Morris Minor Owners Club

Can anyone give me some advice/opinion on spraying cellulose in winter? The position is this-----my garage is part of the house so not actually freezing but in the past spraying in these conditions has resulted in the finish having a 'bloom' to it.
I am wondering if it's the temperature or humidity that is the problem, I suspect the latter. I managed to paint most of the van in summer but want to crack on rather than wait for spring!

I'm no sprayer, but wouldn't anti bloom celulose thinners help stop the bloom?

You would need to heat the garage - but don't spray with the heater running! And only attempt it on a dry/clear day - not when it's teaming down.......

Yes you're right and I've bought some, but not sure how effective it will be in these conditions. In fact I have also bought a dehumidifier for reducing the effect of dampness, however it would be nice to get more info before I go for it. I can heat the garage but want to know if it's the cold or moisture that causes bloom. Thanks for the replies.

It is the humidity - but a cold clear frosty day has very low humidity, most of the moisture has dropped out of the air as frost! But you will still need to heat the place too - or it will bloom.

I'll bear all that in mind, incidentally, do you think primer suffers from this problem? I know you wouldn't see any bloom film on primer but if it was there it would influence the top coat I would think. Although I expect rubbing down in preparation for top coat should remove it if it was present.

Primer is porous so the damp could well get into it before you put the top coat on.

Bad news all round spraying now! I just don't want this project running into another year!

Yes - if primer is put on in damp weather, the bloom will come up through the finish coat. Crisp cold day, 3 kw fan heater in the garage for an hour before you start, then off with the heater and on with the spraying! Just watch out for the concentration of thinner vapours in the atmosphere - I made myself ill a few years ago spraying in a closed garage.. Took a few days to get it out of my system. I ONLY spray outdoors now - in warm/still weather.

It's been a race against time for me this summer, and I lost! I'll wait for a reasonable day and see what happens. Thanks.

blooming in celly is cause mainly by the evaporation of the thinners which drops the surface temp. of the panel,causing the dulling effect on the surface,anti bloom celly thinners has a slower evaporation to lessen the effect.Even in the summer you can get the same problem if you open a garage door when its windy the cooling effect drops the temp and blooming starts.Heat is the answer,get the garage warm and with a hot air gun warm the panel(Do one at a time) don't get it too hot or the paint will dry too fast and not flow out.If you get slight blooming don't worry too much it can be polished out,the best heaters if you can afford one are the infra red one that just warm the panel not the air so you can keep them pointed at the car and continue to spray. probably the only safe way of heating a small garge to spray

I had to do some painting last winter in sub zero temperature. I used the following methods and it turned out to be no problem. I kept the gun, paint and thinners etc. in the kitchen by the Rayburn so it was nice and warm and put a fan heater in the car. I also used a cheap electric patio heater directed at the panel. I also had a hair drier that I used to warm the panels up. It was a large slightly drafty outdoor workshop so no way to heat it and it was during that cold spell when the temperature never rose above zero. The water in the buckets for wet sanding was frozen solid.

But you absolutely must NOT have any ignition source on when spraying - so no 'infra red heater' or fan heater or patio heater - these must be switched off just before spraying.. A gas fired patio heater will introduce moisture into the air - perhaps not the best idea - you want minimum moisture around.

Thanks for all these replies, they give me hope for a reasonable outcome, I will be following your suggestions.

Particularly keeping the celly in a warm place, and maybe even as I have in the past, submerge the pot part of the gun in a bucket of hot water between uses. But watch out for water dripping off if you don't dry it before using again

not sure but the electric infrared heaters don't have an ignition sourse. It's what they use in pro booths,similar to sun beds I think,anyway somebody will know and be posting soon.

I thought the minimum temp to spray celly was 12 - 14c ? other wise you could possible end with micro blisters ? I've thought about spaying one panel at a time in cold but dry weather - using a hair dryer and fan heater to heat a single panel ? but have never tried it
I've got a mini sat in my garage that needs spraying - now waiting for the summer !

When I did a painting course years ago, we were reassured that any blooming on a cellulose finish wasn't a disaster. Simply use the bloom as a 'guide coat' for flatting and buffing. The results came up like glass...
Ok its nice to get a good 'gun finish' but at least if you don't it will be salvageable as long as the paint is keyed on and applied reasonably well!

yes your right ian, I have sprayed dozens of cars over the years and blooming it not a disaster,and with a lot of effort mind ,it can all be polished out but its obviously better to get a shine from the gun,but the celly these days is not as good as that of old,just about all celly is reclaimed . In the old days there was a massive surplus of gun cotton left over from the mod and thats where most of the cellulose base,paint and thinner came from.its very fdifficult now to get a finish that dosent need to be flatted and polished .up to about 25 years ago the shine you got from the gun was the shine that you got, polishing was to an extent not required. No so now.