Jotamastic 90 - 2 x Questions

[conor1n]

Does anybody reckon that Jotamastic 90 works like a primer.

I have Lesonal solvent base coat to go on over it - do you guys think I can add it straight over Jotun or will need an intermediate primer?

I can't get a clear answer if the Lesonal is polyurethane based.

Thank you.

 

[badabec]

I did DA the flat parts of the engine bay, then sprayed with cellulose. I used the epoxy resistant rollers from Toolstation, the skinny 4" rollers.

 

[Torqu-E-Cycles]

Lessonal should work fine as I have urethane coated many guitars that have been filled with epoxy cast resins.

It seems like this jotamastic is pretty much an all in one primer before paint, would love some experienced replies from people that have used it (ideally years ago) to see how it holds up as its cheap in comparison to the usual bodyshop epoxies on the market!

Does it take to filler and does filler take to it or is it best to fill the steel then use it as a filler primer AND sealer all in one? If thats the case I'm game on!

 

[ajlelectronics]

Does anybody reckon that Jotamastic 90 works like a primer.

That is what it was designed to be!

 

[ajlelectronics]

Does it take to filler and does filler take to it or is it best to fill the steel then use it as a filler primer AND sealer all in one? If thats the case I'm game on!

Epoxy primer is a totally different and far better way of thinking. The important thing is to have good protection and good adherence to the substrate. Also useful are the waterproof and inert properties.

The sequence is as follows:

Carry out any major repair work on bare substrate.
Flat the substrate to 120-180 grit dry and clean with solvent.
Spray a good two coats of primer and allow to cure.
Lightly abrade to 180 grit, dry.
Do any filling on top and then flat to 320 grit dry, before applying two or more coats on top as a sealer.
Colour coat can then go straight on top of the epoxy, either wet on wet before full curing, or after cure and flatting as required.
Keep water away from the job until final colour coat polishing.

Important points to bear in mind are :
The curing time. In normal temperature air dry, it will take 12-24 hours to cure before sanding.
Epoxy primer is NON Isocyanate, which means that it does not require the typical air fed mask that 2K isocyanate products do.
Epoxy primer is inert when cured, which means that it will not cause reactions with any other paint product. It can therefore also be useful as a barrier coat, which unlike Barcoat, can be sanded.
Automotive epoxy primers are far easier to spray and sand than thicker mastic types which are possible better for brush application on undersides and chassis etc.

 

[Dcal]

@ajlelectronics replied while I was typing and I agreed with everything he says.

I've used Jotamastic as a high build primer over filler, repaired panels where there is (was) rust, filler, old paint, galv, whatever.
It works on just about anything.

I've overcoated it with epoxy primer, two pack primer, single pack, two pack, base coat and clear and water based paints.
I've only had one failure and that was because I left it too long before overcoating.
Body filler stick better to it than steel so I apply body filler over the Jotamastic as well.

It's an epoxy and like all epoxies it dries hard and the next coat will not soften it.
So, you have to stick to the open times in the TDS (the time / temperature during which it can be overcoated) and if in doubt sand it before overcoating it.
If you don't have heat it can take a while to harden before you can properly sand it, but once hard it sands ok. It doesn't sand like a 2 pack primer or a polyester spray filler but you can't have everything.

If I don't need a apply a heavy coat or want to go wet on wet, I use a standard epoxy primer.

There are some of the results I've had in the post below.

25 year old Alfa 75 back from the brink (hopefully)

Bit of an update. I can confirm that a ball joint boot works very well and although they are a different design I think they are better than the original. I got them on ebay for not much (19 x 28 x 16 if the link doesn't work) https://www.ebay.co.uk/itm/293332421692 To install the boot, I...

www.mig-welding.co.uk

 

[marlinspike]

I'm always impressed by how good brushed or rollered Jotun products look when dry. I know many prefer stuff like the Lechler 29107 on outer panels but the Jotun epoxy looks ideal for underneath. Shame it's not available in smaller amounts.

 

[ajlelectronics]

I'm always impressed by how good brushed or rollered Jotun products look when dry. I know many prefer stuff like the Lechler 29107 on outer panels but the Jotun epoxy looks ideal for underneath. Shame it's not available in smaller amounts.

Yes, a good assessment. Automotive epoxy where it shows, mastics where you want a thick, protective covering.

 

[Torqu-E-Cycles]

What a great few replies thanks guys!
Jotamastic will be ordered this evening!!
Do I bother with the hassle of phosphoric acid or just mechanical rust removal?

 

[Torqu-E-Cycles]

I have the bilt hamber rust remover gel, I may just use that and be patient letting it work over a few weeks of evenings. The car is in the dry under my flat so can be left alone for long periods of time.

 

[Dcal]

I don't use any pre treatment because Jotun (or another manufacturer I know of) doesn't recommend one.

If you do use it, I would apply it, let it do it's thing then rinse or carry out the whatever treatment the maker requires.
I would then dry sand as much off as you can and it should leave clean steel with some of the converted product in the pits which shouldn't do any harm.
It couldn't be any worse than the salts that will be trapped in the pits which the primer has been designed to cope with (up to a point)

 

[Torqu-E-Cycles]

How well does this jotamastic spray?
Just looked at the data sheet for jotamastic 90a winter grade, I will be doing it in January with small heaters on so likely around 12c no hotter.
According to the data it needs a pressure pot at 2100 psi?! I will be brushing underneath but all the engine bay, interior, exterior needs to have a good primer finish to save hundreds of hours sanding brush marks! I have a 1.8 hvlp gravity fed gun....

 

[ajlelectronics]

How well does this jotamastic spray?
Just looked at the data sheet for jotamastic 90a winter grade, I will be doing it in January with small heaters on so likely around 12c no hotter.
According to the data it needs a pressure pot at 2100 psi?! I will be brushing underneath but all the engine bay, interior, exterior needs to have a good primer finish to save hundreds of hours sanding brush marks! I have a 1.8 hvlp gravity fed gun....

If you want to spray it, I would recommend an automotive epoxy, personally.

 

[Torqu-E-Cycles]

Will it do the same job with holding back the pitted rust pores etc?

 

[ajlelectronics]

Will it do the same job with holding back the pitted rust pores etc?

Of course.

 

[Torqu-E-Cycles]

Oh ok, I've been using spectral under 385, shall I continue or is there a particularly better one?

 

[Shedendman]

https://www.ebay.co.uk/itm/31501984...uid=IUoauAtKSrO&widget_ver=artemis&media=COPY

I quite like the look of that,,now scratching chin going hummmmmmmmm

 

[conor1n]

I quite like the look of that,,now scratching chin going hummmmmmmmm

Yeap - i'm probably going for that. Particularly useful for strut towers etc.

They won't ship to Ireland though

 

[Torqu-E-Cycles]

Do you expect to spray jotamastic through that?!

 

[conor1n]

Do you expect to spray jotamastic through that?!

I do anyway.... it says its a 2.5mm tip.

Do you think it's not suitable?