fiberglass over foam?
 

I have a question about finishing foam floats. I recently built this uproar with these short floats made out of white Styrofoam and covered them with econocote. I have ply reinforcement where the float connects to the landing gear and I also glued in a plywood pad at the rear of the float right in front of the step where I thought would take the most abuse (red line in picture). I wanted to keep these floats as light as possible. I have had about 50 or so take off and landings so far on these floats and they have held up pretty well however after the last time I flew, I noticed that the monocote was worn at the step and the ply inside was getting waterlogged. I stripped off the monocote and was going to glass the floats. I still want to keep the floats as light as possible. The monocote has protected the edges of the floats quite well and I would like to avoid sheeting the foam before fiber glassing. The fiber glass I have on hand is 48g / m2 which if I did my math right is about 1.41 oz/ yd2. I did a test piece on some foam last night and it will not fold around a square corner without creating a bubble. I am afraid that if I just fiberglass the sides and the bottom all separately without overlap then the edges will be weak and susceptible to damage. I was thinking of rounding the top of the float edges so the fiberglass will bend the corners well but want to keep the bottom of the float edges sharp. Here was my thought for the bottoms. I was going to cut 1/8” square channels on the bottom float edges and glue in 1/8” square balsa sticks (sort of like ski edges), sand flush with the bottom and sides of the floats and then fiberglass the sides and bottom to the edge. I think the balsa edge will hold onto the fiberglass a little better than just bare foam and will also eliminate the extra weight of sheeting the whole bottom of the float with wood.

So after my long winded description, do you think this will work well and will just the fiberglass on the bottom without sheeting be durable enough? Are the 1/8” balsa edges necessary? Keep in mind, I will leave the short piece of 1/32” ply glued to the bottom rear of the float like it is now. Is there any alternative suggestions anybody has?
Thank you,
John

RE: fiberglass over foam?
 

You will need to use Epoxy with your cloth because fiberglass resin will melt Styrofoam . Other than that you should be okay...I Glass floats all the time.. I usually use about 3/4 oz on the top and 1.5 oz on the bottom... I make the bottom heavier because thats where the wear happens .. It is important to keep the bottom edges sharp so don't round them off..

RE: fiberglass over foam?
 

Want to save a lot of time and money do what i do. Sheet the bottom with 1/32 ply the give them 2 coats of liquid sheeting.
http://www.wowplanes.com/product_inf...c2dd85fe6b5f93

Ken

RE: fiberglass over foam?
 

There are two kinds of foam and I have used both.

The white foam that I have seen is "beaded". It consists of little beads of white foam all tightly packed together like the seeds in a pomegranite. It is very light, but is available in a range of densities.I cut with a hot wire.The problem with this foam is that if water gets in it can work its way throughout the block of foam by filling all the gaps between the beads. It is essential to keep such floats watertight. For this reason I now always sheet them with thin obeche veneer and then cover with glasscloth/epoxy. I once tried glass/epoxy straight onto the foam but the surface finish was unsatisfactory when painted, rough and uneven.

The other kind of foam is a continuous block of foam, full of bubbles like an Aero chocolate bar. It tends to be about double the density of the white foam. However itcuts with a hot wire, or a very sharp knife, or a bandsaw, and it can be sanded with a sharp sanding block to quite a good surface. It is sold in the UK under the name "Floormate 200" as underfloor insulation, usually 50 mm thick but available in 75 mm also. In the UK it is usually a pale blue colour, or pink.
If this is the stuff you are using it will take glass/epoxy directly very well.
I made a pair of floats from this stuff a while ago. I epoxied a ply plate along the top surface for about 1/2 its length (from the front fixing to the rear fixing, plus a bit extra each end). I epoxied a layer of 50g glasscloth to the bottom ahead of the step, and wrapped it around the front edge (3 mm radius) and back about an inch, to protect the bottom. Then the whole thing was painted with acrylic paints, as sold for artists, straight onto the foam. One coat. I kept the edges square, and added a spray strip on the inside edge.
The floats were fitted to my electric trainer E-Tee and worked great. The model was later converted to ic with a 30FS engine (photos)and later a 25 two-stroke, and the paint finish even stood up to those. They lasted for years, hundreds of flights.

I once made a set of "taildragger" floats from blue foam for a small electric model (no photo). I left the blue foam bare, except for the plywood on top, and they were fine. The blue bubble-filled foam does not need waterproofed. The second photo shows a much bigger model (8 ft span) with taildragger floats made like E-Tee's floats.

You are right that it is hard to wrap the glass around a tight radius without getting voids, bubbles. If glassing over, I round off the floats, but the bottom edges have to be sharp. One technique I sometimes use is to glass the bottom first and trim of at the edge. Then glass the top, overlapping the glass beyod the bottom. Then fill the corner with epoxy mixed to a paste with lightweight filler. I make a fillet of maybe 3 mm, or 6 mm on bigger models. Then I trim off the glass when the epoxy sets. The epoxy/filler reinforces the join between the two sheets of glass.

RE: fiberglass over foam?
 

BikerBC, I got the epoxy part figured out and thank you. I only have this 48 g/m2 stuff and there are no local suppliers for anything lighter so I will just have to make due with what I have.

Box Car, I read two threads, begining to end last night about the liquid sheeting (stayed up way too late). That stuff looks pretty cool but right now this is the only thing I need it for and it looks like 8 oz will be more than I need for a long time. About halfway through the first thread, I had a feeling it was some sort of modified bed liner because the bed liner I used for my truck said it needed the moisture from the air to cure.

alasdair, It is indeed the bead kind of styrofoam but the density is the same as the blue foam I have used on other projects ( I weighed a 1 square inch piece of each on my reloading grain scale). I didn't know however that the stuff would soak up water between the beads, I just thought the beads were water tight between them. As I look closer though I do see that in the places I cut and sanded, after covering with epoxy and cloth, I can see the pits where there were voids between the beads.

