depend on what sort of paint you have used on the sides if you would be able to glass the sides. You would need to check with the guys in the shop, they should be able to tell you. It would be better if you could do the sides, but if you can't it shouldn't be a problem as long as you keep the paint in good condition. If you can, it will need a good sanding to scuff up the surface. It would be good if they could get you some finer cloth as you would use a lot less resin and there would be less finishing work.

[ipy]

Friends, I am confused about finishing my caravan box. I can start doing it right now but do not know what option to choose.

If I decide to remove paint from side walls in order to laminate them it would take me very long time as the paint is really strong and tough and when I was trimming roof panels to the side walls edges I realized it is nearly impossible to clean walls from paint. Paint seems to be waterproof as small painted pieces I left on rain are still ok.

If I laminate whole thing without removing paint then laminate can come off from side walls.

If I decide to laminate the roof only I am afraid that place where laminate finishes and painted wall begins will be a point where water can penetrate.

And I do not know how to laminate properly and if I do something wrong there is no undo option.

If i decide not to laminate but paint the whole thing I am not sure what to do. My idea is as following:

First, I think I could use the same paint as on side walls- apply at least 3 layers on the roof plus one more layer on side walls.

Then, I would like to paint gray areas as I designed.

Finally, I would like to cover the whole thing with a varnish so to ensure the whole surface is waterproof.

What do you think about non- laminate option? Is acrylic paint + a varnish a good solution? What kind of a varnish should I apply on an acrylic paint?

[Sheddie]

What sort of paint have you got on the sides? If you are happy with that why not use that on the top and front and back. What is the varnish that you are referring to and why would you put that over the paint?

[ipy]

I have an acrylic paint called Bondex Acrylic Enamel. This is the paint that the capsule was covered with when it got damaged during rain. But, I think water went to the wood through edges and rears of panels that were not painted.

People on Polish caravaning forum say that because of shakes and slight changes of plywood dimensions caused by temperature changes sooner or later filler that is applied on edges and connections will get loose and fall off. Thus allowing water to go into plywood.

Should I expect something like that?

Varnish is a kind of a paint but it is designed for covering wood and because of being trasparent allows to see its structure. It has a similar properties as paint but seems to be more waterproof. I can buy a special varnish to be used on yacht decks and it gives absolute water protection. Plus, it gives stengnth and durability to the surface and in case that I need to re-paint the capsule every couple of years I would not have to paint gray- white pattern again but to cover whole thing with a varnish.

[KCStudly]

People on Polish caravaning forum say that because of shakes and slight changes of plywood dimensions caused by temperature changes sooner or later filler that is applied on edges and connections will get loose and fall off. Thus allowing water to go into plywood. Should I expect something like that?

Yes. As a minimum, you should reinforce the corners (glue and canvas, epoxy and fiberglass tape, or sealed trim after paint).

I would avoid mixing different paint/varnish products that are not specifically recommended as compatible by the maker, or well tested by a larger community.

[ipy]

I made the final decision. I will use the same paint that there is on side walls. But, I will reinforce the whole caravan box with a canvas. Not sure if I should use 1 or 2 layers of canvas. Or first apply strips of canvas around corners and then on the whole thing. Can you tell me?

Should I apply canvas like this: cover a wall with paint, stick a canvas on it and then immediately cover this canvas with more paint?

What would happen, if I apply let us say 4 coats of the paint in total while producer says 2 is ok? Would it break?

[KCStudly]

People have had success using paint to glue the canvas down, but some say that PVA glue (TB2 or equal) is better to work with.

I plan to do the sides first, overlapping top and bottom by a few inches, then cover the top and overlap the sides by a few inches giving double reinforcement for the corners.

The best results appear to come from gluing the canvas down first and letting it dry completely before coating the outer surface with paint. People report that they get less bubbling this way.

Some techniques that have been developed and used by several people include using white glue (not water resistant), either straight or slightly watered down, along lines that you intend to cut. The glue binds the threads together and prevents fraying of the fibers along the cut line. Then when you go to glue the edges down the white glue dissolves in the moisture of the PVA glue and allows the fabric to lay down and conform to corners (whereas a water resistant glue would remain stiff).

Another reason to let the canvas set up first before top coating is that if you have any areas that didn't stick you can us a wet rag as a buffer and a clothes iron to reactivate the glue (provided that the problem wasn't due to a dry spot... you want to use plenty of glue).

Again, if in doubt, do a test sample.

Check out the foamie section of tnttt. There are lots of builds there that use canvas outer skin.