I did a test last night with a small piece of foam and a small balsa edge. The fiberglass does look like it held on to the balsa better than just to the foam. It is not that difficult to cut the groove for the balsa edges so I might just go that route and then fiberglass them with the fiberglass I have on hand. I have Zpoxy to use with the fiberglass cloth. From what I understand, after the glass is saturated and then squeeged off, there is not much more strength added with more epoxy. I dont plan on "filling the weave" for a smooth surface on the sides or top if it will not add any strength. I can live with the weave look.

RE: fiberglass over foam?
 

You can replace the epoxy with polyurethane or maybe waterbased polyurethane if it isn' a float? maybe.  I would think if it is painted it wouldn't be affected by water.

RE: fiberglass over foam?
 

If your blue foam is as light as your beaded white foam then I would suugest using the blue stuff to make the lightest possible floats.
It is much easier to work with, stronger and water resistant.

Do you have problems with spray in the prop with those flat floats? It is a common problem.
The ones I made from blue foam were flared to throw the water out, away from the prop. That, combined with the spray strip, makes sure that all the spray goes outboard from the float, not a drop into the prop. Look at the smooth water surface between the floats, and compare the spray pattern on the inside edge with the outside edge.

RE: fiberglass over foam?
 

I have tried the water based poly before on another project and it just did not ever seem to dry well enough for me. It always was a bit soft or tacky feeling. With the epoxy, I know it will harden and get harder with time.

I get practicaly no spray into the prop with these floats except for one time when I flew in winds of about 20 mph and then with the water a bit choppy, I got a little spray right on throttle up but went away as soon as on step. The nose of the floats are a little less than 2 inches in front of the prop so there is not much room for spray into the prop. When the tail is down the nose of the floats are high up in the water and when the tail comes up, the plane is then on step and so very little spray. I do get some pretty good spray behind and up on the tail at certain taxi speeds. When I found out that the white foam I had was as heavy as the blue foam, I was going to use blue but did not have enough left to cut the floats out so I just went with the white. I got the white from a concrete supplier for $1.00 per 2'x8'x2" sheet a while back and needed to use 18 sheets up. After I used some for wings and under the pool and in my garage walls, it is almost gone now.

RE: fiberglass over foam?
 

$1 a sheet is a deal, we pay 5 times that.  I think the white comes in various densities, but is usually lighter than the pink, and the blue is the heaviest.  I like the pink and blue because it sands easier for most things.  I had some leftover white from an attic.  Lots of 9" strips.  I practised my hotwire cutting with those and some needed a bit of sanding.  There is a brown foam that takes polyester resin too, but it can not be hotwired.

RE: fiberglass over foam?
 

Yes it was. The company misordered it and all the edges of the stack were turning yellow from being out in the sun and he just wanted it gone. The density was however all over the place from sheet to sheet and also within the same sheet. Hot wiring it was sometimes hit and miss. It would start fine and then find a dense spot in the middle somewhere and get hung up. I did get my money out of it though.

RE: fiberglass over foam?
 

Flybyjohn, this is what liquid sheeting is. I no a lot of guys that have used it never when back to glass.


StyroSpray® 1000 is a simple to apply hard coating for carved foam shapes. It is applied by paint brush, foam roller or spray applied with a low cost gravity feed hopper spray gun. It provides a strong, lightweight uniformly smooth appearance, which can be coated with any type of solvent or water base paints. StyroSpray® creates a hard plastic shell over foam fabrication of signs, decorative themeing, paper mache construction and concrete molds. It seals hardens and waterproofs hot wire cut or carved foam shapes for indoor and outdoor

RE: fiberglass over foam?
 

I have dug out a couple of photos of my model with raw blue foam floats, left uncovered and unpainted.
That has to be about the lightest easy way to make floats.
I jst hotwire cut the foam, glued a bit of ply on top for the mountings, and they are done.
The 53 inch span model was designed with pretty curves wings and tail surfaces, and waspowered by a 120 watt bell motor, and 1100 mAh 3Slipo.

RE: fiberglass over foam?
 

I ended up fiberglassing the top and bottoms and then tried to fill the weave with some spar varathane I had left over from another project but it never dried. It stayed tacky for over a week and a half so put them in the oven at 170 deg. for a few minutes trying to set the varathane but it melted the foam under the fiberglass. I built another set of floats and fiberglassed those and then tried to fill the weave with some auto spot putty I had and it melted the foam through the fiberglass. I finally just said heck with it and painted over the slightly melted floats and it is on the water again. They ended up heavier than I wanted but I was able to take off the nose wieght I had to put on before. I will see how long these last, probably quite a while, and then when I build the next set, I will just fiberglass the bottom and paint the top bare foam with foam safe paint. In fact I have to make a set of full lenth floats for my kids trainer so I will try the light and easy method on those.

RE: fiberglass over foam?
 

Yeah,,
I'm sticking with the tried and true West Systems epoxy,, it never goes wrong, dries hard as a rock every time

I tried the Water based Poly once, went on too thin, took many many coats to fill the weave and didn't want to dry either, just made a tacky mess.

RE: fiberglass over foam?
 

I too had some water based Polyurethane that stayed tacky for way too long. I sprinkled a little baby powder on the surface and rubbed it all over with my hand and the tackyness was gone.
Ralph